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" <[email protected]>
Cc: "drakelist" <[email protected]>
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" <[email protected]>
To: "drakelist" <[email protected]>
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"
<[email protected]>
To: "drakelist" <[email protected]>
Sent: Wednesday, July 13, 2011 1:42 PM
Subject: Re: [Drakelist] TR-4C Bias Adjustment
Richard Knoppow wrote:
----- Original Message ----- From: "Garey Barrell"
<[email protected]>
To: "drakelist" <[email protected]>
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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