An interesting follow-up question is why did the r45 viltage not dip?
Curt
KU8L
Garey Barrell wrote:
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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