Article: 102354 of rec.radio.amateur.boatanchors From: "Mike" Subject: FS: 8122 amplfier..... Date: Fri, 19 May 2006 08:43:09 -0500 Message-ID: FS: I have a extra 8122 amplfier tube that I kept for my spare when I owned a National NCL-2000. If anyone needs it it can be theirs for $48.00 shipped. Article: 102355 of rec.radio.amateur.boatanchors From: "Mike" Subject: Free TH-6DXX beam....... Date: Fri, 19 May 2006 11:42:23 -0500 Message-ID: FS: I have an excellent condition TH6-DXX tri-band beam antenna (with stainless hardware) with new still-in-tha-box TH7 kit that was never added. The beam is sitting at 90' on a Ham-M rotor (take it too), all in good working condition. It is free to whomever wants to remove it and take the Rohn 25 tower down. I need some of the tower sections and will let the rest go (including all the guys and hardware) with the antenna also. Tower is located in College Station, TX. IF interested in details, contact Mike via email at: oldrover at verizon.net or phone at: (979) 696-4400 (home), (979)255-3544 (cell). Article: 102356 of rec.radio.amateur.boatanchors From: "JC" Subject: Dentron MLA-2500 Question Message-ID: Date: Fri, 19 May 2006 23:19:47 GMT Hi Group, I have a 2500 that had one bad 8875, and as-is EBay buy, and I am in the process of a conversion to a single 8877. This may not be the best choice of a tube for the application, but I had a good one in a box for nearly 20 years, so I decided to give it a try. Before the conversion I powered it up, and with one tube I could get 450 watts on 80M with 50 watts drive. I did notice however that the variable loading capacitor had to be at full mesh on any band I tried. I blew off that issue because with only one tube the PI-Net was not seeing the as-designed input impedance. My question is from my blurry schematic and parts list. The fixed Centralab loading capacitors in my rig are all 1000pf, and the fixed plate tuning side capacitors are all Centralab 100pf units. The parts list does not show any 1000pf HV Centralab capacitors. Is there a typo in the parts list, or does my amplifier have the wrong capacitors installed in the loading area? I powered up the amplifier last night, and I can get 600 watts RF out on 80 meters with 50 watts drive. The cathode current reaches 0.8 ampere at 1700 volts Plate. So that is 1360 watts in for 600 watts output. That is about 44% efficiency. The variable loading control always wants to be at maximum mesh for maximum RF output. On 160, 40, and 20m meters the loading variable capacitor must also be at maximum mesh. This makes me think my PI-Network is not correct for the impedances involved, and then it sure appears that the Dentron documentation does not match my rig. I might have to reverse engineer that PI-Net. So does anyone have a better set of drawings to see if their MLA-2500 PI-Net parts match the drawings? Regards, Jim WD5JKO Article: 102357 of rec.radio.amateur.boatanchors From: "JC" References: Subject: Re: Dentron MLA-2500 Question Message-ID: Date: Sat, 20 May 2006 17:13:42 GMT Update: The fixed loading capacitors on the MLA-2500B for 75, 160 meters are both 1000pf per Dentron parts list whereas they are 100pf on the MLA-2500 parts list. It looks like a typo in the documentation. Then I measured my 1000pf capacitors in my amp, these both measured about 820pf on my capacitance bridge at 4 Mhz. For sanity sake, I also measured a 820 pf silver mica capacitor, and the bridge read 850pf @ 4 Mhz. So it seems that I uncovered two problems: * Dentron MLA-2500 parts list has typos in it * My two loading capacitors for 75 and 160 are out of tolerence on the low side. This explains why my variable loading capacitor needs to be at full mesh. Anybody have a 8877 Teflon chimney they want to get rid of? Jim WD5JKO "JC" wrote in message news:nosbg.73670$_S7.36849@newssvr14.news.prodigy.com... > Hi Group, > > I have a 2500 that had one bad 8875, and as-is EBay buy, and I am in the > process of a conversion to a single 8877. This may not be the best choice > of a tube for the application, but I had a good one in a box for nearly 20 > years, so I decided to give it a try. Before the conversion I powered it > up, and with one tube I could get 450 watts on 80M with 50 watts drive. I > did notice however that the variable loading capacitor had to be at full > mesh on any band I tried. I blew off that issue because with only one tube > the PI-Net was not seeing the as-designed