Ampeg SVT 1969

[beaulieu]

Hi all. I just got a 1969 SVT head. I am on the fence about tube selection.It currently has(needs) 4146's. The amp needs new tubes and I can either do the mod to clamp the screen voltage low 300?. (keeps 4146's from blowing) Or I can convert it to 6550's. Although this amp is not mint in anyway I still would like to keep it original as most amps were converted to 6550's I would think. Thanks Mark

[soundguruman]

I like to convert it to KT88, and make the preamp heaters DC, etc...also, don't you think you could skip the 6C4?
But yes, it can be converted to 6550's I've done it before.
Whatever it is, the 6C4, 6C5? It's always a problem spot cause we can't get good ones anymore.

[DaveMcLain]

I repaired an old one for a guy one time. His amp had originally come with the 6146b and it had been changed over to use the 6550's sometime in it's life. I went through the amp and found 3 of the 6 "blowout" resistors to be open so I changed all of them and rebiased the amp with a set of the Sevetlana(now =C=) tubes and it sounded fantastic. That's been over 10 years ago and it's still doing just fine and he plays it very often. Those are a heck of an amp, Ampegs from that period are very well built pieces.

[robert]

If possible, use NOS General Electric 6550A.
This tube delivers more power (max. 42W) and is able to handle a higher screen grid voltage (max. 440V) than the 6550.
Compare e.g. the GE 6550A datasheets with the RCA 6550 datasheet.

Of course, good quality (!!!) KT88s (not the Chinese crap!) will work also very fine in the SVT.

Regards

Robert

[soundguruman]

Yup I got the nicest ever with KT88!
I also eliminated the cathode follower between the preamp and the power amp. That follower is microphonic.
But overall no matter how you do it, the SVT is the best bass amp.
I'm not talking about the CRATE SVT, with the ampeg logo stuck on the outside.
I'm talking about the REAL SVT, made by Magnavox.
Don't forget the difference. One is hand made. The other, well...too bad.