by GP49 Tue Dec 06, 2011 12:29 pm
I wrote this for another site in a discussion about the stock Dynaco Stereo 70, about a listener test done years
ago to rank replacements for the out-of-production 7199 tube. Perhaps it would be of interest here. Note that the
target audience wasn't as well-versed in tube amplification as is the typical person here at the Dynaco Tube Audio
forum.
> 7199 tubes are difficult to source, having been discontinued for many
> years. The Russian "7199" that was produced a short time ago was
> not a true 7199; it was apparently a re-pinning of a pentode/triode
> type that was originally designed for some other use rather than
> being optimized for audio. In an audio society listening test
> several years back in the SF Bay Area, substitutes for the 7199 were
> compared using socket adapters to quickly change between them, as the
> 7199 has a unique pinout. The 6AN8A was statistically indiscernible,
> which to some was not a surprise as Dynaco itself used it in the Mark
> III and Mark II. A few listening tests had the 7199 as more
> preferred by one listener, which was not enough to be significant.
> The 7199 was preferred over the 6GH8 by a statistically significant
> margin. Surprisingly the tube that was MOST preferred was a
> "ringer", the 5AN8. Specifications of the 5AN8 are identical to
> those of the 6AN8 but it has a five-volt filament instead of a
> six-volt filament. In the ST-70 the 5AN8 filament is overvoltaged
> and the tube would have a short life; what this indicated to me was
> that the higher emission from overvoltaging the tube's filament was
> making the driver/inverter stage a bit less "overtasked," as some put
> it. One or two people who had converted their ST-70s to
> solid-stage rectification, then took the unused five-volt filament
> source and used it to run a 5AN8; I never heard what
> results they got.