My Collins 30L-1 -- Part Deux

© Copyright Alexander D. Schapira, 2008-2014, All rights reserved

With 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 previously.
The 30L-1

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.
The replacements

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.
Clip clip

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.
30L-1-II 30L-1-II
Before After

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