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.
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.
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.
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.
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
>
> - R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
> www.vcnet.com/measures.
> end
>
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