[Collins] 75S-3 Tubes

[Tony Sokol]

Hi Mike,
    In addition to Tom's reply, it should be noted that 6U8's are
notorious for causing a multitude of problems due to grid to cathode
shorts that sometimes does not show up on a tester.  Swapping in this case
is the only answer.  One of the biggest problems they cause is that of AC
hum which leaves people scratching their heads once all of the filter caps
have checked good.  I have had three bad ones in the last two years!
    That being said, I would go with the 6EA8 if you need to make a
choice.  You may also need to realign due to slightly different inter
electrode capacitance's but you will probably do that anyway.  Of course
if the original chassis is screened for 6U8's and everything is working
fine, you probably don't want to fix it.  :-)  Also note that you really
only want to replace the weak ones before you realign.  Replacing all of
the tubes at once can lead to headaches and is really not a good idea nor
is it necessary.  Some tubes are prone to short life spans while others
will probably outlive both of us put together.


Tony - W9JXN
"Mike, K8LH" wrote:

> First, thank you Gentlemen all, for your help getting me started with
> this S-Line restoration...  I have all manuals except for the 75S-3/A,
> but, I have a schematic...  Now I can start testing caps, resistors,
> tubes, voltages, etc...
>
> Question -- my 75S-3 has 6U8A tubes but they're not on the 75S-3
> schematic...  Are the 6U8A tubes in my 75S-3 compatible with the 6EA8
> tubes on the schematic???
>
> Thanks, Mike- K8LH (Westland, MI)...
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