My Collins 30L-1
Alexander D. Schapira, 2007-2014, All rights reserved
thanks to all who provided suggestions,
I am providing this account of
how I got
my newly acquired 30L-1 on the air.
I hope this will be of
some interest to other 30L-1 owners.
I bought this rig from from a fellow who posted it For Sale on the
Collins reflector. I picked it up at his place where he fired it
up into a dummy load to check it out. It seemed to deliver rated
output, so I took it home despite some obvious cosmetic defects.
There were some discolored
patches near the bottom left of the front panel.
Lower left Front Panel
The plastic trim ring was
Even though it had been powered up recently, I wanted to give it a good
cleaning and inspection before putting it in service. It needed
it! I removed the four RCA 811A's, marked each one with which socket it
in, and put them in a safe place before proceeding further.
The line cord had obviously been previously replaced (with an
flat extension cord) .
The "Original" Line Cord
Note the "pre-existing" burned wires.
I replaced the line cord with 7 feet of black #14 3-wire cord.
as an unpleasant surprise that the AC plug did not fit through the
hole on the rear panel. The plug had to be wired up after passing
through the cabinet holes.
The new line cord connections
The fan before cleaning
After the surface cleaning, the switches and pots got some DeOxit, the
some oil, and the relay contacts were treated with brown paper
saturated with DeOxit. Finally, I cleaned the high voltage standoffs
and plate caps.
I then began a close visual inspection which turned up something very
unusual -- one of the filament wires
was never properly soldered!!
Although the socket filament pin had the red glyptol marking, the wire
to it was loose and pulled out cleanly.
Original Filament Wiring -- It Looked
I reflowed the solder joint. I wonder if the rig always ran with only
three 811A's or if the loose
contact was sufficient to power its filament.
Original Filament Wiring Wasn't Okay!
Not seeing anything else
obviously wrong, I wrapped up the 30L-1, brought
it up to the shack,
and connected it to my KWM-2, and Drake MN-2000 tuner.
Since the fellow I bought
it from demo'd it into a dummy load, I felt okay powering it up with
the KWM-2 and tuner. It *seemed* to
deliver about 600 watts into a dummy load okay (according to the meter
Drake), but I observed three disturbing symptoms:
A 30L-1 expert I met on the CCA Sunday net suggested that problem (1)
is well known
to be caused by a grid-to-filament short in one or more of the 811A's.
I found this surprising, to say the least, since if the relay is is
the inactive (unkeyed) state, the received signal should pass through
the 30L-1 un-attenuated.
- When the KWM-2 is RECEIVING and I merely
switched the 30L-1 AC power ON,
the received signals were attenuated
- As above, i.e. RECEIVING and I merely switched
the 30L-1 AC power ON, the
wattmeter in the Drake MN-2000 (following the 30L-1, of course)
about 5 watts output forward
- As above, i.e. RECEIVING and I merely switched
the 30L-1 AC power ON,
meter deflected half scale negative.
My expert also suggested that I ought to re-cap both the HV supply and
bias supply since the caps are over 40 years old. This I will do,
and while I'm in there, I'll also replace the diodes with 1N4007's as
he suggested. He also suggested that the bias supply should
deliver about 170 VDC (not
120 VDC shown on the schematic) and that the
10uF bias filter cap was
under-spec'd at 150 V. He also mentioned a number of other
R's to check for tolerance. Only after the power supplies are
rebuilt can the real cause of the above problems (if they still exist)
seemed to me the EXCESSIVE
POWER SUPPLY RIPPLE (bad filter caps)
could explain everything. Say there was excessive 60Hz or 120Hz
ripple on the 811A plates, and also modulating the bias supply.
The 811A's might
not be cut off completely in RECEIVE mode causing them to deliver some
output, problem (2). This gets into the receiver causing the AGC
lower the gain causing the received signal to be attenuated, problem
(1). The TUNE meter circuit reacts to the spurious signal and
(3). [I also considered that the 811A's might be oscillating, but I
couldn't detect any spurious signal.]
Back down on the workbench,
I pulled the diode board and the
capacitor board, both with original components.
Original Diode Board
Original Capacitor Board
Although the diodes tested okay, I replaced all sixteen of them (CR1 -
CR16) with 1N4007's.
The resistors on the diode board were all well within spec.
Rebuilt Diode Board
I replaced the filter caps (C3, 5, 7, 9, 8, 12) with new 100uF/450V
Rebuilt Capacitor Board
Turning to the bias supply,
Original Bias Supply
I found that R15, the 10K load resistor, read almost 19K. It got
replaced, as did C10, the 10uF/250V cap, with a 20uF/350V cap, and
the diode, with another 1N4007.
Rebuilt Bias Supply
The two ten ohm, 2 watt resistors in
parallel, R17, R18, from the HV
power supply to the plate circuit were out of spec, so I replaced them
Finally, R28, the 39 ohm 1/2 watt
resistor in the Antenna Relay line,
was way out of spec, so I
replaced it with a 39 ohm 1 watt resistor.
repairs solved all three
The 30L-1 is on the air.
As to cosmetics, I am not that
finicky, but I did improve things
considerably. I cleaned the trim ring with AJAX souring powder,
which completely removed the discoloration and left a near original
finish. I carefully scraped off the hardened goo on the front panel,
some of the paint on the high points of the crinkle finish came off
with the goo. Perhaps I will try to retouch it.
-Al Schapira, W2ADS
Please feel free to contact me at
Page last modified 04/17/2014