|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
81.191.129.78
In Reply to: Bias adjustment Graaf GM-20 posted by edje999 on April 6, 2005 at 11:41:45:
It is extremely important that the tubs er mathed.
The bias current is 30MV. But Graaf has posted that the tubs bias i sett to 25mv (longer lasting tubs).
Follow Ups:
It is extremely important that the tubs ar mathed. The bias current is 30mv. But Graaf has posted that the bias i sett to 25mv (for longer lasting tubs) you also have to set the ofset, which must be as close to null as possible. Ther is one adjustment for each side. You adjust two tubs at the time the same gos for the ofset. This tubs shuld be adjusted every ten hours the first hundred. If not the tubs my fail earlier than expectet.
I own two GM 20 bridge mono/brian
Is the 25mV the voltage drop over the bias resistor? Usually the bias current is stated in mA.
How are the bias and offset regulators reachable. Do I have to dismount the plate at the underside?
Turn the amplifier on. Let it warm up for a while. Turn it upside-down. Remove the bottom-plate. Adjust the bias to 20-30 mV. (maks 30, 20 makes the tubes last longer). Adjust the offset as close to 0 as possible. Make small adjustments and wait for the value to "settle" down.
This post is made possible by the generous support of people like you and our sponsors: