The Amp Garage

I see now, thanks everyone!

Ok, thanks for the info on the B+ and the heater voltages. I didn't know you had a problem with heater voltage until you exceeded the current limit of the PT filament winding (adding more heater draw than designed for). I don't understand how the voltage can rise above the design of the transformer....

Thanks Martin, I was planning on dropping the anode voltage from what the twin PT has via large ample watt resistors. If I can get a B+ of ~380 then I could show 6v6's an 8k primary by using 16R secondary and use JJ6v6's then it looks ok on paper, right? Looking at the TW Express schematic on the Ro...

Thanks,

I know I would have to bring the voltage down for 6v6's. So do you mean low primary impedance for the el34's because of the 4ohm tap being the only one? What do two el34's want to see versus two 6v6's as far as primary on an OT?

Hello all, I want to build an amp with two 6v6 or el34's in a push pull configuration. Loosely based on a TW Express except I'm wanting to use the PT and OT from a recycled 65 Twin Reissue. I can't seem to get my head around figuring out the impedance matching deal. Sometimes it seems clear and then...

[quote="Structo"]As you found out, lead free solder is crap. Dry, crumbly, bad connections abound. Do you own a solder sucker? I would try to remove as much of the lead free solder then re-soldering those connections with lead I noticed that when I emptied my solder sucker that it was all dust and k...

I put some 1n4007's that I found in place of the suspected bad uf4007 diodes and played for almost an hour with no problem as of yet. Hopefully this solved it (or my fiftieth resolder attempt was a success! Tempted to re-install old diodes to see but probably won't. Just try it again later then take...

At work, will try diodes this evening.

My grounds are all along the top (pot side) of the board ending at the input jack ground lug. This also happened with the 130R standard setup before modification. Thought I had it fixed with a solder touch up so I went ahead with the mods. It came back though exactly the same. I haven't deviated fro...

Yes, c13 is intentionally disconnected, was taking out some highs. Pins 3 and 4 are per the schematic to let the filament voltage ride on top of a dc voltage (don't quite understand that but it's in the schematic). The cathode resistor is a 5W. The amp did this before I put the variable bias and oct...

Here is a picture of the entire amp. The bright cap on the voltage divider is intentionally disconnected on one end.

The new diodes didn't help. Maybe I just don't know how to solder! The cathode voltage stayed at 6.8V with or without the hum. Going to reflow connections again.

Ok, I swapped the first and third filter cap and the same thing happened. There was 2.6V AC ripple on the first filter cap before the noise and 3.9 after it started. The AC voltage taken where the two diodes come together was 267 before and dropped to 207 after. I'm going to get two diodes and try t...

Hopefully this is a better pic

Thanks everyone, I haven't checked for ripple yet, just resoldered joints with known good stuff. Filter caps check out disconnected with a meter for what it's worth. Amp did this before I installed extra parallel octal socket and bias pot so it did it with fixed bias on the el84. I just figured a ba...