I'm building a New/old AM Transmitter

[KF9CM]

I'm building a New/old AM Transmitter. The transmitter will fit into a 4' high 18"
rack mount cabinet.  I have a a lot of 1930s knobs, dials and meters, these will look great in a black wrinkle finish cabinet. I haven't decided what tubes I'm going to use in the PA. My choices are two 808s, two HT-100s two TZ-40s or a 4-250. My target output is 300 to 400 watts out. I'm going to use a Thordarson T-6424 modulation transformer rated at 300 watts. I'll be using two 811 in push-pull for the output. I've got a Bogen DB-110 for the driver/speech amp. I'll probably change the output transformer to a small modulation transformer to match the 811 grids. Any constructive criticism or help would be welcome.

TNX de Gary,KF9CM

[Don, W2DL]

Personally, I'd avoid the 808's and 100TH's. These are becoming almost unavailable, at least good ones are. The 4-250A (and it's exact replacement with a bit more plate dissapation 4-400A) are currently available new if needed and also on the used market, there are a lot of them out there. Audio 811's sounds OK, although I might be very tempted to use triode connected 813's, once again, pretty easily available and would be pretty lightly stressed at this RF power level.

Regards,  Don, W2DL

[WA3VJB]

I've got a pair of used 3-400Z I can give you for the price of shipping if they would help.

[WA1GFZ]

Ever since I finished the V2 CDC I've had the urge to do the same thing. I was thinking triode connected 813s for the modulator. Then mount a 4-400 socket and filament transformer. I have a bunch of 813s and 4-125s and a couple 4-400s
4-125 and 4-400 tubes are better at RF above 40 meters.
For now I will continue on the Class e power supply modulator for the next QRO  

[KF9CM]

Thanks for the offer guys I've got several 4-400As. There are a little bigger (in physical size) than the 4-250. The 4-400s are easier to drive and more stable than the triodes. As far as the 813 and 811 combo goes I've already got that set-up in the ART-13. I think what I'm going for is that 1930s look with up to date technology such as a pi network and solid state power supply, etc. I might even try to drive the screens with modulated RF (see attached). I believe I would have to modulate the last driver feeding the grid of the 4-400 in order to make this work. I think A UK ham first devised this configuration back in the 60s.  There I'm getting off on a tangent. Maybe I'll just stick with plate modulation .

[WBear2GCR]

Stu, AB2EZ just did an experiment with a way of doing some added screen modulation with plate modulation - he posted it up here iirc just a week or so ago.

I heard it on the air - it was an improvement over the same rig (it was switchable) without the screen modulation added, fwiw.

        _-_-bear

Btw, have you considered a BC-610? That's fairly buzzardly and of the period, even if the date of mfg is a bit later than 1930, the design is definitely late 1930s... 

          _-_-bear

[N3DRB The Derb]

for inspiration. When you get the right parts it goes together like a plan. 

I never had one problem with my HB rig. More info in my gallery.

[KF9CM]

TNX guys,

Derb, that transmitter is way cool . Mine will be about 3/4s that tall.

Bear, The BC-610 is fine, but I get about 85% enjoyment out of building the rigs. Besides all my machine tools, shears and welding equipment will start to get rusty .


de Gary,KF9CM

[N3DRB The Derb]

Thanks Gary.

It got sold on ebay and went to a bottom feeder in Ohio somewhere. I'm sure it's smashed and in a landfill by now. Hope I'm wrong but I doubt it. I wish I had done things differently but you cant change the past. Learn and move on.

[WBear2GCR]

Derb,

That looked sweet!
I know that you can fool some of the people here. Not me! 

What I want to know is which model time machine did you use to bring that one back with you? (the ones I use aren't big enough to carry that much... ) 

                 _-_-bear

[N3DRB The Derb]

Bear,

no joke. it went out to Ohio somewheres on the back of a pickup. crazy bastard didn't even bother to cover it in case it rained. He just wanted to tear it apart and sell off the tubes & parts on ebay. I sold everything as fast as possible. I'd had it with radio. It did nothing but piss me off. I was burned out and very angry. I basically said fuck everything.

I wish I had done things better but I didnt.

[WBear2GCR]

Derb,

Can't say that I have walked anywhere near your shoes - mine don't fit well all the time - but it's only stuff. I like my stuff, fo' sho' - but it still be only stuff.

Every once in a while I get the thought to sell everything down to the bare walls and start fresh. Go lean and fast, start with things first rate or not at all... It still might happen.

                    _-_-bear