Article: 93560 of rec.radio.amateur.homebrew From: "Tom Holden" References: Subject: Re: Ham radio beginner? Message-ID: Date: Thu, 7 Jul 2005 16:22:55 -0400 An absolutely phenomenal mutual help group is at http://groups.yahoo.com/group/HamRadioHelpGroup/. Its focus is primarily for US licensees or wannabe's but the technical help is universal. Tom Article: 93561 of rec.radio.amateur.homebrew From: Just Cuz Subject: Why don't many high power RF transistor amplifiers use emitter stabilizing resistor and AC by-pass capacitors? Message-ID: Date: Fri, 08 Jul 2005 02:03:51 GMT I have been looking at a variety of RF transistor amplifier schematics including a 50 watt amp shown in the ARRL handbook (1996 - page 17.96) , and they do not have emitter stabilizing resistors and ac by-pass capacitors on the emitter leg of the final output transistors. Is there a good reason for not using emitter stabilizing resistors and ac by-pass capacitors in 100 watt output or more RF transistor amplifiers? Here are some on-line schematics I found of high power RF power transistor amplifiers, and in all of them the emitter goes straight to ground. http://www.ameritron.com/man/pdf/ALS-500M.pdf http://www.cbtricks.com/Amp/txstar/250hdv_350hdv/graphics/ts_dx250hdv_dx350hdv_sch.gif http://www.cbtricks.com/Amp/palomar/elite/palomar_elite500.pdf Article: 93562 of rec.radio.amateur.homebrew From: Bob Liesenfeld Subject: Re: Why don't many high power RF transistor amplifiers use emitter Date: Thu, 07 Jul 2005 21:12:52 -0500 Message-ID: <42CDE124.B70118B2@visi.com> References: Just Cuz wrote: > Is there a good reason for not using emitter stabilizing > resistors and ac by-pass capacitors in 100 watt output or more RF > transistor amplifiers? My hunch would be that most of those amps probably use ballasted emitter transistors which mitagates the need for an emitter resistor. That, plus the fact that any impedance in the emitter lead is an invitation to oscillation, and obtaining a good low Z bypass is tough at HF especially at the current levels involved. Bob WB0POQ Article: 93563 of rec.radio.amateur.homebrew From: Ken Scharf Subject: Re: Looking for 12V tube Rx project info References: <1119556572.530653.109680@f14g2000cwb.googlegroups.com> <3Rkve.6758$Bm.4442@bignews5.bellsouth.net> <1119748538.259718.166300@f14g2000cwb.googlegroups.com> <1119913230.190263.47320@g49g2000cwa.googlegroups.com> Message-ID: Date: Thu, 07 Jul 2005 22:19:11 -0400 LenAnderson@ieee.org wrote: > From: Ken Scharf on Sun 26 Jun 2005 22:41 > > >>LenAnderson@ieee.org wrote: >> >>>From: Ken Scharf on Jun 25, 6:26 pm >>> >>>>LenAnder...@ieee.org wrote: >>> >>>>>>I am looking for a nice schematic, and perhaps additional info, on a 12V >>>>>>(fil. & plate) tube superhet Rx; just something fairly simple for CW/SSB >>>>>>reception without bells and whistles, and preferably for 75M/40M reception. >>>> >>>>> Setchell-Carlson managed to do it with loctal-base tubes running >>>>> off of a 24/28 VDC aircraft bus back in WW2 times. No dynamotor, >>>>> just that cute little box referred to as a "range receiver" or >>>>> BC-1206. > > >>> Converting a "Q5-er" from tubes to FETs would be rather easy. >>> No real need for the 2N2222s. Would have gobs of space left over >>> inside an already compact box. >> >>This is the idea of a cascade fet-bipolar circuit. The drain of the fet >>drives the emitter of the bipolar and the bipolar's base is biased so >>that the base sits about half way up the power supply (two resistors). >>The fet is self biased with a source resistor for the desired current. >>The gain of this circuit is higher than a fet by itself, and the output >>impedance will be higher. >> ____ __ >> ->|_ \_/ >> | | >> >> >>> If the 135 KHz IF has an equivalent total Q of 100, the BW would >>> be about 1.3 KHz, not all that swift for CW and too shart for SSB. >>> >> >> The AnArc-5 Q5'ers had 6 tuned circuits in their If but the '1206 >>only has 3 or 4. So it's BW might be a tad wider. The 1206 also has >>no bfo. > > > The ARC-5 LF version has IF TRANSFORMERS but the insides are > easy to see for detail. The 6 to 9 MHz version IFs (2830 KHz) > had only one tuned circuit in each IF can. > > Can't remember what the BC-1206 used in their IF cans, but that > is easy to change inside the present can (it will look just the > same on the outside). I seem to remember two trimmer caps so I guess there were a total of four tuned circuits. I think the ham radio article I saw on converting the rig did add a bfo using a tv horizontal coil cut down as the bfo coil. I could also remove some wire from an old BC453 bfo coil, of which I have a few in the junk box. (Not to metion about a dozen 85khz if cans). Which reminds me..... I was thinking of building a solid state version of the old Drake 2B receiver with it's 80meter first (tunable) IF, 455khz second if, and 85khz third if (using Arc5 IF transformers) instead of Drakes 50khz (close enough). I'd use a BC454 tuning cap padded down to cover 3.5-4.1mhz just like Drake. The first oscillator would be a PLL to cover everything (beats grinding on ft243 rocks). > > I can't see any advantage of going cascode (JFET-bipolar) when an > insulated gate FET would closely approximate a vacuum tube for > both input impedance (all capacitive) and drain/output impedance > (many hundreds of KOhms). Depends on what is available for the > vacuum-to-solid conversion. Junction fets are rather low gain, though compared to tubes with 28 volts on their plates, probably a good match. The cascade circuit can be built with either two jfets, or one jfet and one bipolar. The jfet/bipolar version combines the high gain of a bipolar transistor with the high input impedance of the fet. That's the reason I'd give it a try (plus I enough of