Thanks to the generous hospitality of Bill Coleman, N2BC (a callsign that deserves a set of chimes!), a pretty good set of photos of the incredible W9TB homebrew station is posted on
http://home.stny.rr.com/n2bc Tell me what you think. 73, Don Merz, N3RHT -----Original Message----- From: Merz Donald S [mailto:[EMAIL PROTECTED] Sent: Thursday, November 07, 2002 1:00 PM To: amradio@mailman.qth.net; [EMAIL PROTECTED] Subject: RE: GB> Update On Supply for PP 304TLs Well, I have discovered the errors of my own making here. Your comments helped me realize where I had gone astray. First, let me say a few words in my own defense. Most homebrew rigs that are passed along come with no documentation. A few come with some documentation. And one in a hundred comes with good documentation. This "W9TB Desk Kilowatt" is in that middle group. In this case, the partial builder's notes that I have were ambiguous and I mis-interpreted them. The power supply notes that I have are for the 4E27-based exciter--not for the 304TL's final amp. I have almost no information on the final amp supply that W9TB used. But I screwed up and thought his cryptic notes were for the final amp. Sooo...I only discovered my mistake when your comments started me thinking about the use of the word "screen". Finally it dawned on me that the notes I was looking at were for the exciter. Screen actually meant screen, not grid. Now it all makes sense. But it means that I am worse off than I thought for information on his original 304TL supply design--there is basically none. At the risk of boring you, let me back off here and describe this rig so you have a complete picture. In a word--incredible. Imagine the finest mechanical and electrical engineering skills pumped into a late-40's homebrew CW kilowatt. It's a complete station with receiver, frequency meter, monitor receiver, exciter, and final. It has provision for antenna rotor control on the front panel. And it has provision for a remote control console attachment. Based on the notes, the rig was built in 1948-49, updated frequently over the years and used on the air until about 1985. I will take some pictures and pass them along. The control console, receiver and exciter are built on top of a removable desktop. Each has its own compartment that it fits into. The desktop itself appears to be commercial. But everything else is built from scratch--sheet aluminum with aluminum bracing. The receiver has been extensively solid-stated. I have not even opened it up yet. But I believe it is 100% solid state. I have opened up the band switching exciter and it is awesome. The construction quality is nothing short of intimidating. It uses a 4E27 final and a National MB-150 tank circuit. It is otherwise partly solid-stated. The transmitter and receiver both use National PW dials for tuning. The two pedestals that hold up the desk are packed with gear. The left hand pedestal holds the final amp--push-pull 304TLs with the biggest plug-in coils that B&W ever made and a variable center link operated by a turns-counter lever on the front panel. One side of the pedestal is a safety-interlocked door that opens to provide easy access to the final. The other pedestal has a Meissner HF receiver built into the top section, followed by a home-made heterodyne frequency meter and a drawer for holding the final coils. I have not looked at the Meissner receiver and freq meter at all. The power supply for this rig was built into a closet in W9TB's house. The parts of the power supply that I have are whatever was salvaged from that closet including the pole pig. It's hard to make sense out of what is here. I think I have HV, screen and filament covered for the exciter from my extensive "junk-box" power supply collection. But the junk box let me down on the final supply. I have no transformer capable of replacing the pole pig. It looks like w9TB was running the HV for both the exciter and the final from the pole pig. But there are no chokes in the "closet parts" that I received with the rig. And some hefty chokes will be needed. So I am only going to run the final from the pole pig and use the junk box supply as-is--unchanged (a lucky break) for the exciter. So that's where this stands. I have no web site. But if someone has someplace I can post some pictures, I would like to hear from you. Thanks. 