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PostPosted: Mon Apr 20, 2009 10:35 am 
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Mark II

Joined: Sun Jun 17, 2007 11:36 am
Posts: 65
PM sent..... just one question, I'm wondering where that 330k resistor is in the schematic.... can't seem to find it anywhere.


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PostPosted: Mon Apr 20, 2009 10:56 am 
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Donating Member

Joined: Sat Oct 01, 2005 2:27 pm
Posts: 5463
Location: Maui Wowee!
All I had were some DC-5 pics. I just emailed them to you.
It should be relatively similar with the exception of the Bias power supply.

Not sure what else I can do for you.

_________________
Elvis said.......
Quote:
Amp techs do get shocked. :shock:


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PostPosted: Mon Apr 27, 2009 8:35 am 
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Mark II

Joined: Sun Jun 17, 2007 11:36 am
Posts: 65
Ok I've done some testing and I'm posting up the results here. What I tried to do is find out where the negative voltage is coming from. I tested the bias supply and the low voltage supply and a components.

here are the links to the charts and schematics:

1) bias supply voltages:
http://farm4.static.flickr.com/3372/3479262359_6cc2b2773b_o.jpg

2) Low voltage supply readings:
http://farm4.static.flickr.com/3602/3479262367_3b33e63913_o.jpg

3) pre amp tube voltage chart (no HV applied):
http://farm4.static.flickr.com/3653/3479284311_786512abb9_o.jpg

4) pre amp tube voltage chart (HV applied):
http://farm4.static.flickr.com/3237/3479284319_d85c4f0e75_o.jpg

Other strange things I noticed:

1) Bias voltage supply.... there is AC voltage coming off the bias diode around 130vAC
2) Low voltage supply.... on one of the diodes I'm getting around 20vAC through
3) No ground to chassis on positive leg of the 10uf 63v electrolytic cap
4) I'm getting negative voltage reading when I touch the top of the 47uf electrolytic cap

any help at all will be appreciated

thanks


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PostPosted: Tue Apr 28, 2009 7:07 am 
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Donating Member

Joined: Sat Oct 01, 2005 2:27 pm
Posts: 5463
Location: Maui Wowee!
If you are missing a ground on a capacitor, that may cause errant voltages.

I would go through the whole amp and test each ground. It may be that simple. Start with the power supply caps and work your way to the other side of the amp chassis.

You should also check every component in the high voltage supply. It could be that a failed capacitor or diode is feeding back into the rest of the circuit.


I know this may be a stupid question, but are you sure that you have the proper transformer for your amp?
If you are using a power converter, maybe try another one, just in case.

_________________
Elvis said.......
Quote:
Amp techs do get shocked. :shock:


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PostPosted: Tue Apr 28, 2009 8:18 am 
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Mark II

Joined: Sun Jun 17, 2007 11:36 am
Posts: 65
No I don't think it's a tranny problem, they're all original and haven't been giving me troubles. I will follow ur advice and start at the HV but I really think the problem is in the LV supply, and I suspect those 2 zener diodes too!


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