[Collins] Having fun (?) with a 30L1 - long

[Dr. Gerald N. Johnson]

On Wed, 2009-04-01 at 17:23 -0700, Brian Harris wrote:
> After doing some challenging surgery on a 30L1 to replace a missing T/R relay in which the connecting wires had been cut (too short) during its removal (by a previous owner) I went about testing the amplifier yesterday.
> 
> At 3.5 Mc, it worked reasonably well (450 Watts out) but the loading control had to be at 1 (maximum capacitance) to get that power.  I felt had there been a little more loading capacitance I might have been able to get more out of the amp.
> 
> At 7.0 Mc, I got power out of it (650 Watts) but had to set the controls way wrong (Loading at 0 or 10, if you please, and Tuning at 9, which is around the 21 MHz range).  Although puzzled at these settings, I moved on to 14.0 Mc where things turned bad.
> 
> I could get no power out of the amplifier on 20 meters, nor any on 15 or 10.  Figuring I had problems with the output tank on 20 and above, I attempted to check the tank's resonance with a GDO.  The results on 80 and 40 agreed with what I saw when using the amplifier but on 20 and above I could not find a resonant point anywhere.
> 
> Fed up with it, I threw in the towel for the evening and came back to it today with my MFJ-259B.  Fortunately I had another working 30L1 to use for comparison.  The results of this exercise were most interesting (to me at least).  
> 
> In these tests I attached the MFJ259B to the RF output connector and clipped a 3K resistor from the input of the pi network to ground.  On 80 meters the the settings to achieve a 50 Ohm match on both amplifiers were similar (a table is below).  On 40 meters the two amplifiers required entirely different settings, which agreed with what I observed earlier with the GDO and testing the amplifier.
> 
> On 20/15/10 things continued to be very strange.  On the 'bad' amp the tuning control had basically no effect on the output Z.  The loading control, on the other hand, had a lot of effect on the X but not on the R.  I could not get a 50 Ohm match regardless of what I did.  In other words, the tank would not resonate anywhere near where it should.  On the good amp, I was able to get a 50 Ohm match on 20 meters with what I feel are normal settings.  What was/is puzzling is that I could not get a match on 15 or 10 meters with the good amp.      
> 
> Now comes the interesting part.  On the bad amp and the good amp, I found there is a resonance at about 6 Mc when the bandswitch is in the 15 and 10 meter position and on the bad amp there is a similar resonance in the 20 meter position.  
> 
> In the bad amp I expect some contacts on the final bandswitch have been destroyed, which may be a result of the T/R relay that went South.  This brings me to the question, how the heck do you get the front panel off the 30L1 to get to the front side of the final bandswitch?  Note: This is my first experience with the 30L1, thus the question.  Also, should I determine that switch is kaput, does anyone have one available?
> 
> I am open to your thoughts on why I could not find a 50 Ohm match on 15/10 meters with the good amp.  If I find out any more about this mis-behavior I will post it to the list.
> 
> 
> Results Table
> 
>      Bad Amp                   Good Amp
> Band R/X   Loading  Tuning     R/X   Loading  Tuning
> 80m  63/10   1       2.1       50/1     1       3.3
> 40m  49/2    6.4     9.1       50/3     2.6     4.6
> 20m  no correct resonance      50/4     2.2     14
> 15m  no correct resonance      no correct resonance
> 10m  no correct resonance      no correct resonance
> 
> 73,
>  
> Brian Harris
> phone 214-763-5977
> email cosmophone at yahoo.com
> website www.myhamshack.com/wa5uek
> 
Plate load R for four 811A in parallel is much less than 3K. Closer to
1 or 2k. That might help explain why no match on the high bands.

It certainly acts like the bandswitch is not making contact or not
moving. I've not used or been into a 30L1, so I can't help there but the
good manual show give detailed instruction on getting inside. Probably
you start by taking off the case the same as taking off the case of a
32S or 75S, a couple screws under the lid and the feet from the bottom.
Perhaps another screw or two from the bottom of the cabinet.

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