Richard -
I _TOLD_ you it would be something simple that we missed... :-) How many times did we trace
that circuit out?
Yes, IDLE current can be measured in either SIDEBAND as long as the relay is
closed, by keying the PTT.
Start by checking the S-Meter when the audio drops. If it holds steady, then probably in the AF
section. If the S-Meter drops, then the problem is probably in the IF, or elsewhere.
If the S-Meter holds steady, use your screwdriver in the AF OUTPUT area, particularly the small AF
Preamp board nearby, and check all the chassis screws for tightness. If they are tight, loosen a
fraction and retighten. DeoxIT the headphone jack shorting contacts. If that doesn't fix it, then
check surrounding chassis screws. If still there, then go through the entire radio, checking each
chassis screw. If ALL are tight, then look at the leads soldered to the PC boards, especially the
solid wire jumpers for cracked solder.
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,
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" <[email protected]>
To: "Donley" <[email protected]>
Cc: "drakelist" <[email protected]>
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" <[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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