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mr c deckard
 
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Default setting bias (again) when there's no peak

just curious: the usual instructions for setting bias is to turn the
bias control until it peaks, then continue until it decreased by the
correct amount (usually -3dB). on this pr99 i'm trying to nurse back
from years of public radio station duty (volunteer-staffed), the
needles are at their maximum at one extreme of the bias pot. i went
ahead and set it until the meter read the correct amount, and the high
frequency sounds good on playback, so i'm going with it, but, it bugs
me. it bugs me that the peak isn't within the bias pot's range. . .

any thoughts?

cheers,

chris deckard
saint louis
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Scott Dorsey
 
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Default setting bias (again) when there's no peak

mr c deckard wrote:
just curious: the usual instructions for setting bias is to turn the
bias control until it peaks, then continue until it decreased by the
correct amount (usually -3dB). on this pr99 i'm trying to nurse back
from years of public radio station duty (volunteer-staffed), the
needles are at their maximum at one extreme of the bias pot. i went
ahead and set it until the meter read the correct amount, and the high
frequency sounds good on playback, so i'm going with it, but, it bugs
me. it bugs me that the peak isn't within the bias pot's range. . .


What tape are you using? Are you sure you have enough bias to handle
it?

You did turn the level of the oscillator down so that the meters were
low enough that you could find the peak? But you still turn it all the
way to the right and it just keeps going higher?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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mr c deckard
 
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Default setting bias (again) when there's no peak

What tape are you using?

brand new ampex, er, quantegy 456

Are you sure you have enough bias to handle it?


no. i'm still kinda new to this -- although i understand it all in
chunks, i've yet to assimilate it all into a working picture. . .

the source of the problem could be my shaky understanding of flux and
overbias (as i said, i understand them as souvereign concepts) -- my
mrl tape is 355nW. i understand this is where to run 456 since it is
a +6dB tape.




You did turn the level of the oscillator down so that the meters were
low enough that you could find the peak?


yeah, i set my 10k tone so that it showed 0db on the deck's meters,
then worked from there.

But you still turn it all the
way to the right and it just keeps going higher?


yes, it doesn't decrease.


--scott


thanks, chris
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Scott Dorsey
 
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Default setting bias (again) when there's no peak

mr c deckard wrote:
What tape are you using?

the source of the problem could be my shaky understanding of flux and
overbias (as i said, i understand them as souvereign concepts) -- my
mrl tape is 355nW. i understand this is where to run 456 since it is
a +6dB tape.


I'd run it at 185 personally... running that machine much higher than
250 is really a bad idea and the head electronics are apt to saturate
before the tape does. But your bias problem has nothing to do with the
operating level.

You did turn the level of the oscillator down so that the meters were
low enough that you could find the peak?


yeah, i set my 10k tone so that it showed 0db on the deck's meters,
then worked from there.

But you still turn it all the
way to the right and it just keeps going higher?


yes, it doesn't decrease.


Can you make it increase in the opposite direction?

I'd suggest trying a lower bias tape to see what is going on. Say throw
a reel of Radio Shack Concertape (red oxide tape, +185 tops) on there.
You should have no problems finding the peak on that.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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