The Amp Garage

Demos sound nice! I know it's not built with an eye toward longevity, but I really like my Studio Vintage, so it makes sense that I'd think this looks nice too. I'm pleasantly surprised when I hear these "little" Marshalls running such low B+ levels and still sounding like their bigger brothers. I a...

I built an SAP clone a few months ago, and I grew pretty frustrated with it after the honeymoon phase ended. It felt very stiff, and I couldn't find an appropriate volume setting where single note lines would sustain while the chords weren't too distorted. In other words, either I'd have a semi-clea...

Thank you so much! The 7V is so that the cathodyne sees both positive and negative signal amplitude rather than just different magnitudes of resistance to ground as with the regular opto trem. I'm totally good with any design as long as it's at least somewhat simpler than the regular Brown 5-triode ...

I'm planning out an upcoming Marshall style build and have been kicking around the idea of adding tremolo. I really like the Brown Fender harmonic tremolo sound, and I also think the regular amplitude style would nice to have available, so I've been trying to design a simple circuit that can be swit...

I think looking at JTM45-50 gets close but that (100w) +3db makes a reactive difference in the guitar hearing the amp along with the other small things. I have a 50w amp with 50/50 mains and screens, 16/16 PI and V2 with 10u (Solen film) input stages that plays a little squash like a pro... a broke...

Coming back to this project finally. I really like the idea of using the JTM45 transformer, especially on the feel basis, Paul. Did you use full wave rectification or a bridge rectifier on those builds? (Does it matter in terms of feel? I keep reading bridge rectifiers are more efficient, so I'm rea...

Used R.G.'s method and found out I had a loose socket -- thanks so much for the help! Thanks for the extra set of eyes on that, maxkracht, and good catch. I took another look at that section and found the output of the tone stack was feeding into the top of the bass pot. The Fender side had another ...

The Fender side lives! Y'all were right about the sloppy lead dress. V1's anode leads were running too close to V1A's grid lead, causing the issue. I ended up replacing the long grid lead with a very short shielded cable and rearranged the anode leads to V1, which has basically resolved the issue as...

So when I did some testing yesterday I detached the wire running from the speaker jack to the board on the jack side. That let me alternate between tip and sleeve, and in both cases the oscillation remained but also the total voltage across the jack also decreased, so it would seem that there is som...

I've been thinking about this approach some more in context of a Hiwatt build I did. I used the "SAP" preamp (https://hiwatt.org/Schematics/DR_Pre2InputSAP.gif) with an added SPST in series with the footswitch in case the footswitch breaks, I forget it packing for a gig, etc. The switch was installe...

Turns out my hasty decision to remove the preamp and negative feedback at once hid an important clue. The oscillation is much, much better without NFB. I was able to redo the power supply to decouple the OT from the preamp in a way similar to maxkracht's drawing with some value changes. The stages a...

When it finally came to completely disconnecting the preamp section (including the NFB lead), there was no more problem. Not sure if I am following. Have you tried just disconnecting the nfb? If no, you should try reversing the primary or secondary of the OT. Weirdly, the output section got biased ...

Y'all are the best -- thanks so much for helping me figure this out. So I tried gradually reducing the power supply as suggested and found the following didn't resolve the oscillation: -Disconnecting the Vox side completely -Disconnecting the parallel 30uF capacitor at the reservoir (didn't fix the ...

Thanks everyone for the help so far! I'm currently reading through the Champ article -- thanks for passing it on, R.G.! [Edit: just finished the article: I think the lack of decoupling may be the issue here -- would decoupling the output transformers be a good starting point? Since the issue appears...

Just finished wiring up a "space saver amp" for my wife and I to do shows together. The idea of the amp was to have one amp that has 2 truly separated channels so we could play small coffee shop gigs together and haul less. Channel 1 is basically a brown panel Princeton (6G2) and channel 2 is a Vox ...