Tube Amp Archive

What I did find though that no matter what bias I had on the grids, whether it be -2v, 0v or +2v, i didn't hear a difference at all. I've become convinced this bias anomoly is just a meter loading problem. The best measurement of the grid voltage will be from the bottom of the grid leak to ground, ...

This might sound stupid, but I was so hung up on these higher values I see in the sss schematics, that I didn't even think that 100k was originally in there. And that it should be fine. Like I said, overthinking..... Anyway, I did try out a bunch of different combinations. It was definitely louder w...

This is a fun experiment, and I'm looking forward to hearing about your results, sound-wise. You are right, the RC corner point will have some effect on the frequency response, but the AC load line will also be rotated clockwise as you lower the load from 1M to 0.5M to 0.1M. That means the positive...

I don't think using 470k instead of 1M is a problem, in fact other versions of this circuit have used that value, or use the 100k the amp has now. Funny I was going to suggest that you parallel the 1M grid leaks with something like 100k back when you were having this issue with the CF powered up on...

Just for experimentation, I made a voltage chart and paralleled different value resistors across the 1 Meg's I have on the board. I still for some reason don't think I am supposed to have too low of a value as wouldn't I lose a lot of signal to ground? Anyway with the weird voltages I did take it of...

Well I don't know what's going on.... when I had the circuit jumpered in, my voltages were correct. Now that I have permanently swapped the wires over, they are back to being wonky. I threw the mains switch, standby still off just to read voltages and I was getting really weird readings. Bias voltag...

I believe the bias vary trem system should work; I think I said that somewhere before (on pg. 2). I've never heard of anyone doing a power tube bias vary trem with CF driver... you may indeed be the first! I believe you did say that. I don't use, or even like tremolo really. But it just sounds so g...

I think it looks pretty good. That is exactly where I was imagining it might go when an LND150 SF was being discussed. There is very little extra wire length to the power tube grids, and the signal level is high, so less chance of noise from the power supply. If there is a problem, maybe some fast ...

Hey martin (pretty sure it's just you and I here) do you anticipate any problems with my layout? I spent a lot of time trying to figure out where and how to put it all in. I'm still skeptical about mounting the tube inside the chassis, but I got it about as far away from everything else as I could, ...

Alright so this is where I'm at...... I built a board and a bracket to hold the tube socket, didn't like it, didn't fit, had to redo it all. Now I have it all installed, power supply hooked up, bias hooked up, not in circuit I was getting the same readings as before. BUT...... when I jumper the grid...

I realized (see above) that the grid leaks are essentially in the position of stopper as it stands. It's possible that your probes leads are causing the issue depending upon where you place them. The right answer is the grids should be below the cathodes by ~1.5V. Re the link above, I'm not sure wh...

http://www.rfcafe.com/references/electr ... 1-1-40.htm

I think I may be on to something here. Very good information.

Grid stoppers didn't help. Tried a 200k to ground with held start up voltage to 116, so that's good. I just seem to be dropping about 4 volts through those 1 meg's. I tried jumpering in some signal to the grids, still didn't help. Any reason the 1 megs are too large a value? Edit.... just clarifying...

Can you add grid stoppers between the 1Megs and grid pins and see if that settles it down? I was just thinking that, but then thought wouldn't the grid leaks act like grid stoppers if i am picking up noise from somewhere, since i have no other connection to the grid? They are the only thing connect...

By tying the CF grids directly to the negative bias you’re ac grounding them, and that will ground out the signal too. This makes me think there was oscillation happening before. Do yo have an oscilloscope? I'm starting to understand now. I'm just reluctant to tear the amp apart to hook this in unt...