I'm trying to figure out a good PT for an Ampeg GU-12 build

[mort]

7591 x 2
800mA heater
85mA cathode current

6U10 x 1
600mA
20mA cathde current

12ax7 x 1
300mA
1.2mA plate current*

12DW7 x 1
300mA
22mA cathode current

*Should I be using cathode current or plate current to calculate load?

And what percent of overspec'ing is reasonable for each set of windings?

ampeg_gu-12 (1).pdf

[Justin Thomas]

Mort,

I've got one. I won't be able to get to it for two weeks, but it's a real deal from q blown amp (OT died, before I knew how to fix it, so I gutted it).

Justin

BTW: awesome Stones amp!!! I think inhave the trek bug,too...

[mort]

Mort,

I've got one. I won't be able to get to it for two weeks, but it's a real deal from q blown amp (OT died, before I knew how to fix it, so I gutted it).

Justin

BTW: awesome Stones amp!!! I think inhave the trek bug,too...

Sweet! I was wondering if the bug was the same as a Fender one.

[mort]

Thanks but I just bounced it off the customer and he wants a new part rather than an original one.

[Justin Thomas]

No problem... more amp for me! Good design choice, though.

Justin

[mort]

Yeah I'm really looking forward to this one because it's a little off the beaten path and it's also not expensive to buy an original but he doesn't care. He wants *me* to build it, and he's also an amp builder himself. That makes it kinda flattering too. He builds nice, higher end modern gainy stuff and has his own brand. He's pretty busy with that so doesn't have time to do it this personal one for himself.

[Justin Thomas]

Well, seriously, this is one I wish I'd waited for. I was only into guitar repairs at the time, and never saw myself fooling with amps, so I gutted the thing. I still have the empty cabinet and PT, but the rest is history... it seriously did a rock thing like 70s Stones... which makes sense, cuz they kinda used Ampegs at the time...
I'd love to revisit it, if I could wrap my head around those Ampeg circuits...

Justin

[mort]

The circuit looks pretty standard to me. It uses a triple triode but there's nothing all that different about the circuitry. Is there something I'm not gleaning that's tricky about them?

[Justin Thomas]

No, I'm just not at the point of understanding the "different" styles of drawing sachems. Even though they're error-riddled, hr Piazza drawing gs are a bit easier for me to grasp cuz they're drawn more co ventionally.

Justin