The Amp Garage

If you are talking about the cathode resistor/capacitor on the the first gain stage, I doubt a change of 300 ohms will affect the flavor of the amp that much. The first stage is not overdriven by guitar level signals and probably has less than 2% harmonic distortion. I wonder if the tone you seek is...

Looking at the curves of the 6550 in that configuration, I'd say that you can go at +5 on g1, but to my hears the direct coupled driver gives more "authority" to the power amp even in AB1. Here below the loadline of your amp (one pair of 6550 is shown). I looked at the 6550 datasheet and it quotes ...

How about resistance from each winding to the core or mounting bolts? If there is somehow a short between the HT secondary and core or mounting bolts, be careful when you do the test with the HT CT un-grounded! I wouldn't want you to become the ground path. Definitely keep that limiter in use. Good...

CraigGa wrote: ↑Fri Aug 13, 2021 9:36 pm It was wound to my spec

320-278-0-278-320V and 5V and 6.3V heaters

Craig

Ah, I see. It has only one set of primary leads then?

Craig, sorry about the troubles with the PT. Which make and model are you working with?

Has anyone successfully implemented AB2 with 6V6 power tubes? If so, could you please elaborate on the maximum grid voltage you were able to achieve safely? I also want to know what maximum peak cathode current can be achieved. The GE datasheet for the 6V6GT lists the peak cathode current as 105mA, ...

A typical cathode follower has the plate connected directly to a B+ node. The plate must be more positive than the cathode. Otherwise, there's no way to attract those electrons that are boiling off the cathode. Well said. And the grid must still be kept negative relative to the cathode. None of the...

ABY switch with iso transformers. I got this one and like it: Radial Bigshot ABY. I just picked up the Radial Twin City which is, as I understand it, a buffered version of the Bigshot--so no tone degradation on that isolation transformer side. So far I'm really liking it. A little more expensive, b...

How does 330 V just disappear without blowing up the tube, OT, power supply, PT, or just blowing the fuse? I eagerly await to find out. :D Is the OP measuring the voltage right off of the OT lead where it is soldered to the socket? I would consider pulling the power tubes and checking voltages all a...

So I'm trying to figure out the load resistance of the 6V6GT in the Champ, which runs at 350v at the plate. I always recommend people to vtadiy.com to try out his universal loadline calculator vtadiy.com/loadline-calculators/loadline-calculator/ . You can select a tube of your choice and try out an...

I installed 5 W potentiometer on the Cathode to the ground Bias control. But every time amperage lowers the voltage goes up and if I turn it the other direction voltage goes down but amperage gets even worse. I'd be really interested to know if there was a bias circuit that would solve this problem...

So you went with a ground bias on the cathode instead of the cathode resistor/bypass cap shown in the AA764 schematic? Interesting! But maybe adding extra complexity that is causing trouble?

Ok, this is all just guess work since we don't have a schematic or typical voltages for this amp. If all four 12AX7s and the EL84 reverb driver are "downstream" from this voltage dropping resistor, then that's quite a lot of current. I have no idea what the exact bias points would be, but let's esti...

A couple questions for the OP.

1. What is the preamp tube complement? I dug up a Fryette guide that said it had (4) 12AX7’s and (1) 12AT7. Is that what your amp has?

2. What is the difference in preamp tube complement between the combo and the head version of this amp?

The image here https://atomiumamps.tumblr.com/post/190408845546/vht-pitbull-45-combo-first-time-for-me appears to show another 10K. I wouldn’t bet my life on it, but that’s what it looks like to me. And you’re right, it’s hard to distinguish between red and orange. It just looks like they both have ...