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In Reply to: Vintage Pilot 260 posted by Al Nico on April 11, 2007 at 08:31:50:
Thanks AL. I'd much appreciate your detailed mail concerning Pilot 260. Please read my mail too. Edmund
Follow Ups:
Finally, I confirmed the AC input can be as low as 0.8 ohm. I connected it to 1117V AC main eventually. No fused burnt, no explosion of any kind. I just put one 5R4 instead of two in place. But the H+ is too high. My fluke meter read 504V DC but circuit shows that should be 430 V . The one should read 295V read 436V in mine Pilot 260. The 240V read 365 V in my Pilot 260. All H+ voltages are over, some even 50% higher. I awared there were two 400 Ohm cement resistors im parallel were added in series with 33 ohm 10 W to the can capacitor. I suspect that was the case the owner make the voltage drop to a reasonable level. In that case , I may have to put that two 400 ohm resistors back to the circuit. That will discrepant with original circuit. Hi friends! Any comments on that issues. Thanks .
Go by the diagram.It looks like the 7 to 8 jumper takes the 295 volt supply through 2 15K resistors in series to ground. I have not worked on it in a while.
The 295 volt supply being loaded down drops all the B+ voltages then. 800 ohm instead of 3000 ohm is too much I think.
Use thr diagram to go back to the factory configuration.
I installed 2 jumpers installed on the preamp socket. One jumper bypases the on off switch. The other puts resistors in paralell with the power supply to compensate for the increased voltages caused by not powering the preamp. This was not clearly shown on the Sams Photofact diagram as I recall.
AI,
You are absoultely right in this issue, I omitted that part. I will put that two 15K 2W resistors back and measured the voltage again. Whether or not to put that two 375 ohm 10W parallel connected resistors back will depend.
All H+ voltages are normal after I connected two 15K 10 W resistors back to the circuit and with all tubes in place.
Thats a good thing. Next try this amp with a passive preamp.
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