The Amp Garage

I'm finalizing plans to build a Fender BF preamp (single 12ax7 only) in a pedal and was thinking of doing the following. 12v/500ma (or perhaps 1a for extra safety) AC wall wart into a 115v/6.3v filament transformer run in reverse (xfmr rated for 300ma on the secondary and total power of 1 volt amp)....

Thanks for the tips! Will definitely look into the depth mod.

Thanks Roberto! I think for now, knowing the voltage is solid, I'm just going to roll the dice on a Soldano pre-amp meets Super Reverb power section/PI and see how that works, hoping the power supply differences between the Soldano and the Super will only change the flavor a bit and not make the pro...

At this point I've got 2 tweed and 2 blackface builds under my belt and am pretty comfortable working in that world. I'd like to build a more modern, high gain circuit but without getting too far from the relative simplicity of those early circuits. Based on some initial research, I'm thinking maybe...

Just thought I share info about the homebrew tube tester I started last October and is now up in running. I had decided by that point I would like to have a tube tester and the more I researched and pondered, the more I thought this would be a cool project, especially to push my knowledge of both tu...

Thanks for confirming that.

Joe

Thanks a million sluckey!!

Joe

Fair enough. For future reference could someone tell me whether the attached diagrams are correct in terms of how to wire the cliff jacks? For better or worse, this is what we followed. I've compared the actual jacks to the diagram several times and the wiring matches. I assume that in the diagram t...

Maker DP, I think I posted at the same time as you. Yes there was a signal all along, even out the speaker, but it was minimal, even with the volume on the amp all the way up. In hindsight, I've measured and it was about a 300mv signal going in from my phone, certainly enough to make a loud sound ou...

Turns out it was indeed the wiring of the jacks. I pulled all of the cliff input jacks and put in a single fender jack with a 680k input resistor. I then decoupled the primary speaker jack from the second one such that, with the ot disconnected, the jack was actually seeing a resistance beyond that ...

Just and addendum to question 2 above.

2.If the speaker jacks are wired properly, and I plug a speaker, say 8 ohms, into the primary (or only) jack, again with the amp off *and the OT secondaries disconnected*, should I see that 8 ohms (+ meter lead resistance) across the jacks terminals?

Joe

Should have said grids to power tubes. I've got the amp and am troubleshooting it now. I'm thinking it could have to do with incorrect wiring of the Marshall style input and speaker jacks. Is it correct to say that: 1. If an input jack is wired properly and I plug a 1/4 inch cable into it, I should ...

Yep, did run a scope through and saw signal on the PI grids, but only the super weak signal out the speaker. Think I'll need to check the preamp stages more closely, including the tubes. Probing the PI grids also put out a little pop, understandably. Come to think of it, early in the day there was n...

Thanks for the tips! We did a series of Ruby inspired slow power ups with a Variac starting with no tubes, etc, while monitoring current on a Kill-a-watt and checking temperatures with a thermal gun. Seemed to go very smoothly, and when all of the tubes were in a scope showed AC all the way to the g...

Howdy, A friend of mine built the mojo JTM45. I went down today to help him power it up but there were some issues. In a nutshell only the lo inputs seemed to pass a signal, and even with my cell phone signal generator cranked and the amp dimed, we only got a super quiet signal out the speaker. Abso...