MODERATOR--I hope this is OK, but if not understand. Thanks in advance.
Quick question. I had the auto bias board installed for me by one of Bob's east coast technicians in 2018.
At that time, I also had him move the blue bias lights onto my driver board so they are visible, along with encasing the unit into a wood frame, add new power switches and speaker posts. The work is now +2 years old and I'm pretty sure the auto-bias board is 1st Gen (i.e., before the boards had the modifications to include an isolation transformer for the 6.3VAC supply).
Everything works fine as far as I can tell, however I've never checked the bias since the board was installed (the amp runs fine and sounds great with KT88s).
If I do have a problem however, how would it manifest itself? Also, I doubt I could undo the board and return the unit to manual bias as Bob recommends, so if it does fail do you have a recommendation with respect to whom I could sent the whole unit to for service (someone with knowledge and experience with the AB board that works with you..)
Thanks in advance,
Hi Jay, Thanks for the message.
If you do not set the BIAS over and over again, nothing will go wrong and the amplifier will continue to work without problems.
I don't know if you have varistor protection connected in the amplifier, which protects AB autobias in case of short circuit of the KT88 end tube:
If there is a problem with autobias in the amplifier, you have two options.
1) send the board with driver & AB or the whole amplifier to my Holger Schaarschmidt representative
2) or me - driver+AB autobias :
Velke Popovice- Lojovice 62
Prague - East
Send the board assembled together with the signal diodes.
You don't have to worry about getting repairs. Hundreds of boards have been working reliably around the world for five years.
Can you please share our interview with others?