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    Building, troubleshooting and testing of these amplifiers should only be
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Help with Dynavox VR-20

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Veke76

Veke76

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Joined 2010
Dynavox VR-20 is vacuum tube integrated amplifier with power: 4 x 6P6P, pre: 2 x 6F2. Outputting 2x10W. If the tube types sound strange: 6P6P=6V6GT 6F2=ECF82

I wonder how biasing is sorted with it. Is it cathode biasing?

700_432vr20[2].jpg
 
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Veke76

Veke76

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Joined 2010
Questions to shop and some answers:

Q. Does the vacuum tubes at power section need bias-adjustment out of the box?
A. The value is preset by the manufacturer.

Q. What is the range of correct bias at millivolts?
A. The range of correct bias is 280-300 mV
 
petertub

petertub

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tubular-well.se
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Veke76 said:
Will do. The amp being of sort a cheap one from China, would it benefit greatly rolling the tubes? I was looking at TubeAmpDoctors and there was some people with Dynavox VR-20 and new tubes.

They used these:
6V6GT-STR TAD PREMIUM Matched
ECF82 / 6U8A / 6KD8 EI/Y

That sort of update would cost 123€
Click to expand...
I would advice you to avoid changing tubes, as you don't have any schematics and no instructions on proper bias adjustments.

Use your money to buy music instead !
 
Veke76

Veke76

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Joined 2010
The Chinese power tubes are biased between 280-300 mV. I would have used this setting to new tubes, but no hurry in here.

Actually I used to own Tonewin/Yaqin MC-10L with EL34, and changed the tubes using the Shuguang rated bias. Everything worked fine. Most benefit I got changing the pre tubes to Svetlanas.
 
Veke76

Veke76

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Joined 2010
Uwe from Sintron(/Dynavox) was kind enough to send me some electrical schematics of VR-20. The Chinese power tubes are biased between 280-300 mV. Can I use the same bias for new tubes?
 

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Veke76

Veke76

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Joined 2010
Apologies of posting the electrical schematics again. I reviewed them, used PNG instead of JPEG and little better resolution.

Uwe from Sintron(/Dynavox) was kind enough to send me some electrical schematics of VR-20. Look at the attachment pictures.
 

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S

Steve Morley

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Joined 2015
Sure, use the same bias settings on new 6V6 tubes. Crank the bias down (lower the voltage) on the old tubes before you remove them and put the new ones in then setting their bias. I've had good luck (very reliable) with Electro-Harmonix 6V6 tubes. Just let them run for 50 hours or so before readjusting the bias, if necessary, then make sonic judgements.

Steve
 
petertub

petertub

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Veke76 said:
The concertina resistors are not equal, probably because in signal and out signal are balanced (fine tuned). You also can mess with this to give a crunchy distorted sound.

There is a video of this:
YouTube
Click to expand...
A concertina IS balanced by itself, all you need is equal resistorn plate and cathode.
See it like this, the same current has to pass cathode resistor, tube and plate resistor. Current X ohm = voltage
If resistors are unequal then the voltage across them will be unequal.
 
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