input impedance. > > My question is from my blurry schematic and parts list. The fixed > Centralab loading capacitors in my rig are all 1000pf, and the fixed plate > tuning side capacitors are all Centralab 100pf units. The parts list does > not show any 1000pf HV Centralab capacitors. Is there a typo in the parts > list, or does my amplifier have the wrong capacitors installed in the > loading area? > > I powered up the amplifier last night, and I can get 600 watts RF out on > 80 meters with 50 watts drive. The cathode current reaches 0.8 ampere at > 1700 volts Plate. So that is 1360 watts in for 600 watts output. That is > about 44% efficiency. The variable loading control always wants to be at > maximum mesh for maximum RF output. On 160, 40, and 20m meters the loading > variable capacitor must also be at maximum mesh. This makes me think my > PI-Network is not correct for the impedances involved, and then it sure > appears that the Dentron documentation does not match my rig. I might have > to reverse engineer that PI-Net. > > So does anyone have a better set of drawings to see if their MLA-2500 > PI-Net parts match the drawings? > > Regards, > Jim > WD5JKO > Article: 102358 of rec.radio.amateur.boatanchors From: "Antonio Vernucci" References: Subject: Re: Dentron MLA-2500 Question Date: Sat, 20 May 2006 21:39:04 +0200 Message-ID: <446f705a$0$36922$4fafbaef@reader3.news.tin.it> It is unlikely that the fixed loading capacitor is as high as 1000 pf, = except for 160m. However if Dentron has really used a Centralab 1000-pf = capacitor as fixed loading capacitor, that is a sign of bad design, = because those capacitors are not suitable for that purpose. As a matter of fact the Centralab 1000-pF capacitors use a different = ceramic material than the 100 pF units, and they therefore have a very = different behavior, as explained below: - the 1000-pF units can withstand high RF current, but cannot withstand = high RF voltage at the same time (DC voltage does not matter). A more = rigorous way to express that concept is to say that the 1000-pf units = cannot withstand high "reactive power" (reactive power =3D RF current = times RF voltage). In practice they are only suitable for bypassing or = plate-to-pi coupling (high RF current but very little RF voltage). - on the contrary, the 100-pF units are suitable for operation in = resonating circuits, where both the RF voltage and the RF current is = high (=3D high reactive power). So they are suitable as fixed loading = capacitors. If one uses a Centralab 1000-pF capacitor as the fixed loading capacitor = of a high-power linear, the capacitor will heat up and change its = capacitance, so detuning the circuit. Prolonged high-power operation may = result in capacitor failure. 73 Tony I0JX =20 . "JC" ha scritto nel messaggio = news:nosbg.73670$_S7.36849@newssvr14.news.prodigy.com... > Hi Group, >=20 > I have a 2500 that had one bad 8875, and as-is EBay buy, and I am = in the=20 > process of a conversion to a single 8877. This may not be the best = choice of=20 > a tube for the application, but I had a good one in a box for nearly = 20=20 > years, so I decided to give it a try. Before the conversion I powered = it up,=20 > and with one tube I could get 450 watts on 80M with 50 watts drive. I = did=20 > notice however that the variable loading capacitor had to be at full = mesh on=20 > any band I tried. I blew off that issue because with only one tube the = > PI-Net was not seeing the as-designed input impedance. >=20 > My question is from my blurry schematic and parts list. The fixed=20 > Centralab loading capacitors in my rig are all 1000pf, and the fixed = plate=20 > tuning side capacitors are all Centralab 100pf units. The parts list = does=20 > not show any 1000pf HV Centralab capacitors. Is there a typo in the = parts=20 > list, or does my amplifier have the wrong capacitors installed in the=20 > loading area? >=20 > I powered up the amplifier last night, and I can get 600 watts RF = out on=20 > 80 meters with 50 watts drive. The cathode current reaches 0.8 ampere = at=20 > 1700 volts Plate. So that is 1360 watts in for 600 watts output. That = is=20 > about 44% efficiency. The variable loading control always wants to be = at=20 > maximum mesh for maximum RF output. On 160, 40, and 20m meters the = loading=20 > variable capacitor must also be at maximum mesh. This makes me think = my=20 > PI-Network is not correct for the