No bias is minimum current flow in a bipolar transistor and most fet
circuits. Tube or depletion mode FET circuits - no bias can mean maximum
current. Maybe were trying to say an open somewhere in the biasing
circuitry could cause maximum PA current?
Regarding pots: I have tried a lot of cleaning/lubricating products
marketed as "contact cleaner", "fader cleaner/lube", etc. over the years
with inconsistent results. Some even marked as "safe" for plastics. etc.
ruined a few slide switches or problems would reoccur with the pots within
days or weeks. I asked Paul Clinton (TT Service Manager) what his
recommendation was for pot cleaners:
Dear Mark:
We use a 2 part cleaner from Caig Laboratories. The cleaner is called
DeoxIT DN5 and the lube is called DeoxIT shield S5. Available at most parts
houses such as Mouser. Use the red first then the blue.
I've been very happy with the results using these exact products. I
obtained these from MCM Electronics. I don't think Mouser carries one or
both the products anymore.
73 de Mark N8COO
Date: Sat, 14 Jul 2012 21:23:58 -0500
> From: "Bob McGraw - K4TAX" <RMcGraw@Blomand.net>
> Subject: Re: [TenTec] Paragon Problem gets very odd
> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
> Message-ID: <C853E82C4FEE4165B47286DA63623BC3@FAMILY>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
> I'll chime in here.,
>
> Likely the driver bias pot or PA bias was open due to it sitting in one
> place for years. Not unusual. No bias, maximum PA current. Then moving
> things around caused it to make contact and all started working.
>
> I suggest noting the physical positions of the pot adjustments and then
> exercising the pots to the extremes several times. Apply a very small
> amount of contact cleaner and then exercise again. Set them to the
> original
> physical position and then with an amp meter in the red lead, adjust for
> the
> correct current draw. I do recall the procedure and current values are in
> the manual. {mine is at the shop}
>
> The clue to no bias was the test at about 4.5 volts when the supply went
> into current limit.
>
> 73
> Bob, K4TAX
>
>
>
> -
>
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