I have a tube pre amp that uses two 12ax7 tubes and two 6350 tubes. I am not real familiar with the 6350. I saw some for sale on line but mostly like Sylvania tubes. What would be a nice tube to replace those with. I was curious if anyone knew.
Tube question
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primosounds
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The 6350 is described as a Medium Mu twin triode for on/off control applications, or, analog computers. There are not many brands of this exact number but there are probably other numbers that are the same type. I am not exactly sure of other types that crossover but one site suggests Sylvania black plates. One tube site suggests that all the common 12au7 , etc, will sub for this tube but i believe that is incorrect since the 6350 has elements arranged as plate/cathode/grid instead of the ubiquitous plate/grid/cathode of most 9 pin mini 2 sections like the 12ax7, et al.
Primo is correct that it has a different pinout so it requires rewiring, just a few pin changes.
I doubt it sounds any different than the ECC82 equivalent or mostly equivalent 12AU7.
The 6350 was designed for digital computer use, not analog, which means the tube must cope with long periods of time spent in cutoff (digital logic is either on or off) and must have a more robust cathode to avoid failure because of the cutoff issue.
Leaving a tube in cutoff, i.e. heater hot but B+ not flowing, causes electrochemistry at the cathode where the cathode's silicon activator reacts with the alkali metals to form orthosilicates, creating an interface layer which ruins the tube. So the computer tubes were designed to active with less silicon. Some silicon was always required, because the alkali metals are pyrophoric in air (burst into flame), so the alkali carbonate was used when the tube was assembled (in air) and the carbonate was then reduced (in vacuum) using the silicon. The silicon also replenishes the alkali surface as the tube ages.
Tektronix used such tubes in the front-end of its oscilloscopes for similar reasons.
I doubt it sounds any different than the ECC82 equivalent or mostly equivalent 12AU7.
The 6350 was designed for digital computer use, not analog, which means the tube must cope with long periods of time spent in cutoff (digital logic is either on or off) and must have a more robust cathode to avoid failure because of the cutoff issue.
Leaving a tube in cutoff, i.e. heater hot but B+ not flowing, causes electrochemistry at the cathode where the cathode's silicon activator reacts with the alkali metals to form orthosilicates, creating an interface layer which ruins the tube. So the computer tubes were designed to active with less silicon. Some silicon was always required, because the alkali metals are pyrophoric in air (burst into flame), so the alkali carbonate was used when the tube was assembled (in air) and the carbonate was then reduced (in vacuum) using the silicon. The silicon also replenishes the alkali surface as the tube ages.
Tektronix used such tubes in the front-end of its oscilloscopes for similar reasons.
Thanks for the great information. So why do you think they went with this tube. It is a VTL 2.5 pre amp. I was just wondering.
As far as I can tell VTL used a mix of tubes like the 12AU7, 12AT7, etc. So no idea why other than a guess. Higher Gm? Cachet? Lower microphonics?
The Gm is over twice that of a 12AU7 or a 12BH7.
My guess is the 12AX7 is the voltage-gain stage for the turntable, and the 6350 is used a current-gain stage. (Grounded grid.)
Current drive is not really important in this application. Not like, say, a phase splitter.
The Gm is over twice that of a 12AU7 or a 12BH7.
My guess is the 12AX7 is the voltage-gain stage for the turntable, and the 6350 is used a current-gain stage. (Grounded grid.)
Current drive is not really important in this application. Not like, say, a phase splitter.
I made a mistake it is 12au7 that it uses. My buddy just sold me some nice old stock mullards to put in it that tested good. I am looking forward to trying them out. I am interested to see how it will help.
