Schematic for Guyatone GA-430?? (6BM8 reverb circuits?)

[cgarai]

Hi

I just bought this little amp with a non working reverb and tremelo. I haven't been able to find much info on it, does anyone have any clues? The controls on this amp are Vol, Tone, Reverb, Trem Intensity, Trem Speed. It has 2 inputs and an 8" speaker.

I suspect it is similar to a Gibson GA1RT1, as it has a reverb and tremelo and uses a similar tube compliment: 2 6BM8, 12AX7, and a small tube I can't read, possibly a 5Y3GT if it is close to the Gibson. The main difference is that it has two 6BM8 vs the Gibson's one. I suspect the additional tube is for the reverb circuit. Is there another Gibson that uses the 6BM8 as a reverb driver?


BTW, how does the GA1RT1 reverb work? It has the input going straight into the reverb tank?!?

Of course I may be on the wrong track altogether if the Gibson GA1RT1 is nothing like the Guyatone, but it seems a reasonable guess for a starting point. The other error I might be making is that the second 6BM8 is used for the Tremelo, either speed or depth.

Thanks,
Chris

[cgarai]

Found the answer courtesy of the guys at Tokyo Sound. Turns out I was completely on the wrong track. The amp is a push/pull output, using the pentodes of the two 6BM8s. One triode is the phase inverter, the other is the tremelo oscillator. The unknown tube is not a rectifier, but 6AV6 which is used for the reverb drive. It has a single diode as a half wave rectifier.

This amp was made in the 60's. The PT indicates 1966 and they Guyatone gentleman sent a picture from a catalog from that year.

Anyone who is curious can see the schematic at:


Now all I have to do is fix the trem and rvb. My first tube repair.

Chris

[cgarai]

The link to the schematic didn't work. Here it is:

http://www.ampix.org/albums/userpics...30-trimmed.pdf

And maybe here if it works: