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Old 7th September 2009, 05:59 PM   #1
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Default Brimar 6V6G different operating parameters to later GT?

Hello All

I'm accumulating parts for a simple 'boozhound' 6V6 strapped as triode amplifier.

A gentleman valve dealer in the UK has found me some used Brimar 6V6G beam tetrodes to play with initially along with some 6J5G triodes. They look lovely.

I've noticed that the Brimar 6V6G data sheet and Tung Sol 6V6G sheet at

http://tubedata.milbert.com/sheets67.html

are giving the maximum screen voltage as 285, and that becomes the maximum anode voltage in triode mode. This is 30 volts lower than the 6V6GT spec. I've seen on other data sheets.

Should I nobble the HT supply to give 300v or less in the Boozhound circuit allowing for cathode bias?
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Old 7th September 2009, 06:04 PM   #2
Salas is offline Salas  Greece
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Don't bother with NOS since the new russian ''Tungsol'' is excellent compared to any NOS. Just my 2C.
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Old 7th September 2009, 07:03 PM   #3
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Originally Posted by Salas View Post
Don't bother with NOS since the new russian ''Tungsol'' is excellent compared to any NOS. Just my 2C.
I shall bear this in mind, but I have these Old Old Stock valves (aka tubes) now. Does anyone who has used a 6V6G have a view on this?
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Old 8th September 2009, 12:04 PM   #4
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The G and the GT only refer to the shape of the glass envelope, G being the "Coke bottle" shape and GT the straight-sided one. I've looked at various spec sheets on Frank's website and you're right that some sheets give up to 315V as possible in triode-connected use, but I would trust Brimar to know their own valves and use a max of 285V. They actually recommend 250V so I would use that.
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Old 8th September 2009, 05:23 PM   #5
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Originally Posted by barretter View Post
...but I would trust Brimar to know their own valves and use a max of 285V. They actually recommend 250V so I would use that.
Looks like choke input filter then, or CLC with very small first capacitor. I'm using a single winding HT transformer with taps at 240 and 260v and a silicon bridge. Any clever ideas for power supply very welcome!
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Old 8th September 2009, 10:39 PM   #6
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Choke input will give too low a voltage. I think your option is using a small input capacitor to "tune" the voltage. At least that way you will be close to choke input and can use a decent dielectric for the first capacitor.
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Old 9th September 2009, 06:55 PM   #7
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Originally Posted by barretter View Post
Choke input will give too low a voltage. I think your option is using a small input capacitor to "tune" the voltage. At least that way you will be close to choke input and can use a decent dielectric for the first capacitor.
Thanks barretter

Yup, I had thought about using a dummy load drawing roughly 75 to 80mA for simulating a stereo pair, and then starting with choke input and slowly adding capacitance to see how the voltage comes up.

My last area of uncertainty is that I'm using a bridge rectifier as there is only one winding on the HT transformer. I'm assuming the capacitor tuning trick will still work.
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Old 9th September 2009, 07:02 PM   #8
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How you do the rectification is irrelevant. I've started a new thread "Allowable voltages on screens in triode-connected pentodes" which you might find interesting.
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Old 9th September 2009, 07:40 PM   #9
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How you do the rectification is irrelevant. I've started a new thread "Allowable voltages on screens in triode-connected pentodes" which you might find interesting.
Yes, I noticed that thread, and thanks for re-focussing on the underlying issue (screen grid max volt lower than anode max).

I'll be conservative first (250v) and then explore later. I suspect I can get a reasonable range of voltage on load from the transformer I have by using both taps and capacitor tuning.
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