impedances involved, and then it = sure=20 > appears that the Dentron documentation does not match my rig. I might = have=20 > to reverse engineer that PI-Net. >=20 > So does anyone have a better set of drawings to see if their MLA-2500 = PI-Net=20 > parts match the drawings? >=20 > Regards, > Jim > WD5JKO=20 >=20 > Article: 102359 of rec.radio.amateur.boatanchors From: "JC" References: <446f705a$0$36922$4fafbaef@reader3.news.tin.it> Subject: Re: Dentron MLA-2500 Question Message-ID: <15Mbg.75119$F_3.25217@newssvr29.news.prodigy.net> Date: Sat, 20 May 2006 21:44:29 GMT Tony, I appreciate the comments. For sure there is something awry in this pi-net. I looked at your tutorial on your web page, and wow, you know your stuff! The schematics of the 2500, and 2500B are at the following link: ftp://bama.sbc.edu/downloads/dentron/mla2500/ Another aspect of this pi-net is that the tank coil consists of tight wound silver plated stranded Teflon insulated wire of about 10 awg. Users of healthy 2500's report 1100 to 1300 watts key down (output), and 1500 watts PEP out with a pulser. This is very good for the size and weight of this amplifier. The loading variable cap is about 50-500pf with a 100pf Centralab in parallel with that. The bandswitch is not a shorting type, so it adds 200pf on 40m, 1000pf on 75, and 1000pf on 160 (all on 2500B schematic and parts list). These do not add up due to the type of rotary switch used. I'd prefer a shorting switch arrangement where on 160m, all the fixed loading caps are in parallel and each unit has less capacitance. I will look more carefully at the capacitors used to see what the part number is. Maybe the correct values are in there, but of the wrong type. I plan to use my impedance bridge from the 50 ohm amp output looking into the amp, and replace the 8877 with the calculated plate load RL going into the pi-net. Hopefully a 1/2 watt carbon comp resistor around 2K (a guess) will represent the plate side impedance. My hope here is that I can evaluate the pi-net 160-10m at a low level (0dbm?) to see what the impedance matching capability is. Maybe the values used are correct, but with high power, the capacitors get lossy (hot), drift down in value, and cause the efficiency of the amp to really stink. I'll let you'all know what I find. Thanks, Jim WD5JKO "Antonio Vernucci" wrote in message news:446f705a$0$36922$4fafbaef@reader3.news.tin.it... It is unlikely that the fixed loading capacitor is as high as 1000 pf, except for 160m. However if Dentron has really used a Centralab 1000-pf capacitor as fixed loading capacitor, that is a sign of bad design, because those capacitors are not suitable for that purpose. As a matter of fact the Centralab 1000-pF capacitors use a different ceramic material than the 100 pF units, and they therefore have a very different behavior, as explained below: - the 1000-pF units can withstand high RF current, but cannot withstand high RF voltage at the same time (DC voltage does not matter). A more rigorous way to express that concept is to say that the 1000-pf units cannot withstand high "reactive power" (reactive power = RF current times RF voltage). In practice they are only suitable for bypassing or plate-to-pi coupling (high RF current but very little RF voltage). - on the contrary, the 100-pF units are suitable for operation in resonating circuits, where both the RF voltage and the RF current is high (= high reactive power). So they are suitable as fixed loading capacitors. If one uses a Centralab 1000-pF capacitor as the fixed loading capacitor of a high-power linear, the capacitor will heat up and change its capacitance, so detuning the circuit. Prolonged high-power operation may result in capacitor failure. 73 Tony I0JX . "JC" ha scritto nel messaggio news:nosbg.73670$_S7.36849@newssvr14.news.prodigy.com... > Hi Group, > > I have a 2500 that had one bad 8875, and as-is EBay buy, and I am in > the > process of a conversion to a single 8877. This may not be the best choice > of > a tube for the application, but I had a good one in a box for nearly 20 > years, so I decided to give it a try. Before the conversion I powered it > up, > and with one tube I could get 450 watts on 80M with 50 watts drive. I did > notice however that the variable loading capacitor had to be at full mesh > on > any band I tried. I blew off that issue because with only one tube the > PI-Net was not seeing the as-designed input impedance. > > My