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Today's Topics:
1. R-4B Mod removal, Part 1 (Steve Wedge)
2. Re: R-4B Mod removal, Part 1 (Pete Juliano)
3. Re: R-4B Mod removal, Part 1 (Steve Wedge)
----------------------------------------------------------------------
Message: 1
Date: Wed, 2 Nov 2011 20:37:37 -0400
From: "Steve Wedge"<[email protected]>
To: "Drake List"<[email protected]>
Subject: [Drakelist] R-4B Mod removal, Part 1
Message-ID:<9DD85426922D4916BD0A771394E465AA@Shack7>
Content-Type: text/plain; charset="iso-8859-1"
I'm not as brave as Pete (N6QW) - if I assume that he restored his R-4B all at
once. Chances are, he didn't, but he did give me a darn good road-map. My
first goals for this evening were to check to see if Radio Shack really did
sell long-shafted 10k pots anymore - they do (!) and so I parted with about 3
bucks and change and brought it home.
The pot will be to replace the RF GAIN control - which the PO had ditched in
favour of rigging up some sort of alternative RF Gain/AGC circuit. This is the
source of that extra knob on the front. This rework will, however, continue
tomorrow night.
Tonight, my actual goals in working on the receiver were to undo the audio
mods, thereby unleashing the 6EH5 again. For some reason, the PO shorted the
grid to the cathode and ran a piece of RG-174 from this to the INJ jack. He
moved the INJ over to the SPARE location and installed another RCA jack there.
Why? Darned if I know. It seems he didn't need the high-level audio, probably
because he was using an external audio amp. I have no idea why he'd want to
move (and cut!) the INJ shielded line. Anyway, as luck would have it, after
removing that piece of RG-174, I determined that it was the perfect length to
go from the correct jack back over to T4. So, I removed the old shielded cable
from T4 to the SPARE jack and installed the free end of the piece of RG-174
over to its correct location on T4. It's very tight in there around the
bandswitch! I removed what I thought was an extra capacitor on the board
nearest the AF GAIN control.
When I turned the rig on, I was greeted with nothing! At least there was no
smoke...
I found a couple of problems. That "extra" cap was moved over to the foil side
of the board to make room for a big electrolytic that's paralleled across one of the
terminals on the can cap (a bad idea that will be addressed later - maybe) I had removed
a .47 that was substituted for the original .01 that couples the audio output to the
speaker! No wonder there was no audio! Put a new .01 on the foil side and voila! Now I
can keep the AF GAIN barely cracked open and get plenty of audio - just like it was
designed to do!
A more troubling matter reared its head - the INJ didn't seem to be working
properly. Strangely enough, if I switched to the transmitter, I was getting
signals as tuned by BOTH PTO's. Obviously, the negative bias wasn't working
for some reason. After metering and sniffing around, I found a wire attached
to the resistor board directly beneath the PTO that wasn't soldered! I'm
amazed this receiver had worked for as long as it did - this was the wire from
T4 to the resistor board. I re-soldered this wire and everything's working as
it should (except the RF Gain, of course).
I'm done for this evening. I sliced open the tip of my left index finger
whilst trimming the RG-174 with my nice-n-sharp Swiss Army Knife. It's now
starting to hurt.
Tomorrow, I begin the process of unraveling the RF GAIN and AGC mods. This
one's going to be a lot more work. Once those changes are done, I'll put two -
count 'em - headphone jacks in: one mono jack where it's supposed to be (on the
side) and one to plug the hole in the front panel, which I'll rig as a
L-R-shorted stereo jack so that one can use stereo phones without an adaptor.
I figure that if the damn hole is going to be there anyway, it might as well do
something useful!
Pete, again, thanks for being the pioneer. With a stone-stock, working R-4B
that I can use - plus Garey's CD - I'm having an easier time than you probably
did. Getting to that 150-ohm resistor is going to be a challenge.
Enjoy Those Drakes...
Steve Wedge, W1ES/4
To be is to do - Socrates
To do is to be - Plato
Do be do be do. - Sinatra
All my computers have my signature with various pearls of wisdom appended
thereto.
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Message: 2
Date: Wed, 2 Nov 2011 18:43:13 -0700
From: "Pete Juliano"<[email protected]>
To: "Steve Wedge"<[email protected]>, "Drake List"
<[email protected]>
Subject: Re: [Drakelist] R-4B Mod removal, Part 1
Message-ID:<F25D9DB6AB144377BFCB63820DFA94CC@UNIT0>
Content-Type: text/plain; charset="iso-8859-1"
Hi Steve,
Actually I did it all in two days so it was a little longer than one afternoon.
But that also included testing all of the tubes, cleaning the chassis top and
putting de-oxit on the switch terminals with the micro-applicator and giving
all the tube pins a shot of de-oxit and back into their sockets. Finding the
missing 2.2M Ohm resistor took the longest. If I had Garey's CD that would have
been much faster. I now have it so any more work will go faster. BTW the 2.2M
resistor was missing on the other radio I know of besides yours. You didn't
mention if you addressed that --but the AGC won't work without that resistor.