BOTH kinds in the junk box). I'd replace the converter tube with three fets, two in differcial for the mixer, and one for the oscillator. > > Note: Both input and output impedances will affect the impedance > and Q of the tuned circuits...and the GAINS...for a conversion > with minimum circuit changes. All that has to be taken into > account. > > >>> However, the BC-1206 tuning range of 195 to 500 KHz results in >>> an image at the converter input of 390 to 1000 KHz away from the >>> desired band. That's worse than the 910 KHz image of an old >>> 455 KHz IF. >>> >> >>The 1206's dial only goes up to 400khz, but it tunes past that. Maybe >>it goes to 420 or 450khz, I don't think it goes as high as 500khz. >>(so maybe I don't have to expand the range for my needs). > > > The variable tuning capacitor max:min ratio is roughly 11:1 (no > external parallel capacity). Since the resonant tuning range is > the square root of that, you could have it tune 190 to 570 KHz > with a 9:1 max:min change in resonance capacity. The only real > problem is getting the variable LO tuning to track the front end > since it would tune 325 to 705 KHz (for the high-side) and that > would be a 2.169:1 frequency ratio or 4.706 capacity change ratio. > Well that doesn't take into account the distributed capacitance of the coil windings, which would be considerable at this frequency what with the required inductance. (ever wonder why a grid dipper covers a much higher min-max frequency ratio as the frequency band goes up?) Also IIRC there are trimmer caps in parallel with the tuning caps for alignment as the coils are fixed. To make the oscillator track, a series padder cap is used to reduce the max. capacitance value of the oscillator section. -OR- a parallel padder could be used to swamp out the range of the section. > > >>> The linear-in-capacity rotation of the 3-gang variable is good >>> for an RX Noise Bridge having an expanded parallel-C range... >>> which is what I used them for. :-) >>> >> >>True, but the rig is just to cute to canabilze. > > > Heh heh heh. I agree with you there. It probably is most dense > of any other 1940s era design using 8-pin "medium" size tubes, > including the very compact ARC-5 receivers. Not quite as dense > as the SCR-300 Walkie-Talkie (BC-1000) which stuffed 18 7-pin > "miniature" tubes, a half-dozen coil/transformer cans, and a > five-gang (!) variable capacitor into an approximate 5" x 10" > chassis. [Galvin/Motorola did real good in packaging there] > > KEEPING the tubes as-is, with the possible exception of the AF > out (28D7 ?) would yield a straight-AM receiver. ADDING a BFO > via under-chassis bipolar transistor would result in minimum > cannibalization (one extra switch on front panel)...RF and IF > could remain the same. I've forgotten the audio output circuit > of it but recall that AF output power for old aircraft was > rather high (ambient noise in old warbirds was terrible). In a > quiet land environment, the audio output needed is rarely 200 > milliWatts into a speaker, much less for headphones. The SCR-300 > walkie-talkie (headphones only) had a maximum of 3 mW audio out! > You can't get much power out of a tube at 28v on the plate. The 28D7 was up to the task being a double power pentode with the sections in parallel (why not push pull?). I wouldn't call solid state conversion canabilzing. > Hint on supply conversion: A 12.6 V "filament" transformer can > do the job for all-12 V filaments in parallel. A voltage > doubling rectifier (even a tripler if need be) will yield the > quite-low B+ for plate and screen. I once did that (long time > ago) with a single transformer and voltage tripler for B+, all > working into a set of power resistor load boxes, all in a half > hour of tack-soldering. Got 30 VDC for B+ at 115 VAC line, > less than 5% ripple. Didn't have the BC-1206 then. A critic > looking on said "that isn't a good enough test...gotta have the > 'real' load on it to 'prove' it." :-) [some folks just aren't > convinced until someone else has made a finished production > product!] > > LenAnderson@ieee.org > Article: 93564 of rec.radio.amateur.homebrew From: "Tom Holden" Subject: Synch AM Special Interest Group Started Message-ID: Date: Thu, 7 Jul 2005 22:35:33 -0400 Information on and discussion of synchronous AM demodulators is scattered widely. There are sporadic discussions on a couple of Usenet news groups but they are restricted to text messages and it's hard to find the wheat in the chaff. This new group can accommodate schematics and pictures and provides a filtered view focussed on this one subject. In time, I hope that its collected files and discussions will make a strong starting or reference point for all with an interest in Synch AM. Please join if you have ever designed or experimented with synch AM demodulators or intend to start. Visit the web site at http://groups.yahoo.com/group/Synch_AM/ to subscribe. Your designs, experiences and participation in the on-topic discussions to ensue will be welcomed. Tom Article: 93565 of rec.radio.amateur.homebrew From: Tim Wescott Subject: Re: Why don't many high power RF transistor amplifiers use emitter Date: Thu, 07 Jul 2005 19:51:36 -0700 Message-ID: <11crqhn32qa2650@corp.supernews.com> References: Just Cuz wrote: > > I have been looking at a variety of RF transistor amplifier > schematics including a 50 watt amp shown in the ARRL handbook (1996 - > page 17.96) , and they do not have emitter stabilizing resistors and > ac by-pass capacitors on the emitter leg of the final output > transistors. Is there a good reason for not using emitter stabilizing > resistors and ac by-pass capacitors in 100 watt output or more RF > transistor amplifiers? > > Here are some on-line schematics I found of