George -
That is an early R-4C. I have attached the correct schematic for that
S/N range from my CD.
I believe I told you earlier that you cannot turn on the receiver with
the PTO out of circuit. The Zener regulator inside the PTO regulates
against R115, dropping from the +150V bus. With the Zener OUT of
circuit, the voltage across C165 greatly exceeds it's rating. Sometimes
they POP, sometimes they just short and burn up R68.
One of the three PTO leads is connected to a ground lug on the gearbox
just inside where the wires come out. That's ground! The Red wire is
the Supply, and will draw current if any voltage about about 11VDC is
applied to it. The Brown wire is I believe the OUTPUT, but if it is, it
will read infinite ohms to ground because the output is AC coupled.
The symptoms you describe below are the result of no injection signal.
The Preselector is peaking at around 5.5 MHz, which is the IF frequency,
giving you a single frequency receiver at 5.645 MHz. If the PTO is
working you will see 4.955 (500 on dial) - 5.455 (0 on dial) MHz output
at about 2 VRMS. This PTO set to 0 on dial, is mixed in the Premixer
with the 18.1 MHz Band Oscillator (40M Band) to supply 12.645 MHz LO to
the First Mixer. The difference frequency between 12.645 and a 7.0 MHz
Antenna input signal produces the First IF of 5.645 MHz.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
George Roberts wrote:
Dear List,
I've been reading the mail in this site for a long time, with much
appreciation for the knowledge and willingness you guys have to share
it with the folks. This is my first input and question:
No signal after cleaning PTO Drive on Drake R-4C as per instructions
on the K4OAH site. I first cleaned bearing and shaft on preselector.
Cleaned switches and tube sockets and pins. Tested tubes with my
Jackson Dynanic 648S Tube Tester. Had to disconnect 3 wires (red,
brown and white) on PTO to work on drive. Re-connecting PTO wires
to PWB #2, the white went to the pin next to the ground lug, the Brown
to the pin just above the white, and the Red to the right of the
Brown. After putting it all together, I get noise that I can peak
ABNORMALLY with preselector as follows:
_Band Switch_ _Slugs_
1.5-3.0 Can't peak
3.5 6/64"
7.0 1/32"
14 Can't peak, louder with slugs at
bottom
21 Can't peak
28.5 Can't peak
but no signal.
.
Connecting freq counter to INJ jack gives no reading. Connecting to
shielded cable leaving PCB 2 after adjusting disks, reading at 500 is
steady 4994.8 Khz. Reading at 0020 (can not go lower because the slug
is at its outer limit) is an erratic 1395-1540 Khz.
Does any of this make sense? Note: I did not "adjust" any trimmers!
Serial number is 20620 and uses 6HS6 instead of 6EJ7 in premixer and
1st mixer. My schematic shows 6EJ7's.
Wondering if the pinouts are the same?
My test gear consists of a 20 Mhz scope, Precision E200D RF Signal
Generator, Victor VC 3165 frequency counter, a DMM and VTVM. I don't
have much successful experience trouble shooting, so I'm asking the
esteemed panel on this Drake website if there is any hope for my R-4C.
Thanks much and best 73.
George K2HRS
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