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I've also seen 6U8, 6BL8, and 6GH8 that seem identical

Posted by Bambi B (A) on June 11, 2009 at 08:31:18

In Reply to: 6GH8s labeled 6U8A? posted by Thermionic27609 on June 10, 2009 at 09:05:09:

PHOTOS: Top: The unusual Sylvania Gold Brand "GB-1252", premium gold pin 6U8 and below, the Amperex 6GH8A- indistinguishable from their 6U8 and 6BL8

Thermionic,

When I was retubing a McIntosh MR67 [stereo tube tuner,1965], I read that Modaferri- who designed the tuner section, suggests replacing the 6U8A with a 6GH8A, which has a higher rating:

6GH8, 6U8, 6BL8, 6EA8 ratings

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

Notice in this list of substitutes the 6BL8, which is the tube used as the "pre-preamp" tubes in the MR67. When I bought NOS Philips made Amperex E80CF- the premium 6BL8, they were identical in construction to the original 6BL8's in the MR67. When I decided to try the recommended 6GH8, the NOS Amperex 6GH8's were indistinguishable from the 6BL8's, making the Philips 6U8, 6GH8, and 6BL8 all seem to be the same tube.

As I use 5 6U8's in 3 pieces of gear, and I thought at the time 6U8's and 6GH8's would never be made again, and I eventually overbought:

6U8A/ ECF82 (5) 3, 1, 1 TOTAL: 24

3- RCA- US- NOS
6- Tung Sol- NOS
5- Siemens - NOS
1- Telefunken ECF82- USED
1- RCA - black pl, stirrup gtr- 1960- NOS
1- RCA- 6678- NOS
2- Sylvania 6678- “Communications Quality”-grey pl- NOS
5- Sylvania “GB-1252" Gold Brand- gold pin- NOS

6GH8A [5] 3, 1, 1 TOTAL: 24

4- Amperex - France - NOS
5- Tungsram -Hungary - NOS
1- Midland- Japan- NOS
3- RCA- black plate- US- NOS
3- GE- US- NOS
1- Zenith- USED
1- Unknown- USED
4- RCA - USED?
1- Motorola,
1- Zenith- USED

I bought the Sylvania Gold Brand "GB-1252" (6U8) out of curiosity- gold pins and a special designtaion. By the way, I read in more than one place that the 6GH8 eventually became a cheap TV tube and to avoid buying any that were branded by TV makers'.

Tube types used in tuners seem to be the best value on NOS tubes, I bought a number of NOS Telefunkens for $3-8: 6BE6, 6AB4, 6AV6, 6CS6, and etc. I think tuner tubes must last nearly forever as the MR67 had all but two original tubes.

And premium versions of tuner tubes are not much more costly As you're fussing with tuner retubing, you will probably be considering 6AU6's. My various gear uses 11- 6AU6's making it the third most common tube of the 132 I use. I bought nice old RCA's, a Mullard 10M EF94 for the McIntosh MX110 and the black plate Tung Sols look beautifully made. As you're using Sylvania 6GH8, you might also look around at Sylvania Gold Brand, gold pin 6136 for the 6AU6's. I eventually settled on Raytheon black plate 7543's for the MR67 which is a low noise, low hum 6AU6.

Cheers,

Bambi B

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