Garey et al,
I made resistance measurements on the RF Output switch on the LOAD shaft
with the switch in place and wires and resistor attached. I got steady
readings but wasn't satisfied. I removed the switch and made measurements
just on the switch contacts. The open positions were obviously open, but the
shorting functions of the switch were unstable. I replaced the switch with
the only thing that I had which was a slide switch with
snap-and-remain-in-position, not spring loaded for easy return. However, the
LOAD shaft spring is strong enough to return the switch.
EUREKA
The old switch mechanism must have been locking the circuit into the RF
output measurement mode.
I can now adjust the bias current with the switches set in the required
position. However, I can also adjust the bias current with the SIDEBAND
switch set in the X position.
Question 1 Is this normal?
I can also properly tune the transmitter. The PLATE control dips current
like it should. The RF output adjusts like it should. I can tune and load
the transmitter to 440 mA plate current with 185 W output on 40 M. (7.164
MHz.). I have not tried any other frequency. When I activate the mike switch
I see the bias or idle current on the plate meter.
Question 2 Is this normal?
When I huff into the mike, the plate current huffs with me.
I have no operating experience with the TR-4C, so I don't know the answers
to these two questions.
I have a proper switch on order.
A new item popped up though. When I just ever-so-slightly twist the chassis,
the volume level on the speaker drops to about 20 %. I don't know what else
might be affected. If I flex the chassis slightly, the volume comes back. If
I press the mike switch or activate the key, which activates the relay, the
volume level comes back. So it doesn't necessarily take flexure to bring it
back. I am thinking bad solder joint somewhere from my continually flexing
the chassis in turning it over repeatedly, or that the relay contacts are
not as good as I thought they looked. I have a new relay ordered also.
Anyway, the major problem seems to be fixed and I can get it on the air.
Garey, I thank you very much for your help and all the others who chipped in
with suggestions. The Drakelist sure works.
Richard
----- Original Message -----
From: "Garey Barrell" <k4...@mindspring.com>
To: "Donley" <donley...@comcast.net>
Cc: "drakelist" <Drakelist@zerobeat.net>
Sent: Monday, July 18, 2011 11:28 AM
Subject: Re: [Drakelist] TR-4C Bias Adjustment
Richard -
OK. Good idea. Sometimes it helps to just step back and look at the
simple things again! :-)
For 'normal' operation of the PA, with the LOAD control at minimum, adjust
the PLATE control while monitoring the voltage across R45. The voltage
should 'dip' at about the same place the output 'peaks'.
IF you were to adjust the RF TUNE control, you _would_ see the output
_AND_ R45 voltage both peak near the center and fall off on both sides.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Donley wrote:
Garey,
I am not offended by any questions about whether I am doing things
correctly. I need reality checks occasionally. I checked over my notes
that I am keeping and see that the current did NOT dip across R45 but
acted just like the RF output and peaked about midrange and fell off on
both sides. I want to go back and redo some of these measurements. I
removed the RF output switch on the LOAD control to make better
resistance measurements on the switch. I found the contacts to be
unstable out of circuit, so I am going to replace it. Maybe the
connection to the LOAD shaft would hold the switch in the right position
to make good contact. I don't think this is responsible for the problem,
but it can't hurt to replace it.
I am going to go back and recheck some of the measurements and make sure
that I am tuning per the manual.
Richard
----- Original Message ----- From: "Garey Barrell" <k4...@mindspring.com>
Cc: "drakelist" <Drakelist@zerobeat.net>
Sent: Saturday, July 16, 2011 10:23 AM
Subject: Re: [Drakelist] TR-4C Bias Adjustment
Richard -
I just another couple of thoughts.........
Looking back through the million or so messages regarding this problem,
I asked if the voltage across R45 'dipped' when you rotated the PLATE
control, and you replied that it did NOT, rather it peaked just like the
RF output, falling off on either side. That's just not right!! :-)
Please don't be offended, but you ARE tuning the PLATE control and NOT
the RF TUNE control.....?
Just remember, 'We do this for fun ..." "We do this for fun ..." :-)
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Donley wrote:
Garey, et al
The PA tubes are Sylvania 6JB6, checked on a Hickok 600A and test good.
I have seen no color to the plates of the finals.
I have been doing all testing on 40 M. I came to suspect one of the
sideband filters so I tried 80, 40 and 20 M., both upper and lower
sideband to see what happened. I got output in excess of 125 W. to the
dummy load in all cases. The cables to the wattmeter and dummy load are
OK, the dummy load (switched to a Bird 8201) is OK.
I took the lid off of the PA cage and placed an all purpose telescoping
antenna next to the cage and ran the input into an HP spectrum
analyzer. I got a very nice signal at 7.3 MHz and also very nice
signals at 14, 21 and 28 MHz. There was no sign of any other
oscillation of the finals. I did notice hash from the laptop computer
switching power supply which went away when I unplugged it. Replacing
and grounding the PA lid removed the extraneous harmonics at 14, 21 and
28 MHz. I also listened to the signal with another receiver and had a
very clear sounding tone with no other noise up and down the dial. I
varied the TR-4C VFO to make sure I was listening to the correct
signal.
I did measure the lead resistance of the Fluke leads. It is about 0.15
ohms, so the resistance of R45 will be about 2.25 ohms, closer to the
nominal value.
I don't think anything is wrong with the output circuitry. If there
was, how could I be measuring power out to the dummy load? The
wattmeter is a Swan 3000. I am not absolutely certain that it is
working OK. I suppose I should try the light bulb technology that I
used as a novice back when I knew it all. Now I have some reasonable
equipment and don't know anything.
Now, the last item puzzles me. I measured the ANT output to ground
(SO-239) and it was 1.4 ohms, no way near 2.2 Megohms. RFC 7 goes to
ground right at the SO-239. I would expect the DC resistance of the
choke to be more than 1.4 ohms but less than 2.2 Megohms. Are we
getting closer to an answer or just more confusion (I know it is the
latter for me)?
Awaiting further task assignments. I appreciate all the help.
73
Richard
----- Original Message ----- From: "Garey Barrell"
<k4...@mindspring.com>
To: "drakelist" <Drakelist@zerobeat.net>
Sent: Thursday, July 14, 2011 10:27 AM
Subject: Re: [Drakelist] TR-4C Bias Adjustment
Richard -
OK. As others have said, we are missing something fundamental, as
transmitters just do not do this!! :-) Verifying that the PA tubes
ARE 6JB6 is a good idea. The Simpson is more than adequate for all
but very low resistance readings, 2 - 15 ohm resistors and the voltage
across them.
You haven't confirmed which band you are using for test purposes. I
suggest 40M. Are the PA plates showing any color that you have seen?
Listen on another receiver and determine if you can hear the TR-4C on
the frequency indicated by the dial reading. Once you find the
signal, does it vary with PTO adjustment as expected?
Since we have already measured the voltage across the three Cathode
resistors and determined that they are approximately equal, nothing is
gained by the risky (dangerous) measurement of 'plate' current. There
is no place else for the current through R45 to come from other than
the plate supply, so measuring the voltage across it is just as
accurate and much less dangerous. Check your ohmmeter by shorting the
test leads to determine if it reads "0.00" or if there is some lead
resistance to be subtracted from the 2.4 ohm reading. 2.4 ohms is 20%
high, but absolute current isn't critical at this point.
I believe that we have determined that the meter IS measuring current
correctly, the current just isn't behaving normally. It appears that
'something' is wrong with the output circuitry of the PA, preventing
it from transferring power from the PA plates to the antenna, or the
'antenna' (dummy load) isn't accepting power.
Measurement of the dummy load would be a good next step. If it
measures near 50 ohms, then measure again at the transceiver end of
the cable to verify that the cable is good. Measure the resistance of
the ANT output jack on the radio, (power off, dummy load
disconnected,) it should read about 2.2 Megohms to chassis. Rotate
the PLATE and LOAD controls through their range with the ohmmeter
connected, watching for anomalies.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Donley wrote:
Garey , Richard I, et al
Since I am the student here, I can only be Richard II.
I measured the resistance of R45, in circuit with the relay pulled.
I'm not sure that made any difference. It measured 2.4 ohms on a
Fluke 179.
Since it is difficult to adjust for MAX or MIN on a DMM, I changed to
a Simpson 260 (I know, maybe not too accurate).
Then set SIDEBAND X, MODE X-CW cranked in some XMTR gain and tuned
PLATE for MAX on the PLATE CURRENT meter (because tuning for MIN
didn't work). Max reading on the PLATE CURRENT meter again occurs
about mid-range and falls off on both sides. The PLATE METER read 200
mA and the voltage on R45 was 0.46 VDC. Since R45 measured 2.4 ohms
from before, the calculated current is about 192 mA. Close to the 200
mA on the PLATE METER.
Then I tried tuning PLATE for MIN voltage on R45 with the Simpson. I
could not tune to MIN, there was a MAX value about mid-range and it
falls off on either side of MAX. The voltage on R45 was very close to
0.46 VDC, the same as above. Again, the calculated current was about
192 mA.
Plate current or RF output?
I checked the slide switch on the LOAD control. I took resistance
measurements in each position and it seems to be working. I added a
little DeOxit.
I looked at the circuitry for RF output on the relay board ( I have
most of Garey's Drake CD's). If the problem is in there, it is going
to be a real pain to get to. I hope someone comes up with the "Golden
Screwdriver" solution. When I was working, our solutions were "Silver
Bullets". Of course, that was before the price of silver skyrocketed.
Richard II
----- Original Message ----- From: "Garey Barrell"
<k4...@mindspring.com>
To: "drakelist" <Drakelist@zerobeat.net>
Sent: Wednesday, July 13, 2011 1:42 PM
Subject: Re: [Drakelist] TR-4C Bias Adjustment
Richard Knoppow wrote:
----- Original Message ----- From: "Garey Barrell"
<k4...@mindspring.com>
To: "drakelist" <Drakelist@zerobeat.net>
Sent: Wednesday, July 13, 2011 6:19 AM
Subject: Re: [Drakelist] TR-4C Bias Adjustment
Richard -
I don't recall a C73 reference.? Possibly C74, which is the
Cathode lead feedthrough?
Rats, I thought we might be on to something. The fact that the
meter reading peak results in
The other Richard I think. C-73 was my blunder from looking at
the TR-4 schematics. Obviously the TR-4C has considerable
differences. I meant to find a point where the collective voltage
drop across the cathode resistors could be measured independandly
of the panel meter. My idea was not to get a precise reading but
only to see if the current there behaved normally, i.e., dipped at
reasonance. The peaking of of the meter when adjusting plate tuning
sure suggests its looking at output not plate current.
Maybe not a bad switch but it could be something in the wiring
there. At any rate an RF amplifier just can't behave the way the
meter says its doing.
I have enountered bad slide switches but not many, it can't be
discounted with something as mysterious as this. It could be
something as simple as a solder butch or something having been
mis-wired in the past.
The idea is to isolate the problem and I think using an
independant meter would help.
There has been a lot of tail-chasing over this problem and I am
afraid I made it worse by making a fundamental mistake, that is
making an assumption, in this case that the two versions of the
TR-4 were mostly similar.
My only excuse is that I am on a medication for the after
effects of Shingles that makes me a little dumber even than usual.
Richard -
Unfortunately, I don't have medication as an excuse! I did have low
blood pressure after rehab this morning, does that count?!? :-)
C74 would be a reasonable place to measure the drop across R45 to
check for a dip coinciding with maximum output. I was trying to set
the BIAS voltage correctly by measuring across the Cathode
resistors, and the resistor's values, 'accurately'. Richard came up
with ~ -50 VDC, which I'm afraid could result in over-dissipation of
the PA, -60 to -65 is more typical for 100 mA.
THIS RF amplifier _MAY_ behave just as described, (max output and
max current coinciding,) with 'some' PA tubes and/or improperly
adjusted neutralization, by oscillating on its own.
Yet another problem is that this transceiver has NEVER worked for
this owner, so a 'golden screwdriver' may yet turn out to be the
problem!!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
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