7591 plate voltage's
- Thread starter tube-a-lou
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cademan
Lunatic Member
Look at the 7591 characteristics online here:
http://www.mif.pg.gda.pl/homepages/frank/sheets/168/7/7591.pdf
As long as your not red plating the tubes, you're fine.
Of course you know that you will need to replace all of the capacitors and this might just bring your voltages into spec.
http://www.mif.pg.gda.pl/homepages/frank/sheets/168/7/7591.pdf
As long as your not red plating the tubes, you're fine.
Of course you know that you will need to replace all of the capacitors and this might just bring your voltages into spec.
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tube-a-lou
Addicted Member
I thanks cademan, I did replace all the electrolytic caps, I'm going to check the bias and the other voltages.
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tube-a-lou
Addicted Member
I tested pin 3 to ground and it's 438/440volts, when I test pin 3 and 8 together it's 10.36/10.41volts.
That's s bit odd, in the end my plate dissapation is around 40.5watts, when I measured the bias it's
-19.47 across the cathode resistor in the schematic it -20 so it's close.
That's s bit odd, in the end my plate dissapation is around 40.5watts, when I measured the bias it's
-19.47 across the cathode resistor in the schematic it -20 so it's close.
Tube; The Gibson voltages are substantially close to an 800c's voltages. The 800c plate runs 430-435 on the plate with 375-380 on the screens. Compare that to a Sansui 1000A with a plate voltage of 478V nominal and screens of 430v nominal. The higher the plate and screen voltage, the tube will require more bias voltage to maintain bias. With a Max dissipation of 19W, I'd run it @ -21 to -22 or more to get a total of about 80% of Max dissipation to keep tube life a bit longer. Determine what the inrush amperage is and add an inrush limiter (probably a CL-80 right off the top of my head) to slow down the peak voltage at startup. If your Main Filter caps are rated for 475-500V you should be ok as they have a surge voltage rating of 50 more volts. or 525v-550v
tube-a-lou
Addicted Member
Hi Larry, I change all the filter caps to F&T and all are 500 volts now, also this is my first amp
with a stand by in the switch with is a good thing. One thing when I measure the plate pin 3
and cathode pin 8 I only get 10.41 volts is that right. When I do it the otherway pin 3 plate red
lead and the black lead of my DVM to ground I get 438 volts
with a stand by in the switch with is a good thing. One thing when I measure the plate pin 3
and cathode pin 8 I only get 10.41 volts is that right. When I do it the otherway pin 3 plate red
lead and the black lead of my DVM to ground I get 438 volts