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" <[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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