2359glenn | studio
Nov 26, 2019 at 12:11 AM Post #34,411 of 39,920
Having fun combing through the eBay bargain bins for ugly little black metal tubes in the 6C5 and 6J5 families. Some of them are rusty or the black paint is flaking off here and there. If you buy them in small lots the cost usually is less than $2-3 each shipped.

As bad as these tubes look, that's how good they sound. I would not be surprised if I end up liking these better than their straight glass and Shoulder Type glass counterparts.

Here is an example of an unrestored Sylvania 6J5 tube. It must be quite old because it has the flashing S symbol on a green oak leaf.


Not sure how to date it - S I probably doesn't mean Staten Island, NYC since I don't think they had a factory there. Some tubes used the word O-P-U-S to designate the quarter of the year. S would then mean the 4th quarter.
"I" could mean 1951 - not sure of these assumptions.
On the other hand there are clearly the letters DL printed on the tube. Cannot find any chart that has those letters - maybe this tube came from DL's (Decent Levi) collection, but how did it end up in Council Bluffs, IA, where the seller resides?
You have to give credit to these tubes - they do not need too much packing material - the lot of six tubes was shipped together in a plastic sandwich bag packed inside a thin breakfast crackers box with some newspaper wrap.
BTW, the seller states that he has 20,000 tubes sitting in a locker - only a few are listed so far.
Another adventurous tube rolling day .....

Interestingly, "6J5 S1" stamped in the base corresponds to an RCA date code indicating January, 1957. And even more interesting, "DL" in the Sylvania two-letter system indicates November, 1957. So sometime in 1957, but we can't be any more precise. And I wonder... do your ears tell you this is an RCA? Or a Sylvania?
 
Nov 26, 2019 at 5:02 AM Post #34,412 of 39,920
Finally got rid of those annoying XLR inputs, switched them out for some very nice RCA jacks today. I replaced the entire back panel, IEC inlet, cut new holes for the mutlivolt switch, RCA jacks, along with new tapped screw holes for the filament rectifier (was happy to redo this since I made a cosmetic mistake last time). Overall, a great success! Not a dramatic change in sound obviously, but it looks nice and I don't have to use XLR to RCA adapters! :sunglasses:



Great work Keenan :)
 
Nov 26, 2019 at 5:10 AM Post #34,413 of 39,920
I have just discovered this fellow and thought that I would leave this hear for those interested in this sort of stuff.
Listening with GOTL 6080 Bendix/ECC33/ZMF Atticus

91YVuFVcLzL._SL1500_.jpg

 
Nov 26, 2019 at 11:53 AM Post #34,414 of 39,920
Interestingly, "6J5 S1" stamped in the base corresponds to an RCA date code indicating January, 1957. And even more interesting, "DL" in the Sylvania two-letter system indicates November, 1957. So sometime in 1957, but we can't be any more precise. And I wonder... do your ears tell you this is an RCA? Or a Sylvania?
Hi gibosi,
Did not think of cross checking if this is a relabeled RCA tube for two reasons: Based on my readings, I was under the impression that the metal tubes were fazed out in the late 40's since the glass tubes were cheaper to manufacture.
Secondly, the green oak leaf Sylvania logo appears on older tubes and it is my impression that they did not use it in the mid 50's but I may be wrong regarding that.
In the same lot were two Tung Sol tubes with a date code of 5652 which would indicate December 1956. One of them has a code 3Y stamped in the base edge and the other Y3; the latter codes possibly indicating either month in a two month period.
So here is my conspiracy theory: These tubes are older production, and labeled/relabeled by the date of sale. But maybe not....and mid 50's production? The stamped letters SI look different than the stamped letters 6J5 on the Syl/RCA tube.
 
