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[ajmogis]

I've got an RCA BA6A that is having some problems. I've never worked on one before so I thought I'd ask here for some pointers before I dig in.  There seems to always be a certain amount of gain reduction happening even when there's no signal present. There also seems to be some of the control voltage getting into the signal path.  Anyone have an opinion on what could be wrong?  I've got a simple shcematic of the thing, but what I'm wondering is what sort of voltages should I be seeing at the calibration points?  Any kind of info would be helpful.

Thanks,
AJ

[John Klett]

This one went by a long time ago and I just spotted it with the unanswered messages feture...

If you are seeing a gain reduction indication with no signal present you are looking at an alighnment problem i.e. balancing and bias issues.  Sometime tube aging can throw the unit off enough that the adjustment ranges don't do it...  so I'd try to get a complete manual and go through the entire alighnment proceedure - there are some iterative parts of the proceedure so you have to loop around...  generally I go through a whole alignment a couple times as this tends to zero in tighter than doing it in a single pass.  If you end up at the limit of ajustment for balance etc. then you are looking at a component that has gone out of tolerance.  This can be tubes and sometimes resitors - especially lower value ones that dissipate some heat - can change value upwards and depending on where it is you'll see a change in bias current or plate voltage...  at that point you may want to hand this off.  Our shop has gotten overloaded and, after talking to Al Grundy to make sure he wants to take this kind of work in, I am sending BA-6's, 660's, 670's etc to him.  He has always done great work and is a source for pretty much everything relating to disk cutting as well

Al's website   http://www.cutterhead.com/



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