Tubes Asylum

Posted by Bambi B (A) on February 28, 2014 at 05:12:37

In Reply to: RE: A bunch of new 6u8 tubes posted by mt10425 on February 26, 2014 at 09:38:57

mt10425,

The ubiquitous 6U8 is a member of a family of related tubes >

6GH8, 6U8, 6BL8, 6EA8

tube....pentode Trans.....power.....triode Trans....power

6GH8......8500 umhos......2.5W......7500 umhos....2.5W
6U8.......7500 umhos......2.5W......5000 umhos....3W
6BL8......5000 umhos......1.5W......6200 umhos....1.7W
6EA8......6400 umhos..... 3.1W..... 8500 umhos... 2.5W

There are a lot of interesting 6U8 family variants, and here are some I bought over the years to help maintain my 450-year supply of 6U8's. Like 6AU6's and some other small tuner tubes, 6U8's seem to last nearly forever,..

6U8/ ECF82

RCA- US- NOS
Tung Sol- NOS
Siemens - NOS
Telefunken ECF82- USED
RCA - blk pl, stirrup gtr- 1960- NOS
RCA- 6678- NOS
Sylvania 6678- "Communications Quality"-gr pl- NOS
Sylvania "GB-1252" Gold Brand- gold pin- NOS

Notice the premium RCA 6678- I suppose that's the military designation, the Sylvania "Communications Quality" 6678 and the Gold Brand, gold-pinned "GB-1252"

Apparently there is some latitude in substitution and Modiaferri, who designed McIntosh tube tuners recommends using the higher output 6GH8A in place of the 6U8 on his designs. I use an Amperex, France 6GH8A in an MR67- very nice. That tube appears to have the identical constuction (heavy twin triangular getter supports) to the Philips 6BL8 / ECF80 /E80CF. The 6BL8 cousin to the 6U8 is a kind of pre-pre audio output tube in McIntosh MR67 and I think the MR71 as well.

6GH8A [6U8]

Amperex - France - NOS
Tungsram -Hungary - NOS
Midland- Japan- NOS
RCA- black plate- US- NOS
GE- US- NOS
Zenith- USED
RCA - 1- Motorola, 1- Zenith

It seems the 6GH8A became an inexpensive TV tube and there are warnings not to use the lower quality 6GH8 that are branded by TV makers.

I don't hear a lot of differences in 6U8 - choices in 6BBL* are more audible, but higher output and stability are probably desirable. Overall, I would suggest Amperex or Tungsram 6GH8A or Sylvania 6678 Communications Quality, but as always, check the numbers for 6GH8 compatibility. I've five NOS but never tried the Sylvania Gold Brand gold pin GB-1252. They might be worth looking into as it was made as a premium version. They're not common but sometimes seen on Ebahh.


Cheers,

Bambi B