I liked the sound of Amperex Holland labelled "Heirlein" or something like that. Tamed some bright or forward upper mid range problems as voltage stage in a Llano Trinity hybrid amp.
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Sweet/warm 12au7 types in my preamp and as an input tube in one of my power amps are:
RCA/Sylvania/GE USA tubes from the 50's/60's (THIS DOES NOT include RCA "clear top side getter" tubes, which I do not consider to be sweet/warm). I also use 5814a's, same brands/vintages as above.
Never used a Euro 12au7 type that I consider sweet/warm with the exception of a handfull of Mullard 12au7 types (have most common Euro Telefunken/Amperex/Siemens versions).
However, you might go broke trying to find a decent warm/sweet Mullard pair, IMO, as their sound/quality for this particular tube type is all over the map (different versions/vintages/productions).
The good news is that the USA versions I mention are common/cheap.
If your Sylvania's have yellow print, then they might be just the ticket (later versions have green print).
Not knocking the Euro types (just don't find them warm) as I do use them when running a Grado phono cartridge as an offset.
Whatever you do don't waste your money on the mid 80's Mullard military 12au7 versions which have flooded the market (the leanest/meanest 12au7 type that I've experienced).
Dekay- I have the latest Sylvania's (green print)
These came w/the 66 Mag. and the original owner didnt use them as he went with R.T.'s
These Sylvania's are supposed to be the upgraded tube for the magnum vs the non-mag 66.
Although I like Rogue Products,I dont like the tubes they offer.
Mark O. gave me a quad of the Russian NOS 6SN7's he was considering adding to the 99 magnum and wanted my opinion.I felt they were no better,no worse than the NOS Penta Labs tubes that I paid more for when I bought my 99.
He went with the Russians anyway.
The reason I mentioned that I doubted the Sylvania's would not sound too hot is because they go so cheap.Maybe Im a simpleton for thinking that way.
I will give the 'green' Sylvania's a listen this week.
Can you describe the difference sonically between the older and the newer Sylvania's and what the price difference is?
Thanks Dekay,I always like it when you respond to my threads.Happy New Year!
I've never tried the later Sylvania's (Green). I have used Green 6922/6dj8's which were pretty good though (they were specialy screened/selected).
You might ask Rogue about using 5814, 6189 and possibly 5963 tubes. The 5963 tolerates less plate voltage than a 12au7, so it's not a direct sub in all circuits.
I'm also curious about Tungstram Ecc82's, but stopped buying tubes quite some time ago. They used to be listed @ ATSI Tube.
Maybe try a "Rogue 12au7" search @ AA? I prefer to research tubes as they are used in my paricular gear.