[Heath] Heath Digest, Vol 89, Issue 3

Tue May 15 22:39:10 EDT 2018

Bill,Electrolytic caps have considerable internal impedance at RF. It is common practice to parallel a 0.1 with a large value electrolytic cap to keep the RF impedance low.  The 30 mfd might be there to help with a aging cap.  However, I would put the small cap back to keep RF on the power supply to a minimum.  That prevents all kinds of problems including instability and feedback.AlWB9UVJ

    On Tuesday, May 15, 2018 11:00 AM, "heath-request at puck.nether.net" <heath-request at puck.nether.net> wrote:

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Today's Topics:

  1. DX40 (Bill)
  2. DX-40 (Mike)
  3. Re: DX40 (Kenneth G. Gordon)
  4. DX-40 (Mike)

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Message: 1
Date: Mon, 14 May 2018 14:43:37 -0400
From: Bill <hony53 at aol.com>
To: Heath at puck.nether.net
Subject: [Heath] DX40
Message-ID: <1635ff710c1-1798-1e45 at webjas-vaa024.srv.aolmail.net>
Content-Type: text/plain; charset="utf-8"

Just acquired a DX 40, not working (of course).

Pretty clean inside, but at least 1 obvious problem, the plate connection at the top of the tube is broken.

The other (possible) problem is capacitor 23-11 (0.1 uf, 600v) has been replaced with a 30uf cp.

Was this a beneficial mod or an error?

Thanks for any help.

Bill, N2KPE
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Message: 2
Date: Mon, 14 May 2018 21:42:10 +0000
From: Mike <MLF42 at Q.com>
To: Heath <Heath at puck.nether.net>
Subject: [Heath] DX-40
Message-ID: <emc9b121f7-1740-40cc-95a7-380ae6155374 at mike-pc>
Content-Type: text/plain; charset="utf-8"; Format="flowed"

Bill...I wouldn't worry about the cap...but fixing the plate cap would 
be a good idea...Depending on when it was last powered up, I'd bring it 
up slow with a variac or a light bulb in series with the AC mains...

Mike AA7WU

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Message: 3
Date: Mon, 14 May 2018 16:20:47 -0700
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: Bill via Heath <heath at puck.nether.net>
Subject: Re: [Heath] DX40
Message-ID: <5AFA19CF.25373.1A5FCFD at kgordon2006.frontier.com>
Content-Type: text/plain; charset=US-ASCII

On 14 May 2018 at 14:43, Bill via Heath wrote:

> 
> Just acquired a DX 40, not working (of course).
> 
> Pretty clean inside, but at least 1 obvious problem, the plate connection at the top of the tube is 
> broken.

Do you mean the top-cap on the tube is broken off? Or just the wire to the plate connector?

If it is the tube, toss it and get another one.

> The other (possible) problem is capacitor 23-11 (0.1 uf, 600v) has been replaced with a 30uf cp.
> 
> Was this a beneficial mod or an error?

Hmmm....my manual does not show capacitor 23-11 in the parts list, nor a capacitor of 0.1 
uF, 600V anywhere. My parts list does show a 2 MF 200 V capacitor part number 23-17. 

Maybe yours was a later factory mod. Where does this appear? If it is in the modulator area, 
it may be the timing capacitor for the controlled carrier modulation system.

If it is, I would think that 30 uF is much too large. There are some enhancements for 
controlled-carrier modulation on an AM site. Perhaps you will find something useful there.

My first transmitter was a DX-35. I have two now, and a pair of DX-40s. If I can help, holler.

Ken W7EKB

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Message: 4
Date: Tue, 15 May 2018 04:14:10 +0000
From: Mike <MLF42 at Q.com>
To: Heath <Heath at puck.nether.net>
Subject: [Heath] DX-40
Message-ID: <em874600c8-01d1-44b8-a35e-d3d6892ebd05 at mike-pc>
Content-Type: text/plain; charset="utf-8"; Format="flowed"

Ken...WRT the DX-40...I think Bill is referring to C-23 in the mic input 
circuit...

Mike

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End of Heath Digest, Vol 89, Issue 3
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