Tube Amp Archive

Lauri wrote: ↑Thu Oct 16, 2025 5:06 pm It's probably AI bots constantly going through the forum posts. I have the same problem on my server and I had to block all IP ranges from China and Singapore to get rid of them.

This !!

Wishing you luck --- however, also commend some slow steady hands and perhaps a dose of applied equanimity ..

Hello -- Good advice on increasing the resistor power ratings. Use 1W for each of the small signal stages. Recommend 25W or larger for the initial power stage and at least 5W for the screens assuming that fits in your topology. Unclear what this project is intended to achieve. Any amp is more than t...

Hello --

If this transformer has an electrostatic copper foil wrap, check for continuity to that white wire.

Best ..

Hmm -- Aluminum is easier to work with and quite rigid. Steel has specific strengths, but those seem less helpful in this application. And also some concerns about steel having higher tendency to carry stray inductance. My shop inevitably has scraps of maple and other hardwoods, and plenty of "balti...

Hello --

Hammond 1444 series aluminum boxes are a preferred affordable and easy to machine "blank slate" that, with a few suitable hardwood strips for reinforcement, can impressively accommodate fairly beastly iron. No doubt some extruded aluminum stock would also work well.

Best ..

Hello —

Measuring 20V across 270 Ohm cathode resistor suggests try a tweak to your bias. Put in 330 Ohm and see where clean output sits. Doubtful you'll see it anywhere near 12W however. Also agree with comment that your test signal is overly hot.

Best ..

Hello --

What is the DC voltage on the input side of your regulator? Ideally this should at most be 4V or so higher than your desired filament voltage. If it's significantly higher, that regulator will be dissipating all the excess as heat.

Best ..

Hello -- Reading quickly through your circuit description it seems all of your interstage coupling capacitors are 0.01uF, which is reasonable for a guitar amp where 80Hz is an adequate frequency to begin reducing signal. For hifi tube amp designs it's typical to use 0.1uF or at the very least 0.05uf...

I can say that an 8k load line looks a little better, passing just below the knee, where a DR 6k6 load line passes just above it. The Mercury specs for various DR products call out 6.0K and 6.1K as the "conventional" primary. A gently circled topic a while back when people doubted Pacific Trainwrec...

imo1 wrote: ↑Wed Sep 03, 2025 1:36 am I used the MM fat stack OT. FBFDR-O-FS

Had presumed F-DELUXE-FS-OM. Curious how you believe that 8K vs a more conventional 6.0K impacts your result.

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Note well --

John runs a small shop, essentially on his own, where the inventory and his web catalogue are somewhat out of sync. That said, he's knowledgeable and helpful, and tests tubes before shipping.

Best ..

Hello -- I suppose the other block for me is I'm up in Canada, [...] Look for some here https://pacifictv.ca/main.htm#N6F or here https://www.thetubestore.com/6gh8 . I find John at Pacific TV to be quite helpful. Canada Post will be reasonable if you aren't in rush. The 6GH8 is not the only option, ...

There is little magic in standard chokes. Choosing one that's equal in size and resistance is as close to perfection as one can get without an original part to test, and replicate. The schematic is a bit messy -- however, 50mA is more than sufficient as Martin has already lent his wise guidance on. ..

jabguit wrote: ↑Wed Jul 02, 2025 10:31 am

Guy77 wrote: ↑Mon Jan 22, 2024 3:33 pm It works so don't change it I guess.

debatable....

OK. So ??