>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?
** the 8122s' 2w control grids should be able to do without an
interlock. How are the 8w screen grids protected from excessive current
caused by too-light loading, from reverse screen current, and from loss
of anode-V?
>----- 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.
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