Fisher X100-C amp restoration help please

[mke52]

Hi, I am crurrently trying to restore an old fisher X100-C. it had been previously restored by changing a few capacitors.
I am strugling with weird voltages right at the begining of the crircuit.
the secondaries of the ransformer are 6,1V and 158V AC. Voltage gets rectified and raised by a two diode circuit and shoud raise it to 430V however I am reading 960 V. Does anyone have any suggestions?
thanks

 

[JonSnell Electronic]

This uses a simple voltage doubler circuit, unlike the earlier valve rectifier amplifier. There should be about 300volts of AC on the transformer but if C25 or C26B has failed the DC output will be reduced.
If you only have 158volts available, check C28, CR1 and CR2.

 

[mke52]

Thanks for the reply Jon, I fear I didn't explain myself well. I had a new transformer made for this amp and it's secondary outputs are 6,1V and 158V .
on the schematic , after CR1 I should see 430V and after R65 360V however in my case I have extremely high voltages there: 960V after CR1and i don't understand why

 

[JonSnell Electronic]

If the primary is definitely 158v AC, there is no way the result can be that high. The maximum is 1.414 X 158 = 223volts. I would check your DVM for accuracy.

 

[Osvaldo de Banfield]

Perhaps, the caps are bad and the dc ripple "stupidizes" the multimeter. Try another voltmeter, as a test.

 

[mke52]

Sorry guys I stupidly had the voltmeter on ac. voltage levels seem to be ok although a bit higher that what they should be. I'll move on in moving down the chain to see if i can sort it. Thanks for your help, I'm sure i will be posting more

 

[Osvaldo de Banfield]

Don't worry, it happens all the time, until manufacturer make a VOM which interpretes itself what one want to measure.

 

[disco]

Don't worry, it happens all the time, until manufacturer make a VOM which interpretes itself what one want to measure.

That would be quite unusable


I'm looking for the big knob, the brass end is missing on my X100-c. Any adresses for these?

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