question is from my blurry schematic and parts list. The fixed > Centralab loading capacitors in my rig are all 1000pf, and the fixed plate > tuning side capacitors are all Centralab 100pf units. The parts list does > not show any 1000pf HV Centralab capacitors. Is there a typo in the parts > list, or does my amplifier have the wrong capacitors installed in the > loading area? > > I powered up the amplifier last night, and I can get 600 watts RF out > on > 80 meters with 50 watts drive. The cathode current reaches 0.8 ampere at > 1700 volts Plate. So that is 1360 watts in for 600 watts output. That is > about 44% efficiency. The variable loading control always wants to be at > maximum mesh for maximum RF output. On 160, 40, and 20m meters the loading > variable capacitor must also be at maximum mesh. This makes me think my > PI-Network is not correct for the impedances involved, and then it sure > appears that the Dentron documentation does not match my rig. I might have > to reverse engineer that PI-Net. > > So does anyone have a better set of drawings to see if their MLA-2500 > PI-Net > parts match the drawings? > > Regards, > Jim > WD5JKO > > Article: 102360 of rec.radio.amateur.boatanchors From: - exray - Subject: Re: Replacement Transformer for Hallicrafters SX-42 Date: Sun, 21 May 2006 01:37:47 -0400 Message-ID: <126vv5go6n2b7f@corp.supernews.com> References: <1148179748.423888.118780@u72g2000cwu.googlegroups.com> jjbunn wrote: > I'm looking for a replacement, or a substitute, mains transformer for a > Hallicrafters SX-42 ... the existing one sizzled and died :-( > > The specifications are: 115V primary, 500V C.T. @ 142mA, 5V @ 3A and > 6.3V @ 5.3A, and the mounting holes are 3.75"x3.00". > > If anyone knows a likely source for a replacement, please let me know. > > Thanks! > Julian > Try http://www.oldradioparts.com And there's always ebay. Unfortunately old large transformers and audiophile prices tend to go hand-in-hand but you might get lucky. I recently found one for an 18-tube set of mine for $19. I guess it was "too big" for audio gear :) The Vintage Electronics category is where to look. GL, Bill Article: 102361 of rec.radio.amateur.boatanchors From: "JC" References: <1148179748.423888.118780@u72g2000cwu.googlegroups.com> Subject: Re: Replacement Transformer for Hallicrafters SX-42 Message-ID: Date: Sun, 21 May 2006 13:48:18 GMT Julian, Any chance the failure is visible, and fixable? An option here is to get your tranny rewound. There are lots of folks that offer this service, or you might take it on as a DIY project. If you go this route, you could simplify the winding task by only making one winding of 250 vac, and use a full wave bridge rectifier consisting of two silicon diodes on the negative side (-) and the vacuum tube 5U4 rectifier on the positive side (+). If you go this route, you can beef up the HV secondary wire size since there will be room, and it may be easier to handle a larger wire than what was originially there. You can also modify the turns ratio to better match today's higher line voltage. I bet the SX-42 tranny was designed for 110 vac AC mains whereas today we often have about 122 vac at our outlets. As a FYI for still working open frame boat anchor transformers, you can preserve them by vacuum impregnating them with transformer varnish. This will fill in the voids where a failure is imminent, but hasn't happened yet. This can be a DIY project where you can use car manifold vacuum, some tubing, fittings, and a suitable container. Take the end caps off first to expose the windings. If the wires have bad insulation, you can cut them 1" >from leaving the core, and strip back. Add on new wires and heat shrink the connection. As for doing the varnish bit, it's neat to watch the bubbles exit the transformer as the air is pumped from the container, and then when you let the air back in, that forces the varnish into all the cracks and pores of the inner area of the transformer. Repeat two more times to get the job done. Then hang until dripping is over, and bake to cure (temp and time depends on varnish used). Instead of varnish I have also used electrical rated RTV thinned out with chlorethane until it is a white milky soup. Jim WD5JKO "jjbunn" wrote in message news:1148179748.423888.118780@u72g2000cwu.googlegroups.com... > I'm looking for a replacement, or a substitute, mains transformer for a > Hallicrafters SX-42 ... the existing one