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Post subject: AB165 or AA864 for bass?
Posted: Wed Apr 20, 2011 2:50 pm
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Hey Folks..Arjay,
For bass playing is the AB165 or the AA864 the better or prefferred circuit?
I have read alot about modding an AB165, making it more suited for guitar.
The one thing I would really like some guidence on is making the AB165 a true bias controled circuit instead of the balance control for the 6L6 tubes.
Also a question about that balance pot. My amp drifts as far as balancing the hum
with the balance pot. I can turn the pot and the hum is quited and a little later its drifts back to humming. I have replaced the resistors on the 6L6's, and replaced the balance pot and those resistors in that circuit. I thought it was the tubes but it drifts with each pair I try. Could the output transformer be breaking down? It's the original.
I am stumped!
Thanks to all those folks who know what I am doing!!LOL
The Tube Dude


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Post subject: Re: AB165 or AA864 for bass?
Posted: Wed Apr 20, 2011 3:19 pm
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tube dude wrote:
Also a question about that balance pot. My amp drifts as far as balancing the hum with the balance pot. I can turn the pot and the hum is quited and a little later its drifts back to humming. I have replaced the resistors on the 6L6's, and replaced the balance pot and those resistors in that circuit. I thought it was the tubes but it drifts with each pair I try.


Doubtful that your O/T is the culprit (though it's possible). I'm thinking perhaps your bias cap is exhibiting some DC leakage, which might account for the periodic drift. Has that been changed out? If not, do so. And avoid those IC caps like an E-Coli tainted Big Mac. Spragues are very good, the F&T's even better (I use the latter as filters when re-capping a P/S).

For clean bass guitar reproduction the AB165 is probably the superior circuit, since there is one less cascaded gain stage in the "bass instrument" channel to generate even-order harmonics within the circuit. For guitar though, the AA864 is superb -- especially so with the channels jumpered.

HTH

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: AB165 or AA864 for bass?
Posted: Wed Apr 20, 2011 4:21 pm
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Arjay,
Thanks so much for that. No I haven't
changed or checked that cap but I will.
You da man!
Thanks Arhjay!
Tube Dude
Ron


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