8pin rectifier?

[super&plexi]

Whilel digging through my stash of rectifiers I ran across this one. There are no discernible Factory markings on the glass and it's just hand scratched   with 5u4g.  I've got another 5u4GB/5as4a ( improved 5u4) but it's just standard basing and 5 pin. Anyone familiar with it. Is it Mismarked possibly?

[kagliostro]

Looking to the soldering on the pin can you argue if the base was swapped ?


Franco

[super&plexi]

Hey good question pins 1 2 4 6 & 8 have wire protruding through them and pins 3 & 7 are filed flat pin 5 is sort of in between I'll see if I can get a better picture off to you

[super&plexi]

Do you think maybe someone custom made it possibly 2 Aid instability. Maybe they help keep it from falling out?

I have two other rectifier questions if you or anyone else wants to take a stab

I'm installing the two protection diodes on my super Reverb and I've seen it done from using unused PS3 or pins 5 or 7. If I remember right There's an issue that's possible using one of the unused pins and a certain rectifier but I can't remember which  pins.   is there one completely safe set of pins to use?

And lastly concerns horizontal placement of rectifier tube. I built a stout in a Crate cabinet similar to ac30 style so the tubes are horizontal and I can't remember is it only certain rectifier tubes that can't be run horizontal or is it in its ultimate rotation / orientation?

[eleventeen]

Check ohms pins 2 <> 8 for the filament. Probably a 5U4GB though I have never seen one with that skinny envelope...the straight-sided ones have been fatter. That dirty = prob from the inside of a TV set.


Google images shows "sylvania 5u4gb" the Sylvania brand in particular appearing to be in that slightly narrower (than RCA or GE) envelope. There are also some "group" pix with a mix of brands and the Syls appear skinnier. That's my vote.


As to your other question, I would prefer not to use the unused rectifier pins for that, for exactly the reason you're concerned about. Perhaps Merlin has a more positive assessment of using the unused tube pins. I would prefer either a small terminal strip or enclosing the series diodes in pieces of good heavy tubing. Not just heat shrink, something more abrasion resistant, would prefer heat shrink around an internal tube maybe made from the jacket of some stripped coax cable.


There is a preferred orientation is you are mounting the tube horizontally, it's in the tube manual. I've never heard of it being a big deal unless you are really thrashing the amp around. I would not do that at all with an indirect rectifier with cathode-around-filament like GZ34 or 5V4. 

[super&plexi]

Do you think maybe someone custom made it possibly 2 Aid instability. Maybe they help keep it from falling out?

I have two other rectifier questions if you or anyone else wants to take a stab

I'm installing the two protection diodes on my super Reverb and I've seen it done from using unused PS3 or pins 5 or 7. If I remember right There's an issue that's possible using one of the unused pins and a certain rectifier but I can't remember which  pins.   is there one completely safe set of pins to use?

And lastly concerns horizontal placement of rectifier tube. I built a stout in a Crate cabinet similar to ac30 style so the tubes are horizontal and I can't remember is it only certain rectifier tubes that can't be run horizontal or is it in its ultimate rotation / orientation?

[Willabe]

Do you think maybe someone custom made it possibly 2 Aid instability. Maybe they help keep it from falling out?

No, I doubt that.

Probably Syl. had those bases laying around and/or just used those because they ran out of the normal 5 pin/4 pin type they had for some 5v rectifiers.

Or they at 1 point used those bases on purpose.   

[sluckey]

The octal socket has 8 pins. No reason to not put 8 pins on the tube base if you want to. Unless you're pinching pennies.

[HotBluePlates]

... Maybe they help keep it from falling out? ...

Probably. Or the all-8-pin bases were ready while the 5-of-8-pin bases weren't.

To me it looks like a Sylvania 5U4. You might check a 5U4 data sheet for typically-unused pins, then check for continuity from an unused pin to any other pin. If no continuity, they're probably just empty unused pins. That would also explain why you don't see a lead poking through the end of the unused pin (they're not "filed" but just solder-filled).