Tube Amp Archive

Crazy conclusion here. I had to leave town for a few weeks this morning, I'm a touring musician, so last night I thought I'd just put the chassis in the head shell while I was away. So I put it in the shell and plugged it into my cabinet and played it for a bit and the problem was gone. Gain knob so...

Yep the plate resistor is really 56k. I've been about pulling my hair out checking and rechecking the values and wiring of everything. I put a 100k on the cathode and no change. I tried several different 12AX7's in all the different positions and even a 12AT7 just to see and they all behaved the sam...

Tried a new tube in V2 and it is just slightly better but still doing it. With the new tube I got some different voltages. Grid is 159v and Cathode is 164 and Plate at 256v. I've been reading the Valve Wizard website for the last hour or 2 under the DC coupled cathode follower section trying to get ...

Replaced the cathode resistor on V2a with 2 820's in series that were testing low so I'm just about 1k5, didn't have any 1k5's and no difference. In that other thread about biasing a triode I used that newly acquired knowledge to get the first gain stage right bias wise so I'm assuming this problem ...

Really cool. I get it now. I didn't get using the load line as the second indicator. I was using the .88mA on the vertical axis and thinking the other point would be the 252v on the horizontal and find where those lines crossed. This is so legit! I know it's still just scratching the surface, being ...

I think you are mixing some things up. I would do it like this: 1) 100k plate load from 252V B+ means 252/100=2.52mA at zero plate volts (Ohm's law). 2) Draw that load line on the 12AX7 plate characteristics plot, from 2.52mA at zero volts to 0mA at 252 volts. 3) The load line crosses the 0V grid l...

So I've gone back and have been studying the AX84 tube theory page and trying to really apply all that knowledge to one of my builds. Here's where I'm at so far: First gain stage is standard triode. -I've got 252v before plate resistor and 101v at the plate on the tube. -Looking at the Plate Amps/Pl...

Woops, R9 is 820 ohms. I'll fix the schematic. Also, I didn't look at the pin voltages after I posted but I had them in a much easier to read format. I guess the forum software bunched them all together. I'll fix that too.

Hey all! I'll take a bit of the heat for the OP's venting. I've built a couple kits and 1 scratch build. I've got another thread going currently asking for some help but, that's in another thread. I just wanted to say seeing this thread and reading through it has lit an additional fire under my butt...

?[/quote] What are the values of the B+, the plate load, and the cathode resistor on that stage following the first volume control? You will get the most headroom if it is center-biased, so you may be able to tweak that. Is there a schematic that you can post?[/quote] B+ at all the nodes are 357v, 3...

What you have now is a full-wave rectifier, using the two diodes in the EZ81. They have a common cathode, at pin 3, and the anodes are pins 1 and 7. If you were to pull the EZ81, and solder in two 1N4007's from 1 to 3, and from 7 to 3, with the banded ends on pin 3, you'd have it. I did this and it...

Awesome! Thanks so much.

Cool cool cool. Thanks so much guys. Yeah I'm pretty happy with it at the moment. I do want to do some things to tighten up the low end but I've got a whole list of simple cap/resistor changes that i hope can accomplish that. And thanks for the clarification on the diode be it tube/solid state thing...

I built one of the trinity 18watt amps recently, not from the kit just used the layout and schematic. I used an old PT I had with 270v HT taps instead of the 290v taps the trinity uses. So as a result all my voltages are lower, obviously, but the amp works, sounds pretty good, is real quiet and the ...

Hey all. I'm hoping to make a light faceplate on my next amp. Just a little maybe 2 to 3 in square with my initials on it. I'm assuming I can just get a clear piece of acrylic, paint the back of it black, then remove the paint to leave just the logo? Then of course run a few extra heater wires to a ...