high power RF power > transistor amplifiers, and in all of them the emitter goes straight to > ground. > > http://www.ameritron.com/man/pdf/ALS-500M.pdf > > http://www.cbtricks.com/Amp/txstar/250hdv_350hdv/graphics/ts_dx250hdv_dx350hdv_sch.gif > > http://www.cbtricks.com/Amp/palomar/elite/palomar_elite500.pdf > Power burnt in the emitter resistor is power that isn't going out the antenna. So it makes sense to use a fancier bias network and no emitter resistor. -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com Article: 93566 of rec.radio.amateur.homebrew From: "Reg Edwards" Subject: Re: Why don't many high power RF transistor amplifiers use emitter stabilizing resistor and AC by-pass capacitors? Date: Fri, 8 Jul 2005 06:12:12 +0000 (UTC) Message-ID: References: > I have been looking at a variety of RF transistor amplifier > schematics including a 50 watt amp shown in the ARRL handbook (1996 - > page 17.96) , and they do not have emitter stabilizing resistors and > ac by-pass capacitors on the emitter leg of the final output > transistors. Is there a good reason for not using emitter stabilizing > resistors and ac by-pass capacitors in 100 watt output or more RF > transistor amplifiers? > ================================= Most RF power transistors in the 50-100 watt range already have an internal emitter resistor. It's usually less than a tenth of an ohm, perhaps only a few hundreths of an ohm. Its purpose is to prevent thermal runaway and make the device more tolerant of overload due to momentary impedance mismatches. Internal resistors have an extemely low inductance. They are NOT wirewound. They are an integral part of the transistor construction and material. The manufacturer may not mention their existence in his catalogue or data book. RF power transistors are usually multi-emitter devices - all in parallel. Each emitter has its own individual series resistor. Such low-value external resistors are not available as discrete wire-ended circuit components. Inductance would be too high at HF and an invitation to self oscillation. Don't attempt to use normal circuit components in emitter leads unless a transistor manufacturer specifically recommends them. HF and VHF power transistors are very fast fuses. They are worked very close to their maximum voltage and current ratings. ---- Reg, G4FGQ Article: 93567 of rec.radio.amateur.homebrew From: waz Subject: tektronix storage scope for sale Message-ID: Date: Fri, 08 Jul 2005 20:23:40 -0400 Tektronix 564B storage oscilliscope. Type 3A72 dual trace amp. Type 3B3 time base. Powers up. I get a signal. It is too complicated for me, (I have a heathkit). $40 Canadian. It must go by the first week of August. Pickup in Montreal Quebec or pay shipping. wazungy@sympatico.ca Article: 93568 of rec.radio.amateur.homebrew From: "Heytubeguy" Subject: FA:Tubes:6L6,6V6Y,807,12AX7,6JS6C..... Message-ID: <69Fze.1105606$w62.46417@bgtnsc05-news.ops.worldnet.att.net> Date: Sat, 09 Jul 2005 00:48:02 GMT Added a few more tubes. Have a look, tnx: http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQsassZheytubeguy + Amphenol 2 pin Mic connector set and 5691 tubes (red base). heytubeguy Article: 93569 of rec.radio.amateur.homebrew From: "Heytubeguy" Subject: FA:5691 Red Base,2-pin mic plug + more tubes Message-ID: Date: Sat, 09 Jul 2005 00:50:47 GMT Added a few more tubes. Have a look, tnx: http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQsassZheytubeguy + Amphenol 2 pin Mic connector set and 5691 tubes (red base). heytubeguy Article: 93570 of rec.radio.amateur.homebrew From: Jim Adney Subject: Re: tektronix storage scope for sale Date: Fri, 08 Jul 2005 23:37:54 -0500 Message-ID: References: On Fri, 08 Jul 2005 20:23:40 -0400 waz wrote: >Tektronix 564B storage oscilliscope. >Type 3A72 dual trace amp. >Type 3B3 time base. > >Powers up. I get a signal. It is too complicated for me, (I have a >heathkit). I understand that you may find it overwhelming, just because the Heath may be so simple, but the 564B is a really nice scope. It's only downfall is that it's only good to 10 MHz (and the 3A72 is only good to less than that.) With a better plugin, like the 3A1 or the 3A6 this is a really versatile scope as long as you don't need higher bandwidth (and most people don't.) Your 3B3 is a good time base. The nicest thing about the 564B is the fact that you can get lots of different plugins for it that do lots of interesting things, from 4 channels plugins to spectrum analyzers. I'd encourage you to sell the Heath, but I'm biased. There's a 564B sitting just to the right of my PC. ;-) - ----------------------------------------------- Jim Adney jadney@vwtype3.org Madison, WI 53711 USA ----------------------------------------------- Article: 93571 of rec.radio.amateur.homebrew From: "Roger Conroy" Subject: Help needed to id components Date: Sat, 9 Jul 2005 09:50:05 +0200 Message-ID: I'd like to know the specs of the variable capacitors used in the MFJ-920 VHF Dual Band Tuner. There are no visible markings on them. They have 6 fixed and 7 moving semicircular plates about 33mm in diameter - spacing between the plates is in the region of 1mm. I want to recycle into something more useful - such as a HF tuner. 