Re: {Collins} 75S-3C Audio Hum



	Congratulations!. Most probably they have heater-cathode leakage.
	With a good tube tester it can be found the best tube for the application.

Regards
Guillermo - LU8EYW/W.

El 11/07/2011 10:30, Paul Christensen escribió:
Thanks for the suggestions, including Fernando's, who got me thinking
more about V8, V11, and the subsequent audio stages.

The problem was V11, the BFO. I went through six 6DC6s before finding
one with no hum. For whatever reason, a GE works best. Several Phillips
and RCA branded tubes produced the most hum. On the GE, I hear a brief
moment of hum at initial warm-up, but then it quickly fades away to zero.

Now, having never owned an S/Line before, I have a rather mundane
question. Anyone have a brief step-by-step instruction set for cabinet
removal? I need to get in and clean some switch contacts, tighten panel
hardware, etc. Maybe I'm missing it, but I see nothing about cabinet
removal in the Collins owner's manual. Tnx!

Paul, W9AC

----- Original Message ----- From: "Charlie T, K3ICH" <pincon@xxxxxxxxx>
To: <collins@xxxxxxxxxxxxx>
Sent: Monday, July 11, 2011 8:39 AM
Subject: Re: {Collins} 75S-3C Audio Hum


Check the PTO tube for a filament to cathode short. I seem to remember
something like this happening occasionally in 51S-1's. The end result is
that a 6.3VAC modulation is injected into the cathode which ultimately
shows up in the AF output..

73' Charlie k3ICH


----- Original Message ----- From: "Fernando ." <huambo@xxxxxxxxx>
To: "Paul Christensen" <w9ac@xxxxxxxx>
Cc: "Collins Collectors Association" <collins@xxxxxxxxxxxxx>
Sent: Monday, July 11, 2011 4:51 AM
Subject: Re: {Collins} 75S-3C Audio Hum


Hi again Paul,

Just something little else I forgot, worth checking: make sure tube V8
(6EA8 most likely) is the right one, and it is good and healthy.
Browsing through old messages in the reflector I came across a 2004
thread describing a similar problem to yours
(http://mailman.listserve.com/pipermail/collins/2004-September/msg00026.html)

and that V8 issue did the trick.

Good luck, and 73,


Fernando
Z21BB
EA4BB



El 11/07/2011, a las 00:20, Paul Christensen escribió:

I've recently acquired a RE 75S-3C and noticed low-level hum on audio
that varies in relation to the AF Control. With the AF Control full
CCW there's no hum at any AF setting. With my Sennheiser headphones
(modern ~ 32-ohm type), I begin to notice hum at about the 10 o'clock
position, although normal audio runs about 9 o'clock. My tests are
performed with the RF Gain full CCW.

My question: Is this a normal hum level for the 75S-3C? Of course,
band noise largely masks the hum. Many tnx in advance!

Paul, W9AC


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NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific
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