Steve -
OK. Well that's more likely to be a Zener or cap problem. Perhaps bad solder.
The brown mica caps are just NP0 mica's. They are still being made and available. The TC caps,
(the white, tubular ones,) are no longer made, and unfortunately the color codes are not
consistent. Some tubulars used in some PTOs don't appear to be TC caps, but it's possible that they
are. You can still get ceramic N750, N1500, etc., caps, they look just like regular disc ceramics,
and of course are also still available in NP0 as well. They are fairly rugged, although the 'tube'
is glass, and can be broken. If your troubleshooting points to one of those, I would suggest
photographing it in place, (some are hanging in air!,) so you can attempt to replace it in the right
place. The PTOs were originally set up by several 'Grandmothers' who would sit and talk about their
Grandchildren or bridge club while 'doing their voo-doo' on them. No one seems to know just what
they did, but like most RF stuff there was probably a bit of 'magic' involved.
I haven't had to work on many, most were bad Zeners, and a couple with bad FETs (bipolar in the
"A"), and some bad solder. If you remove the cover _Carefully_ and are careful to not disturb any
of the physical components, again, some of which stick up in the air?, I have yet to destroy one!.
I have been keeping my eyes open for a defective one that I could experiment with to try and
determine just how they were done, but so far no luck. I don't want to tear up a good one, as they
say, 'they ain't making them like that any more'.! :-)
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Steve Wedge wrote:
The frequency jumps when stopped and gets worse when it's fully warmed up.
Re the "dog-bone" caps: can these be replaced by silver mica units? Or do they have a temperature
coefficient that's different?
I would still love to get a working PTO to swap in so I can not fear wrecking
this one.
Thanks, all, for your help. I'll probably rip it apart again shortly.
Steve Wedge, W1ES/4
To be is to do - Socrates
To do is to be - Plato
Do be do be do. - Sinatra
All my computers have my signature with various pearls of wisdom appended
thereto.
Date: Tue, 05 Jul 2011 12:30:58 -0400
From: Garey Barrell <k4...@mindspring.com>
To: drakelist@zerobeat.net
Subject: Re: [Drakelist] R-4A PTO, Round 1
Message-ID: <4e133c42.6030...@mindspring.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Paul brings up a good point. Does the frequency jump when tuning, or even when
stopped?
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