I recently aquired a filmosound amp by Bells and Howlett from the 50's. I would like to retube it but my tube knowledge does not extend past the everything you wanted to know about tubes thread. This amp uses 25L6GT tubes in the power circuit, one 12AX7 in the preamp, and one 5879 and one undetermined tube, most likely a 25L6GT, in an undisclosed circuit. What are 25L6GT's? I'm only familiar with 6L6GC's and my better judgement would flat out think that the two are NOT interchangeable. The 12AX7, well c'mon, we all know that. But also what are 5879s? They are the same size as 12AX7's, but obviously different. Any help would be great!
Out here you've gotta know where your towel is!
I'm not an amp guy, but I know someone who has an ancient book of tube substitutions. If I remember, I'll look these up for you but I'm not going to get a chance til saturday probably.
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I suggest not screwing with the UGer with the best name on the site.

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I don't see how prostitution is going to help out your string buzz...
the first number on tubes is the heater voltage, those are 25 volt heaters, so they are not interchangable with anything made in the last who knows how long...usually 25V are only found in TVs... so...

If you want replacements for them, they can probably be had at places like www.tubedepot.com and www.tubesandmore.com.

6L6 plugged in there won't have a clue what to do.

EDIT: http://scottbecker.net/tube/sheets/127/2/25L6GT.pdf

Made do to go into radios...so, it's probably a radio/TV manufacturer who decided to make an amp...

EDIT2: had I read your post clearer, I would've known that it was from a TV-like thing...
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Last edited by DLrocket89 at Jan 26, 2009,
A quick google found the 25L6GT tubes and the 5879. The 25L6GT uses the same socket as a 6l6, but the voltages are way off(25v heaters, 200v plate). Some vintage amps used odd tv tubes for tremolo and echo circuits. Tubes that are in some cases impossible to find. I got rid of an old ampeg because 2 of the tubes had gotten horribly rare and expensive and the amp would work without em. Theres a cross reference for tubes similar to the 25L6GT, 6v6 comes up but not a direct drop in with the odd voltages.
Last edited by Tackleberry at Jan 26, 2009,
Wow, that's some good info guys, thank you! Since these are actually TV tubes, it makes sense, because I have to drive this baby WAY hard to get a slight distorted tone (unless I put a Tube Screamer Turbo in there, that dirties it up nice and britishy!) . But the cleans are TIGHT! After a little web searching I was able to find a supplier of the 25L6GT tubes at $6.95 per tube, and that's actually a damn nice price. It needs them too! I was playing through the amp (which I have dubbed "Swift Breeze") yesterday for about an hour, and the old ass tubes were ready to give out, I got that tell tale sulfur cinnamon type smell. I still need to figure out what the other tube is though. It has no markings, it is the same size as the 25L6GTs, but it only has 4 pins, so I know it's different. It has a metal casing tht fits over it, and if I touch the casing, there's a nasty buzz that occurs... It's not on the pre circuit, and doesn't look like the post... What could it be?
Out here you've gotta know where your towel is!
Last edited by ValoRhoads at Feb 23, 2009,
Quote by Invader Jim
The one you're talking about may be a vibrator. IIRC, they convert DC back to AC...

Oh ho ho, you are so my new friend, you know things I don't! Can I get a little more insight on why you think it is a IIRC? (btw, if I come off as an ass, I do not mean to, I seriously need this knowledge so thanks in advance )
Out here you've gotta know where your towel is!
IIRC means "If I recall correctly"...


But I'm sure it's a vibrator. It could be a 6SJ7? Idk. I have an RCA 6SJ7 vibrator from a 50's signal tracer.

edit: Nvm, 6SJ7 is octal, not 4-pin...
Last edited by Invader Jim at Feb 23, 2009,

Sorry but that is just the best thing I have seen in weeks!

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wiliscool is just plain dumb
Quote by wiliscool

Sorry but that is just the best thing I have seen in weeks!

True! That is funny!
Out here you've gotta know where your towel is!
It's a 930 vibrator and is in good shape, no need to replace it, thanks guys!
Out here you've gotta know where your towel is!