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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