The Amp Garage

I misunderstood the first post that included your voltages and agree with Martin that your preamp voltages may be too high, especially since the signal coming out of the last gain stage being higher than spec. That said, I still think the difference likely lies downstream of the 3rd gain stage. The ...

I would try a single 100k to ground after the original 220k mix resistor. A series cap isn't needed. I suspect this is the main culprit, especially since it seems that you've identified the problem as happening with too much signal reaching the PI. You may also want to try replacing the 330k resist...

I'd suggest reducing the 330k after the faux mixing resistor. As it's built now, there's an assumption that plate resistance of normal channel's second stage is infinite, making it so that the only path to AC ground is through the mixing resistor and the normal channel's last stage's plate resistor....

That master volume mod doesn't actually help, I did some tests on this a few years ago with a spectrum analyser and found it made no difference. But YMMV. Dave Friedman puts a 500pF cap across the cathode follower 100K, lowers the first coupling cap to .0022uF, adds a 22uF to the final stage cathod...

Just want to clarify on the OT. I could get the Hammond 1760H (deluxe reverb) which is 20 watts, 6600 ohms with 4-8-16 ohm taps. For flexibility with speaker selection I could use an ohm selector on the output and leave the 16ohm wire unconnected, take the 8 ohm wire connect it to the 16 ohm positi...

If I'm not mistaken, the taper is an intrinsic part of the resistive track of the pot. Reversing the lugs will reverse the direction you'll need to turn the pot to turn it up or down, but the taper will still not be correct.

Schematic looks good! I'd be concerned your primary impedance is too low (the datasheet echoes bepone's suggestion for 12k ohms) -- I'm not sure how much mismatch is acceptable, but a quick Reverb search shows that, for example, a Blues Jr OT can be found for about $25 before shipping. That has a pr...

WhopperPlate wrote: ↑Thu Apr 11, 2024 5:52 pm Not even I can defend this

I was going to hop in with a "tone fuse" joke but was concerned someone down the road might take it seriously

Yeah,263AX should give you a B+ of ~280V. The problem with 263AX is that it doesn't have a 6.3V tap. 269AAX also has a 200V HT secondary but has a 6.3V secondary for the heaters, so that'd be the better option. 261M6 is rated for 215V @ 269mA and has a 6.3V secondary, so it'd also be even closer to ...

Gotcha -- yeah, I don't think there's a ton of difference between the grid stopper values listed anyway, so that makes more sense. Regarding the B+ string, yeah I think that'd be a solid starting point. You may want to tweak values once you get the amp built. You might even want to go with more radi...

Yep, 315 is the maximum rated plate voltage. Assuming you proceed as-discussed, you're still well above that limit (I estimate your B+ to be about 385V with full-wave rectification). I know people run 6V6s all the time way over the rated maximum, but I'm not that familiar with 6k6, so I'll hold off ...

Agree regarding PT being a prior question and that 275-0-275 makes sense if you're trying to run the 6k6 within datasheet spec. Do you have strong preferences either way in terms of low- or high-voltage sounds? If you go lower B+ (probably a good idea), I'd also suggest considering revising your B+ ...

I'm glad I re-searched this because I was about to ask how to scale filtering from 50w to 100w or vice-versa in the tech section. Really helpful mathematical analysis -- thanks! I did want to get clarification on something, though: it's not really clear to me why filtering would scale as a square-ro...

I'm not sure I understand the design goal. Are you after a wet/dry rig with one side doing reverb and the other dry signal? If the goal is reverb-only on one side rather than reverb mixed with the "original" guitar signal, I think that's only possible with two separate channels, whether that's usin...

My understanding is a stereo signal required two outputs, one for "right" and one for "left". A single speaker cannot, by definition, deliver a stereo image. The half wave feed to a speaker seems impossible. Perhaps an alternative would be running two parallel PP output stages, but then how do I in...