Hello Bill,
During the restoration of my amps, I often used a buffered quartz oscillator
(two BJT's) which deliver about 120 to 150 mW to the RF-110.
For one amp I didn't used RF input or output switching relays but direct
connections to the RF-110A input (and the output directly to the dummy load).
Because the RF source was powered from an external separate DC source,
it often happened to forget it on, but no problem at all.
The 8122 input is passive grid configuration (50 ohm R).
Indeed, the 8122 data sheet is not containing info about grid dissipation,
but include tipical data for grid currents and grid input power for differrent
operating conditions.
For example, the absolute maximum DC grid current for CCS class C plate
modulated RF amp is 100 mA (some impressive for such tube !?).
The real problem is to not apply very high level of RF (W).
Take care about the +12V applied to the 850 jack for using it as a low level
driver.
If this voltage will be off ...
73,
Traian
Bill Coleman N2BC wrote:
> 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? 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 - 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
> ~~~~~~~~~~~~~~~~
> Bill Coleman N2BC
> http://home.stny.rr.com/n2bc
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