[Collins] 30L-1 Problem

[Ken Plesser]

Perhaps someone can help me with two 30L-1 problems (they may be related)

 

Problem #1 facts:

Input voltage: 241 VAC (4.8% over 230 VAC nominal)

Plate voltage (no load): 1920 VDC (6.7% over 1800 VDC nominal)

Plate voltage (full load):1750 VDC (9.4% over 1600 VDC nominal)

No reports of hum on my signal.

Question: Why is the plate voltage so much higher than can be attributed to high input voltage?

 

Problem #2 facts:

RF drive from 32S-3: 82 watts CW on 14.2 mHz

Plate current of 30L-1: 430 ma (should be 600 ma)

Advancing mic gain beyond 3 o'clock causes no additional plate current.

DC input power to 30L-1: 1750 x 0.43 = 752 watts (should be 960 watts)

RF output power from 30L-1: 380 watts

Efficiency: 380/752 = 50%

RF drive and output power measurements (into a 1:1 SWR dummy load) the same on both 312B-4 and Palstar wattmeter.

Question: Why such low plate current (hence low input/output power) and low efficiency?

 

Could it be as simple as the 811s are going "soft," hence I can't draw enough plate current, hence the plate voltage rises?  Or is something more subtle taking place?

 

Any hints or suggestions will be appreciated.



Thanks and 73.



Ken, W3ESH

Gilbert, SC