73 Roger ZR3RC Article: 93572 of rec.radio.amateur.homebrew From: "Polymath" References: Subject: Re: Help needed to id components Date: Sat, 9 Jul 2005 09:17:57 +0100 Message-ID: <42cf8949$1_2@x-privat.org> 1. Capacitance Meter? Be a _REAL_ Radio Ham by making one? 2. ISTR that C = nAe/d where n is the number of facing surfaces? "Roger Conroy" wrote in message news:danviv$o5c$1@ctb-nnrp2.saix.net... > I'd like to know the specs of the variable capacitors used in the MFJ-920 > VHF Dual Band Tuner. There are no visible markings on them. They have 6 > fixed and 7 moving semicircular plates about 33mm in diameter - spacing > between the plates is in the region of 1mm. I want to recycle into > something more useful - such as a HF tuner. > > 73 > Roger ZR3RC > Article: 93573 of rec.radio.amateur.homebrew Date: Sat, 09 Jul 2005 09:48:25 -0400 From: -ex- Subject: Re: Help needed to id components References: Message-ID: <54b6f$42cfd5ab$4232bd15$14499@COQUI.NET> Roger Conroy wrote: > I'd like to know the specs of the variable capacitors used in the MFJ-920 > VHF Dual Band Tuner. There are no visible markings on them. They have 6 > fixed and 7 moving semicircular plates about 33mm in diameter - spacing > between the plates is in the region of 1mm. I want to recycle into > something more useful - such as a HF tuner. > > 73 > Roger ZR3RC > > Just guessing, of course, I'd say thats about 40pf. -Bill WX4A Article: 93574 of rec.radio.amateur.homebrew From: "sean" References: <2d5631c0.0506082158.39fb1c20@posting.google.com> Subject: Re: How to turn a radio into a time-bomb??? Date: Sat, 9 Jul 2005 23:22:26 -0400 Message-ID: <42d09367_1@newspeer2.tds.net> Dude, You Really, Really Need To Get Serious HELP! Accept the following : Then only you can choose to accept the following. Only You can choose whether or not to be an assassin. Only You can choose to not HAVE to kill. You only choose to think to kill. No one else chooses for you. You have a choice. You do not need to use a radio as a time-bomb! You only choose to think that you really need to use radio for a time bomb. So, your life as only you can choose it, means what? (rhetorical) "Winnie Oakbob" wrote in message news:2d5631c0.0506082158.39fb1c20@posting.google.com... > I'm an assassin and have to kill a mafia boss.I want to blow him up > with a radio bomb. > > What do I need ? Article: 93575 of rec.radio.amateur.homebrew From: "Polymath" References: <2d5631c0.0506082158.39fb1c20@posting.google.com> <42d09367_1@newspeer2.tds.net> Subject: Re: How to turn a radio into a time-bomb??? Date: Sun, 10 Jul 2005 10:28:35 +0100 Message-ID: <42d0ea2e_1@x-privat.org> Tell that to the cowardly murdering bastards who make up the unlawful invading forces in Afghanistan and in Iraq. "sean" wrote in message news:42d09367_1@newspeer2.tds.net... > Only You can choose to not HAVE to kill. > You only choose to think to kill. > No one else chooses for you. > You have a choice. Article: 93576 of rec.radio.amateur.homebrew From: Tim Wescott Subject: Re: How can a wire wound reisitor be non-inductive? Date: Sun, 10 Jul 2005 19:38:27 -0700 Message-ID: <11d3mst6p914f23@corp.supernews.com> References: KC4IH wrote: > I need to build a 3db pad, 50 ohm, 10 watt, to reduce the drive to my 6 > meter amp. I need 2 X 300 ohms and 1 X 18 Ohm resistors and thought it would > be an easy matter to find them with enough current rating to do the job but > can't find anything larger than 1 watt carbon (not film, which are somewhat > inductive ) resistors. I can find want is called non-inductive wire wound > resistors. I can't understand how a wire wound resistor can be > non-inductive. Could someone explain this? > > > There used to be great big resistors -- essentially carbon composition -- that were truely noninductive. I suspect they're still available. My 1988 handbook has a UHF dummy load design that features a Carborundum part number 889SP500K. With coolant it's good for more than 1500 watts, so it may be oversized for you... You can still find the occasional 2W or 5W carbon comp resistor -- if you're working at HF you can easily parallel these to get the resistance that you need. -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com Article: 93577 of rec.radio.amateur.homebrew Date: Sun, 10 Jul 2005 23:33:29 -0400 From: -ex- Subject: Re: How can a wire wound reisitor be non-inductive? References: Message-ID: <7a312$42d1e88c$4232bdf0$6132@COQUI.NET> KC4IH wrote: > Thanks Ralph, that is what I was thinking but when they are advertised as > non-inductive you would think "non-inductive" wouldn't you. I guess I'll > have to dig around in some old junk boxes or parallel several 1 watters to > get them to work. > I appreciate your information. > Ken Crazy idea but I'll throw it out here anyway. We know that carbon film resistors have some worriable inductance at 6 meters. If a guy were to take a group of say 1-watters to make up the power rating, could you count on the consistency of the outer markings to the extent that you could group them somehow in parallel/inverted so that they cancel each other's inductance in this application? -Bill Article: 93578 of rec.radio.amateur.homebrew From: dplatt@radagast.org (Dave Platt) Subject: Re: How can a wire wound reisitor be non-inductive? Date: Mon, 11 Jul 2005 04:13:30 -0000 Message-ID: <11d3sfahhkb36a9@corp.supernews.com> References: In article , KC4IH wrote: >Thanks Ralph, that is what I was thinking but when they are advertised as >non-inductive you would think "non-inductive" wouldn't you. I guess I'll >have to dig around in some old junk boxes or parallel several 1 watters to >get them to work. >I appreciate your information. Check out the Caddock and Vishay noninductive metal-foil resistors. As I understand it they use a serpentine-path foil pattern, which cancels out the inductance quite nicely. Some of them are advertised as having an inductance equivalent to an equal-length piece of wire. They're available in packages such as TO-220, and can be attached directly to a heatsink (no insulator required). -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 93579 of rec.radio.amateur.homebrew From: Paul Keinanen Subject: Re: How can a wire wound reisitor be non-inductive? Message-ID: References: Date: Mon, 11 Jul 2005 10:44:22 +0300 On Sun, 10 Jul 2005 21:21:34 -0400, "KC4IH" wrote: >I need to build a 3db pad, 50 ohm, 10 watt, to reduce the drive to my 6 >meter amp. I need 2 X 300 ohms and 1 X 18 Ohm resistors and thought it would >be an easy matter to find them with enough current rating to do the job but >can't find anything larger than 1 watt carbon (not film, which are somewhat >inductive ) resistors. I can find want is called non-inductive wire wound >resistors. I can't understand how a wire wound resistor can be >non-inductive. Could someone explain this? Look up for bifilar winding. If your exciter is reasonably clean so that you do not think about proper termination also for the harmonics, you just need an attenuator for a single frequency, which should simplify things a bit. Even if a "non-inductive" resistor has some inductance at 50 MHz, it should not be too hard to compensate for the inductance and turn the system into a very lossy series resonant circuit, in which the impedance is dominated by the resistance in the area around the resonance. An other alternative would be to put a capacitor in parallel with the resistor to form a parallel resonant circuit at 50 MHz and the actual resistance would heavily damp the resonance. If the inductance is sufficiently low, you will end up with capacitances that are practical (i.e. not affected too much by stray capacitances). This kind of approach should work at a single frequency(band), but if multiple bands are needed or if the harmonics also needs to be correctly matched, this approach does not work. Paul OH3LWR Article: 93580 of rec.radio.amateur.homebrew Date: Mon, 11 Jul 2005 04:36:23 -0400 From: -ex- Subject: Re: How can a wire wound reisitor be non-inductive? References: Message-ID: <38247$42d22f8b$4232bd49$21611@COQUI.NET> > On Sun, 10 Jul 2005 21:21:34 -0400, "KC4IH" > wrote: > > >>I need to build a 3db pad, 50 ohm, 10 watt, to reduce the drive to my 6 >>meter amp. I need 2 X 300 ohms and 1 X 18 Ohm resistors and thought it would >>be an easy matter to find them with enough current rating to do the job but >>can't find anything larger than 1 watt carbon (not film, which are somewhat >>inductive ) resistors. I can find want is called non-inductive wire wound >>resistors. I can't understand how a wire wound resistor can be >>non-inductive. Could someone explain this? I found a graph that I copied off the web sometime back showing the reactance of various R vs freq for metal film resistors. The 10-1000 ohm range of resistors show as being dead flat at 50 MHz compared to DC...and well beyond. Above and below values tend to go nuts with frequency, the high >100k values in particular. I don't remember where I found this graph but based on it I'd think you have a good chance of making those particular values work using garden variety ten-cent 1-watt resistors...thinking along the lines that manufacturing of plain old carbon film resistors would follow the same trend. I think its worth a try. -Bill Article: 93581 of rec.radio.amateur.homebrew From: straydog Subject: Re: How big has Somerset, PA hamfest been in the past? Date: Mon, 11 Jul 2005 10:07:59 +0000 Message-ID: References: On Wed, 6 Jul 2005, Bill Smith wrote: > Date: Wed, 6 Jul 2005 16:07:14 -0400 > From: Bill Smith > Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, > rec.radio.amateur.equipment, rec.radio.amateur.homebrew > Subject: Re: How big has Somerset, PA hamfest been in the past? > > > "straydog" wrote in message > news:Pine.NEB.4.62.0506261856170.28426@sdf.lonestar.org... >> >> >> On Fri, 24 Jun 2005, Galen Watts wrote: >> >>> Date: Fri, 24 Jun 2005 08:25:27 -0400 >>> From: Galen Watts >>> To: straydog >>> Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, >>> rec.radio.amateur.equipment, rec.radio.amateur.homebrew >>> Subject: Re: How big has Somerset, PA hamfest been in the past? >>> >>> straydog wrote: >>>> >>>> I think July 17, is the next Somerset PA hamfest and I've been thinking >>>> about going. Its a long drive from here (southern Delaware) and I was >>>> wondering how big and how good it has been in the past. Anyone got any >>>> recollections from the past? >>>> >>>> Art, w4pon >>> >>> They have pictures of last year's fest at >>> http://www.k3smt.org/hf2004/ >>> >>> -W8LNA >>> >> >> Thanks for the info... >> >> I had a look. >> >> W4PON >> >> > > Hello Art, > This is only our second annual hamfest. Last year it was held in August, a > day after the hurricane came thru. Our turnout was only about 300. Feedback > so far this year says we should have between 500-750. Good odds for winning > a door prize or the main drawing. > Worst case, we're only 6 miles from the 9/11 Flight 93 Crash Site / > Memorial. That in itself would make the trip worth it. The Somerset > Somerfest is also running from Friday thru Sunday. Food, Music, Fun... I > should work for the Chamber of Commerce...HiHi > > Hope to see you here. > Bill kb3gun > http://www.k3smt.org > > > Thanks for the further information. However, here is my problem: first, for me its a long drive one way (5-6 hours and I'd have to stay in a motel Sat night, come back home Sunday, PM). Then, I was driving around yesterday and the bigger problem: sticker shock at the gas pump (I was gazing at a sign that showed $2.30+/gal for low test regular) . I'd be spending more money on gas for the round trip than I'd expect to spend on goodies, toys, parts, etc at the fest itself. :-( Art W4PON Article: 93582 of rec.radio.amateur.homebrew From: "Dale Parfitt" References: Subject: Re: How can a wire wound reisitor be non-inductive? Message-ID: Date: Mon, 11 Jul 2005 13:01:19 GMT "KC4IH" wrote in message news:K5GdnZRYW-cFVEzfRVn-gg@adelphia.com... > I need to build a 3db pad, 50 ohm, 10 watt, to reduce the drive to my 6 > meter amp. I need 2 X 300 ohms and 