sizzled and died :-( > > The specifications are: 115V primary, 500V C.T. @ 142mA, 5V @ 3A and > 6.3V @ 5.3A, and the mounting holes are 3.75"x3.00". > > If anyone knows a likely source for a replacement, please let me know. > > Thanks! > Julian > Article: 102362 of rec.radio.amateur.boatanchors From: - exray - Subject: Re: Replacement Transformer for Hallicrafters SX-42 Date: Sun, 21 May 2006 10:29:20 -0400 Message-ID: <1270ua6gtspvtb1@corp.supernews.com> References: <1148179748.423888.118780@u72g2000cwu.googlegroups.com> g. beat <@ wrote: > > Julian - > > An option is a transformer company. Heyboer Transformers > in Grand Rapids, Michigan does this work -- > you may also have a suitable rebuilder one in California. > http://www.heyboertransformers.com/ > > You can provide them with specifications, an the old transformer for proper > sizing - > they matched the wire colors and used the old bells on the new transformer. > Professional job on a rebuild for me late last December. > > BTW, you should specify that primary should be 120 VAC -- > instead of 110 V of the original - due to higher line voltages - > this should operate cooler in the SX-42. > > w9gb Heyboer does nice work and I've used them but I would think they are prohibitively expensive for this project. You'd looking at around $150 for one this size. -Bill Article: 102363 of rec.radio.amateur.boatanchors From: "JC" References: Subject: Re: Dentron MLA-2500 Question Message-ID: Date: Sun, 21 May 2006 15:50:55 GMT > > For reference purposes, here are the Communication Quarterly and KU7G > articles (Adobe Acrobat) > regarding 4CX400a or 4CX800a conversions > http://www.tomstubes.com/images/mla_2500_4cx400a.pdf > > KU7G > http://www.tomstubes.com/images/mla2500_4cx800a.pdf > > w9gb Hi, Thanks for the excellent links. I had seen the first one before. In looking at the article about the 2 times 4cx400a, it jumps out at me that this conversion leads to about 350-500 watts less RF output than original (1100-1300 versus 750-800) even when using tubes with more capability. I attribute this to running Tetrodes at low plate voltage. In this application Hi-Mu Triodes are a better choice. Also the low RF drive need for the Tetrodes make them attractive for low power exciters, and a problem for us with a 100 watt exciter. My conversion is similar to the 4cx800 article except I am using a 8877. I use the same external box to house the socket, and mount the fan. The 8877 may not be designed for use at 1700 volts, but what the heck, I only want about 1000 watt RF output. I need a chimney like what is described for tthe PI-Network he 4cx800. Any idea where I can get a block of Teflon, and then get it machined? That article about the 4cx800 has some good visuals of the pi-net that is being a problem with my 2500. Thanks again, Jim WD5JKO Article: 102364 of rec.radio.amateur.boatanchors From: "S. Reid" Subject: CRT for Tektronix 564B, R564B, or TLDM64 Message-ID: Date: Sun, 21 May 2006 22:39:17 GMT Hi, I have a new Tektronix tube part # 154-0737-00. This is a CRT for scopes 564B, R564B, or TLDN64. This is new in the original box and looks perfect. If anyone is interested, please drop me a note. tube_s@hotmail.com Brian Article: 102365 of rec.radio.amateur.boatanchors From: Roger Subject: Re: Dentron MLA-2500 Question Message-ID: <6pr172t75mqle2rh6ecoahmijlgce4aqoq@4ax.com> References: Date: Sun, 21 May 2006 18:53:04 -0400 On Sun, 21 May 2006 15:50:55 GMT, "JC" wrote: > >> >> For reference purposes, here are the Communication Quarterly and KU7G >> articles (Adobe Acrobat) >> regarding 4CX400a or 4CX800a conversions >> http://www.tomstubes.com/images/mla_2500_4cx400a.pdf >> >> KU7G >> http://www.tomstubes.com/images/mla2500_4cx800a.pdf >> >> w9gb > > >Hi, Thanks for the excellent links. I had seen the first one before. In >looking at the article about the 2 times 4cx400a, it jumps out at me that >this conversion leads to about 350-500 watts less RF output than original >(1100-1300 versus 750-800) even when using tubes with more capability. I >attribute this to running Tetrodes at low plate voltage. In this application >Hi-Mu Triodes are a better choice. Also the low RF drive need for the >Tetrodes make them attractive for low power exciters, and a problem for us >with a 100 watt exciter. > >My conversion is similar to the 4cx800 article except I am using a 8877. I >use the same external box to house the socket, and mount the fan. The 8877 >may not be designed for use at 1700 volts, but what the heck, I only want As I recall the MLA-2500 ran 2200 volts. