Hello everyone. Long time lurker here. I'm just getting into amp repair strictly as a hobby. Kind of a Flip or Flop thing but with amps instead of houses. My first attempt is this Tweaker 15 that I bought with the description of "light on, no sound". Some of you may be wondering WTH is he thinking? The reality is even if I lose money on this one it's been well worth it as I've learned a lot already. I'd just chalk it off to start-up expenses When I first tried the amp there was nothing - no hum, buzz, static. No sound out of the loop into another amp and nothing from another amp back into this. I opened the chassis and the OT was completely disconnected with a piece of tape on it labeled "Bad". Alrighty then - there's my first clue. I tested the PT and that's good. I then tested what I could on the OT (resistance, continuity, shorts, etc.). The only thing that stood out to me was the resistance between the primary leads (below). I don't know if this is ok or not, but later when I checked voltages at the power tubes they look good - so maybe this is fine? Red (CT) to Blue: 164 Ohms Red (CT) to Brown: 61 Ohms Blue to Brown: 120 Ohms I reconnected the OT to start testing voltages and noticed the Preamp tube was dead. I replaced that and now I have sound. However, it's not loud and it sounds really muffled. I then re-tested the loop and connecting another amp's send to this return yields no sound at all. I then connected the Tweaker send to my other amp return and it sounds really good. Loud too! Now I'm getting somewhere. I then cleaned the send/return jacks and swapped the 6V6's for EL34's that I know are good. Back to low, muffled output. Now I'm concentrating my efforts on everything past the loop. I checked every single resistor between that and the power tubes and for the most part all are perfect. I have a few resistors that measure lower than their value, but I did not take them out of circuit so I wondering if that has something to do with it. They don't look burnt or look like they were ever replaced. Also, I'm pretty sure that when a resistor goes bad it's either open, or a higher value, not lower. I then measured the voltages at the power tubes and here's what I have (6V6's back in). I'll list one because they both measure pretty close to each other (DC volts of course): Pin 1 - 21v (Tied to cathode) Pin 2 - 44.6v (Heater) Pin 3 - 362v (Plate) Pin 4 - 355v (Screen Grid) Pin 5 - 0v (Control Grid) Pin 6 - 0v (No Connection in tube) Pin 7 - 45v (Heater) Pin 8 - 21.4v (Cathode tied to Suppressor Grid) Pins 2 to 7 - 6.7 vac I then powered it back up, and with a wooden chop stick, pushed on tube pins, wires, connectors, components, etc. looking for loose connections etc., but nothing stuck out. All the solder connections on the board look good too. So now I'm back to wondering if the OT is bad after all, and if so, how do I confirm it? I'd hate to buy another one at $150 only to find out that wasn't the problem. Anything else I should be checking? Thanks all!