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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Re: Stupid tube question - VTL Super Deluxe posted by Bill Way on August 26, 2006 at 09:15:59:
Find the power supply decoupling resistor. It's the resistor between the last decoupling electrolytic capacitor carrying B+ to the line amp. Substitute a 10 watt potentiometer and set it to the same value as the former resistor in the circuit. Disconnect both filament and B+ from the phono preamp or remove the tubes. Connect a VOM to the lead coming out of the potentiometer and start adjusting the resistance until the needle steadies(when you reach the point where the needle bobbles slightly, you've reached the correct resistance. Then turn the pot the other way slightly releasing the needle bobble. This is the new value of decoupling resistor. Remove pot and measure pot's resistance out of the circuit and substitue a fixed value for the new power supply decoupling resistor. Now just the line amp is drawing current. You also want to make sure that no tube filaments were operated in series at a high voltage like 24 volts, that they are all 6.3 volts and they are all in parallel. It's misleading to an amateur. A 12ax7 is not a 12 volt tube but two 6.3 volt tubes in the same envelope. Ray Hughes
"I take you as you are
And make of you what I will,
Skunk-bear, carcajou, bloodthirsty
Non-survivor.
Lord, let me die but not die out." THE LAST WOLVERINE by James Dickey
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Follow Ups
- An around the horn solution... - grhughes 11:58:19 08/26/06 (0)
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