[Milsurplus] Harris RF-110A A6?

[Keith Densmore]

Hi Eugene,
Wow, are  you ever persistent, I think you have had that amplifier for a 
long, long  time.

I do not have a schematic of this set but FWIW, if the board functions fine 
in one mode and not in another, the likely
culprit is something other than the board itself.
The gradual drift sounds heat related, and that is usually a resistor, 
possibly the mode switch itself , or a transistor.
Get yourself a can of Freeze-it and give each component a spray and see if 
cooling something fixes the problem.

73,
Keith  ve3ts

----- Original Message ----- 
From: "W2HX" <w2hx at w2hx.com>
To: <milsurplus at mailman.qth.net>
Sent: Monday, July 27, 2009 9:10 PM
Subject: [Milsurplus] Harris RF-110A A6?


> Hello all. Been troubleshooting a bias supply problem for over 6 months. 
> I'm
> close to the end of my rope doing the component-level troubleshooting so I
> thought I'd send out a call.
>
> Anyone have a spare A6 board that they would care to sell?  I might as 
> well
> get a spare A5 board too in case the problem is somewhere there. I don't
> think it is.
>
> Let me know what you have!
> thanks
>
> 73 Eugene W2HX
>
> PS. In case you're interested in the details:
>
> 1. The final bias is fine in AB1 mode. The problem is only in CW/RATT 
> mode.
> 2. overtime, the bias increases until the tubes start to conduct. Typical
> range for the grid voltage in CW/RATT goes from -90VDC when first started 
> up
> and slowly drifts to about -72 and the tubes are conducting.
> 3. I have pulled the tubes, so this is not the cause
> 4. I do not have to have the HV on for the bias voltage to shift
> 5. I have replaced several components over time with no improvement
>
>
>
>
>
>
>
>
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