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Russian EL-84's

That is correct this time around. But, I also used two quads of the USSR (not Russian - which would mean current production) in my Mahi monoblock amps and preferred them to the stock tubes (JJ, EH, whatever Manley supplied). However, the Mahi never played well with my speakers, which was too bad. They and my current amp are both rated at 20wpc triode and the Cary sounds great.

Thain - per Dennis Had, the EL84 is a current driver for the 12BZ7 inverter and serves no other purpose. The EL84 is direct coupled to the 12BZ7.
 
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Rocket 88 is a low-gain amp per Dennis Had. Relies on the preamp and sounds great with the TU-8500. Dennis goes into some detail in the description of the design in the manual, which is a free download when googled.
 
I dug up the manual for it. The EL84 is actually the current source for the 6922, which appears to be working as an LTP inverter. Basically the tube stands in for the tail resistor or a solid state CCS device.
 
Too bad Cary/Dennis Had will not share schematics of their older gear. Then we could all look at the details.

The Cary Rocket 88/808 was originally designed with EL84/6922. Towards the end-of-production they switched to EL84/12BZ7. Mine went back to Cary for new caps just before I bought it and they updated it to 12BZ7. As a tube roller, I wish they had left well-enough alone. Not many 12BZ7s out there to roll.
 
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IIRC the life span of tubes get greatly expanded when they are run below their ratings and if their filaments heat up slowly, in other words use a NTC on the primary of your transformers so the filaments do not light up like a flash bulb when you switch the amp on (or use current limited DC for the filaments). There is one firm that is selling "preferred 7189" which are tested and then relabelled 6P14P-EV's. Prices for the 6P14P and variants have crept up over the past few years. Attached the original Russian documentation, although I cannot read Russian the numbers and columns speak for themselves. All the Russian tubes have Pa of 14 watt so in the 6BQ5 / EL84 circuits they run below their ratings and therefor should have a reasonable life expectancy. Due to more variation in the quality of modern production I only use cathode biasing which "future proofs" the amp against "tube rolling" ((I've also have a set of EH 6BQ5). Also for when I am no longer here and no longer am the owener and know what the design exactly is. Cathode biasing also helps with extending life of the tube, FWIW I design and build my amplifiers with a minimum 50 000 hour life expectancy, only the very best of parts will do. I do check the specifications for electrolytics capacitors carefully and select those with the highest temperature ratings with the longest lifespan.

The zipped file compares them all, inclusive the EL84 (6BQ5).
 

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