Using a Dynaco ST-70 audio transformer for a guitar amp

[Sal Brisindi]

I am in the planning stage to build a guitar tube amplifier with a spare A-470 audio transformer from a Dynaco ST-70. Does anyone have an opinion on this.

Any advantages or disadvantage using a "Hi-Fi" audio transformer in a guitar amp? The transformer is rated at 35 watts with push-pull EL34's.

Thanks,
Sal

[Shamrock]

It depends on the sound you're going for. A lot of people (myself included) prefer the sound of the compression (or narrowing of the bandwidth) on a transformer for guitar use. It has a desirable sonic trait (to these ears). Wide bandwidth hi-fi type transformers can be used with no problem what-so-ever, and some amp companies did, but you may not find the sound to your liking.

VTL used Fender bassman transformers in the early days to good effect.

If you have an A470 laying around- try it!

[CharleyW]

Ampeg used Mark-III transformer sets for a long time.

[Shamrock]

Originally Posted by CharleyW

Ampeg used Mark-III transformer sets for a long time.

I didn't know that. Thanks!

[kevinkr]

I think a lot of it is going to revolve around your sonic expectations, if you like a clean sound or something similar to the Standell then this might be an excellent choice for you. I would expect it to be a bit lacking on the crunch end of the spectrum, but you know what? - You can always replace it later if you are not totally happy with the sound..

Try both UL and pentode operation and see what you like best with this transformer.

Consider 6L6 and 807 output tubes as well as the EL34.. Making an amp that will work with both the 6L6 and the EL34 should not be much of an issue..

[Wavebourn]

Originally Posted by CharleyW

Ampeg used Mark-III transformer sets for a long time.

Requirements for bass guitar and Hi-Fi amps are the same, I mean output stage only.

The tranny you have may be used for 100W guitar amp, with twice higher plate voltage and a quad of EL34.

[CharleyW]

Mike (MagneQuest) LaFevre has written that the A470 is good for an honest 60 watts at 30hz.

[Sal Brisindi]

This is all great information, Keep them coming.

Thanks,
Sal

[CharleyW]

The low 'E' string on a guitar is (I think) 83hz (concert pitch). Tuning it to a 'D' (one step lower) is not uncommon (although somewhat rare in the rock world).

[Shamrock]

Originally Posted by Sal Brisindi

This is all great information, Keep them coming.

Thanks,
Sal

Wire that thing up and let it rip! Part of the fun in building a guitar amp is that it can be disarming and fun to experiment with what's laying around.