>
>
>----------
>From: Rich Measures[SMTP:measures@vc.net]
>Sent: Monday, December 08, 1997 12:13 PM
>To: km1h @ juno.com; Peter Chadwick; amps@contesting.com
>Subject: Re: [AMPS] parasitic suppressors
>
>>
>>On Mon, 8 Dec 1997 14:48:20 -0000 Peter Chadwick
>><Peter.Chadwick@gpsemi.com> writes:
>>>Rich has said on a number of occasions, and, I believe, without
>>>contradiction, that it is well worthwhile measuring the value of
>>>parasitic suppressor resistors after a flashover. My question is:-
>>>
>>>Do the values change because of long term over heating, which would
>>>possibly show up in surface colour change?
>>
>>OVERHEATING would show an external change Peter and it would not take a
>>long time to be evident. A 2W carbon will discolor the paint in short
>>order even at 2x overload for 10 minutes or so.
>>You can run the tests for yourself at DC.
>
>Agreed.
>>
>>>One source of discoloration, never mentioned by Rich, is the coil tightly
>>>wound around the resistor. IMO, in poor or marginal suppressor designs
>>>the coil is the primary heat source.
>
>>When #16 -gauge copper buswire carries 15 continuous amperes, it feels
>>barely warm to the touch.
>
>With 15 amps @ 28 MHz #16 gets blistering hot in short order.
- Does it seem likely that Rich would put his finger on a #16 gauge
wire carrying15a at 28MHz? I was talking about 15A DC. Where would the
average guy see 15A of 28MHz current in a VHF suppressor? In a 3-500Z
amplifier, with a 3000V supply, the AC anode potential is about 1800Vrms.
The capacitive reactance between the anode and ground is roughly1090
ohms at 29MHz. The current through Rs-Ls is therefore 1600v/1090 ohms =
1.47A-rms. The current through Ls is probably about 1A. Does it make
sense that this amount of current would generate enough heat in 16-ga
wire to toast Rs?
>Even #12
>gets hot. That's why we use 3/16" to 5/32" tubing at 28 MHz.
>
> It's a sure bet that Rich would not mention
>this is a possible heat source.
With copper conductor material, Rich would not mention that this is a
possible heat source in the suppressor of a typical 1500w amplifier --
because it isn't.
>>The above would usually show a gradual increase in R.
>>
>This seems unlikely considering the apparent lack of heat.
Indeed.
>...snip...
Rich...
R. L. Measures, 805-386-3734, AG6K
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