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Old 12th Jul 2021, 8:14 pm   #1
ToneArm
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Default What is happening to this GZ34 ?

Hi folks,

I've had a GZ34 from eBay, looks new and tests OK. In my amplifier it starts to make a noise as it comes on load. I'm not sure if it is a mechanical rattle or arcing, but it seems to intensify the longer it is on. I haven't dared go beyond 20 seconds..

The seller has been fine and agreed to refund, but I am curious to know what is happening here..

https://youtu.be/fvoY6q01o08

Thanks
Glyn
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Old 12th Jul 2021, 8:27 pm   #2
Sideband
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Default Re: What is happening to this GZ34 ?

Maybe nothing to worry about....'heater rattle'. I've heard this before with TV timebase valves, notably the larger line output valves like PL36 and boost diodes. We never used to bother about it as 'just one of those things that some valves do'. Don't know the full reasons but it's to do with the AC current flowing through the heater causing it to 'rattle' inside the cathode. Maybe all valves do it to some extent but it's only the ones with larger cathodes and therefore larger heaters where you may hear it. Not all valves of the same type will do it or at least you won't hear it.
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Old 12th Jul 2021, 11:53 pm   #3
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Default Re: What is happening to this GZ34 ?

I had a similar problem with a rectifier for an ancient Decca RP. I bought a replacement from a Czech seller on eBay. It ticked - so did the replacement! Eventually he checked all his stock of these Russian replacements and found the good ones - but we never identified the problem! Very good seller tbf.
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Old 13th Jul 2021, 7:29 am   #4
Robert Gribnau
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Default Re: What is happening to this GZ34 ?

Not a comparable situation because the cathode in a GZ34 is connected to its filament but I had an EZ81 rattle like that when I fed the filament from a seperate transformer. Only after I earthed this filament supply, the rattling stopped.
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Old 13th Jul 2021, 10:50 am   #5
stevehertz
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Default Re: What is happening to this GZ34 ?

I'm afraid this type of thing is a problem with cheap, often poorly constructed foreign valves. Obviously they're not made any more but I try whenever possible to use either new old stock, or good, tested 'old world' 'British' valves be they made in the UK, Holland or wherever these 'heyday' valves were made. You'd think that a rectifier valve would be an easy type to manufacture, but so many times I have heard about cheap GZ34 valves being problematic and the problem easily cured by substitution with a known, good Mullard version.
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Old 13th Jul 2021, 11:04 am   #6
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Default Re: What is happening to this GZ34 ?

In TV's a lot of the Mullard and Mazda etc valves used to sing/rattle like the clappers, especially the efficiency diodes and line output valves as Sideband has already pointed out, they also used to sing/rattle in a series heater chain when the heater circuit below the valves that were connected to the supply was open circuit.

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Old 13th Jul 2021, 10:21 pm   #7
ToneArm
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Default Re: What is happening to this GZ34 ?

Thanks for the information. I've had a couple of rectifiers make occasional gentle ringing sound from time to time in the past. This one sounds quite furious! I guess there may be times when the noise doesn't matter, but not good in an audio amp sadly.
Cheers
Glyn
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