[Collins] 30L-1 Problem

[Dr. Gerald N. Johnson]

On Sun, 2006-06-25 at 12:01 -0400, Ken Plesser wrote:
> 
> 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?
> 
Could be that difference is within the turns ratio tolerance of the
transformer maker.

Could be the meter resistors have drifted that much.
>  
> 
> 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)

Could be one tube isn't contributing to the output, each should be
drawing 150 ma to make the 600 ma total.
> 
> Advancing mic gain beyond 3 o'clock causes no additional plate current.

One tube out or weak tubes would tend to saturate.
> 
> DC input power to 30L-1: 1750 x 0.43 = 752 watts (should be 960 watts)

Down right at one quarter.
> 
> RF output power from 30L-1: 380 watts
> 
> Efficiency: 380/752 = 50%

If it wasn't for the feed through power of a grounded grid PA it would
have close to 50% efficiency so long as it stayed linear.
> 
> 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?
> 
Could be. Could be just one ill tube, part could be drift in the
metering resistors at DC.

Could be an open parasitic suppressor at a plate, but that could be
really hard on the grid of that tube with RF drive and no plate voltage.

Could be an open filament on one tube taking it out of the circuit.
>  
> 
> Any hints or suggestions will be appreciated.
> 
> 
> 
> Thanks and 73.
> 
> 
> 
> Ken, W3ESH
> 
> Gilbert, SC

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer