Miscellaneous Master Pro Ramblings from knowledgable fellow Hams over the years on the remailers....


From: dave@pb.ua.edu

I don't have the book in front of me so I can't give specifics, but you may try
to look for a very slight dip in the mult 4 while tuning the first coil in the
next stage. Then tune the second adjustment while looking for some reading on
the next meter position. I hope this makes sense.

If you have a few stages working, you may be able to hear the harmonics at the
operating frequency. You could try listening to the operating frequency with a
receiver and tune the stages while looking for most signal.

I think the stage you're trying to tune may be the varactor tripler. If so, it
can be tricky but should work fine if you can get it going. BTW, someone was on
here a few days ago talking about the MPro going spurious. If this happens to
you, or the PA stage seems to be unstable, try taking the 8072 out and clean the
fingers on the screen contacts in the cavity. Make sure that they haven't been
bent back to the point where they are not making good contact. This can happen
if someone rocks the tube back and forth when trying to remove it. Bend them
back out but don't scratch them. Also clean the screen ring on the tube itself.
I use a clean pencil eraser for both. It is easier to get down in the PA cavity
with the pencil.

I have a Master Pro UHF repeater in operation that still works great! dave/kx4i


Thanks Dave for the tip. I backed up to the MULT 3 tuning step and peaked
the MULT 3 GRID coil. While leaving the test set on the position for that
step, I started tuning the variable capacitor for the next step until I saw
a VERY SMALL movement of the meter. I then moved the test set to the
position for the next step and, low and behold, I had output. I was then
able to move along through the remaining steps and all worked fine. I now
have the transmitter putting out a solid 30 watts. I'm going to go through
this procedure with the other tx I have that stopped working in the same
place. Doug VE7DRF

Glad you got it working Doug. That transmitter should easily put out
60 watts. Keep tweaking and you'll get there. Always check the plate
current (on any band Master Pro), (position G, I think). It is easy to
tune where you have good power output with too much plate current. It
won't last long running that way. Dave KX4I

From: dave@pb.ua.edu

A few days ago, a fellow posted a problem with a Master Pro power supply. His transmitter power output was low. The M Pro power supply has two high voltage supplies. One (low B+, about 300 volts) is used for the multiplier and driver stages. The other (hi B+) is used for the PA. The Hi B+ supply is about 400-450 volts and is wired in series with the lo B+ supply. The result is a hi B+ of about 750 volts. If the hi B+ supply fails, the voltage drops to the low B+ value, dropping the plate voltage on the PA from about 750 volts to less than 300. Depending on the transmitter you are using, the output will drop to 3-10 watts. The Hi B+ is fused with a 1/2 amp fuse, usually F3. If the fuse is good, check the 4.7 ohm resister in series with the fuse. Also there are two 200 K Ohm 2 watt bleeder resistors on the output of the Hi B+ supply. These resistors tend to get hot over time (especially in repeater service) and the value gets lower causing thermal runnaway and eventually blowing the fuse. I automatically replace these resistors with 270K 2 watt units which seems to reduce the dissapation enough to last forever. Make sure all the electolitics are discharged before sticking your figures in this baby! These are great radios if you don't mind changing a tube occasionally! Dave/KX4I


The GE Master radio is a very good radio. There are two versions of the TX
one has a Tuneable coil across the grids of the 5894 tube. This is the 90
watt version and it was also the later version. I t rarely has any desense
problems if the GE tune up procedure is followed. and of course as in every
repeater. Double shielded leads are used for rx & tx antenna cables. The
older version does not have the tuneable coil across the grids. it is rated
at about 80 watts. again follow the GE tune up procedure to the letter. use
double shielded cables and do not exceed 80 watts output. most of the time
you won't have any desense. But I have had some trouble with this tx strip
in that area. I prefere not to use it.

Bill K4JBV


Mastr Pro UHF receiver ER-42-G uses ICOMS. The part number is 4EG26A10.



Here is some text I created documenting my machine...
I've got a RC1000 on mine, but this should work....

For the NHRC2...

TX audio into TB502-12
TX shield/gnd TB502-13
RX Audio input, try TB502-2 (top of vol pot I think...)

PTT active low TB502-10... now my RC1000 didnt have enough current sink to pull this big T/R relay in.
Had to wire in a little relay to perform the function. Not as clean...
But the NHRC has a bigger FET, so it may work directly.

