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 Post subject: Sylvania 5U4GB Question
PostPosted: Thu Jul 23, 2015 9:22 pm 
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Mark I
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Picked up a quad of old Sylvania 5U4GB from eBay and received them today.

They look to be in great shape and were all tested prior to selling.

My question is about the number of pins. I have only seen 4 & 5 pin 5U4's and one of these has all 8 pins like a power tube. I assume its no big deal but want to know for sure before I put it in my Triple Rectifier.

Did a quick search on Google but can't find much information regarding this 8 pin version. It looks identical to the others but all 4 of them have different markings on the bases. They all have the "5U4GB" stamp on the glass and seem to have the same construction.

The three 5 pin tubes have a halo getter but the 8 pin tube has a rectangular or "D" shaped getter.

Any info would be helpful, Thanks.

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PostPosted: Thu Jul 23, 2015 11:32 pm 
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Bottle Rocket

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Most of the NOS octal rectifier tubes I have seen only had 4 pins on the base. The manufacturers probably saved a few pennies by not adding metal pins that didn't connect to anything. That is not to say some of them could have come out of the factory with all 8 pins in the base.
There is a quick and dirty check you can do with a VOM multimeter. If you have a VOM multimeter set it to resistance (ohms) and see if you have any reading between pins 2 and 8. If you do and the tube shape is correct and there is a 5U4 marking on the tube, then chances are good that it is a 5U4. Pins 2 and 8 connect to the tube heater and you should have a few ohms of resistance between 2 and 8. If you check resistance from pin 2 or from pin 8 to any of the other pins (except pins 2 or 8) it should read open (no resistance reading). Pins 4 and 6 connect to the rectifier plates and you should not get any resistance reading from pins 4 and 6 to anything else either. If you have any doubts don't plug that tube in the rectifier socket. Post a picture of the tube if you can.


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PostPosted: Fri Jul 24, 2015 7:23 am 
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Mark I
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Fred2202 wrote:
Most of the NOS octal rectifier tubes I have seen only had 4 pins on the base. The manufacturers probably saved a few pennies by not adding metal pins that didn't connect to anything. That is not to say some of them could have come out of the factory with all 8 pins in the base.
There is a quick and dirty check you can do with a VOM multimeter. If you have a VOM multimeter set it to resistance (ohms) and see if you have any reading between pins 2 and 8. If you do and the tube shape is correct and there is a 5U4 marking on the tube, then chances are good that it is a 5U4. Pins 2 and 8 connect to the tube heater and you should have a few ohms of resistance between 2 and 8. If you check resistance from pin 2 or from pin 8 to any of the other pins (except pins 2 or 8) it should read open (no resistance reading). Pins 4 and 6 connect to the rectifier plates and you should not get any resistance reading from pins 4 and 6 to anything else either. If you have any doubts don't plug that tube in the rectifier socket. Post a picture of the tube if you can.


Yeah, I was going to post a picture of it but it seems that you have to do it through a URL instead of uploading directly to the forum. I'll try this evening.

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