[Amps] 432 Cavity Amps; Thomson TH 331

[John Lyles]

Not likely to find an exact replacement in the USA, as Burle/RCA and Eimac were the only mainland producers of UHF tetrodes like that, and they have reduced production to near nothingness, as the market has dried up after DTV conversions. Only the LPTV analog stations might continue to use a cavity amp/tube, which isn't a lot of business. Scientific service at 400 MHz might be a possibility. Overseas, however, there are 'third-world' nations continuing to use old PAL and NTSC rigs. The TH331 datasheet isn't even listed in my old Thomson catalogs, and only said to be for replacement service, a 1 kW tetrode.  As Carl mentioned, you could contact Chinese or even Russian companies for a look-alike. I quickly checked my Toshiba literature and see nothing close to the Thomson tetrode. So I think it would be a fine project as is, but a waste to try and find an identical replacement device for it, IMHO. Certainly, with enough time and money, you could modify the structure to use another
tube. There aren't that many tubes for UHF in that size to choose from, though. 
73
John
K5PRO


> Message: 1
> Date: Thu, 1 Mar 2012 08:18:34 -0800
> From: Patrick Barthelow <apolloeme at live.com>
> Subject: [Amps] 432 Cavity Amps;  Thomson TH 331

> Friends,
> After being offered for free, a Working Pull complete Tetrode cavity TV amplifier on 470mhz,  (Sans power supplies which would have to be built)  and with possible plans to make a moonbounce Amp, I checked on Pricing/Availability of spares, specifically the Thomson  TH 331 power tube.  The Amp is capable of operation far above the legal limit; ~ 7.5KW, so I wanted to know if it is easy to run at a  reduced  1500 watts out.   
> Then I would be more comfortable with a Spare Tube around, and checked a vendor to find that the   Large  Thomson TH 331 is no longer made, and the vendor could find no equivelant tube, that was still made.  A surprise to me also was the last price list with the tube, in 2006 showed a price of $8700 list, ea.  Ouch.
> My question is,  It it possible to find a similar power tube to  with matching Critical Anode, and other  dimensions that will swap into the matching cavity system, and make cavity tuning changes to accommodate different tube RF circuit  requirements?   Or... maybe impossible with new replacement tube.  Perhaps a lot of TH 331s are out there used?    
> If this is not practical to use/modify for Amateur radio Moonbounce use, it is likely to be donated to a Large Dish installation for their use.   I am guessing interplanetary radar use.  Is 7.5 KW output at 432, useful in, say Moon Radar mapping studies? 
> Here are photos of the tube, and Cavity cabinet: 
> https://skydrive.live.com/?cid=2eb5c45df634a712#cid=2EB5C45DF634A712&id=2EB5C45DF634A712%21783 

> 73,    Best Regards,       AA6EG,  Pat Barthelow