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KT-88 Red plating question

There is a risk with dwindling supplies that tubes with various problems are sold as "perfect". Matching of
tubes are also depending on high volumes.

The alternative is to but from any of the non sanctioned brands, JJ comes to my mind ( eurotubes make good matching)
 
So, I would guess that I already know the answer to this question, but I made my repair to the input rca jack with the broken wire, I have reinstalled the tubes (red plated one as well) and have reset the bias. The amp is holding the bias just fine with no signs of trouble and sounds fine. My question is do I trust that red plated tube? My tube tester will not test that tube or so I believe (Hickok 533) I have 2 new tubes so if I replaced 1 would I also need to replace the other on that side? I'm thinking instead of doing that I would rather sell these 2 new tubes and use that towards my gold lions or JJ's. Thats why I'm experimenting with just getting it back into operation at the moment. Thanks everyone!
 
Even my wife states that all of the little light up thingies look the same so hopefully that's a good sign ;)
 
ConchBoy66 said:
So, I would guess that I already know the answer to this question, but I made my repair to the input rca jack with the broken wire, I have reinstalled the tubes (red plated one as well) and have reset the bias. The amp is holding the bias just fine with no signs of trouble and sounds fine. My question is do I trust that red plated tube? My tube tester will not test that tube or so I believe (Hickok 533) I have 2 new tubes so if I replaced 1 would I also need to replace the other on that side? I'm thinking instead of doing that I would rather sell these 2 new tubes and use that towards my gold lions or JJ's. Thats why I'm experimenting with just getting it back into operation at the moment. Thanks everyone!
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A tube that has become redplating hot might have been damaged. Damage might not be immediately but there is an enhanced risk of another redplating or flash-over.

To be safe it should be replaced. And if it's a pushpull pair it should be replaced by a tube with similar properties as the other tube, which usually is difficult, thus better to get a matched pair.
 
peterh said:
A tube that has become redplating hot might have been damaged. Damage might not be immediately but there is an enhanced risk of another redplating or flash-over.

To be safe it should be replaced. And if it's a pushpull pair it should be replaced by a tube with similar properties as the other tube, which usually is difficult, thus better to get a matched pair.
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Yes, replace the tube.

Get a matched pair. :thumbsup:
 
I might live a little on the dangerous (or cheap) side but if it wasn't red plate for more than a few seconds and it still tests as reasonably well matched to its friend I'd give it a chance. I'd be right at the switch for a good while until it proves itself though.

I've run tubes that were abused and had it be fine, but sometimes its just not going to work. The ones that get dumb tend to test strange though, usually way too strong. Guessing its caused by grid spacing getting distorted from heat or maybe its gas. Either way they run away quickly.
 
tuberadios69 said:
This is from another post but I confirmed this with my Hickok test data manual for the Models 533A, 600A and 605A.

KT-88 setting:
Filament 6.3
Selectors JR-5347-2
Bias 12
English 92
Gm (expected of new) 7000
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Thanks! I will give that a go in a bit...rebuilding a jet pump on a jet ski at the moment :rolleyes:
 
gadget73 said:
I might live a little on the dangerous (or cheap) side but if it wasn't red plate for more than a few seconds and it still tests as reasonably well matched to its friend I'd give it a chance. I'd be right at the switch for a good while until it proves itself though.

I've run tubes that were abused and had it be fine, but sometimes its just not going to work. The ones that get dumb tend to test strange though, usually way too strong. Guessing its caused by grid spacing getting distorted from heat or maybe its gas. Either way they run away quickly.
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I used to do that. Usually, this catches up to you down the road. Often, it is a very short road.

It's tempting to do when using $$$ vintage glassware. ;)
 
gadget73 said:
The ones that get dumb tend to test strange though, usually way too strong. Guessing its caused by grid spacing getting distorted from heat or maybe its gas. Either way they run away quickly.
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I'm not trying to beat a dead horse here; I'm just trying to understand what's going on. I tested it for shorts first and it passed all 5 and then it tests 7000 on the gm. I did not do any other tests.
Ok, I think I see what gadget means, the "good" tube tests around 6000 (if I let it warm up a bit) on the gm. Both of my new tubes test at 7500 gm.
You said a bad tube may test high and maybe that's what I'm seeing. I think it's time for a new set ;)
 
ConchBoy66 said:
I'm not trying to beat a dead horse here; I'm just trying to understand what's going on. I tested it for shorts first and it passed all 5 and then it tests 7000 on the gm. I did not do any other tests.
Ok, I think I see what gadget means, the "good" tube tests around 6000 (if I let it warm up a bit) on the gm. Both of my new tubes test at 7500 gm.
You said a bad tube may test high and maybe that's what I'm seeing. I think it's time for a new set ;)
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You can't put 100% trust in a tube tester with output tubes.

A tester does not run output tubes under the same electrical conditions as an amp.
 
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