The Amp Garage

Shields are the outer braid on the coaxial cables going to and from that pot. I think you can try this as an experiment. Disconnect the wire at the red X, and add a jumper on the main board as shown by the red arch. This seems to be the least invasive way to test the theory. Once you do that, you ca...

Flipping the slide switch layout it looks ok to me.

Yea, not a good idea. I'd ground the shields and the OD trim pot at the input ground eyelet at the center of the board near the 220k. That's probably why grounding the speaker/OT common at the front of the chassis worked well.

Can you post that whole C-tone diagram?

On the snip you posted above, there is an "OD trim pot" connected to the OT common ground. I assume that is the OD entrance trimmer, and I suspect that is the reason it is so sensitive. I would separate that and ground it with the preamp grounds.

You are correct! ~12V higher at 200 mA.

The ripple measures around 2,4 Vac before the choke, and around 0,2 V after the choke. I think that is good? So I concluded that the B+ line is probably noise-free. Note that the ripple voltage on the B+ is 100 Hz due to the full-wave rectification. It's nice to check that, but you could have shift...

Wired up the power supply today to do a preliminary smoke check before proceeding any further... Powered it up slowly with my variac and current limiter. No smoke, pops, or blown fuses. B+ values were around what I would expect for an unloaded amp running through a current limiter. Nicely done. So,...

JJ 6V6S could probably take the voltage. Need to disconnect two of the four speakers to increase the load to 8k. Would that mot result in a 4ohms load ? Or am I refering to something different here ? Yes 4 ohms load and 8k impedance on the OT primary for the 6V6S. Maybe swap in a 5Y3 or 5R4 with th...

JJ 6V6S could probably take the voltage. Need to disconnect two of the four speakers to increase the load to 8k.

The AB568 schematic shows 465V with a very lossy 5U4GB, so the voltage is a bit too high for 6V6, and it will be even higher with the reduced current draw.

As I've said before, it's best to refer to both a schematic and a layout when building. Unfortunately there isn't a schematic that exactly matches the layout, which makes it tough on the new players. Unless you are live on stage and need to switch into OD + PAB quickly, you might as well keep them s...

OT CT (red wire) is soldered to ground while the blue and brown primaries are tack soldered in to the output tube sockets. I ran the test again and still came out with results like those from the Mojotone OT: ~4 VAC on the secondary, ~44 VAC on the brown and blue primaries. Things were much clearer...

Hook-up seems ok, are you measuring the voltages from the plate leads to the secondary hot?

Yes, Cl = Clean, but the Clean Volume and OD Volume are the level controls at the outputs of the Clean and OD sections, respectively. On the layout, the clean volume is called the Master. I suppose that's because it is in the same location on the panel as the Master in the Master/Ratio system. OD En...