Tube Amp Archive

Problem gone. Not sure why. After putting the guts back together to move elsewhere the amp works normally. I think it could have been a loose connection somewhere. The amp has a few suspect-looking ribbon cables, even for heater current for three tubes. There was also one capacitor (100pF C1 on AC-t...

Thank you very much, Roberto, that must have been the reason initially. After poking and doublechecking all the board connections we probably improved the connectors of the heater supply because we noticed afterwards that the V1 voltages were "miraculously improved"; 1.04VDC on the cathode and 236VD...

Correct and I had checked that, poweramp works perfectly, so it was then down to the preamp.

Is it OK that there's a very loud bang from the speaker when taking the DC measurement on the grid of V5A (it looks like the grid is supposed to be at 290VDC)?

Follow-up on V1B- strangely enough it now shows normal readings, which could possibly be due to swapping the tubes around...

Thanks, Phil, I was worried about that too, although I think that's normal with the amp off; the Q3 switch works when voltage is applied to the gate and no current then flows through it. I really can't understand how the V1B cathode voltage is at +0.3V with a 1.5K resistor while the voltage across t...

I wasn't expecting an totally open circuit. Just a high resistance. Ah, yes, that's also a possibility; so I'm guessing that would mean that where I was measuring DC voltage, the reading is correct for the voltage across the resistor but not yet the total cathode to ground voltage across the entire...

Yes, I was thinking about the switch too, but it seems to be intact, the negative leg of C2 measured zero ohm to ground in off mode.
The resistor measured 100K, although not right away; it dropped steadily from a high value to ~100K.

I wasn't expecting an totally open circuit. Just a high resistance. Ah, yes, that's also a possibility; so I'm guessing that would mean that where I was measuring DC voltage, the reading is correct for the voltage across the resistor but not yet the total cathode to ground voltage across the entire...

What resistance do you measure from V1 pin 8 (probe directly on the socket) to chassis? You say the resistor is good but until you make the check I suggested you don't really know if it is connected properly to the tube socket or chassis ground. Thanks, sluckey, Between V1 pin 8 directly where the ...

I'm not a trained eye, but that sounds like one of 4 items that could be bad (maybe more). I am assuming you've swapped the tube and have a known good tube still doing this. 1. the anode resistor is much higher resistance than it should be so it's blocking c urrent flow 2. the cathode resistor is m...

Dear Garage, I have a question about my friend's bass amp that puzzles me (not hard as I'm rusty in the amp DIY department). I was hoping a better trained eye would more easily spot the fault. The amp is a SVT-2 Pro and it has lost volume dramatically. The speakers peak at a few watts instead of ove...

How you know the truck behind you is listening to the same radio station

http://www.wimp.com/truckradio/

Reeltarded wrote:Defy gravity.

[img:500:411]http://i225.photobucket.com/albums/dd31 ... theory.jpg[/img]

One thing I wasn't expecting is when our late dog nowadays decides to pay a visit in dreams, quirky and misbehaving as ever, and I wake up smiling. I wish you many such visits.

I'm sorry to hear this. My dog had a stroke at 11 or 12 years of age. Onset of symptoms was gradual, within a few hours she went from slightly losing balance while standing to lying down/not being able to stand up without falling over, rapidly tilting and correcting the head, also the eye pupils wer...