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    Building, troubleshooting and testing of these amplifiers should only be
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GU 19 VS GU 19-1 What's the difference ?

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so maybe some of you know is there any difference ?
I simply have a source that can give me GU 19 tubes they dont have the -1 written after the GU 19 are they different from the GU 19-1?
at some pics I see some added caps dishes inside the GU 19 that are not present at GU 19-1 atleast not in the ones I have.
 
ok heres the thing , I just inserted the GU 19 not the GU 19-1 but 19 version and from what I read in the spec sheet that came with the old packaging the cathode current is much bigger , as I now inserted them in the Priboi , I started adjusting the idle current which for them seems to be much higher since with previous settings the 6R3S-1 tube was running at normal , now as I played some music in the background just to make sure signal is going through in one channel the cathode fuse simply blew itself like an explosive , before that I had a 1A rated fuse which simply gave up without any noise before I had the chance to see that then I placed a 3.15A fuse which at first was okay but once the bass cam on in the song it suddenly burst itself into a million tiny pieces of glass with a loud bang.

Can anyone tell me why that happened? is it simply because of overcurrent or is there a problem ?
 
ok in case anyone's interested which doesn't seem the case , I continued to regulate the bias current and the next time i switched the power on the fuse wasn't blowing anymore. and everything was ok, now all tubes work , I wonder what caused the fuse to blow in the first place ?

can there be something that can happen to a tube if it has been stored out of use for decades? visually the tubes were all ok but as I said in one channel at first the fuse blew two times and now it works and I haven't done anything other than set up a higher bias current since it was low at first.
 
Those are the type of tubes that are oscillating when they are still in the box. You need to put 4 to 5k grid stop resistor near the control grid and wire wound 4 ohmers on the plate and screen grid. Also about a 10 ohm 3 to 5W metal oxide resistor cathode to ground is better than the fuse. Grounding one side of the heater is not a bad idea either. I like to use sweep tubes in my amps and these measures keep them tame.
 
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