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Topic: Alembic F-2B Static |
Tim Walker
From:
Marin County, CA (originally U.K)
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Posted 14 Oct 2009 12:47 pm |
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I just picked up an Alembic F-2B pre-amp. It's one of the older style units.
The A channel sounds great, but the B channel has a lot of what sounds like static.
Does anyone have an idea of what this may be ?
I can still return it to the guy if I do it today.
Thanks in advance.
Tim |
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Bill Hatcher
From:
Atlanta Ga. USA
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Posted 14 Oct 2009 4:52 pm
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I have 5 of those. Problem I have found over time is the mounting of the filter caps and them coming loose. The static problem in one channel.....try the obvious first...change the tube in that channel. Swap the tubes and see if the problem moves over to the other channel. If not then start wiggling some things with an insulated screw driver with it on and see if you can find the component. Be careful as these have hundreds of volts DC in the power supply. Let me know what you find.
You getting a deal on it?? |
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Tim Walker
From:
Marin County, CA (originally U.K)
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Posted 14 Oct 2009 5:11 pm
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thanks bill, will try the tube. can i just put new tubes straight in there as long as they are 12ax7's ? does it need to be biased ?
it's now happening on both channels.
i tried rotating the pots for a few minutes - it seemed to help somewhat, so maybe that's the issue.
i paid 300 for it.
cheers,
tim |
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Lee Warren
From:
Nashville, Tennessee, USA
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Posted 14 Oct 2009 5:25 pm
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Hey Tim,
Nice find!
These are GREAT preamps.
I've had one for nearly 20 years and would never let it go.
If simple fixes (i.e. cleaning the pots or replacing funky tubes) doesn't work, it's worth having it serviced -- I don't think you'll regret the purchase.
All the best,
Lee (fellow Brit) 
p.s.
To the best of my knowledge, 12ax7s don't need to be biased. |
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Tim Walker
From:
Marin County, CA (originally U.K)
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Posted 14 Oct 2009 5:41 pm
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Thanks Lee - it sounded great b4. Fortunately the guy I got it from is cool as he couldn't demo it for me at his place.
Where are you from ?
Tim |
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Lee Warren
From:
Nashville, Tennessee, USA
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Posted 14 Oct 2009 7:05 pm
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Borehamwood, North London (or 'Bore-em-stiff', as we used to call it!  ).
I've been away a LONG time tho'.
You? |
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Tim Walker
From:
Marin County, CA (originally U.K)
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Posted 14 Oct 2009 7:27 pm
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| cool mate - i sent you an email. |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 14 Oct 2009 7:44 pm
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Good score on a nice preamp.
If none of the other approaches get it, I would try replacing the 100k plate resistors on that tube. They always used the good Allen Bradley carbon comp resistors, but sometimes they can go sputtery on you.
And even if you never fix that one channel, $300 is a good price for just one working channel. Most people only use one anyway.
Best,
Brad |
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Tim Walker
From:
Marin County, CA (originally U.K)
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Posted 14 Oct 2009 8:12 pm
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Thanks for the info Brad - unfortunately, both channels are doing it now.
Does anyone have any suggestions for the best tubes for these ?
Thanks,
Tim |
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Bill Hatcher
From:
Atlanta Ga. USA
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Posted 15 Oct 2009 3:08 am
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| Tim Walker wrote: |
thanks bill, will try the tube. can i just put new tubes straight in there as long as they are 12ax7's ? does it need to be biased ?
it's now happening on both channels.
i tried rotating the pots for a few minutes - it seemed to help somewhat, so maybe that's the issue.
i paid 300 for it.
cheers,
tim |
You don't bias preamp tubes like you do power tubes. There is a trim pot in there that lets you balance the filiment voltage. Just hook up the unit and look at the filiment votage on a digital meter until both sides are equal or listen to the hum in the filiments and balance until it is at its' lowest level.
Find some NOS USA made 12AX7 or 7025 tubes. |
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Tim Walker
From:
Marin County, CA (originally U.K)
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Posted 15 Oct 2009 10:31 am
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| Thanks Bill ! |
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