[Amps] Help with HL2200 6 meter conversion

[Gary Myers]

sorry guys - I'm back....

with NOTHING having changed (believe you me - I'm an engineer that believes HEAVILY in WHAT HAS CHANGED?) today the efficiency is quite low compared to yesterday! 

Yesterday I was able to get almost 1300W out at one point - and the efficiency only got better with more drive/output getting up to as high as 65%... today I can only get about 1050W out and the efficiency is just over 50%... of course the metering isn't the issue here (its all relative) so I'm not focusing on the absolute here (65 - is it "real") ... only on the relative change... and WHY did it change?! 

Second - the plate tune is now at about center (it is a 9 - 45pf) as is the load (I believe about a 15 - 145pf). Again nothing physically has changed. 

How does one increase efficiency in an amplifier? The bias zener hasn't changed so it shouldn't be an issue of pushing it more towards Class A. I know losses contribute to a loss in the efficiency - but again nothing has changed (and for that matter I'm using 1/4" copper tubing for the tank - not sure how I can decrease losses there)... 

As a side matter I had said the suppressors were getting hot - I shortened the "U" part of them today (after all the above - just to see what it would do) and nothing changed other than the resistors do indeed appear to be cooler after this change - but no change in the output. 

If I increase the inductance - does that decrease the amount of plate tune needed and will that effect the efficiency? SHOULD the plate tune be a lower value ("ideally") and thus should a change in inductance be necessitated? 

thanks for any feedback.

g.




  ----- Original Message ----- 
  From: Gary Myers 
  To: Amps 
  Sent: Saturday, January 22, 2011 11:31 AM
  Subject: Re: [Amps] Help with HL2200 6 meter conversion


  I believe I'm there. The diameter of the coil was too large I believe (I got it from a second article by K8SMC which specified 1 9/16" diameter)... I made it 1 1/4" and repositioned it slightly. Now I'm able to get about 59% efficiency with 1080W out and only about 45W drive. I've not pushed it further as the suppressors are still getting too hot. I'm going to try shortening the U loop a bit - not sure how to do that but I'll work on it... hopefully that fixes it.... the K8SMC article just used something very similar to the original suppressors - a 10 ohm with 3 turns of #10... I might try using the originals just to see.... can someone tell me what to expect if they aren't working right (beyond the resistor dissipating too much energy)? I assume it will be unstable but not sure how that shows itself. 

  thanks for all your help - also to Richard Solomon who replied privately and who has done the same conversion. 

  Gary
  K9RX

    ----- Original Message ----- 
    From: Gary Myers 
    To: Amps 
    Sent: Saturday, January 22, 2011 8:49 AM
    Subject: Re: [Amps] Help with HL2200 6 meter conversion


    Gerald,

    duh! Of course its I sqrd R! I guess I was thinking that less current would flow through it if the impedance of the U part were similar. Someone else told me they did this same conversion and indeed found the inductance of the U too high - they reduced it - so I'll give that a try. 

    One concern I have is that I didn't follow the layout as they did it.... I placed the plate tune cap (which by the way is not a 100pf max - it is a 9-45pf cap) closer to the tubes using the available mounting point - this meant that the tank coil had to go over the caps. Not sure if that matters or not - I am a bit concerned that if I tune it up with the perforated cover installed I get about 350W out at a pretty bad efficiency.... if I remove that cover (the HV Short on these amps never did work properly - and is not in this case as well) then I get 550W out with about 800W in! So obviously the tank coil is being effected by the proximity of the perforated top. The coil dimensions I used, because its near impossible to wind 1/4" copper on a 1.25" form per the article, was 1 9/16" which makes it closer to the top (as well as the caps).... my question is this: will it effect the tank at all to have this coil closer to the caps? Not sure if the field will effect the caps or not. Can't quite wrap my head around that one. I'm a EE with pretty good field experience (use to do testing for EMI issues on commercial high power products for CE test conformance) but again not sure what happens with the field around this tank coil. 

    g.
        -----