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Question about power tubes... KT88


It looks like one of my KT 88's in my ASL Hurricanes is not working properly. I noticed this when I went to bias the tubes and this one tube came up as 0.0. I changed tubes (V2 for V3) and the "bad tube" read 0.0 in the new socket.
However, it still lights up and the sound is still fine? What's up??
rwd
marakanetz's avatar
marakanetz
5,473 posts
 
no quiescent current flows through the grid that probably had went away from the tube pin. such tube will do nothing and you probably should hear channel volume difference.
smotyka
62 posts
 
Rwd,

I would guess that the pin for the plate is burned out but the heater elements are lighting up. Note that each pin on a tube provides a different function. This tube is most likely not drawing any amperage.

I would recommend getting a reasonably priced tube tester that checks for shorts and transconductance.

Steve
marakanetz's avatar
marakanetz
5,473 posts
 
Steve, I guess in this case it's enough just to check continuity with simple ohmmeter or DMM instead of breaking the bank through a dedicated tube tester.
smotyka
62 posts
 
Point well taken.

However, a decent tube tester can be had for under 200 on Ebay, if someone does some basic research. I picked up a nice unit that has allowed me to check the condition of the tubes in my ARC / BAT equipment. I also discovered a shorted 7308 tube that could have eventually caused a problem in my amp.

The ASL Hurricaine contains a total of 22 tubes (16 KT-88 & 6 6SN7's. I would want a way to check for the condition of these tubes periodically in a reasonable amount of time.

Nice amp, I just heard it over at Holme Audio (Chicago area) hooked to to a pair of Coincident Totals.

Anyhow, just my opinion - love this hobby - the opportunity for new stuff never ends. Sorry if I blabbed too much.

Steve
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