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com >about 1000 watt RF output. I need a chimney like what is described for tthe >PI-Network he 4cx800. Any idea where I can get a block of Teflon, and then >get it machined? > >That article about the 4cx800 has some good visuals of the pi-net that is >being a problem with my 2500. > >Thanks again, > >Jim >WD5JKO > Article: 102366 of rec.radio.amateur.boatanchors From: Straydog Subject: Hamfest, Georgetown, Delaware, May 27, 2006, 7 am- 5pm Date: Sun, 21 May 2006 19:23:05 -0400 Message-ID: References: <6Zbbg.26026$4H.22143@dukeread03> At Sussex Tech High School, US Route 9 about a mile west of Route 113. Admission free Talk in 147.075 + input more info: n3jvt@yahoo.com w3hrt@arrl.net dsmith@sussex.vt.k12.de.us Also, was mentioned in latest QST Article: 102367 of rec.radio.amateur.boatanchors From: "JC" References: <6pr172t75mqle2rh6ecoahmijlgce4aqoq@4ax.com> Subject: Re: Dentron MLA-2500 Question Message-ID: <3I8cg.13470$fb2.12790@newssvr27.news.prodigy.net> Date: Mon, 22 May 2006 01:44:31 GMT As I recall the MLA-2500 ran 2200 volts. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com Roger: Yes that ia about correct for no load. I am running mine off 120 vac, and the B+ drags down to about 1600 volts at 0.8 amp load. I've seen other conversions that run off 220 vac, and they say about 1700 volts for the same load. The voltage doubler capacitors if increased in value, say 330 uf instead of 125 uf would be better. This however would require adding a soft-start turn on modification to avoid welding the contacts of the power switch, or blowing the diode stack. Jim WD5JKO Article: 102368 of rec.radio.amateur.boatanchors From: "Benjamaniac" Subject: National NC-2-40CS Parts Needed Date: Sun, 21 May 2006 19:51:31 -0600 Message-ID: Looking for a knob for a National NC-2-40CS and also would like to find a picture of the matching speaker (NC-2TS) so I can see if the one I have is missing any trim...it looks like it is to me. Thanks for any help on these things. Ben Article: 102369 of rec.radio.amateur.boatanchors From: "Jim Barnard" Subject: Heathkit SB-303 Manual Date: Sun, 21 May 2006 22:06:23 -0400 Message-ID: I am looking for the schematic and alignment/theory of operation part of the Heathkti SB-303 manual. If anyone has this info, please contact me directly at jbarnard@ftc-i.net. I have one in pretty poor shape that I would like to restore. Thanks, Jim Barnard Article: 102370 of rec.radio.amateur.boatanchors Message-ID: <4471D7FA.3CECC644@sympatico.ca> From: "M. Kassay" Subject: FS: HEATHKIT items Date: Mon, 22 May 2006 11:25:46 -0400 For Sale Unbuilt, still in the box Heathkit HW-9 hf QRP rig, Best (serious) offer. :) Heath PSA-9 power supply $35 US not working ID-4001 weather station, inside unit only $40 US Heath rain gauge, built, but never used. $95 US Heath HD-1410 keyer manual $13 US shipped Heath IDW-2090 digital barograph manual $14 US shipped Heath IO-4550 dual trace scope manual $12 US shipped 73 Mike Article: 102371 of rec.radio.amateur.boatanchors From: Roger Subject: Re: Dentron MLA-2500 Question Message-ID: <9tb472t7m3g8jepvm2gv990tuen4av0iks@4ax.com> References: <6pr172t75mqle2rh6ecoahmijlgce4aqoq@4ax.com> <3I8cg.13470$fb2.12790@newssvr27.news.prodigy.net> Date: Mon, 22 May 2006 17:47:33 -0400 On Mon, 22 May 2006 01:44:31 GMT, "JC" wrote: > >As I recall the MLA-2500 ran 2200 volts. > >Roger Halstead (K8RI & ARRL life member) >(N833R, S# CD-2 Worlds oldest Debonair) >www.rogerhalstead.com > > >Roger: > >Yes that ia about correct for no load. I am running mine off 120 vac, and >the B+ drags down to about 1600 volts at 0.8 amp load. I've seen other I'm assuming that is in the tune position? 