COS (active high, 3V or more) TB502-16
Important note- TB502-15/14 are 117VAC.... careful here...from experience...
The active high COS should be tied into the anode top side of the input opto-coupler on the nhrc, ground
the lower cathode side.

Make sure you tie off the TX F1 and RX F1 selects. Sounds like one of your strips is probably already defaulted
inside the RX strip since it's only one freq.

Also the TB501-10 interlock should have something wired to it. It's used to deactivate the unit when the door was opened.
Needs to be tied high to +12. Tie over to TB501-9 (+12) to permanently defeat the interlock....

I have some info on tieing in a TS-32 into the GE. IF your unit is PL equipped, the pl deck may be encode only,
decode only or both. BUT, it doesnt full duplex each at the same time... So you have to pick encode or decode, whereas
the TS32 can full duplex for a repeater.... Just use the PL detect from the TS32 if you want a PL'd repeater detect
into the TS32. (although I've taken COS high and PL detect low on both sides of the opto-coupler and that works too..). de WB4TUR


misc msgs to others I have responded to...

gud luck, i've put many a mstr pro on the air as repeaters and mobiles.
I once musta bench tested over 100 vhf/uhf of these mobiles at a commo shop...
BE CAREFUL of whacking the final while its hot.
I've ruined the expensive tube just by putting on the base station cover on the
tx strip... only beef I have...otherwise they just run and run and run.
get you a couple of spare mobiles for extra
strips (& final tubes...). any lowband, vhf or uhf strips will bolt in for any band or cross band
applications....I sold another mstr pro rptr that was uhf to a vhf group along with a vhf mobile for
conversion, that was 5 years ago and it's still cranking...
Some of the older base power supplies have paper electroylitics....I'd replace them if they are paper.
Dont be tempted to run the t-power mobile supply for a repeater...wont take the duty cycle...

The spec is 60W for a good tube on the PRO.
I've got a moto motrac base amp w/8072 thats rated to 90W, so it will do a little more with more HV.
On my uhf pro rptr I get about 40W out the other side of my duplexer on tx (w/60 watts in).
Yours sounds like the PA is tired. I assume this is a deskmate AC supplied rig? The dc-dc
on the mobile wont hold up to rptr service. If it is the AC supply, there's a tap for various voltages to
run the tx at...perhaps yours is tapped to the lower plate voltage point...
New 8072 are $$$$, so find some more used tx strips...(if you find a pile let me know too...).
It is real easy to just swap in a whole new tx strip, easier than pulling the tube...
No tricks to tuning, the uhf ge pro is about as easy as I've seen.
Once up, you'll have years and years of service. I've had bunches of pros in ham service.
One warning, dont hit,vibrate or shock the tube while hot. Even trying to put the cover back on,
I've bonked the tube into oblivion. I plan on putting tune access holes thru the cover to resolve that

The base ac supply should have 1 fan than runs all the time over the tx cooling fins already??
The one in my supply was dead when I got it originally.
I did add two more 5" muffins at the back on the top vent to move some more air into the rack
(inside deskmate cabinet). They run all the time...Never too much air.

Between us, we will get your ole'reliable mstr pro going... great radios,
just keep workin, out lasted my moto micor at another site by far...

okay here goes.

K501 'S' is the PTT ground. Goes from TB501-10 and local mike J902-2 to
tx strip P101-7. So far so good. Out P101-2 comes the PTT, probably to let
inside PL deck do reverse burst or Time out or something. Dont have the
tx strip schem in front of me. Make sure its coming back out. K501-2 will be
+12.6 with no TX and 0 V with PTT low. Your's is doing that, so it looks like
the PTT is coming back out the TX strip. So far the tx strip looks good.

Now here is where you have the problem. No +12 VDC on K501-F. Could be
the diode is shorted, but doubt it. 1n4001 would swap in there. Could be K501
is dead, but you dont even have +12 across it just yet.

There is an interlock thats gotten you.
If you open up the box, it wouldn't let you inadvertantly TX. A microswitch
lever is somewhere and detecting you have the box opened up. Short across the
switch or just tie TB501 pin 9 to pin 10 to defeat this. I bet good money this is
your problem. Maybe it's a bad switch....

So, I hope thats it. If not, I'll look again.