73, Don Merz, N3RHT -----Original Message----- From: Merz Donald S [mailto:[EMAIL PROTECTED] Sent: Friday, November 01, 2002 3:28 PM To: amradio@mailman.qth.net; [EMAIL PROTECTED] Subject: GB> More On Supply for PP 304TLs "Screen" is what the original builder's notes show instead of "grid" or "bias". So I was propagating the mis-wording when I used "screen." The 304TL is of course a triode. Otherwise the audiophools could not love it. It looks like he was running the grid bias at about 80 volts. He had the primary of the HV transformer connected to a motorized variac that slowly brought up the HV. This sits behind a mechanical timer assembly of WWII surplus vintage that only starts the variac moving after the filaments have been on for a while. He's got the relay sequence set up so that you can't get HV if you don't have bias--er, I mean "screen" voltage. It's all a bit overly-clever if you ask me. But W9TB ran it for almost 40 years from the late 40's to the mid-80's. And he's got a pretty impressive log here to show for it. I've got all his old parts and his original diagrams so I'll probably duplicate the whole thing--except for that doggone HV supply. That is going too far for me. The thing with the HV supply is that he converted to solid state diodes at some point. But the lower voltage drop of the new diodes left his HV and "screen" supply too high. But instead of building a new supply, he took transformer filament windings and hooked them up backwards to buck down some of the voltage. When that wasn't enough, he inserted these huge ceramic resistors in the line in banks of 3 or 6 in a haywire parallel/series lash up to lower the voltage to where he wanted it. The rest of the rig is built like a fine Swiss watch. But I guess he sure didn't want to buy a new power transformer. So he made what he had work. But I'm not going to heat the house with all these resistors or fool around with bucking transformer windings. And the pole pig is just too damn big. I have some perfectly good HV supplies here that are not in use--sitting in my garage. I want to adapt one of those somehow. That's my goal. 73, Don Merz, N3RHT -----Original Message----- From: George Pritchard [mailto:[EMAIL PROTECTED] Sent: Friday, November 01, 2002 2:52 PM To: amradio@mailman.qth.net; [EMAIL PROTECTED] Subject: RE: [AMRadio] Re: Supply for PP 304TLs ?? Use 3000 Volts max. I use a pair in AB1 Audio. No... I did not pay $85,000 for it! I would not sell it for that either!!! Having to much fun. Anyway, No screen supply needed since they are triodes. Neutralization is a big must. For class C, I would use 304THs since the bias requirement is higher, and will give better efficiency and class C linearity when plate modulated. They do require plenty of drive however. The TLs versions are more linear for audio. Use a pair of THs for the class C, and a pair of TLs for the audio... if you have them. Audio phools are driving the price up on these. Glad I bought spares years ago! Have fun, George AB2KC -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Brian Carling Sent: Friday, November 01, 2002 1:33 PM To: amradio@mailman.qth.net; [EMAIL PROTECTED] Subject: [AMRadio] Re: Supply for PP 304TLs ?? Here you go DOn. This outfit sells transformers for building a 304TL amplifier. You can even buy the complete amplifier kit for $85,000 Hehe - yes guys, that IS $85,000 http://www.alumrocktech.com/prices.shtml Of course, it's a stereo audiophool amplifier. Looks like you could get a set of transformers for a mere $14,000 or so. On 1 Nov 2002 at 11:59, Merz Donald S wrote: > By any chance is anyone running an HF amp or transmitter with > push-pull 304TL tubes in the final? I have this homebrew here that > uses this configuration. But the power supply it came with is in > pieces and it is a mess. It was modified many times over the years by > the builder and has been patched more than a Microsoft software > product. > > So this thing needs a filament, screen and HV supplies. I can use some > of the original parts. But for the HV, I don't want to use the > original design because it is built around a 230V pole pig transformer > and has lots of quirky design anomalies that I can live without > (Anbody need a 125 pound pole pig? It'll give you 1700 to 2200 volts > all day. The only drawbacks are that it is huge and weighs a ton). > > So I'd like to cheat and see how someone else is powering their rig to > get some ideas. References to complete designs in any of the popular > literature would be useful too. Can anyone help? > > 73, Don Merz, N3RHT > _______________________________________________ > AMRadio mailing list > AMRadio@mailman.qth.net > http://mailman.qth.net/mailman/listinfo/amradio _______________________________________________ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio _______________________________________________ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio
