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Drake TR-4 questions
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Ernie
Apr 4, 2012, 10:03:26 AM4/4/12
to
I've stared at the underside and tried to follow wires buried deep in the
tightly-bound wire bundles till my eyes are about to pop out. Can anyone
direct me where to find resistor "R-63" which is 22 meg ohm? My receiver is
very very weak, almost sounds dead although I can hear signals at a very low
level and am thinking my AVC may be the culprit.
tightly-bound wire bundles till my eyes are about to pop out. Can anyone
direct me where to find resistor "R-63" which is 22 meg ohm? My receiver is
very very weak, almost sounds dead although I can hear signals at a very low
level and am thinking my AVC may be the culprit.
Tim Wescott
Apr 4, 2012, 6:05:19 PM4/4/12
to
don't know if the TR-4 does it, but many radios just hook the S meter
into the AVC line, and many just control the AVC line with manual gain:
if the TR-4 does both of those, and if the S meter doesn't move when you
change the RF gain manually, then that would be a good indication that
something is messing you up.
And, if you can manually crank up the RF gain and get a nice loud signal,
then you know it's AVC!
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Ernie
Apr 5, 2012, 10:08:03 AM4/5/12
to
Thanks for your thoughts Tim.
No, there's not means to switch the AVC off. The TR-4 has a scheme whereby
signal is taken off an IF transformer and applied to an "AVC amplifier" that
feeds it
across a plate resistor that develops current which then varies the voltage
to the grids of the
preceding IF amplifiers and detector. As the voltage is varied, the output
from their plates
increases or decreases the gain, depending on whether the signal is stronger
or weaker which provides the AVC control. The S-meter comes off of the same
system. My S-meter will not adjust any lower than "S6" with the S-meter zero
pot, so I am guessing that there is too much current being drawn somewhere
resulting in too much grid bias which provides too much AVC action, which is
the same thing that rotating the RF GAIN control down does.
My problem is that I hear almost no "receiver hiss" even with the volume
control all the way up. I do hear signals, but they are very weak and
rotating the IF and RF transformer trimmers has an effect on the amount of
signal from my sig gen that I get. But the overall volume is way, way down.
In addition, if I inject a 9 MHz signal to the grid of the 1st IF
transformer, I get lots of
signal from the plate. But if I inject a signal to the grid of the 2nd IF
transformer, the signal level from its plate is very low. Ordinarily that
would mean the tube is defective, but it's not. I've swapped two NOS tubes
(that all test well on a reliable professional tube tester).I've checked
that IF amp's bypass caps and load resistors. Nothing.
So my focus is still on the AVC.
By the way, I was mistaken. What I thought was a "22 Meg" resistor is
actually a 2.2 Meg. I thought the 22 meg figure was a little "out there" but
until I compared my copy of the manual with another copy, I discovered the
printing of the
schematic was somewhat blurred causing the decimal point to be unseen. So
finding the "missing
22 Meg resistor" isn't an issue anymore. Unfortunately, as it turns out, the
2.2 Meg resistor was within tolerance. That would have
been just too easy.
No, there's not means to switch the AVC off. The TR-4 has a scheme whereby
signal is taken off an IF transformer and applied to an "AVC amplifier" that
feeds it
across a plate resistor that develops current which then varies the voltage
to the grids of the
preceding IF amplifiers and detector. As the voltage is varied, the output
from their plates
increases or decreases the gain, depending on whether the signal is stronger
or weaker which provides the AVC control. The S-meter comes off of the same
system. My S-meter will not adjust any lower than "S6" with the S-meter zero
pot, so I am guessing that there is too much current being drawn somewhere
resulting in too much grid bias which provides too much AVC action, which is
the same thing that rotating the RF GAIN control down does.
My problem is that I hear almost no "receiver hiss" even with the volume
control all the way up. I do hear signals, but they are very weak and
rotating the IF and RF transformer trimmers has an effect on the amount of
signal from my sig gen that I get. But the overall volume is way, way down.
In addition, if I inject a 9 MHz signal to the grid of the 1st IF
transformer, I get lots of
signal from the plate. But if I inject a signal to the grid of the 2nd IF
transformer, the signal level from its plate is very low. Ordinarily that
would mean the tube is defective, but it's not. I've swapped two NOS tubes
(that all test well on a reliable professional tube tester).I've checked
that IF amp's bypass caps and load resistors. Nothing.
So my focus is still on the AVC.
By the way, I was mistaken. What I thought was a "22 Meg" resistor is
actually a 2.2 Meg. I thought the 22 meg figure was a little "out there" but
until I compared my copy of the manual with another copy, I discovered the
printing of the
schematic was somewhat blurred causing the decimal point to be unseen. So
finding the "missing
22 Meg resistor" isn't an issue anymore. Unfortunately, as it turns out, the
2.2 Meg resistor was within tolerance. That would have
been just too easy.
