The Amp Garage

The strange looking plate curves may be oscillation. I guess you could try shortening your leads or adding ferrites.

Since the "Ampeg" procedure as described on the SVT schematic is prescribed, it is balanced, as for Hi-Fi. See in the Dumble files section: https://ampgarage.com/forum/viewtopic.php?f=4&t=38853
There is another long thread stickied, but the above was an attempt to start fresh.

roberto wrote: ↑Sun Oct 11, 2026 12:58 pm 8k Raa for a pair of 6L6GC seems way too low IMHO, especially with g2 at around plate voltages.

I agree. I don't do that with mine.

Fischerman wrote: ↑Sun Oct 11, 2026 10:20 am EDIT: comparing them now I would have expected the plate resistors to be more lopsided toward the in-phase side of the PI in the Bluesmaster due to the 9k1 tail as opposed to the 24k tail in the regular OTS above.

But in any case the PI trimmer is there to adjust the balance.

roberto wrote: ↑Sun Oct 11, 2026 8:27 am Has anyone ever tried different load lines (even simply by mismatching a 16 Ohm cab in a 8 Ohm output, with or without modifying the nfb)?

I recall numerous comments on TAG saying that ODS with Twin Reverb OT (single 4 ohm secondary) were often operated using an 8 ohm speaker load.

Maybe a cut-away showing the mechanism will clear it up.

As long as the leads from your socket to the uT ASGK terminal block are short, you should be fine. Are you only looking at Quick Test results? If so, try tracing a full set of curves and see if they are well behaved.

If I understand correctly you are showing the lug side of the switches as viewed from the rear through the open side of the chassis. To close the contacts the bats would be thrown toward the open side of the chassis, “up” in your drawing. Looks good to me.

Not that I am aware of.

The Super Lead schematic at the link above marked early, ca. 1967 doesn’t have any treble peaker caps, while the Unicord schematic dated 1970 has one of the channels shown with a 500pF and a bright cap on the volume.

Comparing the GNFB network in the typical Dumble 4k7/390 (7.7%), and a 12AX7 PI, to the Fender Twin Reverb which uses 820/100 (10.9%) and a 12AT7, the Twin has lower open loop gain and more feedback.

Clone is a term that deviates from the strict biological definition in popular usage. I would say an amp with an identical circuit, original appearance and materials, and NOS parts is the only true clone. Anything else, with similar cosmetics built using new parts might be more accurately called a r...

Look here: https://www.drtube.com/marshall-jmp/

See JMP 1959 Super Lead schematics.

The short answer is it's a clean power amp, with a bit more reservoir capacitance than the Fender designs from which it came. Nearly all of the distortion is generated in the preamp.

So let’s say the goal for DPS is to produce a small number of clones at a very high price and prevent others from cloning— hypothetically. FWIW, I'd say this is indeed the plan. Somebody mentioned designer handbags, which is a good analogy. Artificial scarcity, pricing far above manufacturing costs...