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JJ KT88 tubes glowing bright yellow.

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#21
bottletop said:
Taj, do you know what the score is on using GE Jan 6550a tubes in place of kt88? My gold lions test at Ip:71, Gm:8,300. The JJs test at PC:70, TC8. The 6550a are both different at PC: 49.8, TC: 5.9 and PC:42.6, TC:5.6. The chap at the shop with the tester said the 6550a's test as new but are not matched. So how can 6550a tubes be a direct drop in replacement for KT88 with such different PC and TC ratings? I did have a bad 12au7 tube that had a short on the same channel as the puffed resistor. Heard a buzz/hum through the speaker as well. Perhaps it was that.
Click to expand...

The GLs had their plate current (Ip) and transconductance (Gm) measured at some operating point (voltages/currents applied to the various tube pins). The others were measured with some other system that I'm not familiar with, so I have no idea how to interpret those PC or TC numbers. I suspect PC is also "plate current", but I don't know what TC is (TransConductance using different units?), and we don't know what operating point it was measured at so, it's difficult to really derive meaning from the numbers or compare the GL's to the others.

Yes, that bad 12AU7 may have caused some downstream 'collateral damage''. It depends how bad 'bad' was ,what was shorted, and what the circuit looks like. But I'm no expert there either.

..Todd
 
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#22
bottletop said:
Tom, yes you have described exactly what I am seeing. The grey anode plates are not changing colour at all. It is the part in the top top of the tube that is in the middle of the mica. Do you have any light to throw on the tube values above?
Click to expand...

I don't think you have issues then. Sit back and enjoy the music.

If you post a picture, it would probably eliminate some of the guesswork, though.

I'm not intimately familiar with the KT88, but one indirectly heated tube is not that different from another in terms of basic stuff like heaters, cathode sleeves, etc. Not on an intuitive level anyway. I have some Sovtek 5AR4 rectifier tubes where the heater pokes out and glows bright yellow/orange like you describe. A google image search for "KT88 glow" turns up this: tube glow 2 | Flickr - Photo Sharing!. Does that look like what you're seeing?

~Tom
 
#23
Yes the JJ's look like that, if anything not as red through the holes. I have spent about 1/2 an hour now trying to upload a couple of images by going advanced. No joy as yet but i will get there. The GL tubes I have glow less on the top than on the tubes in the link you have sent.
 
#24
After you "Go Advanced", use the paperclip icon to the right of the font selector and happyface icon, which opens the attachment window. Browse to your image and select it, then click the upload button and close that little window and ...

..Todd
 

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#29
If youv'e got a tube behaving like in pic.....electron beam is concentrated on one side..it's a gonner. Came out of an inverted Fender amp and due to vibrations the cathode slipped in the mica causing misalignment. Manufacturer should have known better.

richy
 

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#31
Richy, none of my tubes look like than thank goodness. The one I had was a 12au7, the short caused the anode to start to glow very quickly. The glow and sudden buzz was not a good experience for my amp.
Tom, Glad you liked the Phonograph, my friend and my Wife's boss has a Jack Russell so there is potential.
 
#33
Seems to listening somewhat intensely. Must be enjoying the music! Just to say a big thank you to all who have helped with my amp problem and my questions. Greatly appreciated. A friend in the states is looking for a simple phono stage schematic that uses two 12ax7 tubes and P2P wiring throughout. He has got the tubes a transformer in great condition, a set of tube sockets and a chassis. Can anyone point me in the right direction? Anyone interested in a pair of 1978 GE Jan 6550a tubes that are not a matched pair, (matching numbers and correct boxes etc)?
 
#35
Thank you I will email him this. I am sure it will go down well. It just shows you to keep as much stuff as you can as it might come in handy. I had a bunch of 12at7 tubes; some GE & Mullard as well that I eBayed a couple of months ago. Hows the dog?
 
#39
I've busy all day with one thing and another. Not been a bad day. New Old LP? NOL instead of NOS. What spinner are you using? Wish I had my Father's dynatron still. I have had this confirmed but I am somewhat hesitant on this. MY amp is a single ended triode using one kt88 per outpur. self/auto biasing. Is it ok for me to use unmatched output tubes on this for sure?
 
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#40
Finding a Sweet, Original LP that's 40 yrs. Old is always Fun...I spin them on a gutted Garrard A.T.60 with a DIY Arm...They're played through a 6DJ8 Phono Pre-Amp with the Circuit that I posted, and a Modified ST70...
 

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