AMC CVT 3030 Bias Procedure - diyAudio
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Old 8th April 2009, 04:40 AM   #1
360freq is offline 360freq  United States
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Default AMC CVT 3030 Bias Procedure

Before I bias the el34 tubes in this integrated amp, I wanted to make sure my procedure and sequence is correct. Please bear with me as this is my first thread. I am not a technician or a DIYer like you guys.. but I do have a meter, alligator clip leads, and familiar with the safety concerns.

From past threads, I see there are a couple members that serviced the AMC line and hopefully they will see this and offer suggestions. The 3030 was recently purchased used and mishandled by UPS in transit. For various reasons, the seller can't offer assistance on the claim.. so I decided to keep it with these issues:

In 2 of the source inputs (DAT + CD), only left channel audio is coming through both L/R speakers with some distortion. The other 4 sources sound normal. I may get this repaired later on when I save some $.. for now i'll use 4 RCA plugs, solder the hot to ground, and use them as input jumpers to cancel those 2 source input signals.

These are the biasing notes I compiled from talking to Retrodazeaudio and reading the instruction PDF. The Svetlana tubes have not been used much and I will burn them in for 48 hours. Pls forgive the redundancy.

---------------------------------
A. Tube DC Offset to Zero:
1. turn OFF amp and unplug from socket
2. connect black lead (ground) to large R520 resistor (B+ supply) lead - right side center of board
3. connect red lead (hot) to plate voltage / pin 3 of tube - on left side first
4. connect a source or jumper RCA's to AUX in, then turn ON meter and set to DC voltage
5. turn ON the amp and let run for 2 minutes -- only use one hand in the chassis (or gloves)
6. turn LEFT trimpot slowly clockwise to adjust plate current as close to 0 volts as possible
7. turn amp OFF and unplug from socket...then turn OFF meter/source
8. connect red lead (hot) to plate voltage / pin 3 of tube - on right side
9. turn RIGHT trimpot slowly counter-clockwise to adjust plate current as close to 0 volts as possible
10. turn OFF amp, source and meter...disconnect leads

B. Center Voltage / DC Offset to Zero:
1. connect red to RS17 upper resistor center lead
2. connect black to RS19 lower resistor center lead
3. turn ON meter, source, amp in correct sequence
4. adjust VR501 trimpot for 0 volts
5. turn OFF amp, source and meter...disconnect leads

C. Tube Bias:
2. connect black lead (ground) to large R520 resistor (B+ supply) lead - right side center of board
3. connect red lead (hot) to plate voltage / pin 3 of tube - on left side first
4. connect a source or jumper RCA's to AUX in, then turn ON meter and set to DC voltage
5. turn ON the amp...let run for 2 minutes
6. turn LEFT trimpot slowly clockwise to adjust plate current to 5.5 volts
7. turn amp OFF and unplug from socket...then turn OFF meter/source
8. connect red lead (hot) to plate voltage / pin 3 of tube - on right side
9. turn RIGHT trimpot slowly counter-clock to adjust plate current to 5.5 volts
10. turn OFF amp, source and meter...disconnect leads
11. go back and adjust the LEFT and RIGHT sides again for drift
---------------------------------

Unless I follow directions like this, I may forget something which could be crucial, fatal or just plain bad - please inform if I miss anything. ~ thanks, Brian
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Old 10th April 2009, 03:39 AM   #2
360freq is offline 360freq  United States
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Join Date: Oct 2008
I think the guys that may know about this amp are Customdaveus (Dave) and Anatech (Chris - DIY moderator)
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