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In Reply to: RE: 6883B plate dissipation IS 35 watts, not 20 posted by Steve O on April 10, 2015 at 15:54:52
There is a link on the Mastero amp, which sports a pair of 6146 tubes that makes 90 watts a side (circa 1952).The Acrosound To-350 schematic uses a pair of 6146's for 100 watts a channel.
This tube can provide some clean high wattage.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Edits: 04/10/15Follow Ups:
I'm quite familiar with the "Maestro": it was part of the Sarser & Sprinkle trilogy of amps beginning with the "Musician's Amplifier", the U.S. version of the original Williamson and ending with the Maestro. They were featured in the "Audio Anthology" series published by Audio Engineering (Audio mag).
You'll note that the operating point chosen for the Maestro's finals is firmly within the ICAS region of operating conditions @ 750V on the anodes and ~ 22W dissipation (25W is max under the "absolute" rating system). Also note that the reader was not informed of this detail nor was there any discussion of the potential consequences this operating point might have on finals life. Thei primary objectives were to achieve higher power than the "Musician's Amplifier Senior" more efficiently and in a more compact package.
It's also interesting to look at RCA's use of the 6146 in audio apps. One relatively common product was the MI-12182 power amp. This one ran the 6146 finals at ~ 570V and 28 mA (16W) and 210 reg V on g2 for short term output of 70W or 35W continuous. Clearly RCA chose to stay within CCS ratings for their commercial offerings. Legend has it that even under these relatively conservative operating conditions there were reliability issues such that conversion to 6550s was a common mod not unlike what happened to the Ampeg SVT, another 6146 amp.
The bottom line here from my perspective is that tubes are extraordinarily forgiving wrt how they're used but with tradeoffs. The tube manuals had operating points for EL34, 6550 and 8417 where 100W could be obtained if one wished to push ratings to the limit. Most commercial products avoided the extremes to gain reliability. In this case the tradeoff is probably power vs life. If you have a large stock of finals, the possibly shorter life may be a good trade for the resulting power and compact packaging. You be the judge.
Thanks, Steve. Some good insight provided.
The purpose of this project was to come up with an amp that would provide between 75 to 90 watts that had excellent sonic character, used quality tubes that don't break the bank and are readily available, and good reliability. Also was looking for a slightly different variation from the 1625 amp sound.
The choice of the 6883B was made because the "B" version is the most rugged version of the 6146 family, and it's 12 volts. The 12 volt tubes are generally less to purchase, draw only half the current of the 6 volt types, and in this case, plentiful, as it was used in FM gear extensively.
The amps succeed on all counts. I got tired of shoddy performance and questionable longevity from the current production Chinese/Russian 6500/KT88 types (not to mention cost).
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
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