My Collins 30L-1 -- Part Deux
Alexander D. Schapira, 2008-2014, All rights reserved
thanks to all who provided suggestions,
I am providing this account of
how repaired my 30L-1 after one of the 811A's failed and took some components with it.
I hope this will be of
some interest to other 30L-1 owners.
I have used this 30L-1 for about a year having repaired it and restored
it to operating condition as described
Recently one of the four
811A's developed a grid-to-filament short causing excessive grid current to
cook its associated grid resistor.
This manifested itself first as a burning smell followed by a sparking
sound and a little smoke. On the bench down in the shop the problem was obvious.
One grid resistor was cooked
One of the four 47 ohm grid resistors (R21, R22, R23, R24) was split, obviously resulting from
overheating due to excessive current. I measured the other three grid resistors
and found that two were within spec but the third was a little off.
The four original grid resistors
Although it may not be clear in the picture, it was obvious that
two different brands of
grid resistors were used in this 30L-1 by Collins when it was originally manufactured.
Differences in the size and coloration of the stripes and finish
of the resistor bodies were evident.
I decided to replace all four resistors.
I prepared for the replacement of the resistors by masking the underlying wafer switch
and other components with thin cardboard.
Preparation for surgery
I clipped the leads of the original resistors near to the terminal strip, and removed
the remaining ends. During this desoldering, I used aligator clips as a heat sink on
L3, the inductor which remained connected to the terminal. The four resistor leads
came off the terminal strip easily.
And the four new resistors were installed.
The four new resistors in place
The finished surgery
It seemed a pretty good bet that only the one 811A corresponding to the cooked
resistor has shorted out. So I replaced it with a NOS RCA branded one, the same
type and vintage as the original 811A's.
While I had the 30L-1 on the bench, I gave the relay contacts a cleaning with
a strip of brown paper soaked with DeOxit. Once in place, a thin strip of brown paper
can be pulled back and forth
while exterting slight pressure on the normally open contacts, and with the relay's own spring
tension bewteen the normally closed contacts.
Cleaning the relay contacts
Finally, I cleaned up and retouched the discoloration on the front panel that had been bothering me.
With the repair completed and the new 811A installed the 30L-1 is as good as new
and back on the air!
I hope this account of my work on this 30L-1 was of some interest.
-Al Schapira, W2ADS
Please feel free to contact me at
Page last modified 04/17/2014