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Author Topic: Ameritron AL-572's parasitic suppressor values?  (Read 3382 times)
N8CBX
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« on: January 16, 2013, 09:45:22 AM »

I would like to know the component values of the AL-572 parasitic suppressor. I would to scratch build a pair for my pair of 572s
Thanks,
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
N8CBX
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« Reply #1 on: January 16, 2013, 01:55:42 PM »

Here's a picture of it from W8JI's website
http://www.w8ji.com/images/Amplifier/AL811H/AL811H-parasitic-top.jpg
Jan
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Dayton Ohio - The Birthplace of Aviation
WA7PRC
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« Reply #2 on: January 17, 2013, 12:31:15 PM »

All the AL811H parts list says is 100Ω/2W, and the photo shows them to be ±10% tolerance.  The AL572 parts list doesn't dig down to the component level for the parasitic suppressor assemblies.  The resistors need to have very little inductance, which eliminates wirewound and some film resistors. Carbon composition could be used but they don't take heat very well, and there's plenty of that at the tube anode connectors.  One expert prefers Ohmite OY (ceramic composition) resistors. You would look for pn OY101KE. Digi-Key, Mouser, Allied, and Newark all show stock on hand.

vy 73,
Bryan WA7PRC
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N8CBX
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« Reply #3 on: January 19, 2013, 11:26:12 AM »

Ameritron sells the whole suppressor assembly for about $37, so I'm going to do just that.
Thanks Bryan, but why doesn't one buy the "Little Devil" Ohmite type which is an original carbon resistor?
Jan
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Dayton Ohio - The Birthplace of Aviation
K1ZJH
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« Reply #4 on: January 19, 2013, 01:15:30 PM »

Carbons will shift in value. Many resistors in suppressor service have doubled in value. Modern carbon comps are also made differently and have more internal inductance.

Pet
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WA7PRC
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« Reply #5 on: May 17, 2014, 08:22:45 AM »

Ameritron sells the whole suppressor assembly for about $37, so I'm going to do just that.
Thanks Bryan, but why doesn't one buy the "Little Devil" Ohmite type which is an original carbon resistor?
Jan

Carbon composition resistors are no longer produced. As one fellow mentioned, they do drift.  The 47 Ohm / 2W resistors in my SB220 took almost 40 years of almost daily use to drift to nearly 100 Ohms.  However, they still functioned fine. I found New Old Stock Allen-Bradley CC resistors on eBay.

Note that, in the photo provided by W8JI, the suppressor assembly uses capacitors in series with the resistors.  I found a certain ceramic composition resistor to have a lot of inductance (1.6uH), while NOS A-B carbon composition resistors had much less (20nH).  The 3-1/2 turn 14ga inductors in my SB220 measured approx 80nH.
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N8CBX
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« Reply #6 on: May 17, 2014, 10:54:51 AM »

The vintage "Little Devil" Ohmite type are carbon resistors and can still be found in surplus stores. I found a whole bag full of 52 ohm/2w at a surplus store and they worked very well in my home brewed 4 tube, 572b amp.
Why buy new when one can fine them surplus. It just takes some patience & time to find them.
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
WA7PRC
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« Reply #7 on: May 17, 2014, 01:34:32 PM »

The vintage "Little Devil" Ohmite type are carbon resistors and can still be found in surplus stores. I found a whole bag full of 52 ohm/2w at a surplus store and they worked very well in my home brewed 4 tube, 572b amp.
Why buy new when one can fine them surplus. It just takes some patience & time to find them.
Jan N8CBX

Hi Jan,
Whatever floats your boat.  However, there're not many surplus electronic parts stores left in my area (Western WA).  I bought NOS 47 Ohm / 2W Allen-Bradley CC resistors from ebay seller "bigsmythe74" for a reasonable price, and didn't have to drive anywhere.  Wink
vy 73,
Bryan WA7PRC
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N3QE
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« Reply #8 on: May 17, 2014, 01:45:28 PM »

I think this is the "Truly Improved Parasitic Suppressor" about 3/4 of the way down on http://www.w8ji.com/vhf_stability.htm
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WX7G
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« Reply #9 on: May 18, 2014, 06:24:16 AM »

Carbon composition resistors are alive and well in the year 2014. They are even available in surface mount. IRC, Kamaya, KOA, Ohmite, TE Connectivity, Xicon and others manufacture CC resistors. Digikey and Mouser stock leaded CC resistors in 1/4, 1/2 and 1 watt sizes. I have not found a source of currently manufactured 2 watt CC resistors. How to keep them from shifting value too far? Don't overheat them.

http://www.digikey.com/product-search/en?pv174=17&FV=fff40001%2Cfff80482&k=resistor&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

http://www.mouser.com/Search/Refine.aspx?N=254365
« Last Edit: May 18, 2014, 06:28:29 AM by WX7G » Logged
N3QE
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Posts: 2280




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« Reply #10 on: May 18, 2014, 06:52:06 AM »

Carbon composition resistors are alive and well in the year 2014. They are even available in surface mount. IRC, Kamaya, KOA, Ohmite, TE Connectivity, Xicon and others manufacture CC resistors. Digikey and Mouser stock leaded CC resistors in 1/4, 1/2 and 1 watt sizes. I have not found a source of currently manufactured 2 watt CC resistors. How to keep them from shifting value too far? Don't overheat them.

Ohmite OY Ceramic (aka Metal) Composition 2W are superior in every way (well, except in value to audiophiles) to carbon compositions.
« Last Edit: May 18, 2014, 06:56:47 AM by N3QE » Logged
WA7PRC
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« Reply #11 on: May 18, 2014, 10:08:50 AM »

Carbon composition resistors are alive and well in the year 2014. They are even available in surface mount. IRC, Kamaya, KOA, Ohmite, TE Connectivity, Xicon and others manufacture CC resistors. Digikey and Mouser stock leaded CC resistors in 1/4, 1/2 and 1 watt sizes. I have not found a source of currently manufactured 2 watt CC resistors. How to keep them from shifting value too far? Don't overheat them.

http://www.digikey.com/product-search/en?pv174=17&FV=fff40001%2Cfff80482&k=resistor&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

http://www.mouser.com/Search/Refine.aspx?N=254365
I stand corrected. However, I see nothing above 1W. The ebay source I mentioned above has them.

Ohmite OY Ceramic (aka Metal) Composition 2W are superior in every way (well, except in value to audiophiles) to carbon compositions.
See my post #5, above.  Also, Ohmite does not say they're superior in every way.  From their datasheet (http://www.ohmite.com/cat/res_ox_oy.pdf), they state only:

"The OX/OY resistors can often replace
carbon composition resistors
which can be difficult to source."

vy 73,
Bryan WA7PRC
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