Tube Amp Archive

No schematic to offer you, but out of my own curiosity, I looked up the JRC 9/15 to get a sense of how it's laid out, and found this description on Doug's Tubes: "Starting from right to left, the single input of the amplifier (high and low sensitivity) feeds the inputs of two 5879 Pentodes, each wi...

Still looking, in case this catches the eye of someone with info, thanks!

Has anyone here mapped out the Divided by 13 9/15 amp schematic? I'm especially interested in the dual 5879 preamp section tolearn what they are doing there.

Tell me more about the PT having enough amps for a second 5y3 Not much to say. One 5Y3 needs 5V@2A. Plenty of PT choices available. Two 5Y3s need 5V@4A. Fewer choices and they are likely to be BIG and HEAVY. the two examples above seem to be wired differently in relation to the PT and each other. M...

You are basically making the rectifier more efficient and handle more current. A single (larger) bottle would do the same thing basically. I suppose you could pull one for more sag, but I would worry about drawing too much through the one tube might be asking too much. Dual rectifiers is not about ...

I have a PP 6AQ5 amp that runs dual rectifier tubes, both 6x4. I love it, and have always been curios why there are two rectifiers. In this amp it looks like each 6x4 rectifier is fed by a different side of the PT, then the outputs are bridged. https://i.imgur.com/gAVeWnf.jpg There is also a paralle...

sluckey wrote: ↑Thu Jun 09, 2022 6:02 pm Just use a very common 24VAC transformer.

I think Rob Robinette used a Hammond 166N12 for his bucking project. So maybe the Hammond 166N24?

I see you used a Radio Shack part for yours - I'm open to parts suggestions if there is a good readily available 24v T up to the task.

I also need to figure out a bucking transformer, as I have 122v at my wall, and a 100v made in Japan tube amp that I want to use. I've seen some posts about making a bucking transformer to get down to 110v, but I need 100v. Ot is it better to just get a step-down transformer? I also have a couple 22...

Stevem wrote: ↑Fri Apr 22, 2022 5:41 pm!

Thanks for your help along the way. It was a sneaky problem, and I certainly learned a lot exploring all of the different aspects of the amp to try to sort out the problem.

I got the amp to stop blowing fuses by swapping the Power Transformer from another of the same amp. The original PT seemed to test fine, but under working conditions was problematic.

Now I'm working on biasing, and tweaking a few things, but it sounds great!

I think you may be subconsciously sabotaging yourself by labeling the amp's problem "the short". It is an overcurrent, and it might be caused by a short, but as I mentioned, I'm leaning to a problem with the output tubes losing their bias somehow. Maybe funny stuff on the shared cathode resistor, m...

Please don't add any new parts to the amp at this point unless they are being put in to replace confirmed bad parts! Resistors that have drifted in value even by 25% will not stop a circuit from working. It looks to meat this point that the issue it has now was caused by you possibly by replace a f...

I've been reading the thread, trying to soak it up. I'm going to just say that I got from this, so correct me if I've missed something. > PT and OT resistance measurement seem normal. I think that "UL" reading may just be what your meter says on a complete open circuit. > PT and OT don't seem to ha...

I went through the turret board and removed every component. Everything tests with no shorts and the values were correct, albeit many had drifted 10-30% from original spec. I have then traced wires, and am checking everything for continuity to ground where it should or shouldn't be. Everything looks...

Please report back with your findings. I removed the C203 leg from R206, and both test to spec. I must have had a bad reading as they were in the circuit still. I soldered PT wires back on and did the additional tests. It is worth noting that the oscillator section of the circuit has been entirely ...