The Amp Garage

Roe wrote: ↑Mon Oct 12, 2026 9:58 am Lower voltages gives a softer attack with less punch.

That is the point in using the ccs as a tail: define the working point, improve linearity and balance, recover some volt by having the grids referenced to ground, and setting the working point in a more precise way.

you can just ignore the current, because there really isn't much there and we're not driving the grids into grid-current, so it is class AB1. It’s not that easy. You need to drive the output tube that has its own capacitances even in A1. Plus, depending on the tube tou use, sifferent currents give ...

dbharris wrote: ↑Sun Oct 11, 2026 3:51 pm Very curious to see and hear what circuit you end up implementing.

Hi Dan, I have something in mind I will propose here in the next days. There are few options I need to check.

Fischerman wrote: ↑Sun Oct 11, 2026 3:39 pm It's really about double that increase. The 82k is increased to 100k and the 100k is increased to 110k+10k pot.

Thanks, in any case with the 220k in parallel the gain should be 49x vs 54x, that’s less than 1 dB. It’s more a working point imho.

Hi Dan, thanks for your feedback. So you oftern play your amp in “jtm45-lamd” in terma of loadline. It would be interesting to try different voltages on g2 (lowering it by 50V each time while modifying bias voltage to reach the same plate dissipation) and target the sound tou prefer with that very f...

Thank you again martin, So it seems that the choice I had in mind to use a ccs as the tail of the ltpi can be a good starting point towards symmetry of the ltpi, with the bonus of having the grids of the ltpi grounded, so one cap less and more dynamics in the ltpi. The flattish load line of the outp...

martin manning wrote: ↑Sun Oct 11, 2026 12:17 pm But in any case the PI trimmer is there to adjust the balance.

but is it generally set to be exactly balanced, or to introduce some asymmetry?

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. Thanks martin! Flattish load lines makes the amp intrinsically more linear, and Zout lower before applying any feedback. 8k Raa for a pair of 6L6GC seems w...

Here's a couple of layouts. …due to the 9k1 tail as opposed to the 24k tail in the regular OTS above. Also interesting is that they both attempt to eek out a bit more gain than the typical 82k/100k you see in most Fenders and Marshalls. Thanks! I will search the schematics of those layouts. I see t...

It appears the philosophy was to keep the power amp and speaker quite clean, with most of the amp's character coming from the preamp stages. So towards hi-fi land, without going that far. The experience I did on LPTI and power amps in that field can come handy, as with the SE version. It is interes...

What about the standard Dumble PI vs the Bluesmaster? Can you give me a reference link of the two specific schematics you want to be compared? As for the bandwidth, generally the high Zout of the amp makes the speaker and cabinet control it in a good percentage. Coupling cap, presence control and o...

Not that I am aware of. I don’t have a Dumble, of course, and the Two Rock is gone years ago, so I can only similate to have an idea of it (not 100% correct, but at least in the ballpark). Can you please confirm B+ around 460V, Raa 2k2 for the 4x 6L6GC, bias around 70% of plate dissipation, feedbac...

Thanks martin, has anyone measured the Zout of those amps? Or at least estimated?

Thanks Guy! It's usually a balance of how stiff the amp can be vs how dull it becomes if there's too much gnfb. That's why I would like to try some of the tricks I've used on the SE for the PP too. Trying to get more benefits without too much drawbacks of the standard configuration. I will for sure ...

Thanks martin! That was what I got from the Two Rock while playing at it and from the feedback of some builders specialized in this kind of amp. It's good to read same information confirmed here. The concept of the reservoir is another details I've been pointed to. The poweramp needs to let the prea...