help with amp conversion

[Glazierman]

I come across this amp and not sure of two driver tubes , but think other six are 8950's would like suggestions on tube replacement and links if any one can help thanks will try to show pics .http://i25.photobucket.com/albums/c70/glazierman/100_1081.jpg
http://i25.photobucket.com/albums/c70/glazierman/100_1082.jpg
http://i25.photobucket.com/albums/c70/glazierman/100_1086.jpg

 

[dudmuck]

The drivers have the same sockets and wired the same as the other six?
If so, then its was probably just two 8950 driving six 8950.

The 8950 was a bit of an oddball with its 12volt heater.
Most other sweep tubes were 6 volt heaters.

The Siltronix 1011 used the 8950 tube, so you might find information from notes on replacing the tube in that radio.

 

[fnkycoldmedina]

8-8950`s ......ha....might as well just buy another amp.those are the most expensive sweep tubes around.

 

[ExitThirteen]

If the amp takes 8 x 8950's, you can sub in 8 x 30KD6, wire the filaments in series in 2 groups of 4, and wire the filaments to your AC line switched. 4 x 30v filaments in the 30KD6's = 120v. I used to do that with the Maco 200's all the time, worked fantastic, and a LOT cheaper too. Granted, the 8950 tubes are 40 watts max plate dissipation, vs. 34 watts for the 30KD6, but losing a couple watts is a small price to pay for trying to buy 8 x 8950's. Another alternative is use 6LF6 tubes, and tie 2 tube filaments in series and use the 12v output on the filament transformer, but 6LF6 tubes are also pricey. If you really want to keep full output, you can substitute 8 x 27LF6 tubes and wire the filaments up same as the 30KD6 mentioned above. Hope this helps!


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[Glazierman]

I'm not so sure about the front two tubes being the same if you look at the pics you'll see that two of the sockets have a slot in them where the other six sockets do not ??

 

[ExitThirteen]

Upon further inspection, the only difference I see between the driver section (2 tubes) and the final section (6 tubes) is that the 2 driver tubes are grid tuned with a variable capacitor, and the final 6 tubes are run grounded grid. Looks like you could still run all of the same tube, and the sockets are physically the same. Just make sure you use a tube that has at least 34 watts of plate dissipation per tube. If you're unsure of what tube to run or which tube has 34 watts of plate dissipation or better, you can google a tube number and you get info on the tube there.
Good luck to you!


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