[Collins] 75S-3B audio output tube

[Jaime Gomez]

I have installed a 6AQ5 in the 75S-3B and it is working OK. I had to replace
C60 in the negative voltage supply, it was in fact charging the circuit
badly, the voltage was too low and that caused the 6BF5 to short out.
Thank very much to all who answered my request and gave me very usefull
indications.
Merry Xmas and a very Happy New Year to all,

Jim, HK1N

On Sat, Dec 13, 2008 at 5:03 PM, Robert Jefferis <jefferis at antelecom.net>wrote:

>  Pete,
>
>
>
> That sounds like one of the few practical suggestions I've heard on this
> subject. I think I'll find one of those shields and repeat the surface
> temperature measurement survey I made a while back on a 75S-3. I wonder if
> you have actually made any surface temperature measurements with the shield?
> I'm referring to the tube socket temperature. I found that the 6BF5 socket
> really gets baked over time when compared to the other sockets in the 75S-3.
> I have concluded that from a thermal management standpoint the 6BF5 was a
> real Thanksgiving (gobble gobble) design choice.
>
>
>
> Bob KF6BC
>
>
>  ------------------------------
>
> *From:* collins-bounces at mailman.qth.net [mailto:
> collins-bounces at mailman.qth.net] *On Behalf Of *pete wokoun, sr.
> *Sent:* Saturday, December 13, 2008 1:44 PM
> *To:* collins reflector
> *Subject:* RE: [Collins] 75S-3B audio output tube
>
>
>
>
>
> The best thing you can do for that HOT 6BF5 is to put an IERC 5025B heat
> dissipating tube shield on it.  It makes a BIG difference in its
> temperature.  The next step:  put a lo-noise muffin fan on top of the rcvr
> to pull the heat out.  These fans run at 1800 rpm instead of 3600 and don't
> have that characteristic whine to them.
>
>
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>
>


-- 
Jaime Gomez Rueda
Barranquilla, Colombia
Tel: +57 312 6642680
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