1 X 18 Ohm resistors and thought it would > be an easy matter to find them with enough current rating to do the job but > can't find anything larger than 1 watt carbon (not film, which are somewhat > inductive ) resistors. I can find want is called non-inductive wire wound > resistors. I can't understand how a wire wound resistor can be > non-inductive. Could someone explain this? > > Wind up approx 40' of RG-174 into a small coil and tie wrap it. It will handle 100W + at 50 MHz and have a great return loss. Lots easier than fooling around with resistors of questionable characteristics and heating problems. Dale W4OP Article: 93583 of rec.radio.amateur.homebrew From: "JB" Subject: Re: How can a wire wound reisitor be non-inductive? Date: Mon, 11 Jul 2005 06:46:02 -0700 Message-ID: References: Use a length of lossy coax for only 3 db. A lot cheaper. None of the non-inductive wirewound or laser cut resistors will be truly non- inductive at those frequencies. Realize that the values need not be exact, because return loss will keep the SWR down. If you can't get Carbon, Use the coax. You might also want to adjust Drive or ALC in the amp. The Collins 30L-1 used to come with a length of lossy coax for this reason. ac6tk http://tekstuff.freespaces.com "KC4IH" wrote in message news:K5GdnZRYW-cFVEzfRVn-gg@adelphia.com... > I need to build a 3db pad, 50 ohm, 10 watt, to reduce the drive to my 6 > meter amp. I need 2 X 300 ohms and 1 X 18 Ohm resistors and thought it would > be an easy matter to find them with enough current rating to do the job but > can't find anything larger than 1 watt carbon (not film, which are somewhat > inductive ) resistors. I can find want is called non-inductive wire wound > resistors. I can't understand how a wire wound resistor can be > non-inductive. Could someone explain this? > > > Article: 93584 of rec.radio.amateur.homebrew From: "JB" Subject: Re: Why don't many high power RF transistor amplifiers use emitter stabilizing resistor and AC by-pass capacitors? Date: Mon, 11 Jul 2005 06:51:36 -0700 Message-ID: References: > Most RF power transistors in the 50-100 watt range already have an > internal emitter resistor. It's usually less than a tenth of an ohm, > perhaps only a few hundreths of an ohm. Its purpose is to prevent > thermal runaway and make the device more tolerant of overload due to > momentary impedance mismatches. Internal resistors have an extemely > low inductance. They are NOT wirewound. They are an integral part of > the transistor construction and material. The manufacturer may not > mention their existence in his catalogue or data book. > > RF power transistors are usually multi-emitter devices - all in > parallel. Each emitter has its own individual series resistor. > > Such low-value external resistors are not available as discrete > wire-ended circuit components. Inductance would be too high at HF and > an invitation to self oscillation. Don't attempt to use normal circuit > components in emitter leads unless a transistor manufacturer > specifically recommends them. > > HF and VHF power transistors are very fast fuses. They are worked very > close to their maximum voltage and current ratings. > ---- > Reg, G4FGQ > yup! Article: 93585 of rec.radio.amateur.homebrew From: "Bill KB3GUN" References: <42BBFBB7.20706@nrao.edu> <42cc39e2$0$52206$ec3e2dad@news.usenetmonster.com> Subject: Re: How big has Somerset, PA hamfest been in the past? Date: Mon, 11 Jul 2005 10:58:02 -0400 Message-ID: <42d288da$0$52197$ec3e2dad@news.usenetmonster.com> "straydog" wrote in message news:Pine.NEB.4.62.0507111002200.21971@mx.freeshell.org... > > > On Wed, 6 Jul 2005, Bill Smith wrote: > >> Date: Wed, 6 Jul 2005 16:07:14 -0400 >> From: Bill Smith >> Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, >> rec.radio.amateur.equipment, rec.radio.amateur.homebrew >> Subject: Re: How big has Somerset, PA hamfest been in the past? >> >> "straydog" wrote in message >> news:Pine.NEB.4.62.0506261856170.28426@sdf.lonestar.org... >>> >>> >>> On Fri, 24 Jun 2005, Galen Watts wrote: >>> >>>> Date: Fri, 24 Jun 2005 08:25:27 -0400 >>>> From: Galen Watts >>>> To: straydog >>>> Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, >>>> rec.radio.amateur.equipment, rec.radio.amateur.homebrew >>>> Subject: Re: How big has Somerset, PA hamfest been in the past? >>>> >>>> straydog wrote: >>>>> >>>>> I think July 17, is the next Somerset PA hamfest and I've been >>>>> thinking >>>>> about going. Its a long drive from here (southern Delaware) and I was >>>>> wondering how big and how good it has been in the past. Anyone got any >>>>> recollections from the past? >>>>> >>>>> Art, w4pon >>>> >>>> They have pictures of last year's fest at >>>> http://www.k3smt.org/hf2004/ >>>> >>>> -W8LNA >>>> >>> >>> Thanks for the info... >>> >>> I had a look. >>> >>> W4PON >>> >>> >> >> Hello Art, >> This is only our second annual hamfest. Last year it was held in August, >> a >> day after the hurricane came thru. Our turnout was only about 300. >> Feedback >> so far this year says we should have between 500-750. Good odds for >> winning >> a door prize or the main drawing. >> Worst case, we're only 6 miles from the 9/11 Flight 93 Crash Site / >> Memorial. That in itself would make the trip worth it. The Somerset >> Somerfest is also running from Friday thru Sunday. Food, Music, Fun... I >> should work for the Chamber of Commerce...HiHi >> >> Hope to see you here. >> Bill kb3gun >> http://www.k3smt.org >> >> >> > > Thanks for the further information. However, here is my problem: first, > for me its a long drive one way (5-6 hours and I'd have to stay in a > motel Sat night, come back home Sunday, PM). Then, I was driving around > yesterday and the bigger problem: sticker shock at the gas pump (I was > gazing at a sign that showed $2.30+/gal for low test regular) . I'd be > spending more money on gas for the round trip than I'd expect to spend on > goodies, toys, parts, etc at the fest itself. :-( > > > > Art > W4PON > I understand completely, Art. I'm in the same boat when it comes to distant hamfests. I have to run premium in my jeep and it's running $2.50 now. Thanks anyway for you interest. 73 Bill kb3gun Somerset PA Hamfest http://www.k3smt.org/hamfest Article: 93586 of rec.radio.amateur.homebrew From: straydog Subject: Re: How big has Somerset, PA hamfest been in the past? Date: Mon, 11 Jul 2005 22:21:48 +0000 Message-ID: References: On Mon, 11 Jul 2005, Bill KB3GUN wrote: > Date: Mon, 11 Jul 2005 10:58:02 -0400 > From: Bill KB3GUN > Reply-To: Bill KB3GUN > Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, > rec.radio.amateur.equipment, rec.radio.amateur.homebrew > Subject: Re: How big has Somerset, PA hamfest been in the past? > > > "straydog" wrote in message > news:Pine.NEB.4.62.0507111002200.21971@mx.freeshell.org... >> >> >> On Wed, 6 Jul 2005, Bill Smith wrote: >> >>> Date: Wed, 6 Jul 2005 16:07:14 -0400 >>> From: Bill Smith >>> Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, >>> rec.radio.amateur.equipment, rec.radio.amateur.homebrew >>> Subject: Re: How big has Somerset, PA hamfest been in the past? >>> >>> "straydog" wrote in message >>> news:Pine.NEB.4.62.0506261856170.28426@sdf.lonestar.org... >>>> >>>> >>>> On Fri, 24 Jun 2005, Galen Watts wrote: >>>> >>>>> Date: Fri, 24 Jun 2005 08:25:27 -0400 >>>>> From: Galen Watts >>>>> To: straydog >>>>> Newsgroups: rec.radio.swap, rec.radio.amateur.boatanchors, >>>>> rec.radio.amateur.equipment, rec.radio.amateur.homebrew >>>>> Subject: Re: How big has Somerset, PA hamfest been in the past? >>>>> >>>>> straydog wrote: >>>>>> >>>>>> I think July 17, is the next Somerset PA hamfest and I've been >>>>>> thinking >>>>>> about going. Its a long drive from here (southern Delaware) and I was >>>>>> wondering how big and how good it has been in the past. Anyone got any >>>>>> recollections from the past? >>>>>> >>>>>> Art, w4pon >>>>> >>>>> They have pictures of last year's fest at >>>>> http://www.k3smt.org/hf2004/ >>>>> >>>>> -W8LNA >>>>> >>>> >>>> Thanks for the info... >>>> >>>> I had a look. >>>> >>>> W4PON >>>> >>>> >>> >>> Hello Art, >>> This is only our second annual hamfest. Last year it was held in August, >>> a >>> day after the hurricane came thru. Our turnout was only about 300. >>> Feedback >>> so far this year says we should have between 500-750. Good odds for >>> winning >>> a door prize or the main drawing. >>> Worst case, we're only 6 miles from the 9/11 Flight 93 Crash Site / >>> Memorial. That in itself would make the trip worth it. The Somerset >>> Somerfest is also running from Friday thru Sunday. Food, Music, Fun... I >>> should work for the Chamber of Commerce...HiHi >>> >>> Hope to see you here. >>> Bill kb3gun >>> http://www.k3smt.org >>> >>> >>> >> >> Thanks for the further information. However, here is my problem: first, >> for me its a long drive one way (5-6 hours and I'd have to stay in a >> motel Sat night, come back home Sunday, PM). Then, I was driving around >> yesterday and the bigger problem: sticker shock at the gas pump (I was >> gazing at a sign that showed $2.30+/gal for low test regular) . I'd be >> spending more money on gas for the round trip than I'd expect to spend on >> goodies, toys, parts, etc at the fest itself. :-( >> >> >> >> Art >> W4PON >> > > I understand completely, Art. I'm in the same boat when it comes to distant > hamfests. I have to run premium in my jeep and it's running $2.50 now. > > Thanks anyway for you interest. > > 73 > Bill kb3gun > Somerset PA Hamfest > http://www.k3smt.org/hamfest Well, thanks again. FWIW, it sure would be nice if for some of these fests someone could go around, at the end, with a video camera or d-cam and take pictures (something like for that URL of the last one) of the unsold major stuff (and maybe guys selling parts?) and post these on the club website as a "possibly still available" item and an email address (or something like that). All a guy would need is: a cardstock with price and email address in felt tip pen ink, held in front of the gear. That shouldn't be too hard, or the guy selling the stuff could provide his own jpeg images on a floppy disk. I'm not particularly interested in eBay/auctionering stuff (since you have to play the escalating price game, then the shipping question, etc). But, if a guy said "Here is X, I'd like Y dollars for it, and subject to negotiations" I could get more interested in this. Art, W4PON Article: 93589 of rec.radio.amateur.homebrew From: Allodoxaphobia Subject: Re: SP-600 Transmitter project Date: 12 Jul 2005 15:19:53 GMT Message-ID: References: On Mon, 11 Jul 2005 18:06:13 -0400, GBrown wrote: > Any one have a suggestion as to a model number for this homebrew xmtr? > Something along the line that will go good with "SP-600" 006-PS ? It does sound like a fun and creative project. gl. Jonesy -- Marvin L Jones | jonz | W3DHJ | linux Pueblo, Colorado | @ | Jonesy | OS/2 __ 38.24N 104.55W | config.com | DM78rf | SK Article: 93590 of rec.radio.amateur.homebrew From: "Dave" References: Subject: Re: SP-600 Transmitter project Message-ID: <1121186639.c6617136487cc476519a22f2267db457@meganetnews2> Date: Tue, 12 Jul 2005 09:43:56 -0700 "GBrown" wrote in message news:tbudndlEEerLcE_fRVn-hw@gwi.net... >I just got done restoring an SP-600JX-1. I am now looking for an SP-600 > front panel, side supports and the two window escutcheons. The reason > being......... I am going to reverse the panel and build an AM transmitter > using the reverse panel as the front panel to the home brew