This is the tone circuit from a vintage bogen amplifier E30. I am a newbie to schematics and am unsure of the value. It needs to be replaced . Thanks.
No value is listed on the schematics, but a replacement with the center tap terminal
is no longer made. Try cleaning instead of replacing it.
is no longer made. Try cleaning instead of replacing it.
What does the parts list in the Service Manual say?
Probably a 1 meg tapped control.
Probably a 1 meg tapped control.
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I don't know the answer, but...
There seem to be resistors of 50 Mohm, 100 Mohm and 500 Mohm on the schematic. The only audio circuits I'm aware of that use such high resistances (and often even higher) are the preamplifiers built into condenser microphones. Am I misinterpreting something or is this a very unusual design?
There seem to be resistors of 50 Mohm, 100 Mohm and 500 Mohm on the schematic. The only audio circuits I'm aware of that use such high resistances (and often even higher) are the preamplifiers built into condenser microphones. Am I misinterpreting something or is this a very unusual design?
I have tried cleaning but it is still rough sounding. If the m is supposed to be k that makes more sense.
500 MΩ would be hard to maintain. A little bit of moisture in the air or a fingerprint on the resistor body would quickly ruin that. 🙂
The tone control would probably work okay-ish with a plain (non centre tapped) pot, but it would not have the same characteristic as the original. I'd try to maintain the original control if possible. Deoxit Gold contact cleaner and Deoxit FaderLube are your friends in need.
Tom
The tone control would probably work okay-ish with a plain (non centre tapped) pot, but it would not have the same characteristic as the original. I'd try to maintain the original control if possible. Deoxit Gold contact cleaner and Deoxit FaderLube are your friends in need.
Tom
There must be more to it than that, 47K can't change into 50M by missing a decimal point.
Anyway, this schematic makes more sense. It's a pity it also doesn't have a value for the tone control potmeter resistance and the resistance up to its tap.
The three resistors shown in the opening post as 100M, 50M and 500M are 100K, 47 K and .47 MEG in the schematic of post #7. I don't see any value for the tone potmeter.
Might be able to use an audio taper volume control with loudness tap. I'd try to find one in 1M or 2M Ohm if still available; maybe made for the guitar amp market.
All good fortune,
Chris
ps: this is assuming that you've cleaned the pot with Caig D5 or maybe D100. Nothing else is worth doing, and many are dangerously wrong.
All good fortune,
Chris
ps: this is assuming that you've cleaned the pot with Caig D5 or maybe D100. Nothing else is worth doing, and many are dangerously wrong.
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Noisy or scratchy operation can also be due to unexpected DC on the potentiometer, due to another circuit issue such as leaky capacitor.