A Few tips:
If you ever blow the +12.6 regulator, I've designed a newer technology way to go.
Watch those old large paper electrolytic caps, if its an older p.s. model. I'd
replace all of them for good measure if they are paper.
I've rewired my fan B501 to run all the time, not just on TX
and added a couple of extra muffins at the back of the deskmate box mine is in.

well chris, I hope that's enought to get you going.... at least until you buy xtals and want to retune to the ham

ralph WB4TUR


Subject: [REPEATER] UHF Master Pro Rx problems

>I have two separate problems with to rx.
>#1 This strip was just pulled from service. For the first 5-10 minutes
>of a conversation it is just fine. Then slowly it starts getting
>popping and crackling static type noise that eventually covers up the
>audio even on very strong signals. When the squelch opens it will be
>fine for the first few seconds then the static creeps in. Any

Sounds like a bad capacitor. Can you play the receiver on a bench? If so, get a can
'o cold and spray various caps on the audio board.

This is in response to some questions about Mastr Pro from one who knows, trust me!

Pres Waterman W2PW

>From what I remember from years of maintaining my own repeater network
loaded with MASTR PRO's cabinets
if you have bad or weak 8106 or 8156 ( compactron ) you would not get any
position " E ", on the GE testset , above the idle current to be indicated.
You must have a good reading at position " E ", and the reading as noted in
the tune-up procedure should be at or above .7 volts, before attempting to
tune the varactor tripler stage which represents position " F " on the
I have seen the 8156 either be gassy or with internal arcing inside that
would not let you get any kind of reading, above the idle current, on
position " E ".
When you get past the problem with this stage and C-104 and C-115 give you a
maximum reading on position " E ", you should be able to see a change in
the meter readings at " E " when you adjust C-121 and C-122, on the varactor
tripler assy. , you should see a small dip in the reading on " E " with the
first adjustment and then a small increased reading with the second
If you get this type of reaction at position " E ", then you can look at
position " F " and adjust the grid tuning capacitor on the PA cage to get a
sufficient reading
according to the tune-up procedure.
Here are some other hints that may help you out with the tune-up of the
When you replace the 8072 or just remove it from it's socket, before you
re-install it make sure that the screen ring contacts are all clean and
slightly bent in towards the center of the tube socket.
This is very very important to have a good connection to these fingers that
come in contact with the screen ring, because a poor connection can cause a
very high reading on position " F " when transmitting, which will quickly destroy the grid of
the 8072. If you see this happen, an oscillating condition is existing in the PA cage
most likely from a poor contact condition or the 8072 is not firmly seated
in it's socket.


Another helpful thing to know is that you may have to remove both of the
output tuning screws and have new ones made that are about 3/8 of an inch
longer to permit better tuning action and therefore improved operation of this transmitter at
or below 442 MHz.

When I tuned up any of the MASTR PRO equipment I have had in service and
obtained a moderate power output from each transmitter, I would let the
transmitter stay keyed up continuously for a period of not less then 5 to 10
minutes and only then make any final adjustments to the both the PA tune,
output filters adjustments and output power control potentiometer.
This will assure that when the transmitter is keyed up from a cold start the
power will rise to a maximum level after a few minutes and not reach this
level too quickly and "fall over the edge" causing the transmitter to de-tune it self as it gets

The last thing to check is to see if you have a stable transmitter by removing the frequency control element ( XTAL ) while being keyed off and on and see if you get any indication of power output being present.
If you are doing this last test on a repeater installation, remove the cable going to either the receiver or pre-amp before keying the transmitter. This will save you from having another problem being created by having any
out of band energy from a possible spurious transmitter being introduced back into the receive port of the duplexer.

Pres Waterman W2PW


Misc 6 mtr ramblings...

I took this a set further. I needed to run my machine continous duty, so I
replaced the PA coupling cap with a 1000PF 5KV doorknob (I blew two of the
disk type). I drilled vent holes in the end of the case behind the PA cage
and cut a hole in the cover between the PA cage and the finals. A bit of
hardware cloth (1/4" weave) and a 12V PC fan finished the mods. No thermal
drift! As a final touch, I spread the coils in the harmonic filter just a
touch and got 10 more watts.

Larry - WA5KBQ

At , claypots wrote:
>When I modified several 42-50 MHz mobiles for six meter service,
>cutting 1/4 turn off of the PA Tank Coil did the trick. Full 110 watt
>output. The receiver went to 52/53 MHz without any mods.
>Mark Cobbeldick, KB4CVN
>>Date: Thu, 30 Dec 1999 08:54:43 -0600
>>From: "CHRISTOPHER (Chris) W. BOONE" <cboone@earthlink.net>
>>Subject: Re: [GE] Want: Working MASTR *Pro* transmitter on 52 MHz
>>Remember a GE MSTR PRO transmitter does require some mod in
>>the driver and PA stages to make it work at 52-53 MHz efficiently..
>>otherwise it does NOT tune up correctly..


