low volt high current

[Andy Le Blanc]

I've been fiddling with numbers running a SE 6v6 at low plate voltages.
The issue Ive found is that, eventually, if you bring the valve up to max plate dissipation,
the current figure exceeds the only max current figure I can find for the cathode.

The only rating I can find is a peak figure for a vertical deflection amp, 115 ma..

I remember a posting on the forum with absolute max figures...

What is the cathode of a 6v6 rated to handle for current?

Interesting question, completely the opposite convention apposed to the anode rating in watts.

[martin manning]

I see a 105mA figure on the '55 GE data sheet for peak, 35mA is listed as max, that's continuous, I assume.

[Andy Le Blanc]

so far I'm seeing 35-45 ma. consistently, but there are a few out there 47-50ma.
all depends on application, new gc and gca types have the higher rating.
the highest marks are associated with Triode A1

[jjman]

I've idled 6v6's at up to 47ma under various conditions. A friend's old Ampeg was running 51ma before I overhauled it. My SFVC was running 51ma before re-biasing.

Never thought about this spec. Not sure if it is a concern. Max plate voltage is spec'd at 350 after all while many amps were designed to run them over 400 and actually run them over 420.

[Andy Le Blanc]

I found some absolute max cathode ma figures on svetlana sheets

el84... 90ma, 6l6...120ma, kt88...235ma, but no figure on 6v6 yet

but the 35-45 design max seems to fit if the rating is in the ballpark of el84

[Andy Le Blanc]

After more digging, it begins to look like the real constraints to low plate voltage is the current handling ability of the OPT.
The other topic that has jumped out is a correlation between the current in the OPT and the bandwidth of the amplifier, less current gives a better fidelity.
I seen many repeated statements about how a higher plate voltage has advantages, but its current in the opt, higher anode V really means less I.
a 20w plate dissipation @ 400v is 50ma, but @ 100v it's 200ma.,... it really ups the practical cost of the opt, you can do it,
but the same 5w of raging power cost 5x as much just to handle the current to get it at the lower voltage

I can't wait to hear what the design limitation of low plate voltage sounds like in a guitar amp.

[Firestorm]

I can't wait to hear what the design limitation of low plate voltage sounds like in a guitar amp.

Me too. I think where this leads is high voltage preamps and low voltage PAs. I don't think that's been done: backwards of conventional design.