Odd ROWE 250 watt driver board issue

[lilshawn]

I mentioned in another post about how the "auto bias adjust" driver boards (40710105) didn't work properly with some new transistors we purchased. It didn't really get resolved and I have experienced it once again.

In the 61024903 amp, I had some blown output transistors. after replacing both of the driver pair the channel still sounded blown. after changing the "auto bias adjust" style driver boards (40710105 REVision C) with some older style "manual bias adjust" driver boards (40710104 REVision J) the channel sounds fine. (the transistors are fine) I replaced the transistors with some old stock spares and re-installed the original 40710105 board and they sound fine.

Basically what i'd like to find out, is there any particular reason that these boards aren't adjusting properly with these particular transistors? They are STmicroelectronic we ordered from a reputable source. (IE: not Ebay) Is there a theory of operation available for these boards that explains the process of adjustment or possibly a known issue with these boards that causes this behavior?

[Ken Layton]

I have yet to encounter those driver boards.

[lilshawn]

they were issued as replacements if you ordered new driver boards from rowe or came as stock items in some CD100I models amps. (seems to be 50/50 chance)

the idea is good in theory but i believe there is a flaw in the execution.

[Ken Layton]

We never had anything newer than a "D" or "E" model on our route. That's probably why I never saw any of those drivers.

[ed12]

yes
back in the day rowe built to :mp's:
the 1's we get today are not :mp's:,they say they are
but u need a tranistor curve tracer to see the diff
it is enough to drive the self biasing diodes out,
u are tech enough to tinker with there values

ed

[tcw16505]

You can build a curve tracer... https://www.instructables.com/Transistor-Curve-Tracer/

Tom