Gregory Reverb 900

[mattleblanc275]

H
Hello all - any info or schematics for this amp would be greatly appreciated. Available Info on inter-web for Gregory Amps is spotty/contradictory. It runs 2 7189’s in the output section. Has a Quam 12” speaker (oh boy!)

[Chuck H]

I was unable to find a schematic for that "Gregory" model. In the process of looking though I learned that Gregory was a private brand made by Harmony. Now, Harmony use to have amps made by Valco. And somewhere in there Supro, Kay and Airline (wards) and a few others were also involved with Valco. For a time Harmony amps were made by Sound Projects Company too. FWIW a lot of players know a little something about these convoluted histories but I don't know any experts. It's just too much information. And many amps made by these makers of affordable line instruments and amplifiers have no known schematic anywhere. It's possible you may find an amp of another brand made by Valco (Valco, Supro, Kay and Airline) or Sound Projects Company (Harmony and ???) that has the same tubes and controls as your amp. Maybe it's the same circuit. Maybe not. Sometimes amps of the same circuit were made for several brands but there was a change to each brand like the addition of a different tone control, the use of different power tubes or instrument input or speaker arrangements. While otherwise the amps were almost identical. Alas there is no comprehensive crossover list for this. But maybe this gives you some idea of where and how to look around. Otherwise...

It's just a tube amp. Some of the circuits used in these Valco and Harmony amps are unusual by modern standards, but not impossible to understand. A schematic can actually be made by starting with tube sockets drawn and then connecting the dots with components as they occur. You'll want to do this in pencil and have an eraser handy

[glebert]

I have no technical info on that, but I think it is a cool looking amp. I've considered trying to get a Gregory just since that is my name. I've never loved the name too much, maybe if I had a namesake amp it would be better.

[mattleblanc275]

Thanks gents.

[dmeek]

Here is a Gregory amp page from the Wayback Machine diy guitarist site: https://web.archive.org/web/20100923...regoryAmps.htm
There is a schematic shown for the Reverb 900 but it uses EL84s and has no reverb. There are other schematics there. Here is one for the Reverb 1500 with 7189s

Gregory Reverb 1500 Circuit.pdf

[Chuck H]

Here is a Gregory amp page from the Wayback Machine diy guitarist site: https://web.archive.org/web/20100923...regoryAmps.htm
There is a schematic shown for the Reverb 900 but it uses EL84s and has no reverb. There are other schematics there. Here is one for the Reverb 1500 with 7189s

[ATTACH]n973499[/ATTACH]

I have to say kudos and that this is a very conscientious effort, but I find that schematic highly suspect on technical grounds. I think errors must have been made by whomever analyzed the circuit.

[Chuck H]

Interesting that the schematic for the 800/900 doesn't include the reverb circuit at all. There is also a typo I saw (and maybe more?) at the cathodyne PI where the grid should be connected above the 10M resistor, but there is no trace there.

As far as the power tubes, the el84's and 7189's have the same pinout. The 7189 is a high performance version of the el84. Provided operating conditions are suitable they are interchangeable. All the other "Reverb 900"s I've looked at have el84 tubes. So it's probable the 7189's were put into this particular amp arbitrarily and aren't the spec'd tube for this model. But since there's no performance disadvantage there's no harm in using them in that amp.

All the other "Reverb 900"s I've looked at also have the same two 12ax7 preamp compliment. So I expect the reverb in the 1500 and 900 are the same transistor circuit. But, again, it's not a complete and comprehensive circuit for the reverb that is demonstrated so the hand drawn reverb circuit schematic is also suspect.

I think the factory schematic should be ok as things go, though there may be differences to the actual amp. It's common. But how the reverb is coupled remains a mystery.

[Chuck H]

I pulled a printed reverb schematic from another amp with similar implications for the coupling of the circuit on the above linked site. No indications on the reverb tank or transistors. This may be a schematic for the amp. Sort of. And depending on any unlisted changes to actual production models.

[Chuck H]

On a related note I would say that powering the transistors from the cathodes of the power tubes is clever for the era, BUT... By todays standards it's very blunt. If I were trying to keep the amp as stock as possible I would probably bump the cathode bypass capacitor for the el84's (or 7189's) to 220uf (not practical in that era but it is now) and perhaps include some zener regulation for the voltage supply to the transistors. But I'm just thinking out loud on it.

[mattleblanc275]

Thanks to all! This is some great info that I will share with my amp tech. Happy Thanksgiving to all.