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Chris Berry
 
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Default Marshall 2204 problem...

My new 2204 copy works - except for the presence control.
With no input and the master volume on zero, depending on the speaker
cabinet the amp oscillates at 100Hz or much more.
With one cab, the presence control actually controls the oscillation but
with the other, there's no control possible even with all the controls on
zero. Funny thing is that with the THD hotplate speaker attenuator, the
oscillation disappears even with just 4dB attenuation.
Any ideas guys?
cb

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Chris Berry
 
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Found the problem - presence was out of phase so the "replacement" isn't an
accurate Marshall replacement.
Emailing supplier for the proper spec sheet.... at least I only used a 16
ohm load on the highest impedance secondary...

cb

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Just flipflop the thansformer wires that go to the plates of your power
tubes.
That will fix your phase problem.

BTW, once you really start pushing the volume and overdriving the phase
inverter, the presence control really doesn't do much.



Chris Berry wrote:
Found the problem - presence was out of phase so the "replacement" isn't an
accurate Marshall replacement.
Emailing supplier for the proper spec sheet.... at least I only used a 16
ohm load on the highest impedance secondary...

cb

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Chris Berry
 
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wrote in message
oups.com...
Just flipflop the thansformer wires that go to the plates of your power
tubes.
That will fix your phase problem.

BTW, once you really start pushing the volume and overdriving the phase
inverter, the presence control really doesn't do much.




Thanks... figured that one out with my plexi - very few controls work at
extreme overdrive.
cb


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