Gibson GA55V schemo

[Willabe]

Thanks Ian.

I'm not sure that Gibson drew it up the phase shift circuit correctly? It's different then their GA-83S, GAV1 and the Wurlitzer vibrato that Gibson copied it from. (It's different from Vox's version of Gibson's too.)

So I re-drew the GA-55V modulator/mixer circuit hoping to untangle it to see the circuit a little better, not sure it helped.

Here's 2 versions. The 2nd version I did because I'm thinking that the resistive dividers/grid leak R's of 510K/1m should be as close to the 6SN7's grids.

Do you think this circuit will work or did Gibson get the mixer/modulator part of the schematic drawing wrong too?

Thanks, Brad

Edit; I added a re-drawn Wurlitzer vibrato circuit to compare with.

[didit]

The first few were obvious & easy to confirm. I'm on the road with limited time & tools. I'd need to spend more time closely analyzing, or go to the effort to build a spice model before knowing if are any issues hiding inside phase shifter. Looked at it for five minutes just now; seeing nothing obvious?

Best .. Ian

[Willabe]

Thanks Ian for having a look at it.

I'm working on a bread board so when I finish it I can put the circuit on it and see if she fly's.

But if she doesn't I'll have no idea what might be wrong.

Gibson's GA-83S does work as Vox copied it for their AC15/30's.

I was thinking that Gibson found a little different way to wire up the mixer/modulator phase shift circuit as the GA-55V is different then their GA-83S and GAV-1.

And if I can get the 55V running on the bread board I will A/B it against the 83S to see if 1 sounds noticeably better than the other.

Thanks, Brad

[cbass]

Hey Brad, good to see ya over here. My offer still stands if you guys make it down this way. Bring some of yer amps too.

[Willabe]

Hi cbass!

Some fine day we'll go back down to Ark. and thank you we will drop in and see you.

Brad