Originally posted by greengriff
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Marshall 2103 Cold Maximum Bias Mystery
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My band:- http://www.youtube.com/user/RedwingBand
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I think he's now talking about just piggy backing another resistor (soldering in parallel on the exposed resistor leads) across the 56k resistor. I've seen this done A LOT."Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz
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Originally posted by greengriff View PostIt's going to be a tricky job as there's not a lot of the original leads sticking out of the boards, what there is is partially covered with plastic that's bled over from the resistor body,..
EDIT: I think you must mean that the enamel the resistor body is covered in is also partly covering the leads? It took me several mental images to put that together. But yes, I've seen that before."Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz
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"Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz
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Originally posted by Chuck H View Post??? I've never seen plastic bleeding off a resistor body so this is confusing (and concerning) me.
EDIT: I think you must mean that the enamel the resistor body is covered in is also partly covering the leads? It took me several mental images to put that together. But yes, I've seen that before.
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Originally posted by pdf64 View PostTotally confused by this - Chuck was referring to the bias supply for a 50W model, which is derived from the HT winding. Whereas your 100W amp’s bias supply is derived from a dedicated winding. The resistor value between winding and rectifier diode is 10x different for the different designs.
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I think half the problem is the way this forum sorts the threads.- Own Opinions Only -
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Originally posted by pdf64 View PostWhat are the voltages at the screen grids pin 4? And control grids pin 5 (to avoid oscillation it may be bet to take those measurements with the ECC83 in the phase splitter socket removed)?
And the bias supply output, at the node of the 220k bias supply output and grid leak resistors?
Maybe its just a matched set of weak EL34s, any others to try in there?
Pin 5: -39v
Bias supply output: -48v
Do these sound about right?
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That applies to all 4, and anodes still at 475Vdc?
If so that all looks fineMy band:- http://www.youtube.com/user/RedwingBand
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I didn't check all 4 sets of pins. Do you think it's worth doing that?
Any time I am in a tube amp, I go down the power tubes checking for B+ on both plate and screen pins and for bias on the grid (or cathode).Education is what you're left with after you have forgotten what you have learned.
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Originally posted by Enzo View PostNever think up reasons not to check something. It takes a very few seconds to go down the row of tubes checking voltage.
Any time I am in a tube amp, I go down the power tubes checking for B+ on both plate and screen pins and for bias on the grid (or cathode).
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Even if something all comes from the same source, checking at each tube verifies all connections like sockets, etc.Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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