Tube Amp Archive

If anyone is bored or needs a good laugh, would you mind taking a look at this layout and see if anything is just plain stupid. I was doing a layout for a Liverpool, then a rocket/Zwreck and then down the concorde rabbit hole and threw this together last night over a Bourbon or two. I recently built...

Quick question for the masses - has anyone experienced there (in this case Express) amp just sounding better with an impedance mismatch? I have been playing the amp allot through several cabinets and plugged into the cabinet I had mainly been playing the amp through, and it just sounded better. It's...

Got the amp/cabinet finished and she screams. I put the HV windings on a switch and love running a pair of 6k6's in it. They give up a very vintage growl that I love in this circuit. I added a 6 position switch (shift) that chooses the TS coupling cap 10p through 1000p. This does a really cool job o...

This is a layout mistake on my part. The original layout did not have a MV and the grid stoppers were on the board. I put the ppimv in and forgot to add new resistors off board. Dumb mistake on my part.

xtian wrote: ↑Mon Dec 09, 2024 10:49 pm So you've got some major instability, I guess, and since you've got a non-standard layout, lead dress might be the issue. Oh yeah, I see one major no-no: your green OT primary (output tube socket pin 3) is touching the phase inverter grid wire (pin 7, white wire).

Thanks xtian!

xtian wrote: ↑Mon Dec 09, 2024 10:06 pm Disconnect NFB loop from OT tap. How does this affect the issue?

That makes the issue come on faster, so worst

*New pics Below* [original post] I Just finished this Express build and everything was great from the first firing....well, almost everything. Plate to cathode is 401v, with -33v @ bias. When i try to bias el34s to around 40ma with the MV opened up, the amp gets unhappy. rolling the MV back stops th...

These get addictive. Did a ZWreck/Rocket type of a preamp with a few adjustments and tweaks. Very happy with the result. Extremely dynamic and reacts great with the guitar volume. The following sound sample (based on a popular song harmony) is Tele only for the two guitar tracks. Will do some more ...

R.G. wrote: ↑Sun Oct 22, 2023 5:23 pm So it was a shorted snubber cap??

I didn't test any of the caps when pulled. I just replaced all the diodes and moved on. So far so good. I played a show with it yesterday and amp worked perfectly.

Just wanted to follow up and say that replacing the snubber caps with diodes has cured the amp. I've go probably 20 hours and 100 cycles on and off with no issues. Thanks for the quick help!

remove the snubber caps.. put 2 diodes insted on one, so in total 8 pcs..move standby to the AC line, DPDT, sw.off both lines of transformer instead this DC Thanks bepone, I'll ditch the snubber caps first see if this stabilizes things bepone has a good guess: failing snubber cap. In situations lik...

johnnyreece wrote: ↑Thu Sep 28, 2023 7:29 pm Just checking; do you have the PT center tap *and* the diode bridge connected to ground? I believe that would do it.

center tap is tied off and not grounded

After about 20 hours of play,tune,play,tune with this 100w amp I've built. The mains fuse blows. I pull the tubes and it blows again, so now I go through the debug process. AC line only - fuse holds Wire in HV and fuse blows. So I find a failed diode in the rectifier section. I replace all 4 and C12...

maxkracht wrote: ↑Sat Aug 05, 2023 3:04 pm Should put some of that silicone sitting above your bench on the tilted filter cap. It will eventually rattle loose if you leave it like that.

Wes indeed. I'll go through and silicone things once I am done tweaking.

Just on quick examination, your flying bare PT 6.3V heaters look like they’re frighteningly close to your PT screen resistor leads. I once had an OT primary that used different colors and had my primary CT connected to a PT plate. Disconnecting and testing the primary resistance helped me connect i...