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In Reply to: RE: Tube life considerations. tt verses oxide posted by amnesiac on August 07, 2017 at 05:17:49
The article was by and/or about Thorsten Loesch and another designer/scratch builder (forget who).
The jist was that a lowly Sovtek 2a3 sounded remarkably good, though with reduced output/watts.
Think they were using a 5K OT as well (not 2.5K) with the 2a3.
Anyway, I can't locate the article (from 10+ years ago), but perhaps you can as it's food for thought.
Follow Ups:
I have near finished a 2a3 amp. I have to finish the filament supply chassis. I am hoping to stay regulator free but have allowed plenty of chassis space for regulators. I have simmed the supply crcrcl and it looks ok. I only have a fundamental understanding of the duncan ps simulator. I have these lovely Russian rheostats on all 4 supply's making it very universal. The amp can run 2a3 or 300b with 10y driver. I am going to also use 6b4g and 6a3. I have been collecting tubes or years.
I really like 2a3 sound but the upper mid slam of tt I am addicted to But I try to keep an open mind and keep trying different things. I want to start on another 2a3 amp with a c3m pentode driver So I can go back to a simple 2 stage integrated approach. This would be a big saving on tubes.
I have been reading more tonite about oxide filament. below
Reducing the heater
voltage in an oxide cathode tube will conserve oxide material but
this reduces emission capabilities. Fortunately most applications
use far less than the available cathode emission, so heater voltage
reduction will, if properly performed, result in a worthwhile increase
in tube life.
And the
The high peak emission for short pulse operation (defined as
approximately 10-20 µs) is often considered the most significant
advantage of the oxide cathode. Oxide cathodes can provide peak
emission in the range of 1 to 3 A/cm2
for short pulse applications
I find this interesting because to me tt have Superior slam. I guess the high cathode peak omissions isn't the reason why and probably has no audio benefits.
.... heaters.....just make connections short and twisted if need be.
... and if still noisey add a hum pot !
Willie
I was thinking about trying ac on a 45pp but any hum would bother me.
I re simmed my latest dc dual filament supply today. crcrcrl symmetrical r and the l is on both passes on each driver and output.
The driver has one more cr stage it will be very quiet. For the price of the carbon film resisters 15 paralleled up to 1 watt at a cost of about 12 watts of extra power burnt on the driver stage filtering less on the output. It also gives me the flexibility to try just about any driver tube.
What is good is I have the output supply set up so I can pull the 2a3 and put in a 6a3 or 300b with almost no adjustment of the filament supply even though I have adjustment there. I have a switch on the output cathode resisters to adjust the bias also.
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