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Old 5th Oct 2018, 1:55 pm   #41
poppydog
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Default Re: Pye 1352 excessive current

I've quickly tacked a jumper wire across r20 and its the total current is lowest its been for ages 7ma . Will do more tonight
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Old 5th Oct 2018, 2:04 pm   #42
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Default Re: Pye 1352 excessive current

Could c26 (if I’ve read the number on the schematic correctly - I mean the capacitor actor the driver transistor) be the problem? If it’s leaky it would increase the current through the thermistor etc and increase the current in the output transistors, and the feedback would turn off the driver to maintain the correct mid point voltage and cause the distortion. Leakage on the PCB would cause the same symptoms, it might be worth trying the set with the driver transistor removed. The quiescent current should be very low, and the mid point voltage should be 9V.

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Old 5th Oct 2018, 2:04 pm   #43
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Default Re: Pye 1352 excessive current

Don't forget that it's usually the quiescent current for the output pair only that's of interest.

EDIT: Post crossed

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Old 5th Oct 2018, 2:27 pm   #44
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Default Re: Pye 1352 excessive current

C26(tone) was looked at a while back and was not good so a 2.2nf ceramic was tacked in its place, I was also hoping that was going to cure the shrillness, but it didn't.
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Old 5th Oct 2018, 3:16 pm   #45
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Default Re: Pye 1352 excessive current

Quote:
Originally Posted by ms660 View Post
All the freezer spray is doing is what it would do to any other conductor or semiconductor,

Freezer is good for helping to pinpoint components that go faulty in a S/C, O/C, breaking down/crackling (noisy) sort of way etc due to thermal expansion and not much else.
Um - try telling that to a factory bench service engineer when a dvm comes in with customer complaint of 10uV noise after 3 hours. No board swapping allowed - so it's warm air blower and freezing spray to locate the leaky FET or whatever. You cant see 10uV noise on a scope when probing analogue switching FETs with 18 volt gate drive signals.
No argument about using for finding poor joints and other faults.
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Old 5th Oct 2018, 3:25 pm   #46
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Default Re: Pye 1352 excessive current

I said I would stand-off from this thread as unfamiliar with the specific circuit. I have looked at a couple of other circuits and note that in the similar Pye one attached, three of the resistors are marked as 5% tolerance. Manufacturers did not use those unless it was really necessary.
In the vaguely similar Pam circuit (running from 24 volt supply) the adjustment procedure is set to RV4 for symmetrical clipping on sine wave then adjust RV5 for 10mA in VT9 collector with no signal.
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Old 5th Oct 2018, 3:54 pm   #47
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Default Re: Pye 1352 excessive current

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Originally Posted by buggies View Post
Um - try telling that to a factory bench service engineer when a dvm comes in with customer complaint of 10uV noise after 3 hours. No board swapping allowed - so it's warm air blower and freezing spray to locate the leaky FET or whatever. You cant see 10uV noise on a scope when probing analogue switching FETs with 18 volt gate drive signals.
No argument about using for finding poor joints and other faults.
The point I was making (to try and help the OP) was that if you had a radio or whatever with semiconductors and sprayed them with freezer the voltage or current would vary in tune with the changing temperature of the semiconductor but that in itself doesn't mean to say that particular component is faulty.

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Old 7th Oct 2018, 7:35 pm   #48
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Default Re: Pye 1352 excessive current

The total current draw is now 7ma as previously stated, the current draw at the collector of VT7 is just under 1ma. So I need to find a lower value resistor to go in the place of the 47r that will give a collector current of around 8ma as ukcol suggested way back in post 15. I’m just a little confused why I need to do all of this, when it should be ok with what is/was already in there, voltages were/ have always been spot on. That’s why I keep going back over everything I have done. Will try a couple of low value resistors and see what things are like.
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Old 7th Oct 2018, 9:19 pm   #49
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Default Re: Pye 1352 excessive current

This one is all sorted, I was thinking about this earlier whilst looking for low value resistors what with the bridging of R21, and started thinking about the thermistor again. I removed a thermistor from a pye 1363 (same circuit) I had off a forum member for the speaker, it measured around 100r, my original measures 270r. I tacked it in and readjusted RV2 after about 5mins and all is good.
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