I've now been testing the amp with some Cambridge Audio Minx XL -bookshelf speakers. So far it gives enough volume and nice warm sound. The configuration is factory tubes and settings.
Cambridge Audio Minx XL:
Sensitivity. 87dB.
Frequency response. 50Hz - 22 kHz.
Impedance. 8 Ohms.
Recommended amplifier power. 10-100 watts.
Drivers. Tweeter: 1 x 25mm (1") silk dome tweeter Mid/Bass: 1 x 135mm (5.25") treated paper cone.
Crossover. Two way.
Ported. One rear.
Cambridge Audio Minx XL:
Sensitivity. 87dB.
Frequency response. 50Hz - 22 kHz.
Impedance. 8 Ohms.
Recommended amplifier power. 10-100 watts.
Drivers. Tweeter: 1 x 25mm (1") silk dome tweeter Mid/Bass: 1 x 135mm (5.25") treated paper cone.
Crossover. Two way.
Ported. One rear.
Hi everybody,
I have two questions about the VR 20 please:
I´m looking for the C 5 in the VR 20, it must be in the feedback-stage, the normal value is 100pf, it should be replaced by 47pf to get more and clearer hights.
In the schematics are 2 100pf C but no number behind, so which one ist the C5?
2. I got one stil new and not pimped, it seems to have to many distortions? Is this a problem of the wrong bias ? Or must I wait x x hours for burn in?
A helpfull anwere woulb be very kind, thanks in advance and all stay healthy and clean BR Joe
I have two questions about the VR 20 please:
I´m looking for the C 5 in the VR 20, it must be in the feedback-stage, the normal value is 100pf, it should be replaced by 47pf to get more and clearer hights.
In the schematics are 2 100pf C but no number behind, so which one ist the C5?
2. I got one stil new and not pimped, it seems to have to many distortions? Is this a problem of the wrong bias ? Or must I wait x x hours for burn in?
A helpfull anwere woulb be very kind, thanks in advance and all stay healthy and clean BR Joe
Hi.
C5 is in the power supply drawing, and is not 100pF.
I guess you should change the C9, 100 pF. It's in the feedback section.
C5 is in the power supply drawing, and is not 100pF.
I guess you should change the C9, 100 pF. It's in the feedback section.
Who says that C5 should be changed ?
Bias settings should be in your manual. Earlier in this thread 280 - 300mV is suggested.
Does it distort ? How much and at what power ? ( figures please )
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Just some observations:
No g1 grid resistor to ground on the input tube.
2 grids on the concertina tube are not connected.
Missing the ground connection on the output transformer common.
Just need to check the PCB and wiring to complete the in-complete schematic.
No g1 grid resistor to ground on the input tube.
2 grids on the concertina tube are not connected.
Missing the ground connection on the output transformer common.
Just need to check the PCB and wiring to complete the in-complete schematic.
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According to what has yet been written in this thread, the small signal tube appears to be a pentode triode combination with the triode as the Concertina.
All in all, the schematic is drawn in a very lousy way, imho.
Best regards!
All in all, the schematic is drawn in a very lousy way, imho.
Best regards!
This information seems to come from a upgrade of Dynavox VR-70E (https://www.diyaudio.com/forums/tubes-valves/317767-mods-audio-institute-vr-70e-3.html#post5328938) See post #21-24.
The schematics of VR-70E is very similar to VR-20, so it could benefit of this change as well.
I would call this "upgrade" as there is no figures whatsoever that supports
any changes and if they are to the better (or worse).
Hello, I was a long time offline, but thanks to all of you, I find it, fix the bias and it sounds great now, thanks!
Based on the schematic on Post # 13:
(any other schematic may, or will, have different answers).
The reason for the bias pots on the fixed bias is so that it is adjustable fixed bias.
It is adjustable, so that you can set the tube current between 28mA and 30 mA.
And, it is adjustable so that you can set both tubes to exactly the same current.
That keeps the output transformer happy (keeps it from saturating way too early).
Set to 28 & 28, 29 & 29, or 30 & 30. (280mV/10 Ohms = 28mA)
Make sense?
(any other schematic may, or will, have different answers).
The reason for the bias pots on the fixed bias is so that it is adjustable fixed bias.
It is adjustable, so that you can set the tube current between 28mA and 30 mA.
And, it is adjustable so that you can set both tubes to exactly the same current.
That keeps the output transformer happy (keeps it from saturating way too early).
Set to 28 & 28, 29 & 29, or 30 & 30. (280mV/10 Ohms = 28mA)
Make sense?
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