Re: {Collins} Very strange problem discovered during LAB alignmentonKWM-2 RE



Take a look at the mechanical filter itself. It could be an internal issue.

-----Original Message-----
From: kc9cdt@xxxxxxx [mailto:kc9cdt@xxxxxxx] 
Sent: Thursday, July 07, 2011 9:12 PM
To: wcarns@xxxxxxxxxxxxx; david.hallam@xxxxxxxxxxx; jsternmd@xxxxxxx
Cc: collins@xxxxxxxxxxxxx
Subject: Re: {Collins} Very strange problem discovered during LAB
alignmentonKWM-2 RE

This problem is vibration sensitive...and only efffects the 455 KC IF.....so
something in that area has a problem....
I was hoping for something specific as far as help in that circuit. 
This is a tough one...nothing I prodded, pulled, moved, or idividually
banged lightly on effected it...only chassis vibration of moderate amounts.

I'l off right now to the workshop to have a fresh look at it.
73,
Lee



-----Original Message-----
From: Bill Carns <wcarns@xxxxxxxxxxxxx>
To: david.hallam <david.hallam@xxxxxxxxxxx>; 'Jerry O. Stern' 
<jsternmd@xxxxxxx>
Cc: collins <collins@xxxxxxxxxxxxx>
Sent: Thu, Jul 7, 2011 7:20 pm
Subject: Re: {Collins} Very strange problem discovered during LAB
alignmentonKWM-2 RE


No, in this case, the problem is the noise generated by the ballast and 
the
plasma that is struck in the tube. It has a very large bandwidth and 
the RF
components radiate into the probe. That is why the problem goes away 
when
the probe is terminated with a low impedance like a dummy load. You just
have to keep the probe away from the light (noise source) when in use.


Bill Carns, N7OTQ
K0CXX, Trustee MRCCC
President Collins Collectors Association
Editor, Signal Magazine
Founding Member # AC94-0009
512 618 2762 (Cell + VM)
512 847 7010 (Home + Fax)



-----Original Message-----
From: David C. Hallam [mailto:david.hallam@xxxxxxxxxxx]
Sent: Thursday, July 07, 2011 5:01 PM
To: Jerry O. Stern
Cc: collins@xxxxxxxxxxxxx
Subject: Re: {Collins} Very strange problem discovered during LAB
alignmentonKWM-2 RE

Would that indicate that there is some wavelength of radiation from the
fluorescent lights that affects the polystyrene nose piece on the 
probe?
Do you always have the probe grounded when working on the low scale?
That would seem to be the only difference when you are using the T.

David
KW4DH

On 7/7/2011 10:49 AM, Jerry O. Stern wrote:
> Is it only with light exposed diodes?  I found WILD VARIABILITY of 
the
> RF voltage probe in both of my HP 410's (one tube one SS) when
> measuring on the lowest scale (0 - 0.5 VAC) if I have any fluorescent
> workbench lamp too close (even a few feet).  I have see these lamps
> kick the probe up to half scale on this low range.  I have several
> probes, standard and heavy militarized and happens on all.  Only
> exception is when I plug them into the T connector between the RF out
> and dummy load.  Many moons ago when I first saw this, HP410 expert 
Ashley
(KISS) said that's to be expected.
>
> 73 Jerry
> K1JOS
>
>
> -----Original Message-----
> From: k7fm [mailto:k7fm@xxxxxxxxxxxx]
> Sent: Thursday, July 07, 2011 8:44 AM
> To: collins@xxxxxxxxxxxxx
> Subject: Re: {Collins} Very strange problem discovered during LAB
> alignmentonKWM-2 RE
>
> If you are talking about the carrier level, be aware that clear 
diodes
> such as the 1N34 are sensitive to light and exposure to light will
> change the null.  For this reason, final null should be done with 
them
> covered as they would be in operation.
>
> I suspect this was the reason that early computer which used many
> diodes, covered them with a phenolic case.
>
> 73,  Colin K7FM
>
>
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--
Before I came here I was confused about this subject.  Having listened 
to
your lecture I am still confused. But on a higher level.
Enrico Fermi

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SHARE THE FUN: JOIN THE COLLINS COLLECTORS ASSOCIATION TODAY !
http://www.collinsradio.org/membership/

 NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific
  SUNDAYS: 14.263 MHz-2000 UTC  +  AM Net: 29.050 MHz-1200 Central
  1st Wednesday AM Net 3.880 MHz-2000 local (ET, CT, MT, PT)

The Collins Reflector reserves the right to refuse access to anyone.

LIST HELP?  ADMIN EMAIL:  collins-owner@xxxxxxxxxxxxx
This ONLY goes to the list admins and does not post to the group!



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