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Posted: Sat Aug 14, 2010 1:46 pm
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So the test showed one out of four "coke bottles" is ok with the bias in the amp, right ? There is some amount of negative voltage in the bias circuit, just don't know how much. I would order some rugged tested tubes from a reputable vendor. IMO The bargain tubes are a risky purchase. At $68 for a matched quad, that seems hard to pass up. But which ever tubes you decide on, be sure that they can handle 500-600 plate volts. I think JJ and Sovtek have 6L6GC's in this range. And like the guys said, a trip to the tech would be a good idea, and then you would be sure all is well. Art

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Posted: Sat Aug 14, 2010 7:21 pm
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Addendum: Sorry, after thinking about this problem, there is one other time when you need to worry about putting new tubes into an amp. If the "ok" tubes are old. Sometimes, the bias somtimes gets hotter about the same amount as the old tubes conduct less current. I see this in amps with adjustable pots for idle bias current more that ones without. The owner or a tech keeps cranking the bias pot to compensate for tubes growing weaker.

Then, when a new set of tubes are placed into the amp, they run too hot. In any event, others are correct you should have the bias checked with the new tubes in place.

BTW #2: If you have the tech alter the bias power supply circuit so the BALANCE pot is changed to an idle BIAS POT, prolly best to get near "matched" power tubes. Say within 15% of each other's conducting current in your amp. As, one pot will be adjusting all tubes.

Whew! Sorry for all the yaddy-yaddy.

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Posted: Sat Aug 14, 2010 8:48 pm
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All good advise, as usual, BMW. Actually, I think the bias balance opton is one of Fender's best ideas, as is the heater hum control. If they could have only incorporated these with an overall bias control, they'd be sittin' on top of the amp world. But I guess there is that inherent stability problem, that would reguire some added engineering and quality parts. And I think it was Randall Smith, who said, that in a way you don't want to give the average consumer a chance to screw up the amp. Oh Well ! Art

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Posted: Sun Aug 15, 2010 3:50 pm
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IMHO, Putting cheap glass in a good amp, is a bit like running regular grade gas in a Ferrari.

Just Sayin'

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Posted: Tue Aug 17, 2010 5:33 am
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And you can tell how old some of us are by words used to describe them....
"chi-com"....it's an affectionate term used to describe things like tubes and weapons used to kill GIs in RVN. :D


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Posted: Tue Aug 17, 2010 9:32 am
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Rebelsoul wrote:
"chi-com"....it's an affectionate term used to describe things like tubes and weapons used to kill GIs in RVN. :D


"Affectionate"

Yes......

My buddies and I had even more 'affectionate' names for our adversary than that (probably not suitable for a "family-friendly" discussion forum such as this......).

:mrgreen:

Arjay

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Posted: Tue Aug 17, 2010 11:15 am
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Retroverbial wrote:
Rebelsoul wrote:
"chi-com"....it's an affectionate term used to describe things like tubes and weapons used to kill GIs in RVN. :D


"Affectionate"

Yes......

My buddies and I had even more 'affectionate' names for our adversary than that (probably not suitable for a "family-friendly" discussion forum such as this......).

:mrgreen:

Arjay
yep! affectionate...like in "love you to death". 8)


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Posted: Tue Aug 17, 2010 11:28 am
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Rebelsoul wrote:
yep! affectionate...like in "love you to death". 8)


Indeed!

Image

Arjay

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