Misc audio interface ramblings...

From: "John..Mackey!!!!!!!" <jmackey@usa.net>

I've been meaning to try various audio inputs on my EP-38A12 power supply for my
master pro repeaters. I Disconnected all the other circuitry & used strictly the
"mic" input. 3
repeaters ALL sounded better & needed MUCH less audio drive than following the GE
suggested input.

I am using an RLC-3 controller operating Mastr Pro tramsmitters on 6 meters, 2
meters, & 440 MHz.

Note: Before I had NOT jumpered around the diode or supplied 10volt biasing
so this isn't very surprising.

Ed Yoho wrote:

> From: Ed Yoho <edyoho@home.com>
> Doug,
> Those are the correct audio points.
> Audio coupler hi is connected to the high side of the volume control (pin 5 on
> your receiver). It is de-emphasized.
> Audio hi is connected to mic hi through a series diode and resistor. The stock
> controller (KC19) would switch +10V on the transmit audio to forward bias the
> diode and gate on the audio. You should either short out the diode or add a
> 4.7K to 10K resistor from audio hi to +10V (TB501-7).
> Ed Yoho
> "Davies, Doug A FOR:EX" wrote:
> >
> > From: "Davies, Doug A FOR:EX" <Doug.Davies@gems3.gov.bc.ca>
> >
> > I'm attempting to connect an RC-100 controller to a Mastr Pro repeater. I'm
> > using an ET-57A transmitter, an ER-41C receiver and an EP38-A12 power
> > supply. Previously, I have just used the stock GE controller with an
> > outboard ID'er.
> >
> > I'm having some difficulty routing the audio through from the receiver to
> > the transmitter. Using 'squelch hi' doesn't seem to work. I am able to get
> > receive audio from the 'aud. coupler hi' connection on the EP-38 but I'm not
> > sure if this is de-emphasized audio or not. The quality of this audio is
> > less than desirable. Is this the proper place to pick off the receive audio?
> >
> > On the transmitter side, I have the controller hooked up to 'audio hi'
> > connection on the EP-38. This appears to be connected to the mic. input.
> > Is this the correct spot to route the audio from the controller to the
> > transmitter?
> >
> > If someone who has done this can look at their schematics and give me some
> > help, I would very much appreciate it.
> >
> > Doug VE7DRF


From: John Mackey KSØF <jmackey@usa.net>

To: <Repeater@yahoogroups.com>

Sent: Tuesday, May 22, 2001 2:03 AM

Subject: Re: [REPEATER] GE MASTR PRO Icom's

> I have several Mastr Pro repeaters on the air from 6 meters to UHF. The early UHF Mastr
> Pro tripled past the low power stages using a tube, it SUCKED!! The later Mastr Pro
> was tripled in the low power stage & the tripler was solid state, it worked very well
> Also, base & repeater station Mastr Pro UHF did use a ICOM to 2ppm tolorance. (Occasionally,
> they were seen in 150 MHz also)


From: john d lock <kf0m@juno.com>

Doug: I don't think that point is de-emphasized audio. On ours we take
the audio from that point and run it through an r-c deamphasis circuit
before feeding it to the controller.

John Lock
Wichita Ks EM17

On Thu, 22 Jul 1999 09:13:55 -0700 "Davies, Doug A FOR:EX"
<Doug.Davies@gems3.gov.bc.ca> writes:
>From: "Davies, Doug A FOR:EX" <Doug.Davies@gems3.gov.bc.ca>
>Now that I have the RC-100 controller hooked up to the Mastr Pro
>repeater, I
>notice that the audio out of the repeater is not the same quality as
>when I
>was using the stock GE controller. It is very 'tinny' sounding and
>has a
>sort of rough edge to it. I have tried adjusting the controller
>levels to
>get a better sound but the adjustment pot in the RC-100 is VERY touchy
>doesn't allow for much fine tuning.
>I am taking receive audio from the 'audio coupler hi' connection on
>EP-38 power supply which is de-emphasized audio. From the controller,
>audio goes to the mic. input on the EP-38.
>Any suggestions on how I might get better quality audio with this
>Doug VE7DRF


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