Look carefully and the 6BZ6 and you might find that 150 Ohm resistor has just
been moved slightly out of the way and not removed totally. That was the case
in two radios from that lot. If it is there then a clean up of the Cathode pin
with solder wick it will let you slide that puppy right in place and you are
there. If you want to plug the hole in the front panel then you can use a 5/16
black plastic plug and it will fit nicely and the hole sort of disappears into
the front panel. I found one such plug at my local hardware store.
73's
Pete N6QW
From: Steve Wedge
Sent: Wednesday, November 02, 2011 5:37 PM
To: Drake List
Subject: [Drakelist] R-4B Mod removal, Part 1
I'm not as brave as Pete (N6QW) - if I assume that he restored his R-4B all at
once. Chances are, he didn't, but he did give me a darn good road-map. My
first goals for this evening were to check to see if Radio Shack really did
sell long-shafted 10k pots anymore - they do (!) and so I parted with about 3
bucks and change and brought it home.
The pot will be to replace the RF GAIN control - which the PO had ditched in
favour of rigging up some sort of alternative RF Gain/AGC circuit. This is the
source of that extra knob on the front. This rework will, however, continue
tomorrow night.
Tonight, my actual goals in working on the receiver were to undo the audio
mods, thereby unleashing the 6EH5 again. For some reason, the PO shorted the
grid to the cathode and ran a piece of RG-174 from this to the INJ jack. He
moved the INJ over to the SPARE location and installed another RCA jack there.
Why? Darned if I know. It seems he didn't need the high-level audio, probably
because he was using an external audio amp. I have no idea why he'd want to
move (and cut!) the INJ shielded line. Anyway, as luck would have it, after
removing that piece of RG-174, I determined that it was the perfect length to
go from the correct jack back over to T4. So, I removed the old shielded cable
from T4 to the SPARE jack and installed the free end of the piece of RG-174
over to its correct location on T4. It's very tight in there around the
bandswitch! I removed what I thought was an extra capacitor on the board
nearest the AF GAIN control.
When I turned the rig on, I was greeted with nothing! At least there was no
smoke...
I found a couple of problems. That "extra" cap was moved over to the foil side
of the board to make room for a big electrolytic that's paralleled across one of the
terminals on the can cap (a bad idea that will be addressed later - maybe) I had removed
a .47 that was substituted for the original .01 that couples the audio output to the
speaker! No wonder there was no audio! Put a new .01 on the foil side and voila! Now I
can keep the AF GAIN barely cracked open and get plenty of audio - just like it was
designed to do!
A more troubling matter reared its head - the INJ didn't seem to be working
properly. Strangely enough, if I switched to the transmitter, I was getting
signals as tuned by BOTH PTO's. Obviously, the negative bias wasn't working
for some reason. After metering and sniffing around, I found a wire attached
to the resistor board directly beneath the PTO that wasn't soldered! I'm
amazed this receiver had worked for as long as it did - this was the wire from
T4 to the resistor board. I re-soldered this wire and everything's working as
it should (except the RF Gain, of course).
I'm done for this evening. I sliced open the tip of my left index finger
whilst trimming the RG-174 with my nice-n-sharp Swiss Army Knife. It's now
starting to hurt.
Tomorrow, I begin the process of unraveling the RF GAIN and AGC mods. This
one's going to be a lot more work. Once those changes are done, I'll put two -
count 'em - headphone jacks in: one mono jack where it's supposed to be (on the
side) and one to plug the hole in the front panel, which I'll rig as a
L-R-shorted stereo jack so that one can use stereo phones without an adaptor.
I figure that if the damn hole is going to be there anyway, it might as well do
something useful!
Pete, again, thanks for being the pioneer. With a stone-stock, working R-4B
that I can use - plus Garey's CD - I'm having an easier time than you probably
did. Getting to that 150-ohm resistor is going to be a challenge.
Enjoy Those Drakes...
Steve Wedge, W1ES/4
To be is to do - Socrates
To do is to be - Plato
Do be do be do. - Sinatra
All my computers have my signature with various pearls of wisdom appended
thereto.
--------------------------------------------------------------------------------
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Message: 3
Date: Thu, 3 Nov 2011 08:33:55 -0400 (GMT-04:00)
From: Steve Wedge<[email protected]>
To: Pete Juliano<[email protected]>, Drake List
<[email protected]>
Subject: Re: [Drakelist] R-4B Mod removal, Part 1
Message-ID:
<29727547.1320323635757.javamail.r...@wamui-hunyo.atl.sa.earthlink.net>
Content-Type: text/plain; charset="us-ascii"
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End of Drakelist Digest, Vol 41, Issue 7
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