[TenTec] Herc II and 9420 duty cycle

[Phil Chambley, Sr.]

Hi Ken....

Each of the four amplifiers should draw 450-500 ma idling current.  If your
Ic meter is accurate, then you have found the problem...way too much forward
bias.

First be sure all four power supplies are delivering the same voltage.
Adjust them if necessary.

Get a 1 or 2 Ampere full scale meter, go into the amplifier and pull the
push-on power connectors off the amp boards (all four).  One at a time, put
the meter between the power supply lead and the amp connector.  Set the bias
so the collector current is 500 ma.  Then disconnect that one again and move
to the next amp.

Phil

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----- Original Message ----- 
From: "Ken Brown" <ken.d.brown at verizon.net>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Monday, February 21, 2005 1:52 PM
Subject: Re: [TenTec] Herc II and 9420 duty cycle


> Hi Phil,
>
> Thanks for the suggestion.
>
> I see how the currents to the four PA modules is monitored by the
> voltage drop across the 0.015 ohm resistors on the DC Distribution
> Board, and then combined together to feed the Ic meter. And I see the
> individual bias adjust pots on the Bias Board. I do not see a convenient
> way to measure the PA module current for each PA module individually.
> Perhaps I could just put my DMM across the 0.015 ohm resistors one at a
> time. Or I could arrange to actuate K1, K2, K3 or K4 individually, one
> at a time and use the Hercules Ic meter.
>
> My manual does not state what the idling collector current ought to be,
> either for each PA module or the total, and there is no procedure
> described for adjusting the bias. The Ic meter shows about 12 or 13
> Amperes (half way to the 25 A hash mark) idling collector current.
>
> I suppose I could measure the voltage drop across across the 0.015 ohm
> resistors, and then adjust the appropriate bias pot until whichever
> current is highest is brought down to be equal to the lowest, or maybe
> the average. I'd rather know what it is supposed to be first. Does
> anyone know the specification the Hecules II idling collector current,
> either total or for each individual PA module?
>
> Ken N6KB
>
>
>
>
> Phil Chambley, Sr. wrote:
>
> >I think it would be a good idea to check the idling collector current on
the
> >finals.
> >
> >
> >
> >
> >
>
>
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