Spare rectifier socket pin for neutral AC tie?

JPH118

Silver Supporting Member
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4,751
just tried this technique for the first time (previously used wire nuts or a free terminal strip post), and also happened to notice some arcing inside the GZ34 tube after a few days of testing... i don't believe the two are related, and would bet it was just a bum tube, but figured i'd ask around before i risk another $15.

Also had a loose filament connection on a 6L6 that blew an AC fuse (or so I believe caused it), i'm just trying to rule out one thing at a time... could the open short have stressed the GZ34 enough to cause damage?
 

xtian

Gold Supporting Member
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2,700
In THEORY, you could tie anything you want to an unused (and internally unconnected) tube socket pin. But in practice, don't do it. That's just lazy, confusing, and potentially dangerous. Remember, it's easy to find miswired house power outlets, and then you've got 120vAC on that rectifier pin!
 

trobbins

Member
Messages
382
I also wouldn't connect a non-related part of the circuit to a spare rectifier pin. Similar to PP output stage arcing across pins 2-3, the rectifier can have high PIV between anodes and between anode and heater, which is why rectifier bases often don't include a pin 3, 5, or 7, as over time, pollution and moisture can start some arc tracks across the socket. Some valve bases lose their alignment spigot, making it quite easy to accidentally insert the valve rotated one pin to the left/right.

About the only time a rectifier socket pin is typically used is when adding ss diodes in series with the valve anodes, as a protection against arcing inside the rectifier tube. But even that is risky, and I would not recommend it for the same reason of applying high PIV between two adjacent pins.
 

JPH118

Silver Supporting Member
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4,751
Remember, it's easy to find miswired house power outlets, and then you've got 120vAC on that rectifier pin!

That's a fantastic point! I'll rewire this one later, it does seem a bit precarious to me. I know the wire nuts are kind of looked down upon in the amp world, but i find it funny that they're found inside the wall sockets that said amps are plugged into. Reminds me of the HiFi guys who spend $100 on an AC cable just to go into the wall with it...
 
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pdf64

Member
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8,910
A bit of tagstrip can be mounted with the same fastener as the rectifier socket, and provide a few spare terminals for this sort of use. It also provides a handy chassis grounding eyelet.
 

Tony Bones

Member
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1,212
I would avoid using pin 1 on octal tubes. It was used to connect to the can of metal tubes. I don't know if there were ever any metal rectifiers, and you might think you'll never put any metal tubes in your amp, but it's better to avoid potential trouble.
 

JJman

Member
Messages
994
I was surprised the 1st time I saw an unused pin used like that. I choose to use wire nuts in my amps instead. I use a tie strap to ensure against strain and movement. Never has one come loose.
 

JPH118

Silver Supporting Member
Messages
4,751
i went with a soldered pigtail splice and two layers of heat shrink, plus a couple tiewraps to keep the pair together... feels more secure to me than a wirenut, but i've used them in past builds as well.

as for octal pins, i use the spares on power tubes to connect resistors, as seen on many Fenders, Marshalls, etc. Not as scary to me as AC voltage hitting a rectifier.
 

JPH118

Silver Supporting Member
Messages
4,751
A bit of tagstrip can be mounted with the same fastener as the rectifier socket, and provide a few spare terminals for this sort of use. It also provides a handy chassis grounding eyelet.

I've done exactly that on EL84 builds, with the lack of spare pins available! Felt more like a point-to-point build dealing with 4 of them...
 

zenas

Member
Messages
8,871
Open up an an early octal preamp 6v6 Ampeg Reverberocket sometime. Look at the wires on the 5y3's socket. . . . .
 




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