Scott Dorsey
Apr 5, 2012, 10:20:15 AM4/5/12
to
Ernie <sag...@brrr.net> wrote:
>In addition, if I inject a 9 MHz signal to the grid of the 1st IF
>transformer, I get lots of
>signal from the plate. But if I inject a signal to the grid of the 2nd IF
>transformer, the signal level from its plate is very low. Ordinarily that
>would mean the tube is defective, but it's not. I've swapped two NOS tubes
>(that all test well on a reliable professional tube tester).I've checked
>that IF amp's bypass caps and load resistors. Nothing.
I'd be much more apt to suspect the IF transformer (or the ceramic cap
>In addition, if I inject a 9 MHz signal to the grid of the 1st IF
>transformer, I get lots of
>signal from the plate. But if I inject a signal to the grid of the 2nd IF
>transformer, the signal level from its plate is very low. Ordinarily that
>would mean the tube is defective, but it's not. I've swapped two NOS tubes
>(that all test well on a reliable professional tube tester).I've checked
>that IF amp's bypass caps and load resistors. Nothing.
used to peak it) rather than the tube. Still, I'd check plate and cathode
voltages on the tube to make sure they're realistic.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Richard Knoppow
Apr 5, 2012, 1:27:51 PM4/5/12
to
"Ernie" <sag...@brrr.net> wrote in message
news:mNKdncerRfJeyeHS...@earthlink.com...
TR-4 from Garrey
www.k4oah.com This has a lot of information not in the
handbooks including photographs of the wiring. It also has
the handbooks and schematics for all variations.
I doubt very much that its the AVC. But check the RF
gain control to make sure its not turned way down, this is
the little lever under the receiver volume control.
Another thing to check is the protection lamp. This is
a pilot lamp in series with the antenna to prevent burn out
from strong signals, remember the TR-4 was intended for
mobile use. This is a small bi-post lamp in the compartment
with the final tubes. If its open or if the socket has
gotten corroded the antenna is effectively disconnected from
the receiver. If the thing is dead on all bands this is a
possibility.
There is also a switch on the left side near the back
for Receiver or Transceiver. It can also become dirty. Just
working it a few times will usually fix it.
Beyond that clean the band switches and make sure the
tubes are tight in their sockets.
Tracing wiring is difficult because of the very compact
construction. Check these obvious things first.
--
--
Richard Knoppow
Los Angeles
WB6KBL
dick...@ix.netcom.com
Richard Knoppow
Apr 5, 2012, 1:48:00 PM4/5/12
to
news:P_ednWeV__TDOuDS...@earthlink.com...
OK I didn't see this post when I replied. The up-scale
reading of the S meter does suggest something is wrong with
the bias. Have you checked the voltages around V13a? It is
also worth swapping V13 in case you have a gassy one. My
other suggestions don't apply other than getting the disc I
mentioned.
reading of the S meter does suggest something is wrong with
the bias. Have you checked the voltages around V13a? It is
also worth swapping V13 in case you have a gassy one. My
other suggestions don't apply other than getting the disc I
mentioned.
Ernie
Apr 6, 2012, 10:31:05 AM4/6/12
to
Thanks Richard. Yes I checked all the obvious stuff first...RF gain control,
persnickety "RCV/TRCV" slide switch on the side, antenna bulb fuse etc. Also
removed and checked the trimmer and coils of the IFs. I'm now focused on
a -0.25 VDC bias measurement on the 2 IF tubes instead of the -0.10 VDC
shown on the voltage chart.
Will update as progress is made.
persnickety "RCV/TRCV" slide switch on the side, antenna bulb fuse etc. Also
removed and checked the trimmer and coils of the IFs. I'm now focused on
a -0.25 VDC bias measurement on the 2 IF tubes instead of the -0.10 VDC
shown on the voltage chart.
Will update as progress is made.
Richard Knoppow
Apr 6, 2012, 3:08:38 PM4/6/12
to
news:1YydnQzSwYSqY-PS...@earthlink.com...
Ernie, I think you may get more help by joining one of
the Drake mailing lists. There is one at:
http://groups.yahoo.com/group/DrakeRadio/join
and another at:
http://mailman.zerobeat.net/mailman/listinfo/drakelist
Nearly the same people on both. In particular Garrey
Barrell is quite expert and may know what has happened
immediately.
the Drake mailing lists. There is one at:
http://groups.yahoo.com/group/DrakeRadio/join
and another at:
http://mailman.zerobeat.net/mailman/listinfo/drakelist
Nearly the same people on both. In particular Garrey
Barrell is quite expert and may know what has happened
immediately.
Ernie
Apr 8, 2012, 8:45:57 AM4/8/12
to
Problem found.
Actually two problems.
