[Boatanchors] general PA question

Sun Apr 12 16:58:46 EDT 2009

I really don't recall what the idling current of the RF-110 amplifier is. 
Been too many years since I worked on one.  There were too many other 
troubles which "clouded" the memory!  I do know the ones I dealt with were 
very troublesome and were also very difficult to actually work on.

Mackay built a transmitter that used a pair of (or was it a single) 8122 
tube.  One of these entirely autotuning things.  It too was very difficult 
to troubleshoot and also work on.  Can't remember the nomenclature.  It ran 
around 400 watts PEP out on SSB.

ALL the "entirely automatic" tuning transmitters I have dealt with were in 
one way or another a "real bear" to deal with.  Some operated fairly well, 
others were always doing something strange or unpredictable.  They had 
automatic antenna tuners that were sometimes positioned a ways away from the 
actual transmitter which compounded the troubleshooting problem.  A lot of 
the gear that as coming online when I retired in the mid-90's that was meant 
for a "non radio operator" to use fell into this "problem child" category. 
One has a tendency to loathe remembering some of these encounters and forget 
just how much agony you had trying to revive one when it was dead.

Does your RF-110 have a cooling blower that sounds not unlike a loud siren 
on an EMT vehicle?  I'm glad I don't have those to deal with any longer, as 
they can cause a lot of "hair pulling" and angst!

I do wish you "good luck" with it.  Hopefully you won't run into any of the 
bad problems I have seen with them!

A lot of the GMDSS Maritime radio gear comes with what is (or at least was) 
called "CAT" features.  (Computer Assisted Troubleshooting)  This is 
allegedly supposed to eliminate the service technician and actually tell you 
which module is bad and cure a problem!  All the ones I have seen WILL 
assist you sometimes in finding a blown fuse, but not determine which part 
is causing the problem or fault!  That, for the most part, must still be 
done by an experienced human service engineer!

73,

Sandy W5TVW

----- Original Message ----- 
From: "W2HX" <w2hx at w2hx.com>
To: "'James M. Walker'" <chejmw at buffalo.edu>; <boatanchors at mailman.qth.net>
Sent: Saturday, April 11, 2009 10:09 PM
Subject: Re: [Boatanchors] general PA question

> Give that man a cigar! Yes, this is a harris RF-110A.  I have the manual,
> apc and ppc cannot be set according to the procedure. Basically the steps 
> to
> set these do not give the prescribed results.  This is what started me 
> down
> the road to figuring out what is wrong with this amp. This along with the
> other problems:
>
> The unit runs in AB1 for voice and class B for CW and RTTY/RATT. So why 
> are
> the finals designed for 0ma in idle?
>
> a) 100ma plate current when idle (manual says 0ma even in AB1). According 
> to
> the manual the unit is keyed on and off through the bias levels applied to
> the 4 tubes. The keying circuit switches the bias voltage for the driver 
> and
> final amplifier tubes from cut-off to operate.  Is it possible that 0ma 
> for
> plate current is consistent with cutoff?
>
> b) plate current exceeding specification. >800ma when spec says no more 
> than
> 750ma. Could I have parasitic oscillations?
>
> c) overload condition on 80 meters (using a dummy load). Overload circuit
> trips for a bad condition on either the plate voltage, cathode current or
> SWR. This is not SWR related (I checked that) but could be excessive
> instantaneous plate current that can't be see on the meter (shuts down 
> very
> quickly)
>
> I will send a note to the harris lists about this as well. But it seems 
> most
> folks agree that there should be some plate current when not keyed in a
> normal operation of a 4cx1500B. Seems harris had other ideas.
>
> Other operating parameters.
> Amp keyed, no rf input, the plate current should be 240ma-280ma.
>
> Ok, it sounds like either
> a) bias is off
> b) tubes are causing grid current to flow which is affecting bias
>
> I'll keep digging. Thanks everyone
> Eugene W2HX
>
> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net
> [mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of James M. Walker
> Sent: Saturday, April 11, 2009 2:47 PM
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] general PA question
>
> Sounds like you are running a Harris RF-110 PA.
> If so you will need the manual for the Amp to check the
> APC and PPC control settings.
> Jim
> WB2FCN
> "Yep I got one of those"
>
> ----- Original Message -----
> From: "john" <johnmb at nc.rr.com>
> To: <boatanchors at mailman.qth.net>
> Sent: Saturday, April 11, 2009 12:26 PM
> Subject: [Boatanchors] general PA question
>
>
>> >The unit runs 2 4cx1500B's in parallel driven by 2 8122's in parallel.
>> >YWhen keyed at 1KW output, I get a little 750-800ma plate current.
>>
>>
>>
>> You ought to be able to get about that just out of the 8122's themselves.
>>
>> John K5MO
>>
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