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Old 12-11-2010, 05:14 PM
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Default parasitic choke


anyone have suggestions on making a parasitic choke for a sb220 amp. was thinking either using 68ohm 3w resistor and wrap 3-4 turns around it. metal oxide of course. Or use a couple of 3w 100ohm resistors in parallel and then parallel a small 3 turn coil about 3/8" diameter across these. either one will probably work. just wonder what everyone has used. i also have 100ohm 5 watt resistors metal oxide.


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Old 12-11-2010, 06:06 PM
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I use the Rich Measure type parasitic suppressor

Circuit Improvements for the Heath SB-220 Amplifier

good reading for your 220

Improved Anode Circuit Parasitic Suppression for Modern ...Tubes
Good read on the parasitic suppressors

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Old 12-11-2010, 07:07 PM
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Agreed. Best part is, call Rich up, tell him your tubes, and plate voltages, you'll have a set of suppressors delivered.

BUT, if you are a "ten" meter operator, beware! The Nichrome suppressors at 10 meters will turn a slight orange when you're keyed up.... The nichrome DOES dissipate some power at 10.

--Toll_Free

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Old 12-11-2010, 07:30 PM
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yup, it would be on 11 meter band, so I am sure it would heat up as well.

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Old 12-12-2010, 03:35 PM
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I was reading a few articles and looks like copper and silver are the best conductors. Nichrome is very lossy and best, or using stainless next for a parasitic choke as the have a much lower Q and more lossy. I think I read about 10 times more lossy. How does brass compare. Didn't find a chart and was wondering. Have lots of brass stock and figured would have more loss and maybe use this instead of braid strap as well. Any input would be welcome. Also the articles above were very helpful. Thank you.
.

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Old 12-12-2010, 04:06 PM
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Quote:
Originally Posted by Crusher View Post
I was reading a few articles and looks like copper and silver are the best conductors. Nichrome is very lossy and best, or using stainless next for a parasitic choke as the have a much lower Q and more lossy. I think I read about 10 times more lossy. How does brass compare. Didn't find a chart and was wondering. Have lots of brass stock and figured would have more loss and maybe use this instead of braid strap as well. Any input would be welcome. Also the articles above were very helpful. Thank you.
.
Brass makes a great parasitic choke... Just make sure you look at a 'skin depth gauge' and ensure you're using brass that's thick enough....

I PREFER to make hairpins for my inductors.... I've had better luck with them, you can assemble the resistors to be IN the airflow, AND that helps keep them fresh, so to speak... Look to the Pride DX300 / KW-1 for this type.

--Toll_Free

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Old 12-12-2010, 05:30 PM
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Yeah, i know whatyou are talking about. On my 35B project, i used 2 100ohm 5W resistors in parallel and then did a horseshoe. if i remember correctly end to end about 1.5" and 2" deep.

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Old 12-12-2010, 05:32 PM
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will have to check, but have plenty of 1/4", 1/2", 3/4" and 1" .032 and .064 thick brass stock.

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