[Amps] More on Toroidal Tank Circuit Issues

Wed Mar 26 00:36:08 EDT 2014

So here is the real fix!

I removed the 80 and 160 meter toroids all together. Installed a 2" dia X 
3.5" long ceramic coil with 42 turns of #14 wire and hooked it to the end of 
the 40 meter coil. The new coil is perpendicular to the 20-40 meter coil.

Works perfectly!  No more 10 meter heating! And on 80 meters, with lots of 
keydown at 1600 watts out, the coil gets to about 125 degrees F, and on 160 
a little less. But I normally don’t run RTTY on 160 meters. As of yet, all 
RTTY contests are on 80-10.

The best bet will be to find a ceramic coil or just the coil-form that I can 
wind with #12 or #10 wire. 10 is probably a bit too big. I guess I could 
wind 80 meters with #10 and 160 meters with #12. I really want to stay with 
a ceramic coil-form to keep it from deforming like a air-dux coil would.

I know Carl has a ceramic form on the auction site but it too is wound with 
#14 wire.

Anyone have a 2" (and it must not be more than 2-1/4" X 5 or 6 inch long 
ceramic coil-form with grooves for winding? It has to have at least 36 
grooves for 36 turns of wire.

This has been an interesting experiment to say the least!

Thanks all
73
Jim W7RY

-----Original Message----- 
From: Jim W7RY
Sent: Saturday, March 22, 2014 1:25 PM
To: Dan Hearn
Cc: AMPS
Subject: Re: [Amps] More on Toroidal Tank Circuit Issues

So I used the measurement technique from Tom W8JI that he has on his site 
and found that the 160 meter toroid was certainly resonate on 10 meters! No 
matter what I did. Sure, I could move my hand around the toroid and get the 
the lamp to dim and sometimes go out. But there didn’t seem to be any place 
moving the windings that would help.
http://www.w8ji.com/rf_plate_choke.htm

So..... I made a center tap on the 160 meter toroid and simply shorted it to 
one end with a normally closed vacuum relay. I open the relay only on 160 
meters.

See here:
http://s900.photobucket.com/user/w7ry/media/8877%20Amplifier/IMG_0250_zps17bca129.jpg.html?sort=3&o=0

Seems to work just great. No arcing or sparking. As you can see, the leads 
are pretty long and the relay is just taped to the Plexiglas. I used the 
bench power supply to energize the relay on 160. There was no interaction 
with anything. Even had the lid off when testing 160 meters.

The toroid seems to run perfectly cool (about a 10 degree temperature rise 
on 10 meters measuring with my Fluke IR thermometer) when operating on all 
bands. Tuning seemed better and more power output with less drive and lower 
plate current for the same output power (1600 watts) on 10 meters just like 
removing the toroid all together.

I'm going to move the 160 meter toroid back to where it was, and move it 
further from the load vacuum cap. If I had it to do over again, I would have 
mounted the caps closer to the outside walls to give me more room to work 
between them.

I’ll also have to wire up the relay to energize on 160 meters. Rather than 
tie into the tuned input switching, I’ll just put another switch contact 
between the front panel and the sub panel.

73
Jim W7RY

From: Dan Hearn
Sent: Friday, March 21, 2014 5:47 PM
To: Jim W7RY
Cc: AMPS
Subject: Re: [Amps] More on Toroidal Tank Circuit Issues

Jim, I would try a small air wound coil similar to what you would use in a 
parasitic suppressor in series with the toroid, maybe in the lead to the 
switch.

Dan, N5AR

On Fri, Mar 21, 2014 at 4:46 PM, Jim W7RY <w7ry at centurytel.net> wrote:

  Both leads are shored by the band switch when on 10 meters guys. 
Interesting that 3 of you came up with the same possibility...

  Not sure where to put the capacitor if both leads are shorted together. 
Perhaps I could center tap the toroid (bare the Teflon wire) and solder a 
cap from the center tap to one of the output leads.

  I removed the toroid and the major heat in the 3 turns of wire is where 
the winding is within 1/4 inch of the vacuum loading cap. Which is probably 
to close.
  See: 
http://s900.photobucket.com/user/w7ry/media/8877%20Amplifier/P1010217.jpg.html?sort=3&o=16

  I was simply going to move it away from the loading cap and see what 
happens. I was also thinking of install a wire coil. I have a ceramic coil 
form that would work. 30 turns, 2”dia 3.5” long which is 20uH. I have room 
to mount this.

  Thanks all!
  73
  Jim W7RY

  From: Dan Hearn
  Sent: Friday, March 21, 2014 3:02 PM
  To: Jim W7RY
  Cc: AMPS
  Subject: Re: [Amps] More on Toroidal Tank Circuit Issues

  Jim, I think your 160 toroid when shorted is self resonant with its 
distributed capacitance on 10m.  You might be able to solve this by putting 
a small cap across the 160 m toroid to move its self resonance.

  73, Dan, N5AR

  On Fri, Mar 21, 2014 at 1:08 PM, Jim W7RY <w7ry at centurytel.net> wrote:

    I may have to eat some crow here about using dedicated toroids on 160 
and 80 meters...

    I built an 8877 amplifier based on the K8RA (SK) 3CX1500D7 amplifier. 
http://www.k8ra.com/index_049.htm

    Mine is shown here: 
http://s900.photobucket.com/user/w7ry/media/8877%20Amplifier/DSC_0037.jpg.html?sort=3&o=47

    And here: 
http://s900.photobucket.com/user/w7ry/media/8877%20Amplifier/P1010225.jpg.html?sort=3&o=13

    The lower toroid is 160 only and the upper one is 80 meters only (with 
10,15,20 and 40 coils added in of course).

    I’m using a shorting band switch 6 position.

    On 10 meters, the 160 meter toroid (lower one) gets so hot, the 
fiberglass tape has turned brown, and the Teflon wire is melting the 
Plexiglas that the toroid's are mounted on.

    I know all about trying to use a tapped toroid for multiple bands is 
wrong (except on the L coil of the Pi-L circuit, and see my postings about 
the Commander HF-2500 and K1TTT’s pictures of same) but WHY is the 160 meter 
toroid getting so hot when using 10 meters?  It's mounted very close to the 
loading vacuum capacitor is the only thing that I can think of. But the 
weird part, is that this just started. During all of the testing, there was 
no problem, but now, its really getting HOT!

    When testing, I had the top cover off of the amplifier, now that I’m 
using it, the top cover is on. I’m going to try the test again with the top 
off and see what happens.

    On 80 and 160 meters, the toroids are normal temperature (around 100 
degrees) and everything works just fine since I’m not shorting turns on the 
toroids.

    Ideas?
    Thanks and 73
    Jim W7RY
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  -- 
  Dan Hearn
  N5AR

-- 
Dan Hearn
N5AR
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