JI makes good points as to why an 80/160 only tapped toroid works well and
is simply repeating what others knew in the late 70's and possibly earlier.
Size the toriod properly, dont get carried away with the Q, use the lowest
possible loss wire and locate where it can "breathe" and get a bit of air.
This almost guarantees that somewhat long leads to the switch are used.
In the L section of a PiL the demands on the core are less.
Carl
KM1H
----- Original Message -----
From: "Gary Schafer" <garyschafer@comcast.net>
To: "'Carl'" <km1h@jeremy.mv.com>; "'Larry Benko'" <xxw0qe@comcast.net>
Cc: <amps@contesting.com>
Sent: Thursday, August 05, 2010 10:19 PM
Subject: RE: [Amps] Shorted turns experiment
> Here is W8JI's response about tapped toriod coils: It was over 3 years
> ago,
> I thought it was only a year.
>
> http://lists.contesting.com/archives//html/Amps/2007-03/msg00361.html
>
> This was my original question on the subject and the start of the thread.
> http://lists.contesting.com/archives//html/Amps/2007-03/msg00348.html
>
> Here is another link to a past discussion on tank circuit Q, part of the
> ongoing discussion on my TMC amp's inefficient tank circuit. More toroid
> losses are discussed.
> http://lists.contesting.com/archives//html/Amps/2007-04/msg00155.html
>
> 73
> Gary K4FMX
>
>
>> -----Original Message-----
>> From: Carl [mailto:km1h@jeremy.mv.com]
>> Sent: Thursday, August 05, 2010 8:06 PM
>> To: garyschafer@comcast.net; 'Larry Benko'
>> Cc: amps@contesting.com
>> Subject: Re: [Amps] Shorted turns experiment
>>
>> Gary, Larry, I could especially understand that if the toroid was in the
>> Pi
>> and used/tapped up thru 30 MHz, I wouldnt use one that way either. I
>> tried
>> that decades ago with poor results above about 14 MHz using a 2 Mix.
>>
>> Ive been discussing 160/80 taps in a pi and all band taps or maybe 10/15
>> in
>> an air coil and 20-160 on the toroid in the L section in existing
>> commercial
>> amps that show no apparent difficulty in making good efficiency on any
>> band.
>> If the output isnt drifting there cant be excessive
>> losses/heat.....agreed?
>> Tuning drift is almost always due to the fixed padder caps used on 80/160
>> in
>> my experience....thats where the manufacturers cut corners on cost.
>>
>> An air coil is highly influenced by its surroundings. In any steel cover
>> amp
>> do the cover on and off test on any band. A toroid is much less
>> influenced
>> resulting in a smaller amp volume.
>>
>> If the efficiency at 1500W is 1-2% less in the toroid.....who cares? Just
>> size it so that it stays well within its temperature specs.
>>
>> Carl
>> KM1H
>>
>>
>> ----- Original Message -----
>> From: "Gary Schafer" <garyschafer@comcast.net>
>> To: "'Larry Benko'" <xxw0qe@comcast.net>; "'Carl'" <km1h@jeremy.mv.com>
>> Cc: <amps@contesting.com>; "'Dennis OConnor'" <ad4hk2004@yahoo.com>
>> Sent: Thursday, August 05, 2010 7:56 PM
>> Subject: RE: [Amps] Shorted turns experiment
>>
>>
>> >I have an old TMC (technical materials company) amplifier that uses a
>> pair
>> > of 3-500s that has an auto (preset) tune tank circuit. The tank coil
>> > has
>> a
>> > tapped toroid core in it. I replaced part of that coil with a copper
>> tube
>> > air wound coil and the output power increased by 200-300 watts. Off
>> > hand
>> I
>> > don't remember exactly. The efficiency of the amps was quite low. I
>> > posted
>> > about it on hear around a year or so ago and had discussions about the
>> > tapped core with W8JI as well. He also suggested that it is a bad idea
>> to
>> > short turns on a toroid.
>> >
>> > 73
>> > Gary K4FMX
>> >
>> >> -----Original Message-----
>> >> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
>> On
>> >> Behalf Of Larry Benko
>> >> Sent: Thursday, August 05, 2010 4:41 PM
>> >> To: Carl
>> >> Cc: amps@contesting.com; Dennis OConnor
>> >> Subject: [Amps] Shorted turns experiment
>> >>
>> >> Carl and Denny,
>> >>
>> >> Hope you don't mind me butting in here. I had a private exchange with
>> >> another guy and will post an experiment I did here as it might help.
>> >>
>> >> This following reply was in reference to a particular amp that I was
>> >> mistaken on concerning the output network which had some shorted turns
>> >> in the output inductor which was wound on a powdered iron core:
>> >>
>> >> Shorted turns must not cause enough heat to be a problem since this
>> >> amp
>> >> design has been around and is well respected. As I indicated before
>> the
>> >> "designer" made a decision here given some set of constraints.
>> However,
>> >> shorted turns ANYWHERE that are cut by flux lines will produce a
>> current
>> >> and result in loss. An amplifier designer is in a predicament given
>> the
>> >> fact that band switches are becoming one of the biggest cost items in
>> an
>> >> amp after the tube and the transformer. Some of the bizarre custom
>> >> switches that we saw 40+ years ago will never be seen again unless you
>> >> had switch volumes big enough to get the attention of the switch
>> >> manufacturer so we use what is available.
>> >>
>> >> Just for grins I just did a little experiment. I found a #2 powdered
>> >> iron core which happened to be already wound and center-tapped with
>> >> about #18 wire. I did a quick measurement and the inductance of 1/2
>> the
>> >> winding was ~3uH. I put this winding in parallel with a dummy load
>> >> and
>> >> preceded it with a large "L" network tuner to give the amp a 1:1 SWR.
>> I
>> >> turned up the power until I got some moderate heating. At about 600W
>> on
>> >> 1.8MHz the core temperature rise was about 10 deg. C in 2 minutes.
>> >> Then I let it cool down a and shorted the other half of the coil (it
>> was
>> >> open in the 1st test). The SWR was no longer 1:1 (as expected) so I
>> >> re-touched the tuner and again applied 600W. This time the temperature
>> >> rise was about 22 deg. C in 2 minutes. Clearly the shorted turns
>> caused
>> >> the additional temperature rise. However the 22 deg. C rise is still
>> >> very much within the allowable temperature rise for the core. So one
>> >> person might say the shorted turns are bad and someone else say they
>> are
>> >> acceptable. It is very possible that an amp designer might increase
>> the
>> >> core size a little and live with the shorted turns as the best
>> >> compromise. However if I was designing an amp I would try to avoid
>> this
>> >> scenario unless I did some REAL testing to understand what the effects
>> >> will be.
>> >>
>> >> Good designs are always compromises and if "my" legal limit amp was
>> >> 20W
>> >> more efficient than "your" amp but "your" amp cost $300 less than "my"
>> >> amp you might sell a lot more amps than I would. :) Thanks for the
>> >> discussion.
>> >>
>> >> Just a FYI data point guys and there is no reason to believe that
>> >> another design would have the same relative temperature rise as my
>> >> experiment.
>> >>
>> >> 73,
>> >> Larry, W0QE
>> >>
>> >>
>> >> _______________________________________________
>> >> Amps mailing list
>> >> Amps@contesting.com
>> >> http://lists.contesting.com/mailman/listinfo/amps
>> >
>
>
>
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