800 mills sounds kinda high in the tune/CW position. Also I was able to get well over 1500 watts PEP out of a pair of 8873s without driving them hard. >conversions that run off 220 vac, and they say about 1700 volts for the same It should be just a transformer tap change for 220. >load. The voltage doubler capacitors if increased in value, say 330 uf It sounds like they are tuning in the SSB mode. The voltage stays right up there in SSB so if tuned up with carrier in that mode the tuning will not be correct for SSB. >instead of 125 uf would be better. This however would require adding a >soft-start turn on modification to avoid welding the contacts of the power >switch, or blowing the diode stack. That lack of regulation is why they run a lot more output PEP when tuned in the tune/CW position instead of the SSB position. Years ago I sold and worked on a lot of the Dentron Amps. Good Luck, Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com > >Jim >WD5JKO > Article: 102372 of rec.radio.amateur.boatanchors From: "JC" References: <6pr172t75mqle2rh6ecoahmijlgce4aqoq@4ax.com> <3I8cg.13470$fb2.12790@newssvr27.news.prodigy.net> <9tb472t7m3g8jepvm2gv990tuen4av0iks@4ax.com> Subject: Re: Dentron MLA-2500 Question Message-ID: Date: Mon, 22 May 2006 23:05:09 GMT > I'm assuming that is in the tune position? 800 mills sounds kinda > high in the tune/CW position. The MLA-2500 has no tune / cw switch like some other Dentron's do. I guess the amps you are referring to must have a tap in the HV transformer to run 1KW DC input on CW at lower plate voltage. Is that correct? I'm sure glad this DC input stuff is past tense, and 1500 watts PEP output is simpler. Of cource the AM'ers that ran 1Kw dc input with plate modulation got their power cut back because it was legal for them to run ~ 3kw PEP output with a 750 watt carrier. I was one who did that back in the 1980's. That was a blast! My MLA-2500 has a "Cont Duty" switch that forces the fan on high speed whenever the amp is keyed. > > Also I was able to get well over 1500 watts PEP out of a pair of 8873s > without driving them hard. Aren't the 8873's a conduction cooled version of the 8873,8874,8875 family? Those have reduced plate dissipation, but no need for a fan. > >>conversions that run off 220 vac, and they say about 1700 volts for the >>same > > It should be just a transformer tap change for 220. Yea, that asummes there is a 220 vac outlet in your ham shack. :-) I still need a verification of them pi-net capacitors in the MLA-2500. It appears that the original documentation is incorrect, and so is a redrawn schematic on Bama. Jim Article: 102373 of rec.radio.amateur.boatanchors From: Roger Subject: Re: Dentron MLA-2500 Question Message-ID: References: <6pr172t75mqle2rh6ecoahmijlgce4aqoq@4ax.com> <3I8cg.13470$fb2.12790@newssvr27.news.prodigy.net> <9tb472t7m3g8jepvm2gv990tuen4av0iks@4ax.com> Date: Mon, 22 May 2006 20:47:16 -0400 On Mon, 22 May 2006 23:05:09 GMT, "JC" wrote: > > >> I'm assuming that is in the tune position? 800 mills sounds kinda >> high in the tune/CW position. > >The MLA-2500 has no tune / cw switch like some other Dentron's do. I guess >the amps you are referring to must have a tap in the HV transformer to run It has been along time, but there was a way to tune them to get full power on SSB. I was remembering a CW/SSB switch which aparently isn't correct. >1KW DC input on CW at lower plate voltage. Is that correct? I'm sure glad >this DC input stuff is past tense, and 1500 watts PEP output is simpler. Of >cource the AM'ers that ran 1Kw dc input with plate modulation got their >power cut back because it was legal for them to run ~ 3kw PEP output with a >750 watt carrier. I was one who did that back in the 1980's. That was a >blast! Most of the legal limit amps I ran at 1KW average including exciter would hit about 2200 PEP out. > >My MLA-2500 has a "Cont Duty" switch that forces the fan on high speed >whenever the amp is keyed. > >> >> Also I was able to get well over 1500 watts PEP out of a pair of 8873s >> without driving them hard. > >Aren't the 8873's a conduction cooled version of the 8873,8874,8875 family? >Those have reduced plate dissipation, but no need for a fan. Oops! I'm talking about a new, stock, MLA-2500. Make that a pair of 8875s, The transverse cooled ones that are nigh on to impossible to find. I did have an amp that used the 8873s, but if you did much operating you put a couple of fans on the heat sink. The 8873, 74, and 75 and the same tube with different cooling. >> >>>conversions that run off 220 vac, and they say about 1700 volts for the >>>same >> >> It should be just a transformer tap change for 220. > >Yea, that asummes there is a 220 vac outlet in your ham shack. :-) There wasn't here, but there soon was<:-)) It's quite easy to add a circuit breaker, some wire, and a couple of mutiple outlet boxes IF you own your own home and your wife is also a ham. <:-)) > >I still need a verification of them pi-net capacitors in the MLA-2500. It >appears that the original documentation is incorrect, and so is a redrawn >schematic on Bama. All I remember is they switched in extra capacitance on the lower bands. