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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Re: Why No Voltage Drop Across 725 ohm Resistor?? posted by blue_z on August 1, 2006 at 01:37:55:
No current, right. I finally got it figured out. The cathodes of the 6BQ5s are connected to a 250 uf 25v cap on the amp chassis but then to a 12AX7 on the preamp chassis through the umbilical that powers the tuner/pre. No cathode resistor though. It just goes to the heater of the 12AX7 and then to ground. Is this an unusual arrangement? Does the internal resistance of the heater act as a cathode resistor?Anyway, I added a resistor to the amp chassis so I can now use the amp without the tuner/pre. I experimented with values until I got close to the 10v spec on the cathodes of the 6BQ5s. I'm using a single resistor for all four of the 6BQ5s. Is there any problem with this arrangement?
Another odd thing I've noticed on this amp is that the voltage on Pin 7 of the 6BQ5 is higher than the voltage of Pin 9. The schematic calls for 290v on 7 and only 270v on 9. On all the other 6BQ5 amps I have the voltage on 9 is typically about 5 volts higher. What's up with that?
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Follow Ups
- Got It - And a Few More Questions - FlaCharlie 09:40:45 08/02/06 (1)
- Re: Got It - And a Few More Questions - blue_z 01:58:52 08/03/06 (0)
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