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Re: [Amps] 2 Section Tune Cap Wanted

To: "Carl" <>, "MU 4CX250B" <>
Subject: Re: [Amps] 2 Section Tune Cap Wanted
From: "Jim W7RY" <>
Reply-to: Jim W7RY <>
Date: Tue, 24 Jun 2014 06:36:04 -0700
List-post: <">>
Here is the info from OE.

Internal part number:  73-2-75-56

Complete part number:  73-315-65-2K5-B-N38S1A0N1A184

Description: M73, two sections, at max simultaneously; front section 22pF min to 315pF max, rear section 10pF min to 65pF max. 0.075 inch air gap rated at 2.5kVrms. Nonmagnetic construction; stainless steel shaft 1.5 inches long; mounting feet; narrow strap contact rated at 2 amps; 7.25 inches long (not including 0.66 long feet, or shaft).

Jim W7RY

-----Original Message----- From: Carl
Sent: Tuesday, June 24, 2014 6:21 AM
To: MU 4CX250B
Cc: Jim W7RY ;
Subject: Re: [Amps] 2 Section Tune Cap Wanted

Jim, even Ameritron uses the middle version for Tune! That should tell you


----- Original Message ----- From: "MU 4CX250B" <>
To: "Carl" <>
Cc: "Jim W7RY" <>; <>
Sent: Tuesday, June 24, 2014 8:50 AM
Subject: Re: [Amps] 2 Section Tune Cap Wanted

I agree, Carl, those values don't sound quite right. They were marked
in pencil on the back of the cap, but I don't know how they got there.
I'll do an accurate measurement today and update the values.

The cap came out of a 3-tube 230CA. It has the inexpensive wiper, but
so far as I know that was never a problem. I'm going by memory, but I
believe the same wiper was used on the L4B tune cap. As Jim noted,
it's probably best to upgrade the wiper for the load cap.
Jim w8zr

Sent from my iPhone

On Jun 24, 2014, at 4:00 AM, Carl <> wrote:

As with all OEP 73 series caps there are 3 different current handling versions; the cheapest is not the best and the highest isnt necessary.

I have the original Alpha built by Cardwell 154-10-53 cap here, as used in the Model 86 and all other Alpha dual 3CX800 amps, never used and last one left. Sections are 7-60pf and 15-210 pf (200 on the schematics) It has three heavy duty wipers as shown in the manual. Dimensions are the same as the OEP mentioned and I dont see how they came up with those values as I sold the OEP version thru Radiokit back then and it was the values I quoted for the Cardwell.


Thanks Jim!

I emailed them and they answered right back!

They are $129.00 each in lots of 1 for the "75". 4 week delivery.
That will fit the bill exactly!

I've had several ARD230 amps, but only the ones with 2 tubes.

Thanks for the tip!
Jim W7RY

-----Original Message----- From: Jim Garland
Sent: Saturday, June 21, 2014 12:23 PM
To: 'Jim W7RY'
Subject: RE: [Amps] 2 Section Tune Cap Wanted

Hi Jim,
Here's info on an OEP dual section capacitor that is fairly close to your
requirements: p/n 73-2-75-56BE, 2-sections, 17-65 pF and 25-318 pF, with
.075" spacing, nominal rating of 2500V. This is the cap that was used in the
ARD 230CA amplifier, which ran three 3CX800A7 tubes and covered 160m-10m.
You can easily swap plates between the two sections to obtain different
capacitance ranges, so long as the total number of plates remains fixed at 56. The cap measures 2.5in x 2.5 in x 7.25 in, not counting the shaft. the "75" in the part number refers to the .075" plate spacing, and if you change
that to, .e.g., 80, it would widen the spacing to .080"  (and of course
change the dimensions). Other spacings are available in the same series.
Jim W8ZR

-----Original Message-----
From: Amps [] On Behalf Of Jim W7RY
Sent: Saturday, June 21, 2014 11:33 AM
Subject: [Amps] 2 Section Tune Cap Wanted

Now that I have found some 3CX800s and sockets (thanks to the list)!

I'm looking for a 2 section air variable tuning capacitor like in the
Alpha amplifiers.

1 section around 50 pF and the other section 250 to 275pF. I'd even take a
2 capacitors as
long as I can hook them end to end (larger cap in the front) as seen here:
Only problem with this is the assembly gets a bit long... So the dual
section would be best.

I quickly looked on the Oren Elliott page but I don't see any pictures or
values. If someone
has a part number, I could get one from them.

Thanks and 73!
Jim W7RY
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