G2 voltage spec

What people are working on at the moment
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8882
Joined: Mon May 21, 2007 9:42 pm

#1 G2 voltage spec

Post by Paul Barker »

It’s the only mental block that is niggling away in my head like an earwig.

Right, triode connected gk71 is a non starter if you respect g2 voltage limit.

But I believe comrades here have got the old gk71 T shirt in their bottom drawer. What g2 voltage have you got away with for how many hours total?
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8882
Joined: Mon May 21, 2007 9:42 pm

#2 Re: G2 voltage spec

Post by Paul Barker »

Here is some food for thought. I was checking whether I could use triode connected 6550 in 801a amp for every day. I keep searching for a more moderate alternative but g2 limits are spoiling my fun.

Image

Image

So you will see from the Vade-Mecum data above for 6550 there is a slight conundrum. In case mecum tube data Fig 1 is the nomenclature for triode connection. So we can glean triode connected 6550 is good for 450v b+ RCA data sheet limit g2 to 400v.

So it seems as a triode there is a very small higher g2 voltage tolerance.

But there is a much bigger difference with what people are doing in diy community gk71 and I can’t find provenance for such e reckless ignoring of voltage tolerances inside the envelope during triode operation.
Last edited by Paul Barker on Sun Feb 20, 2022 11:30 am, edited 1 time in total.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#3 Re: G2 voltage spec

Post by Nick »

I wonder what would happen if you just left g2 unconnected?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8882
Joined: Mon May 21, 2007 9:42 pm

#4 Re: G2 voltage spec

Post by Paul Barker »

Probably floats and as it’s widely spaced electrons pass to plate with very few bouncer offers flying around at random. The fig one chart in vade mecum implies that, but the fig one diagram always shows g2 at plate.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8882
Joined: Mon May 21, 2007 9:42 pm

#5 Re: G2 voltage spec

Post by Paul Barker »

I like you’re way of thinking on this matter Nick, we need to experiment.

By the way ref the leakage I was expecting from those Mullard Mustard caps : you were right about that. There was zero leakage unsought if differences in capacitance and esr between the 6 or so I tested. Couldn’t fault them for leakage no current, not a flicker not a twitch. Tested using gerantium low current led and microammeter for good measure. As with all leakage tester the led gives a tiny puff as cap charges then goes out. That’s normal. Importantly it doesn’t come back on.

Makes you wander if a warning led worth adding to a coupling cap scenario though? As I don’t use coupling caps it’s a lame idea. But you know, vintage gear suffers from leaky oil caps and tantalum caps going dead short especially in tek scopes.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#6 Re: G2 voltage spec

Post by Nick »

Makes you wander if a warning led worth adding
I find a glowing valve and exploding cathode cap is normally a good indicator.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8882
Joined: Mon May 21, 2007 9:42 pm

#7 Re: G2 voltage spec

Post by Paul Barker »

These are the things i. trying to avoid, having experienced them. As were talking about high voltages. That potted choke that arced when it was powerd by my 6kvct brick which is about 30kg and ive not used it since. If id not been there house would have burned don before transformer fused. Would have still been powering the burned to a frazzle listening room!

These transformers im considering are more appropriate.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#8 Re: G2 voltage spec

Post by Nick »

Yep, one of the several reasons I don't build stuff with big triodes and high voltages.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8882
Joined: Mon May 21, 2007 9:42 pm

#9 Re: G2 voltage spec

Post by Paul Barker »

maybe g2 at cathode potential with beams at negative voltage?

Or make it class D and inject the audio signal into g2 : kidding!
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8882
Joined: Mon May 21, 2007 9:42 pm

#10 Re: G2 voltage spec

Post by Paul Barker »

I dont think Ill ever use my gm100’s. Just saying!

But there is some mileage in Ongaku sized amps.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#11 Re: G2 voltage spec

Post by Nick »

Paul Barker wrote: Sun Feb 20, 2022 1:32 pm maybe g2 at cathode potential with beams at negative voltage?

Or make it class D and inject the audio signal into g2 : kidding!
I use g2 as the feedback injection point for the d3a front of the reference phone design.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8882
Joined: Mon May 21, 2007 9:42 pm

#12 Re: G2 voltage spec

Post by Paul Barker »

Useful idea. My use of D3a much higher signal level: im already using positive feedback through unbypassed cathode R good for this design. Not much gain loss.

But realise you’re way is innovative and doesn’t have unbypassed cathode resistor compromises.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#13 Re: G2 voltage spec

Post by Nick »

My goal was partial to stabilise the gain when used with a part CCS anode load and pentode operation. Meant I could get a repeatable 40db gain from the front end. Also used a low Cgs MOSFET to provide a low impedance grid drive while allowing a high impedance summing point. First version used a triode instead of the MOSFET. but was too noisy
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8882
Joined: Mon May 21, 2007 9:42 pm

#14 Re: G2 voltage spec

Post by Paul Barker »

Not many phono stages with that much work gone into compared to what you’ve achieved.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#15 Re: G2 voltage spec

Post by Nick »

Interestingly the only valve that I tried that was quiet enough to drive g2 was the EH Gold Pin 6072a, the normal non gold version was 10dB or so nosier.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Post Reply