Tube Amp Archive

keithrick wrote:Glad you got it sorted out Dave! Hows it sound now? I have all the parts here for my build just need some time!

Keith

Sounds really good! My only complaint is that I wish it had a little more headroom. It's breaking up pretty good at about 9 o'clock on the volume.

That's great dab! What brand of filter caps were in there before and what did you switch to? Can you use your DMM to measure the caps you pulled out? Measure for capacitance and resistance and since they're e-lytic it will matter which way you connect them. Just curious if there is anything easily ...

Sorry, got real busy at work and had to stop having fun for a while. Don't you just hate it when some guy (me) starts a thread about some problem and then when you get to the end of the thread you never find out what was wrong with the amp? In this case it was one or more bad filter caps. I replaced...

Fischerman, Awesome. thanks for taking the time to post this. It was very helpful and i appreciate the opportunity to learn from you. i will try what you suggest and get a supply voltage. Dave dab, FWIW, when you post the voltages it's really helpful if you also post the supply voltages. Just knowin...

ant wrote:Check your powertubes are matched try swap the phase inveter 12ax7

Thanks, I did those things. Unfortunately no change. Still trying to track the problem down.

Dave

Thanks for the info. I retook the V3 grid voltages using the 1M ground reference and they were fine. Guess I need to learn more about how the Phase Inverter works

So, I am back to square one. I am at the point where I am going to have to just start replacing random parts.

OK here are the voltages. V1 160 0 1.58 - - 137 0 1.2 - V2 207 0 2.2 - - - - - - V3 191 37 48 - - 191 36 48 - V4 - 0 8.8 - - - 313 - 291 V5 - 0 8.8 - - - 311 - 291 V6 - 0 8.8 - - - 313 - 291 V7 - 0 8.8 - - - 315 - 294 I am a noob so if I say something really stupid you will know why. Look at V3. I h...

I am gonna recheck all the voltages and post them. Thanks for the feedback guys.

Dave

I am still getting 4.4vdc for cathode voltage on V2. It just has a 10K resistor to ground with no cap (like the schematic shows). I am thinking I need to increase the resistor value to lower the cathode voltage. it should be bout 2.2vdc. Or, should I be looking for something else that could be causi...

ah yep. makes sense thanks

Okay I found something and I need you guys to help me understand (I am an electronics dufus). the coupling cap between V2 and the PI (pin 1 of V2 to Pin 7 on the PI) showed DC on both sides of the cap. I switched it out with a new Sprague 715P series. Retested and things looked good (No DC showing o...

Used an audio probe. Signal is clean to the PI. Coming out of the PI it has a lot of gain boost and is distorted. I don't know if that is normal. You can hear the signal but it is definitely louder and trashier sounding on both Pin 1 and Pin 6. It stays like that until it gets to the power tubes. Co...

Thanks for the replies. I think maybe it was there a tiny bit but not enough to really notice. Now it is very obvious. I have tried several speaker cabs with the amp and it does it with all of them. I will be doing some mass parts replacements on Friday (tube sockets, rewire, some caps, etc.) so i w...

Hi guys, I have started getting a buzzy distortion behind each note or along with a chord. It starts with the pick attack (kind of a buzz behind the note). It quickly fades away leaving only the clean sound. I have checked for microphonic tubes, loose hardware, changed out all of the tubes more than...

It's cookin now!! Took it off of the bulb limiter and all the voltages straightened right up. THANKS!! It's got that glitchy oscillation kind of sound when you pick hard with it turned up a bit. I will try out the advice on locating the offending triode now. i will also mess around some with lead dr...