Thanks Rich
There is indeed a termination resistor - before the blocking cap there is a
.22uH coil to a 56 ohm resistor to ground. The input is quite flat from 160
through 10M according to my analyzer.
So... does that load protect the tubes & nullify the need to interlock
application of RF drive?
~~~~~~~~~~~~~~~~
Bill Coleman N2BC
http://home.stny.rr.com/n2bc
----- Original Message -----
From: "2" <2@vc.net>
To: "Bill Coleman N2BC" <n2bc@stny.rr.com>; "AMPS" <amps@contesting.com>
Sent: Friday, May 09, 2003 9:38 AM
Subject: Re: [Amps] Protecting the tubes!
>
>
> >I am in the early stages of lashing together a Harris RF-110 amp. It
runs
> >a pair of 8122s in class A driving a pair of 4CX1500Bs. I am driving it
> >with the transverter output of my Kenwood TS-850, about 20 to 30 mW.
> >
> >I'm sure that when mated to the proper Harris exciter, there is
fool-proof
> >interlocking between the exciter and the amp - i.e. applying drive
without
> >HV. I haven't yet found a convenient way to do this with the Kenwood.
> >There are a couple possibilities, but they involve feeding some signals
> >out of the amp & if you know the innards of this thing, additional output
> >lines will be at least a small challenge because of the physical layout
of
> >things.
> >
> >Anyway - to the real question: Am I worried about a non-problem? If I
> >apply 20 or 30mW drive to the 8122s without plate or screen voltage, will
> >they be damaged?
>
> ** In Class A, there is no grid-current, so all of the exciter power
> flows into the grid terminating resistor. If there is no 50-ohm grid
> termination, your radio will likely be in a state of vexation.
>
> > The input is untuned and unswitched, fed directly to
> >the grids of the 8122s thru a .01uF cap. Looking at the datasheet for
the
> >8122, the control grid appears to be pretty tough
>
> ** as I recall, the rated control grid dissipation is 2w max and the
> screen is 8w.
>
> >- but grid dissipation
> >per se is not specified. I can't imagine a couple volts of RF doing any
> >damage. WATSA?
> >
> >By the way - this is a pretty nifty box. 20mW in, 1000W out, brick on
the
> >key, no tune-up, etc etc.
> >
> >Thanks! 73, Bill
>
> - R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
> www.vcnet.com/measures.
> end
>
>
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