[AMRadio] Need some help here

[Bill Smith]

Sounds like some stages are self-oscillating, Dan, and the crystal is not
able to overcome.  Such stages are not stable anyway, you will have to take
steps to isolate them so they will not take off without excitation.

Haven't worked on any Gates, so can't offer specific suggestions, sorry.

73 de Bill, AB6MT
billsmith at ispwest.com

----- Original Message -----
From: "Dan Hall" <kj7fx at tdn.com>
To: <amradio at mailman.qth.net>
Sent: Monday, March 04, 2002 11:32 AM
Subject: [AMRadio] Need some help here


> Greetings Gang:
> I have just about gotten my BC1-J up on 3870.  I'm using crystal control
and
> have wound a plug in coil for the oscillator. It's on frequency and dips
> well. The Gates manual says it should make about 2-4 MA of grid drive for
> the 6146 exciter pair. It does. I have re-tapped the exciter coil and get
a
> dip when it is tuned, though no where near as sharp as I would like to
see.
> The manual says it should provide about 140 MA of grid drive to the 833A
PA
> tubes. It does not. I'm getting about 25 MA. I have shorted the low grid
> relay so that I can put plate voltage to the finals and it will tune, with
> 2000 VDC on the plates to about 5-600 Watts. The problem is that the
> frequency is all over the place depending on the variable coil setting. By
> that I mean , when moving toward the dip the frequency will rise from
> 3869.667 (funky crystal, thanks Jan) to around 4050 KC. The frequency
shift
> is not in jumps either but seems relatively smooth. There is no decent dip
> at all until the PA begins to act like a doubler, then she dips good.
When
> tuned and loaded through much trial and error to about 350 Watts, and on
> frequency, the frequency is not stable and can jump to 3900+/- or higher
> when switching between transmit and standby (exciter and PA plates turned
> off). On top of all that, the modulator isn't modulating. I get the 80 MA
> idle current and the current jumps around when speaking into the mic, but
> nothing out on the peak meter.
>
> ????
> Dan
> KJ7FX
>
>
> _______________________________________________
> AMRadio mailing list
> AMRadio at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/amradio