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wrea398 · Post by **wrea398** » Tue Mar 29, 2011 1:52 pm

Well.. I figured I would give an update after making a small resistor change. After the bias would not heat up over 22mA, I decided to replace the 27K dropping resistor with a 47K. I set the bias at PIN 8 at 37.5 which is the coldest I can get it using the trimmer. My formula calls for 38mV. Since I was near the formulas setting, I played the amp for about an hour (Sounded great except that it appears my Presence pot does't work and sounds a little scratchy). After an hour I re-checked the bias at Pin8 on V4-V7. I turned all the controls back to zero before I checked. Before they were all between 35 and 38mV. Now V4 is 29, V5 is 32, V6 is 34. and V7 is 39.5. My B+ voltages are 452 instead of 462 as I originally started with. Is this variance typical after breakin? 10 whole millivolts between tubes? My B+ voltage is also off now. From 462V at PIN 5, I now have 452V. 10 volts off? Would the 47K dropper do this? I am going to post my results in the help section as well.

Please let me know what you think. Thanks!

vh junkie · Post by **vh junkie** » Tue Mar 29, 2011 5:45 pm

None of this sounds out of the ordinary (except fot the presence thing.). If you move the hottest tube to the other side of the quad, the hottness will likely stay with the tube. Keep an eye out for red-plating.

wrea398 · Post by **wrea398** » Tue Mar 29, 2011 6:37 pm

I rewrote my expalinations from beginning to end in the NEWBIE section. Neikel had me check my grounds to bias. Is the 27K drop resistor suppose to have continuity to ground? Mine does. The only thing hooked to it the bias lead from the tranny. Hmmmm.

vh junkie · Post by **vh junkie** » Wed Mar 30, 2011 4:12 am

Three different forums now, huh?

wrea398 · Post by **wrea398** » Wed Mar 30, 2011 7:51 am

Yeah Im going to dump two of them. Not much response.

Strat78 · Post by **Strat78** » Wed Mar 30, 2011 8:04 am

If you are going for the VH vibe, drop pin 3 down to at least 400v with an external variac and then start getting your values diald in for the proper bias. I have a dropping resistor of 27k and 46k going to the bias pot, seems to do the trick for me whith pin 3 down to 380v. EH 6ca7?

wrea398 · Post by **wrea398** » Wed Mar 30, 2011 7:20 pm

I didn't want to do it with the switch. I went to the 47K and it was too much. I spiked the mV at PIn to no lower than 46mV. The 56K lets me get it to 37.9 max. I backed it off to 36mv and played it for an hour. This thing sounds strong and better than I expcted. More than enough gain and pretty darn quiet.

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