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Old 22nd Oct 2020, 7:56 am   #26
crackle
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Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: HMV 2152 Restoration

Quote:
Originally Posted by frsimen View Post
The DC voltage measure across the speaker terminals is what I would expect. It is caused by the bootstrap connection formed by R79 and the loudspeaker.

R79 is connected to the base of Q13 which, given the mid rail voltage of 11.5V, will be at a potential of 11.4v, give or take a bit. R79 is 390 ohms, an 8 ohm impedance loudspeaker will have a resistance of about 6 ohms.

V across the loudspeaker = 11.4 x 6/(390+6) = 172mV, which is pretty close to the 172mV measured. That seems to be working correctly and isn't an indication of leakage in C83.

Paula
Thanks for clarifying that, I missed that resistor.
Mike
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