![]() ![]() ![]() Scraping the enamel off the traces corresponding to pins 2 and 6 on the bias board connector and mounting a support connector to connect both traces together into a common bias feed to the power tubes. Who knows about these connectors, I guess they're ok now that I've tugged at them while the amp is working with no apparent sign of weakness - still, the fact that the bias lines are going through two sets of connectors before making it to the main circuit is pretty balsy, almost contradictory to some other overkill safety features in the amp. ![]() Installing it as such elliminates that 2-way variable and, more importantly, renders the bias circuit as a whole more immune to circuit 'opens' via vibrationary action and faulty/intermittent connectors which I also had to rule out as a potentially likely possibility for frying tubes. I went to single control because having two degrees of adustability made it difficult to isolate the source of 'long term' bias drifting I was observing on the bench - basically I wasn't sure if grid current draw on one pair of power tubes was affecting the bias on the other side of the output stage. Siding with reason and caution I decided to hard wire a standard/classic single 10k bias pot directly to the mother board (all other bias circuit component values remain the same). My original beef with general dual-biasing is outlined in my Tube Amp book (IF&MTA), but the beef I have with mutually interactive versions of that idea is way worse.
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