Hi Gary -
Ron's unit was locking ok except on the top of 10M...... The regulator
is specified +/- 1V (+/- 4%) so from what you say, a changed regulator
might be in order. The "A" version is +/- 2%.
Your message does bring up a question that I have been pursuing. You
mention the wire loop around the transformer as holding the core
sections together. It doesn't! :-) The wire loop is wrapped around
the lower core half, 90 degrees from where it would be to hold the
sections together. The wire is also stripped and soldered together,
forming a shorted turn. I "think" its purpose is to shunt the external
field from the transformer, much like the copper band around many power
transformers.
The other thing that Ron is seeing is that the unregulated 30V is
considerably lower (~27V) for the first 10 seconds after turn-on, when
it jumps up to 32+. I was wondering if the multivibrator was slow to
start, and your mention of the added resistors and/or caps is interesting.
For the R-7 they gave up entirely, and used a single transistor
oscillator driving a power Audio Amp chip.! Lots simpler....
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Gary Poland wrote:
Ron,
I haven't been following the thread but of the TR-7's that I have
owned or serviced the lowest I have seen the +24 volts and not had an
issue with the PLL locking up on 14 mhz and higher was 23.6 volts.
That's not to say 23.3 vdc is bad, I just haven't yet seen it. The
voltage just needs to be high enough for the VCO to work on higher
frequencies.
The 30 vdc input for the 24 v regulator is derived from the DC
inverter Q2104, Q2105, T2101, and associated parts. Some times the
powdered core halves of T2101 will separate and lower the 30 volts
input. In that case just reposition them and tighten the loop wire
holding them or use hot glue to keep them in place. Some power supply
boards will have 68 ohm resistors soldered across R2129 and R2130.
This may also help to raise the 30 volts from the regulator. I also in
one case I replaced C2117 and C2115 with .033 ufd to get the voltage
up. Like the 68 ohm resistors some boards have those same capacitors
soldered on the backs of the board so I suspect Drake had issues with
the design.
73, Gary W8PU
http://home.roadrunner.com/~w8pu <http://home.roadrunner.com/%7Ew8pu>
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