>Hi all,
>
>The screen voltages for drivers and finals is derived from the +500V
>8122 drivers anode voltage and is stabilised using power zener string.
>So, if the drivers anode voltage fail, no problem for their screens.
>
** Good engineering.
>RF-110A include also various protections including anode RF voltage
>sampling, (dependant of load), anode finals current, output both peak
>and average forward power, output reflected power, air flow,
>PS overheating and interlock.
>It include its own output power limiting and protection feedback system
>(PPC and APC, a sort of internal ALC) which act to the drivers bias
>(and can be used also with an external exciter), and even a protection
>for the case of arc discharge inside the tubes.
>If properly aligned, the RF-110A should not have problems, unless
>internal component failure or missalignment will occur.
>
** with the screen circuitry you described, damaging the screens should
be virtually impossible.
>The output power limiting feedback system can be adapted for use
>with the TS850 by using an external adapter/level converter which to make
>the conversion from the RF-110A PPC output signal to the needed ALC
>level for the 850.
** it seems unlikely that ALC could safely hold the 100W output of the
TS-850 down to 30mW. 100W would easily drive the grids of 2, 4cx1500Bs
directly - without the 8122 buffer.
>These signal levels and their action are stated in the respective manuals.
>(RF-110A PPC output signal is positive, ALC needed is negative).
>For this must to experiment.
>
>Anyway, when I used TS850 for the RF-110A, I choose not to use
>the 850's transverter out but to use a power attenuator.
** sounds good
>The 850 is switched to the transverter state by applying an external
>voltage to one of its jacks. The low level output is available at the
>same SO239 output jack as the normal full power.
>So, if this external switching voltage is missing, a full 100W instead
>the 30mW out will be applied to the load (i.e. 8122 grids)...
>This is of great concern for the grids, not the 100mW level, no matter
>if the anode or screen voltages are on or off!
>And this because Kenwood choose to be cheaper with the separate
>low level output $1 cost jack...
>
>
>73,
>Traian
>
>
>
>2 wrote:
>
>> >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
>>
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