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com > >Jim > Article: 102374 of rec.radio.amateur.boatanchors From: "JC" References: <6pr172t75mqle2rh6ecoahmijlgce4aqoq@4ax.com> <3I8cg.13470$fb2.12790@newssvr27.news.prodigy.net> <9tb472t7m3g8jepvm2gv990tuen4av0iks@4ax.com> Subject: Re: Dentron MLA-2500 Question Message-ID: Date: Tue, 23 May 2006 04:36:37 GMT >> >>Yea, that asummes there is a 220 vac outlet in your ham shack. :-) > > There wasn't here, but there soon was<:-)) > It's quite easy to add a circuit breaker, some wire, and a couple of > mutiple outlet boxes IF you own your own home and your wife is also a > ham. <:-)) > Roger, It aint ever easy! I'm in a ranch style house with two breaker boxes. Both boxes are full of breakers! I do have breakers for an electric stove and I have gas, and I have a breaker for a sauna, and I have none. Those come from the far away box. The stove outlet is opposite a wall to the ham shack, so that is my best chance to use that, and change the breaker to 15 amps. Still need to pull the stove, and put a hole in the wall. The XYL is not a ham! Regards, Jim Article: 102375 of rec.radio.amateur.boatanchors From: "Ed" References: <1148064272.143963.161480@y43g2000cwc.googlegroups.com> Subject: Re: Matching speakers for vintage receivers Message-ID: Date: Tue, 23 May 2006 05:25:04 GMT You asked on your site about the Hallicrafters R-8. The R-8 is just like the R-12 floor model except with an eight inch speaker. "Nick KD4CPL" wrote in message news:1148064272.143963.161480@y43g2000cwc.googlegroups.com... >I have created a web site attempting to list the matching speakers as > advertised for most vintage ham radio receivers. > http://www.virhistory.com/ham/speakers.htm > > Additions and corresctions are welcomed. > Send e-mail to nick@3rdtech.com > > 73 & Have Fun, > Nick KD4CPL > > Article: 102376 of rec.radio.amateur.boatanchors Date: Tue, 23 May 2006 16:12:13 +0200 From: ADMIN Subject: Earn up to 1000 $ per month only for reading your Mails!!!!!!!! Message-ID: <4473168b$1$59880$afc38c87@news6.united-newsserver.de>

 

Article: 102377 of rec.radio.amateur.boatanchors From: "Jim Barnard" Subject: SB-303 Date: Tue, 23 May 2006 22:11:54 -0400 Message-ID: I am looking for a power cord for my Heathkit SB-303 that I am restoring. Should you have one available, please contact me directly at jbarnard@ftc-i.net Thanks, Jim Article: 102378 of rec.radio.amateur.boatanchors From: "Mike" Subject: Rax Military receiver..... Date: Thu, 25 May 2006 10:55:49 -0500 Message-ID: If anyone is interested in a good RAX WW2 military radio receiver, I just put one on eBay at http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=9730726456&rd=1&sspagename=STRK%3AMESE%3AIT&rd=1 Article: 102379 of rec.radio.amateur.boatanchors From: "Mike" Subject: Digital hanging commercial scale... Date: Thu, 25 May 2006 11:03:26 -0500 Message-ID: If anyone needs a good near new digital hanging scale that ranges 0-2000 lbs, excellent for weight measurements needed for building race cars, weighing large animals, weighing items sold by the pound, etc., I just posted one on eBay with no reserve price (currently $30.00) at; http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7622485481&rd=1&sspagename=STRK%3AMESE%3AIT&rd=1 Article: 102380 of rec.radio.amateur.boatanchors From: et472@FreeNet.Carleton.CA (Michael Black) Subject: Re: Digital hanging commercial scale... Date: 25 May 2006 16:26:42 GMT Message-ID: References: "Mike" (mlinger@tamu.edu) writes: > If anyone needs a good near new digital hanging scale And you prove what's bad about this newsgroup. This isn't a buy and sell newsgroup. When it was created, there was debate about whether ads should be allowed, and even back then (1995 or maybe it was 1996, I forget now) it was a hot point, because the Internet was still morphing >from it's traditional ways to the sadly more commercial arrangement. Finally, they decided ads would be allowed, but if you check the charter, they come way down after discussion. SO it's bad enough that too many treat this as a buy and sell newsgroup for old radio equipment. But you violate that further by using it as a general buy and sell newsgroup. And if advertising old radios is sort of borderline, it's quite clear that ads like this one does not belong here. Michael VE2BVW