Peter Wieck wrote:
On Nov 24, 6:40 pm, Ian Bell wrote:
I see in all my substitution books that the 6CG7/FQ7/GU7 are
functionally equivalent and may be substituted for each other.
*Purely* speculative SWAG here - it is entirely possible (and based on
other similar tubes) that the original model was developed and
patented for a specific use. Other makers wanted "in" on the
substitution market, or created a similar device requiring that sort
of tube. So, several iterations were developed ultimately combined in
the data-base after the 'separate need' went away.
So, so you happen to know if the 6CG7 preceded the 6FQ7?
From what little evidence I have (vintage RCA tube manual & several
substitution/characteristic books by Sams, RCA & Sylvania) yes. But
not by much.
Or, the original tube was refined over the years by different makers -
therefore they assigned different numbers to it.
Yes, quite possible.
On the evolutionary side: A 6GU7 shows a 6FQ7 and a 6EV7 as possible
subs. But *NOT* a 6CG7. 6EV7 reverses to only those two as well. A
6CG7 only goes to 6FQ and 6GU....
So, do you have any experience of the 6FQ7 in audio applications?
Same books list it as a "Medium Mu Dual Triode" for "General Use". I
have never seen these tubes in an audio application, but "general use"
means just that.
Peter Wieck
Melrose Park, PA
I just found a web site called appropriately enough
www.6SN7.com which
has loads of info on this tube. In the history section it states:
"In 1954, RCA came out with the 6CG7, which was pitched as a direct
equivalent of the 6SN7GT. Although audiophiles found that the 6SN7GT
typically sounded better, this was the beginning of the end for
widespread usage of the 6SN7GT. The 6CG7 was unique in having a shield
between the two sections. This was removed as a cost-cutting measure in
the 6FQ7."
It also states that:
"According to Ludwell Sibley's Tube Lore, the 6SN7GT was registered with
the RMA on March 3rd, 1941, with data from RCA and Sylvania. RCA was
likely the developer, since it had assigned a development number of
"A4273B". The immediate predecessor of the 6SN7GT was the 6F8G,
developed by RCA in 1937."
Lots of other interesting stuff about this tube on this site too.
Cheers
Ian