transmitter. > Thinking about a single 813 with maybe some 6146's as modulator. I don't > care what the condition of the panel is. I would also like to find some > SP-600 knobs. I am going to use a VFO from a junker HT-37 and just run 75 > and 40 meter AM/CW. I think this is going to be a fun project. Any one > have > a suggestion as to a model number for this homebrew xmtr? Something along > the line that will go good with "SP-600" Neat project! Call it TX-600 or HB-600 ("Home Brew") Article: 93591 of rec.radio.amateur.homebrew From: Curious George Subject: How to build an amplifier chassis???? Date: Tue, 12 Jul 2005 12:56:09 -0400 Message-ID: I've seen several books that detail the electronic how to when it comes to building an HF RF amplifier from 100 watts to 2 KW. Great! They also show the amps sitting in these finely crafted metal cabinets. Ok well.... I don't know how to build a nice metal cabinet, and the books don't tell me. So....Now that I've decided I really want to build one of those nice home brew amps I need to know how to make the metal cabinet to put all those electronic parts in. Is there a book or web page that teaches how to build a nice metal cabinet to put those homebrew amplifiers in? Curious George Article: 93592 of rec.radio.amateur.homebrew From: "Mike Andrews" Subject: Re: How to build an amplifier chassis???? Date: Tue, 12 Jul 2005 20:19:18 +0000 (UTC) Message-ID: References: <1121188743.628871.171620@z14g2000cwz.googlegroups.com> Tim Shoppa wrote: > In the traditional world, the chassis and enclosure are related but > separate items. The common technique is: > 1. Electronics built on aluminum chassis box. Available > pre-fabricated from Hammond etc. Or make your own from sheet metal. > 2. Front panel bolted to the chassis box. Knobs and switches and > meters go on the front panel. And are either wired to the stuff inside > the chassis or control variable caps etc. on the chassis via long > shafts. Front panel for a big project is often 19" wide rack-mount > panel (again a standard size available from Hammond et al.) > 3. Enclosure is a sheet metal box that slides on from behind. Made > using sheet metal tools. > At the high end, "sheet metal tools" are a big shear for cutting and a > brake for bending. At the low end you make you own brake out of 2x4's > and hinges, and cut with hacksaw/table saw/aircraft snips (depending on > type of cut, thickness, and material.) > For the really classy look all the holes you need can be cut with > punches. More likely for a hobbyist is drills and hacksaws and files > and the most valuable tool of all: the nibbler. And if there's a good sheet metal shop in your area (there is in mine), you may be able to get the owner to custom-make stuff for you for prices that merely make you want to scream. But that way you'll get what you want, or at least what you told the owner you wanted. My preference, when I get to indulge it, is for rackmount panels with one or more chassis boxes bolted to it, and subchassis inside those as seems appropriate. -- Mike Andrews W5EGO 5WPM mikea@mikea.ath.cx Extra Tired old sysadmin working on his code speed Article: 93593 of rec.radio.amateur.homebrew From: "Joel Kolstad" Subject: Re: Simple questions on receivers Date: Tue, 12 Jul 2005 14:01:00 -0700 Message-ID: <11d8bpfoa35o6c3@corp.supernews.com> References: <1121199166.494373.59190@g49g2000cwa.googlegroups.com> "dave.harper" wrote in message news:1121199166.494373.59190@g49g2000cwa.googlegroups.com... > How well-defined is the gain for a cap-coil loop, like in an AM radio? > (i.e., how fast does the gain droppoff as you move up or down from the > 'tuned' frequency?) Is it a function of L and C? Or just frequency? For the L-C resonator itself, the falloff will be 6dB per octave (doubling of frequency) once you're well outside of the center (tuned) frequency. The 3dB bandwidth will be determined by the Q of the circuit, and this is often not particularly well defined during the design stage -- often a well-defined bandpass filter somewhere "down the line" (e.g., at an IF stage) will ultimately define what the radio receives. The 6dB/octave drop comes from just looking at the impedance or transfer function of an LC(R) resonator -- you'll end up with an s^2 (frequency squared) term in the denominator of the equation. > (different combinations of L and C will tune to the same frequency, but > is the gain the same?) No, although for low Q resonators, it's often pretty close. > How come the coils on many of the CR schematics I've seen have multiple > tap locations? It seems that with a variable cap, you should be able > to tune to whatever frequency that's in your range. Is it to increase > the range of your radio's coverage? Or because the gain at certain > frequencies is better with different C/L combinations? They're usually trying to match the impedance of the LC circuit to the input impedance of "the next stage" (i.e., a transistor amplifier) to maximize power transfer. So, while it's not really "gain" (we haven't amplified anything yet -- this is more like a resistive divider), the output will be higher with different C/L combinations. Generally speaking, most relatively simple AM receivers are really only intended to pick up relatively strong, nearby transmitters. As such, you can get away with an awful lot of "cut and try" when it comes to designing the circuit (largely ignore matching impedances, Q's, etc.) and still obtain acceptable results. ---Joel Article: 93594 of rec.radio.amateur.homebrew From: "Jeff James" Subject: Buy and Sell your Tube Gear! Message-ID: Date: Tue, 12 Jul 2005 21:22:54 -0400 You never know what you'll find.. http://www.dealamerica.com/deal/cgi-bin/ads/bcads.cgi FREE ads Dedicated to Vintage Amateur Radio...