In addition to the atypical grid voltage readings on the IF tubes leading me
to suspect AVC involvement, R195 (68 ohms) that feeds the cathodes of the IF
tubes (V11 and V12) and is delivered to those tubes from a jumper from V5
(6BA6) was open. Once replaced, I still had very low voltage (1/2 volt)
instead of 1.5 volt on the cathode. What else can be left? The filament? Hey
those things NEVER go bad, right? So I checked the filament voltages and,
while V12 was good (12.8 VAC), the 1st IF (6BZ6) was missing. Back and forth
a hundred times checking the little white wire from V5 that feeds the
filaments too but it was good. I look at the filament string on the
schematic and there's a 0.005 uF capacitor in parallel with the filament of
V11 which was good. Here's the very odd thing: Of course the filament for
V11 uses only one side of the leg of the filament string to develop its
voltage BUT MY VOLTAGE CHART SHOWS IT SHOULD BE 12.8 VAC. In addition, it is
clearly silk-screened on the chassis of V5, "12BA6." But yet the voltage
chart refers to V5 as a "6BA6." Figuring I'd better double check the 6BA6 or
12BA6 or whatever was in there I discovered it was a 12BA6 with its
lettering almost rubbed off. Voila. Exchanging the 12BA6 for a 6BA6
immediately returned my filament voltage on V11 to 6.3 VAC (so I notated the
correction on the manual's voltage chart), cathode voltage returned to a
healthy 1.5 VDC, S-meter easily zeroed and worked and finally
again...hissssssssssssssss.
This transceiver was given to me by a gentleman who said the receiver didn't
work very well. I think I know why.
Thanks to Scott, Richard and Garey for your suggestions. They were all good
ones but I think Richard's crystal ball may have been closest when he
stated, "check the obvious."
Actually two problems.
In addition to the atypical grid voltage readings on the IF tubes leading me
to suspect AVC involvement, R195 (68 ohms) that feeds the cathodes of the IF
tubes (V11 and V12) and is delivered to those tubes from a jumper from V5
(6BA6) was open. Once replaced, I still had very low voltage (1/2 volt)
instead of 1.5 volt on the cathode. What else can be left? The filament? Hey
those things NEVER go bad, right? So I checked the filament voltages and,
while V12 was good (12.8 VAC), the 1st IF (6BZ6) was missing. Back and forth
a hundred times checking the little white wire from V5 that feeds the
filaments too but it was good. I look at the filament string on the
schematic and there's a 0.005 uF capacitor in parallel with the filament of
V11 which was good. Here's the very odd thing: Of course the filament for
V11 uses only one side of the leg of the filament string to develop its
voltage BUT MY VOLTAGE CHART SHOWS IT SHOULD BE 12.8 VAC. In addition, it is
clearly silk-screened on the chassis of V5, "12BA6." But yet the voltage
chart refers to V5 as a "6BA6." Figuring I'd better double check the 6BA6 or
12BA6 or whatever was in there I discovered it was a 12BA6 with its
lettering almost rubbed off. Voila. Exchanging the 12BA6 for a 6BA6
immediately returned my filament voltage on V11 to 6.3 VAC (so I notated the
correction on the manual's voltage chart), cathode voltage returned to a
healthy 1.5 VDC, S-meter easily zeroed and worked and finally
again...hissssssssssssssss.
This transceiver was given to me by a gentleman who said the receiver didn't
work very well. I think I know why.
Thanks to Scott, Richard and Garey for your suggestions. They were all good
ones but I think Richard's crystal ball may have been closest when he
stated, "check the obvious."
Bill M
Apr 8, 2012, 7:49:54 PM4/8/12
to
Ernie wrote:
> Problem found.
> Problem found.
>
> Thanks to Scott, Richard and Garey for your suggestions. They were all
> good ones but I think Richard's crystal ball may have been closest when
> he stated, "check the obvious."
Good catch, Ernie.
> Thanks to Scott, Richard and Garey for your suggestions. They were all
> good ones but I think Richard's crystal ball may have been closest when
> he stated, "check the obvious."
Ernie
Apr 9, 2012, 10:58:04 AM4/9/12
to
Thanks Bill! Every once in awhile I accidentally surprise myself :)
> Good catch, Ernie.
> Good catch, Ernie.
Tim Wescott
Apr 9, 2012, 11:52:07 AM4/9/12
to
press magazine with a bunch of factoids about TV repair. One of the
things I remember reading is that 50% of service calls were at that time
(early 1970s) because the TV wasn't even plugged in.
Then I grew up to be an electronics engineer, and while you'd think I'd
have known better, I can't count the number of times I've had the back
off of a piece of electronics, or was getting ready to, before I
discovered that it just wasn't plugged in, or some switch had been
flipped, etc.
"Check the obvious" is good advise -- and advise that isn't always easy
to remember to follow!
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