Hi Richard -
See below.......
Richard Knoppow wrote:
I just got a TR-4. It has some problems, I have Garey's disc and
have gone over it although there is a lot of stuff there so I may
easily have missed something. The rig came with an AC-4 with the
Heathkit shop mod. I have also tried with the modified AC-4 I use for
my T-4XB to eliminate the power supply as the cause.
Serial number?
1, As received power output was very low, about 60 Watts on 20 and
40m, did not check it on 80. I replaced the tubes with some I had,
probably used, got the level up to about 80 watts on 80 and 40. I have
not yet tried a tune up.
Most likely alignment. Similar power on 40 and 20 usually indicates at
least fair to good tubes. The LOW power is most likely due to weak low
level tube(s). Alignment holds pretty good, UNLESS someone has been
'fixing' on it.
2, Receiving; on 40 meters the RF tune will creat what sounds like
regeneration at some points. There is a definite peak in the signal
and then the ringing. Could this be a bad cap somewhere, is it common?
Dunno. Haven't run into that.
Receiving; on ten meters, all three segments, there is considerable
hum and the frequency is off and drifts. I think three separate
crystals are used, maybe all three are bad but I think is has to be
something else.
Yes, there are three separate crystals, which often drift 20 kHz over 30
years. Highly unlikely that all three are drifty though.
3, Both sides of the meter bounce badly. One of the notes in Garey's
compendium suggests this is due to age but permanent magnets don't
often behave that way unless shocked or subjected to a strong
demagnetizing field. What is going on here?
I HAVE seen this before. I don't _know_ what causes this, but I
suspect there is some sort of 'goop' in or on the bearings to drag it
down. This 'material' either dries out, wears out, or .... It MAY
respond to a large value capacitor (1000 uF ?) across the meter.
When first fired up one of the receiver sidebands was obviously
way off and was affected by wiggling a tube. I opened the bottom and
probed around a little. I found that evidently the IF crystal had
moved enough to touch something and pushing a bit cured this problem.
There could well be other artifacts of shipping despite there being no
apparent damage.
Also affects Carrier centering, suppression, etc.
All of the above problems, except for the low power, may respond
to the usual voodoo of working screws and poking at wires. I will know
more tomorrow.
Good approach
Other observations: The receiver seems to be quite hot and has
very good selectivity as one would expect from 8 pole filters. Audio
quality is very good. The dial takes some getting used to, my eye
keeps drifting off the band in use. Calibration is OK, the PTO is
reasonably linear. I intend to use this rig primarily for SSB so the
lack of a CW filter and means to adjust the tone is of little concern.
Brief transmitting tests into a dummy load and monitoring on the
R-388 indicates the transmitted audio quality is very good. The AGC
works well and allows significant increase in average power without
distortion.
A final note on the MS-4 speaker; I got the MS-4 with the rig.
I've tried with and without the AC-4 installed. I also checked it
using an audio oscillator and compared with an ancient jensen 10"
speaker for a Hammarlund HQ-129-X, which is the best of the speakers I
have at the moment.
It is not any "thinner" sounding than the Hammarlund, which has a
pretty good Jensen speaker in it. It has good voice communication
quality, I am not sure replacing the cone with something else would
really make a desirable difference although a modern high compliance,
low efficiency, speaker would have more low end. Keep in mind that the
rig has very narrow and sharp filters in it so there really is no low
end to be reproduced. The speaker sounds perhaps just a bit better
without the power supply in the box but it also probably has a tube
resonance (tubular enclosure not vacuum tube), I will have to
calculate it.
While one note in Garey's collection states that using a 4 ohm
speaker is critical I think this really should make very little
difference considering the lack of constant impedance of any free-cone
speaker and the nature of the amplifier. In fact, the
Hammarlund/Jensen is an 8 ohm speaker (measured) and is just as loud.
Actually, its louder than some 4 ohm speakers I have both on the Drake
rigs and on the R-388. BTW, while the Collins RX is 4 ohms out also
the Collins speakers are advertised in the old catalogues as being 8
ohms and the parts list shows them to be 6-8 ohms. Its a non-issue.
I don't personally believe that a 4 ohm speaker is 'critical', but since
the impedance the AF OUTPUT tube 'sees' is reflected directly from the
speaker load, the tube is looking at a 4000 ohm load rather than the
design goal 2000 ohm. All that is lost is 'efficiency' of the stage,
(same as a mismatched RF stage,) which typically is not of concern in
home use. I think there is sufficient audio overhead to overcome this
loss in the home situation. The TR-4 audio was marginal for 'mobile'
use, resulting in a retrofitted, transistor AF PREAMP stage. This stage
was included in the TR-4C.
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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