The Amp Garage

Charlie Took some more voltage readings for for grins I Installed the 10 meg back into the amp. The mv readings actually went up with the 1000 hz signal being I injected into the amp at 1 volt. Ac on the grids were at 19.80 and 20.97 Delta on 1 ohm resistors 19.1mv and could never get below 18 Dc vo...

Charlie you asked me for some readings yesterday and again you are correct. My meter does measure millivolts and the decimal point was in fact in a different position when I flip to millivolt range. The final reading was 12.1 mV I could never get it to zero. This was with the one Meg in place not th...

Charlie

I will get that shot of the measurement tomorrow and send it over

Delmar, so the question I have is, were you able to get a balanced output before with the 1 meg grid leak and now with the 10 meg are not? This whole conversation started because I was putting V3 and V4 at a 6 1/2 volt imbalance. This was checking grid to ground. I never tried to get them equal prio...

Yes. On the grids to ground measurements The cathode measurements were cathode to cathode With a dvom and a 110k plate load resistor and the original 1 meg at the PI. The range on meter was set to mv range So the measurement was .011 mv and the entire sweep of the potentiometer only varied .002 mv. ...

Final adjustment. Set controls on amp to how I play. Put 1000 hz tone into amp. While measuring V3 and v4 input grids for vac, I adjusted the volume on the input to around 20 volts. Then fine tuned the pot. Got the voltage delta to .65 vac. That was the closest I could get. Using a matched set of JJ...

Using a signal generator app on the cell. Can pick various frequencies and the output on the cell is not the same as coming out of the cell speaker. It is a stereo out and is very quicker clean signal. I know when I turn the volume up on the cell, the vac goes up on v3 and v4 substantially. I will t...

I was plugged into the bright channel volume and tone both set to 6. However the tone coming in was from my cell and volume may have been way up on the input So you want to keep ac around 20 vac? Does keeping the voltage writer on their improve accuracy in setting the potentiometer?

Well, I see that the output of the phase inverter hits the coupling cap and goes to the pair of 220 K resistors however I see no junction point with a 1.5 K that you speak of at that area unless you want a measurement at pin 6 of v3 and v4 , which is where I started in the first place ! In addition ...

Also installed a 100k in the 110k spot. Still never crossed zero, and remained at .002 no matter where the potentiometer was. So I’m guessing without a scope this adjustment cannot be accomplished successfully. Any thoughts ?

22.5 volts is at the v3 and v4 power tube cathode

Correct on the location of the 44.3

At idle V3 from pin 8 Across 1 ohm to cathode resistor .044 vdc
At Idle V4 from pin 8 Across 1 ohm to cathode resistor .046 vdc

At idle from v3 pin 8 to v4 pin 8 .002 vdc

Let me know if you want any more readings. Give me a call if needed

Followed your suggestion. Installed 1 ohm 2 watt 1% on the Cathodes of both tubes. Tied the ends together with the feed from the cathode resistor Using a Fluke 88 Measured cathode voltage with no signal. 22.5 vdc Measured at top of 10 meg 44.3 vdc Bottom of 10 meg and at pin 7 of the PI. 3.9 vdc Inj...

So you are not measuring the voltage at pin 6 of v3 and v4,but setting voltage to zero at pin 8 of v3 and v4 via 1 ohm resistor by adjusting the pi potentiometer. I thought it was the feed from the coupling caps to pin 6

Charlie

So if one does not have a scope , what is the best way to set the PI trimmer? Also , you want v3 and v4 matched regardless of what is hitting the phase inverter tube?