Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on July 18, 2015, 11:46:54 pm
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Hi guys, Doing a tart up on an old aussie amp.
It has a 5Y3 that has the B+ connected to pin2 and I know that in most cases the B+ is connected to pin8.
The amp has had some work done to it, but the solder joint on the socket looks original.
DO I need to change it. Thanks
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The original 5Y3 had a directly heated filament, rather than a cathode, so pin 2 and pin 8 were electrically identical ( other than being at opposite ends of the filament ), and could be used interchangeably for DC out. Modern versions of the 5Y3 are indirectly heated and have the cathode connected to pin 8, so this is the pin which should be used for DC out.
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Thanks Darryl, Now I know the difference between direct and indirect heated valves.
The amp is an old Maton http://el34world.com/Forum/index.php?topic=18905.0 (http://el34world.com/Forum/index.php?topic=18905.0) and as usual there is no info on it and has had some work done on it, so I can't say that it's original.
It has a miniwatt 5Y3GT in it,this also may not be the original valve.
I can only go on the fact that the solder joint on the valve socket DOESN"T look like its been touched.
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While it is true that you "should" use pin 8 on the newer indirect-heat (unipotential cathode) rekyfiers, I can't see that it does any harm to leave it on the other end.
The extra 5V ripple is nothing compared to the 300V ripple we always start with.
The maybe-100mA DC current going through the heater is not a big deal against the 2,000mA of AC already there. I'm not even going to think if it always-adds or sometimes-opposes; just doesn't matter.
And there is much to be said for leaving good original vintage work unmolested.
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Thanks PRR, Unfortunately the amp has already suffered some renovations, so I would rather bring it up to a more modern standard.