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MU524 Vari-Mu Tube Compressor
VARI-mu build
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Topic: VARI-mu build
February 17, 2023, 06:28:41 AM
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forcemusicgroup
Newbie
Posts: 37
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VARI-mu build
Having issues with build -
Going on step 5-6 - tube isnt really warming up - (not as warm as ive felt others)
Sound is passing - Oddly When input pot is turned up - the volume goes down.
The meter lights up just fine. Output pot does give gain. haven't had a chance to test the recovery.
I've done readings on all test points
The reading goes as follows:
V+ 15.69
V- -15.74
TP1 - 40.59
TP2 - 40.05
TP3 - 0
TP4 - 0
TP5 - 0
TP6 - 0
PLEASE ADVISE..
Thanks keenan
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February 18, 2023, 11:58:05 AM
Reply #1
JPK
Administrator
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Posts: 1085
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Re: VARI-mu build
Do you get the power up sequence correct? And 6VDC between the side pins?
the voltage slowly increases from 1 to 2V as the tube gets hot then more rapidly to 6V after 10 seconds.
Check in the dark to see if the tube gets redish inside.
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JPK
February 19, 2023, 03:14:17 AM
Reply #2
forcemusicgroup
Newbie
Posts: 37
Karma: +0/-0
Re: VARI-mu build
the voltage stayed around 2v.... maybe I was too anxious... ill look again...
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February 19, 2023, 03:28:37 AM
Reply #3
forcemusicgroup
Newbie
Posts: 37
Karma: +0/-0
Re: VARI-mu build
after 10 secs??? then no its hanging around 2.4 vdc
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February 20, 2023, 09:31:53 AM
Reply #4
JPK
Administrator
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Posts: 1085
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Re: VARI-mu build
What DC voltage do you get between V- test pin and the right side pin of the tube holder PCB (marked H).
Is the transistor Q4 getting hot?
Check that no electrolytic cap is reversed (in particular C32, C33).
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JPK
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MU524 Vari-Mu Tube Compressor
VARI-mu build
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