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Old 26th February 2012, 12:26 PM   #1
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Default 5k plate to plate, el34 triode strapped, 400v b+

one of my el34 got burnt after 6 month of service. I was putting it on an amp that was belong to 6550 Only by minor mod on bias voltage. I always notice the sound of over dissipated plate every time i turned off the amp after listening session. I read on claus brinth 30w pp article that 5k A-A was to tough for el34 triode mode. What would be a better option for me to run el34

1. Lowering the b+ voltage , or
2. Replace iron with higher plate to plate resistances


If opt 1 chosen , please recommend me safe b+ voltage into 5k a-a,
If opt 2 chosen , please share nominal a-a which sounds the best with el34 triode strapped based on your experience.

Thx and regards,

Andry
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Old 26th February 2012, 12:29 PM   #2
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Here's a chart from Mullard:

El34 operating characteristics.jpg
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Old 26th February 2012, 12:40 PM   #3
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Quote:
one of my el34 got burnt after 6 month of service.
How much was the idle current/tube ?
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Old 26th February 2012, 12:43 PM   #4
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Iddle current is 35 mA per tube,

Thanks rntlee for mullard chart,
I'm thinking of 8k, but mullard suggest 10k,
Is there someone with listening impression could share their experince,

Thx,

Andry

Last edited by blue andry; 26th February 2012 at 12:51 PM.
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Old 26th February 2012, 12:57 PM   #5
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The idle power is well below max. rating. I think the tube has been weak from the beginning. (only one damaged ? )

I can not imagine that with such idle power any sort of normal listening can overload the tube that much.
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Old 26th February 2012, 01:08 PM   #6
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Yes only one been burnt, but i can hear cling cling sound every time i turned off the amp.
so i would be better off with either one option before pluggin new tube.

Thanks
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Old 26th February 2012, 01:46 PM   #7
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I've been running triode strapped PP EL-34's at 400V/60ma into 5K ohms for a couple of years without issues. 400V x 60ma =24W, right at the dissipation limit.

Your 35ma bias current at 400V is way under the limit for these tubes.
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Old 26th February 2012, 04:10 PM   #8
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Hi boywonder,
It's nice to hear from u again.
if your amplifier do stable with this operating condition,
Then mine surely had something wrong.
I was very confused of crackling sound every time i turn off the amp.
Is it normal? do grid leak resistor 100k for 6550 should be replace with usual 220k for el34?
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Old 26th February 2012, 05:02 PM   #9
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The crackling sound comes from different expansion coefficients of metal, mica and glass. When the tube is powered on or off there are some slight sudden movements which produce this sound. Tubes with self supporting system like that 211 or 845 without the mica on top wont produce that sound becausse they're clamped to the bulb only at the bottom and can expand in the top direction.
Nothing to worry about.
When you turn your car engine you hear a similar sound.
Aluminum heads on a cast iron engine block work well. So do iron anodes in glass tube.
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Old 26th February 2012, 06:11 PM   #10
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Quote:
Originally Posted by blue andry View Post
Is it normal? do grid leak resistor 100k for 6550 should be replace with usual 220k for el34?
Are you running cathode bias or fixed bias? Sounds like either of those grid leak numbers are reasonable; my amp has 150K grid leaks, and it's fixed bias (Poindexter's 6GK5/EL34 MM).
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