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Old 4th November 2006, 11:43 AM   #1
rossdt is offline rossdt  Italy
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Default Sparks inside GZ34

In my new amplifier I use JJ GZ34 tube but I have
some problems. During the operation I noted sparks inside the tube. Why?
The PSU is very simple.
TA:
Vin=220 V rms;
Vout=450 V rms off-load;
8.7 ohm primary;
120 ohm half-secondary.
The following filter is a CLC filter (C=22 uF, L=20 H, C=33 uF).
Load: I(DC)= 200 mA
The temperature of GZ34 is about 110 - 120 degree.
Could you help me?
Thank you in advance.

Alessandro
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Old 4th November 2006, 01:10 PM   #2
Trout is offline Trout  United States
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Quote:
In my new amplifier I use JJ GZ34 tube but I have some problems. During the operation I noted sparks inside the tube. Why?
I have had that exact problem but ended up setting the tube aside and using a less desireable 5U4.

I did not know if it was just my particular tube, or a circuit issue, But either way, It has not happened since I switch, BTW, the 5U4 I used was a well seasoned ( about worn out) GE.

Trout
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Old 4th November 2006, 01:15 PM   #3
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Could you try a resistor before the first cap or a smaller first cap to see if the problem stays or goes?
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Old 4th November 2006, 02:21 PM   #4
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to see this good website
http://www.jacmusic.com/html/article...w/blueglow.htm

bye
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Old 4th November 2006, 03:47 PM   #5
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don't know if it helps in this case.....

try some resistors on both legs of the transformers secondary, before the rectifier...
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Old 5th November 2006, 03:18 PM   #6
bembel is offline bembel  Europe
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Hi all,
I had the same problem with an EZ81, the first cap was to big (though smaller than datasheet Cmax), in fact electrolytic caps (especially old ones) are rated for -20% tolerance but on the other side +50%. the cap was in fact double its nominal value.I changed the cap and everything went fine.
I suggest that you measure your first cap, hope this helps
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Old 5th November 2006, 07:39 PM   #7
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Quote:
JJ GZ34
Same here. I am not using the JJ's anymore. Instead I use Sovtek 5AR4/GZ34's which do NOT display that behaviour in the SAME circuit. I am very happy with JJ's other tubes...for example KT77...but their GZ34's are not kosher IMO.
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Old 5th November 2006, 10:16 PM   #8
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Quote:
I had the same problem with an EZ81, the first cap was to big (though smaller than datasheet Cmax), in fact electrolytic caps (especially old ones)
Me too, also EZ81s on eico HF81. I replaced the first caps in PS going to 40uf from 30uf and for several hours after cap replacement there were occasional sparks. Also a bad humm/hiss. It wen't away after a few hours and never came back.
The sparking was only minimal at it's worst.
Steve
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Old 5th November 2006, 11:43 PM   #9
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Hi Alessandro ,

Before you replace the tube , try these 2 tips :

1) Between one output tap of power transformer and
the pin 4 of GZ34 , put a wirewound 68 ohms x 5 W
resistor , do exactly the same , between another tap
and the pin 6 , with another 68 ohms x 5 Watts resis-
tor . BE SURE that you are making the output conne-
ction at the pin 8 .

2) Check the first capacitor ( 22 uf ) and the second capa-
citor ( 33 uf ) , if they donít have any kind of leakage to
ground , DO THE SAME WITH THE CHOKE . Using a
ohm meter that can measure at least 20 Megaohms

If one or the two tips above , donít solve the problem ,
replace the tube by another GZ34 , donít use a 5U4 because
the voltage drop , inside the tube will be higher , and the
heater current rating is higher , too .

I hope it helps . Regards ,

Carlos
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