The Amp Garage

Ok, I allready figured out what was that. If you have same issue check heater supply. Especially R48 and R47 (100R resistors in AD200B mk3). They caused the heater to be unbalanced. Measure heater voltage and then check voltages between heater and ground. Totally missed this where you named the res...

I just checked the Orange. The heater setup has a center tap, but right near where the connector to the lamp goes are two brown-black-brown resistors R48 and R47. I can't find them on the schematic and they measure at just under 1M, one side is to ground. A major clue. I have to go to work, but I'm ...

Thanks for the responses. So... I had to put this amp off to the side for a minute because it was frustrating me so much. In a VERY SAD twist of fate an amp I built from scratch, which I have successfully built before, (completely different but with 4x6550) has THE EXACT SAME PROBLEM. The heaters on...

I have an Orange AD200B with the most frustrating hum I've ever come across. It might be something easy, but I'm at my wits end and could use some more minds. It sounds like a ground hum to me, but I'm not positive. -Controlled by master volume (goes away when master down) -Can remove first tube and...

I will try that. I thought about this briefly, but the belief that I had seen this done along with the ease of putting a relay there and the idea that I wouldn't be stressing all the pre-amp tubes all the time caused it to slip my mind I guess.

Thanks.

I don't. Imagine 2 completely separate JCM800 Marshall preamps, with a relay switching between the very first grid (inputs) of each one (straight from the input jack), and also a relay switching between the two outputs from the Master Volume pot into the PI cap (this is the one that I think is fine)...

I built an amp with a relay right on the input, switching between the grids of two channels. Perhaps obviously, it clicks when I switch channels. The weird thing is that I feel like I got this idea from an amp I had repaired in the past. Anyhow, is this ever done? I tried all the standard tricks (gr...

Just run it in parallel with the heaters. Keep in mind the #44 bulb draws 250ma, but I doubt it will matter.

Is it an 8" chassis? I do my OT's on the input side, but just put them in the back. The primary's just go straight to the back and run along the back edge and up to the sockets. All wires remain a good distance from any input circuitry. On my Model T, I used terminal strips and the put the socket ri...

Dudes, it turned out to be a bad mica cap to the send section. I finally got a chance to set up another amp side by side, realized it was the send, jumped the cap with another one, heard a bunch more reverb and 5 minutes later had it fixed. My gut was wrong, and I was surprised to have a cap treat t...

I used a small R. F. choke that AES sells, I think it was the 2.5mH one. The mid switch sounds cool. I'm pretty sure I wired it incorrectly, I ignored the SS pole and used a SPDT. I have no idea how they do it in an original. I used to have some killer pictures of one I repaired but I lost 'em. I'll...

Well, new tube in that spot with no problems so far after playing an hour. Everything sounds great and it's putting out almost 200 watts wide open.

Smokebreak, I used Hammond 1650T, with two hammond 1.5H 200mA chokes and a huge 800VAC PT. B+ is about 520.

It's probably more likely I switched them up in my head. I did reverse the wires on both reverb tanks which gave me no reverb at all. Also I got the exact same resistance on both tanks which are different brands.

in is 217 ohms and out is 1.2 ohms. It came with a 8AB2A1B, and that's also what I swapped out to test.

That's a very interesting gain stage, and it seems to contridict accepted wisdom in terms of biasing a 12AX7. Nirmally, the cathode is at some positive voltage wrt to the grid. In this design, when the bass control is all the way down, the grid has a 43K DC path to ground, yet the cathode is held a...