The Amp Garage

Looking over your voltages, something's definitely not right on V2. The cathode follower should have significantly more voltage on its plate than the preceding gain stage's plate since there is a plate load resistor feeding the preceding gain stage versus the cathode follower's plate being connected...

I built an amp like this and second TUBEDUDE and didit's suggestions. The amp I built had a single shared toroidal transformer feeding to completely parallel, dissimilar amps (a Brown Princeton and an AC15-ish preamp each feeding an ECC99 push-pull output section). Beyond the PT, there are no shared...

After wrestling with some hum issues in an older build, I decided to just start over with a clean slate. The old amp is a 6G2 Princeton using an ECC99 push-pull output stage, but it was a really early build of mine and there are a whole host of grounding issues that I haven't been able to resolve, a...

It's your decision, but since I think I was probably the most optimistic poster previously, I feel obligated to underscore that I would strongly recommend walking away if you can't get information on part sources. At that point the only things I'd trust would be the speaker and cabinet, and even the...

That price is ridiculous. You can buy a quality kit new for that price. Of course, that's no speaker and no cabinet. Still, buying someone else's problems for that price? You should pass or offer $250. I agree and forgot to mention that if you're looking at buying this you still shouldn't pay anywh...

Since ghosting is a power supply issue and the amp seems to have been essentially rebuilt (except for the PT, which I think is likely fine), I'd want to know how everything measures in the amp currently. Are you getting any AC current anywhere without anything plugged in? All B+ and cathode voltages...

Others have covered that it can be a losing game to pick up other people's mistakes, especially when you're starting out, but I did want to add that it can be worth picking up depending on what parts it has. I'd specifically want to know what cabinet, transformers, speaker (you already know V30), an...

Glad the amp is working how you wanted it to! Also really cool to hear the OT worked out -- the concept kind of reminds me of JTM45 OTs with high Z ratios. I'm still curious as to why the 47k and 330k to ground weren't enough to tame the input to the PI The 47k and 330k to ground aren't truly in par...

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...