The Amp Garage

For the 2K pot, something like this https://www.mouser.com/ProductDetail/Alpha-Taiwan/RV24AF-10-15R1-B2K-3LA?qs=8%252Br4Hz5Xir%2FCukvpdPXxww%3D%3D Most people sub 220 uF caps for main filters. If you really want 330 uF, then you probably have to go to a snap in style cap and wire for your board acco...

Hey Glenn, I have that same PT in my #102 and my B+ hangs around 420-425 volts depending on line voltage. But the rest of voltages were about right with the standard dropping string. Maybe moving preamp tubes around will help.

-Dan

Hey Dan, the amp is definitely not as gainy as a #102. I found that reducing the 1m2 bypass resistor in the funky entrance to 1m helped in this regard (plus plugging into the FET!). I also found that reducing this value too far makes the OD too dark. Its definately a lively amp. I love mine :) This...

Raoul Duke wrote: ↑Tue May 28, 2024 12:01 am Looking good Dan!

Thanks Marc! It's been great following your build threads and helped me quite a bit.

Very nice! If you find that you are using one setting for the Ratio control, you could replace it with a fixed divider, but I'm interested to hear how you are using it. IMO the ODS was a continuously evolving concept, with the changes HAD made over the generations being improvements. For the PI bal...

Here is modded with the single speaker jack and ratio control on the back. I'll order a 560K piher when I order more for an SSS. PXL_20240527_185919859.jpg PXL_20240527_185928956.jpg PXL_20240527_190050234.jpg I also swapped the choke leads today. I could hear a noticeable difference between the two...

Seemed like I had a better balance between the channels too but that required maxing out the volume and keeping overdrive around 50%. Was a low dB test though and may not be reflective of normal playing levels. More fun later tonight after work.... I ran a simulation including source impedance for ...

bepone wrote: ↑Fri May 24, 2024 3:43 pm 1mV AC balance on cathodes? this is negligible... also 2mV is negligible (impossible to hear that), i would leave this like it is

Thanks. I am leaving the circuit as is. I will see if the new tubes are matched better. If not I will throw one of those NOS tubes in the JM amp.

-Dan

Dale plate resistors removed and some Mk5 roederstein now in place with values matching the layout. Best I can get is a 0.2mv offset measured at the power tube cathodes. PXL_20240524_132641240.jpg I do think that if I had reversed the resistors as to the layout (51K followed by 47K) that the trimmer...

Thanks, Martin. I do plan to swap the plate resistors.

That lead me to recall some prior discussions here that you are not really balancing the PI as much as the whole power amp. Is that a fair statement or am I misunderstanding? You are correct. The best approach is to arrange the power tubes to get the best DC balance, and then use the PI trimmer to ...

I think with 51k/47k plate loads and 22k tail as shown in the 2nd Gen layout, a perfectly matched 12AT7 would have very nearly balanced outputs. Any particular tube might be off in either direction, so keeping the original offset in place with a +/- capability via the trimmer would be the way to go...

While waiting on some parts to arrive I "balanced" the PI. Scare quotes because with the 5K trimmer I installed and the tubes in the amp, I could get close using the ampeg method but not all the way to a 0v offset. It settled around 1.7. I do have another 12AT7 and may try that to see if it gets me...

Glad you got everything working!

-Dan

While waiting on some parts to arrive I "balanced" the PI. Scare quotes because with the 5K trimmer I installed and the tubes in the amp, I could get close using the ampeg method but not all the way to a 0v offset. It settled around 1.7. I do have another 12AT7 and may try that to see if it gets me ...