"Peter Bent" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Hi Gary
I am happy, but very embarrassed to report that I should have been
talking Hertz not Kilohertz. I just ran a more careful test. After fifteen
minutes the Tr7 increased (went from 3999.0 to 3999.2), 200 Hertz. I am
going to track it for the next half hour and see what the read out is. It
"seemed" to me that the read out this morning, after warm up, shifted more
than in the past. Although the radio was in the morning sun..but I will
check the read out in 30 minutes.
I am still printing out the information that you sent so I can put
it in the TR & file. Thanks for your help... with a red face, N2CME
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Garey Barrell
Sent: Saturday, August 25, 2007 3:10 PM
To: [EMAIL PROTECTED]
Subject: Re: [drakelist] Drift on TR7
Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Peter -
The specification is "total drift is less than 100 Hz after warm up" and
"total frequency change is less than 100 Hz over the 11-16 V-dc input
supply range."
So no, yours is not typical! :-) Basically the TR-7 is about the same
stability as the 4 Line separates, and shouldn't move noticeably after a
5-10 minute warm up period. Some claim the dial lamp causes instability
by supplying heat so close to the PTO, but in my experience all it seems
to do is to speed up the warm up process.
Obviously the +10, +10R and +10T must be stable to begin with. Do NOT
adjust the +10 pot on the small power supply board unless you are
prepared to do a complete alignment.
If yours is moving +/- 1 kHz, there is a problem, most likely with the
PTO. There is a 10V Zener diode inside the PTO can that can cause
problems, along with the FET oscillator device, although the FET is
usually more of a "wandering in small jumps" problem.
Another problem I have seen is with the MC14016 (U1) on the Parent
board, that handles the RIT control, becoming flaky. Again, this usually
presents as dithering in small jumps rather than "drift".
About all you can do is to measure the PTO with a counter and see if
that IS the source, and if it is, look at the RIT DC control voltages in
and out of U1 and see if they are stable or can be correlated with the
drift. The rest of the oscillators are either crystal controlled or
phase locked to a crystal and aside from really strange problems are
either locked and stable or wildly wandering.
Maybe some of the other repair guys on the reflector have some other
ideas!!?
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Peter Bent wrote:
>
> Am a happy new owner of as Drake tr 7. The rig checks out so far, on
> all fronts. There does seem to be some drift in frequency. After it
> warms ups, about 45 minutes, it pretty much stablilizes, but seems to
> wander up and down a bit. About 1khz +/-. I certainly can live with
> this problem. is this typical for the TR7? Any sage advice from
> anyone. thanks.
>
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