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Old 13th April 2003, 01:11 AM   #11
diyAudio Member
Join Date: Jun 2002
Location: Denver, CO
Default Pentode

Hi Tim, thanks for taking the time.

The screen is now tied to the full B+ (above the OPT). I wasn't sure whether I needed to limit the current on the screen with a series resistor and did it anyway just to be safe. I took them out now.

Heaters have about 26 v on them. I used a separate 25 vac trafo but with my power service it goes to 26v. It's ok? (+ or - 10% is ok?) Funny thing though, I have smoked 3 - 100 ohm hum pots now on this circuit. Can't figure that out either so I just eliminated it. Still a tiny bit of hum without it.

Put in a grid resistor of 100k ohm resulting in low volume. Changed that out with a dual ganged 100k audio taper vol pot resulting in the same low volume.

Hooked the whole rig up in parallel SE mono and worked just fine! This is strange. It should work in SE mono phase inverted via trafo--just like a P-P???

Bias at -2.3v, cdp input signal peaking near there. Can't hear any clipping. B+ looks fine. Suppose I need to test input trafo for proper operation.

I assume Peter is correct in that the primary inductance is the load to the cdp.

Your thoughts appreciated,
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Old 13th April 2003, 04:09 AM   #12
diyAudio Member
Join Date: Jun 2002
Location: Denver, CO
Default Bad input trafo

Before you waste anymore time on this, I tested the input trafo and found that it did not produce the sec. voltage as indicated on the label. Not sure how this happens....

My bad. Thanks for the attention. I did learn a lot, however.

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