The interesting thing about these receivers is that they do work, out of the
box, pretty decently. You do run afoul, however, once you try to do a factory
alignment. Unfortunately, whatever Bob's brother did to these rigs was not
documented and that is the cardinal sin. If I had been provided with altered
alignment info, a set of schematics marked up as an ECO or FCO and a
description of what was done and why, I would have given this much more thought
before endeavouring to undo all of the mods.
At the very least, the first thing that needs to be un-done is the removal of
the audio amp disable mod. To do this, cut the jumper across the 6EV7. That's
it. You will then have full audio power at the SPEAKER jack. everything
beyond this is returning the rig to factory specs and removing the "fine
adjustment" of the AGC time constant. For myself, I feel that Drake pretty
much had it set right from the beginning. Their time constant for CW was fine
and so was their constant for SSB. I'm a 90% CW guy. Go ahead and undo the
AGC mods.
73,
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.
From: Bob
Sent: Friday, November 04, 2011 8:30 PM
To: Steve Wedge ; Pete Juliano ; Drake List
Subject: Re: [Drakelist] R-4B Mod removal, Part 1
Hi Steve and Pete, I too have one of these R4B modified receivers. I really
appreciate your correspondence in sharing the findings. I have not yet had the
time to dig into it. Looking forward to the final resolution. Thanks so much.
Be in touch, 73, Bob, W3QJ
----- Original Message -----
From: Steve Wedge
To: Pete Juliano ; Drake List
Sent: Thursday, November 03, 2011 8:33 AM
Subject: Re: [Drakelist] R-4B Mod removal, Part 1
Yep - I confirmed the 150-ohm is sitting there, off to the side. I haven't
looked for the 2.2M yet, but I'm betting that mine's exactly the same.
The INJ is still intermittent - when I push on the hookup wire at the
terminal strip near T4 that goes over to the resistor/neon control board, I can
make the control problem come and go. When I don't touch the wire, it's mostly
working with both PTO's controlling the receive frequency. Methinks the wire
is broken inside and intermittently contacting. Luckily, there's more than
enough of a service loop in that wire, so I'll be cutting it and re-soldering
tonight.
Steve, W1ES/4
-----Original Message-----
From: Pete Juliano
Sent: Nov 2, 2011 9:43 PM
To: Steve Wedge , Drake List
Subject: Re: [Drakelist] R-4B Mod removal, Part 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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