I was looking for the date of first manufacture of the 6CG7 because a guy on Ebay is offering a pair of highly overpriced ($200!) 6CG7 and claims they were made in the 1940s, which I doubt.
In doing so I ran across a website that is new to me, www.fourwater.com which had an interesting article on grid support clips. I always wondered what that C-clip on top of the RCA blackplate 6L6GC was for.
Apparently these were used to combat microphonics by forcing the grid support wires apart so they hold better against the top mica support.
Pretty geeky stuff to be sure, but I tend towards tubegeek-iness!
Anyway, I looked over my RCA 6CG7s, and no C-clips. Then I looked at current EBay offerings and sure enough, there is a pair of RCA 6CG7 with the clips, see pic. These have red printing, and I have not found any with white printing that have the clips. I always wondered which came first, red or white, and it seems to be white. Those pictured are '61, but I have seen red and white lettering mixed in timewise. It puzzles me that the added cost of the C-clips don't show up on the '50s tubes where you might expect them, yet are there on a '61.
Anyone have the history on this? And yes, I do have a life, but a little geekiness can't hurt.
Tube Grid Clips-Antimicrophonic Device
Moderators: pompeiisneaks, Colossal
-
David Root
- Posts: 3540
- Joined: Fri Aug 04, 2006 3:00 pm
- Location: Chilliwack BC
Tube Grid Clips-Antimicrophonic Device
You do not have the required permissions to view the files attached to this post.
Re: Tube Grid Clips-Antimicrophonic Device
Cool article.
Never heard of grid clips before.
Perhaps the vintage long plate 12AX7's could have benefited from them before they all went to short plates.
Never heard of grid clips before.
Perhaps the vintage long plate 12AX7's could have benefited from them before they all went to short plates.
Tom
Don't let that smoke out!
Don't let that smoke out!
-
David Root
- Posts: 3540
- Joined: Fri Aug 04, 2006 3:00 pm
- Location: Chilliwack BC
Re: Tube Grid Clips-Antimicrophonic Device
That's a good point Tom, I didn't think of that. Maybe they did, I never looked!
It's possible that the microphonics problem with the 6CG7 was worse than with the long plate 12AX7, because the 6CG7 plate is 24mm vs. the 12AX7 at 17mm. So they had to do something. Its gain is a lot less than the 12AX7's though.
The other thing they could have done is extra top mica(s). I have seen a few with double top micas.
I have six used '50s RCA 6CG7s and none of them are microphonic, however one has a weak #1 triode that I suppose could have been damaged by microphonics. Can't complain, I only paid $29 for all six.
There was a short plate 6CG7, labeled Amperex USA, but it's a much later tube, I would guess '80s, rather than '50s or 'early '60s.
The consensus appears to be that the best sounding 6CG7s are '50s RCA blackplates and '60s RCA cleartops.
It's possible that the microphonics problem with the 6CG7 was worse than with the long plate 12AX7, because the 6CG7 plate is 24mm vs. the 12AX7 at 17mm. So they had to do something. Its gain is a lot less than the 12AX7's though.
The other thing they could have done is extra top mica(s). I have seen a few with double top micas.
I have six used '50s RCA 6CG7s and none of them are microphonic, however one has a weak #1 triode that I suppose could have been damaged by microphonics. Can't complain, I only paid $29 for all six.
There was a short plate 6CG7, labeled Amperex USA, but it's a much later tube, I would guess '80s, rather than '50s or 'early '60s.
The consensus appears to be that the best sounding 6CG7s are '50s RCA blackplates and '60s RCA cleartops.