Nov 26, 2019 at 12:33 PM Post #34,415 of 39,920
Hi gibosi,
Did not think of cross checking if this is a relabeled RCA tube for two reasons: Based on my readings, I was under the impression that the metal tubes were fazed out in the late 40's since the glass tubes were cheaper to manufacture.
Secondly, the green oak leaf Sylvania logo appears on older tubes and it is my impression that they did not use it in the mid 50's but I may be wrong regarding that.
In the same lot were two Tung Sol tubes with a date code of 5652 which would indicate December 1956. One of them has a code 3Y stamped in the base edge and the other Y3; the latter codes possibly indicating either month in a two month period.
So here is my conspiracy theory: These tubes are older production, and labeled/relabeled by the date of sale. But maybe not....and mid 50's production? The stamped letters SI look different than the stamped letters 6J5 on the Syl/RCA tube.

"Y3" and "3Y" stamped in the base corresponds to the RCA date code indicating 1956. And as you surmise, Y3 indicates May, 1956, and 3Y indicates June, 1956. And the date code 5652 indicates that Tung-Sol packaged this tube in December, 1956. Also, there is considerable evidence that RCA continued to manufacture metal tubes using this dating system at it's Harrison factory until at least 1968.
 
Nov 26, 2019 at 12:49 PM Post #34,416 of 39,920
"Y3" and "3Y" stamped in the base corresponds to the RCA date code indicating 1956. And as you surmise, Y3 indicates May, 1956, and 3Y indicates June, 1956. And the date code 5652 indicates that Tung-Sol packaged this tube in December, 1956. Also, there is considerable evidence that RCA continued to manufacture metal tubes using this dating system at it's Harrison factory until at least 1968.

The tube-identification knowledge of all of you experts is amazing. I have a question related to RCA 6J5s and their age. Does the design of the RCA logo have any meaning in terms of when it was manufactured? I am under the impression that the one on the right in this link is an older-style logo and the one on the left is a newer logo, but I could be totally wrong.

https://www.ebay.com/itm/Strong-Pai...022026?hash=item288977ce4a:g:bZgAAOSw~bld2Y-w
 
Nov 26, 2019 at 2:21 PM Post #34,417 of 39,920
I don't really have all that much "tube-identification knowledge". I just know where to look. :)

Yes, the one on the right, with the "meatball" logo is the oldest. "K1E" indicates Jan/Feb, 1943. The one on the left, with the stylized silver letters "R C A", is later. "LM" indicates Sep, 1959.
 
Nov 26, 2019 at 2:31 PM Post #34,418 of 39,920
I just had a material reduction in my noise floor. Putting the amp on something squishy removed noise - presumably; transformer -> tubes. This has made my day. Some sort of isolation feet are in my future. I can't believe how stark the difference is...

On a less Glenn amp related note, I am happy to report more positive "cable flogging"; As recommended to me by keen cable DIYers; Neotech UP-OCC copper headphone cable is proving a step up from stock cabling and also from my Forza Hybrid (copper/ silver). Solidly recognisable.

And finally, a few more 6J5 pics. Not used yet. Still enjoying current setup too much!

20191126_191818.jpg

20191126_192239.jpg
 
Nov 26, 2019 at 2:49 PM Post #34,419 of 39,920
Question related to the KT66/KT88: why on the GOTL compatibility table these are marked as "non compatible"?
The voltages and currents seem in line and these are really kicking ass on the F.A. amps.
 
Nov 26, 2019 at 2:57 PM Post #34,420 of 39,920
I don't really have all that much "tube-identification knowledge". I just know where to look. :)

Yes, the one on the right, with the "meatball" logo is the oldest. "K1E" indicates Jan/Feb, 1943. The one on the left, with the stylized silver letters "R C A", is later. "LM" indicates Sep, 1959.

Knowing where to look is important knowledge.

And this is what I thought about the logos. On RCA tubes with the circle logo where I have been able to identify the date (or the seller has), they are commonly 40's. On tubes with the text RCA logo where I knew the dates, these have commonly been 50's. I've also seen the term "meatball" used and I assumed it was referring to this circle logo but that had never really been clear to me. Thanks for this information.
 
Nov 26, 2019 at 3:04 PM Post #34,421 of 39,920
I just had a material reduction in my noise floor. Putting the amp on something squishy removed noise - presumably; transformer -> tubes. This has made my day. Some sort of isolation feet are in my future. I can't believe how stark the difference is...

On a less Glenn amp related note, I am happy to report more positive "cable flogging"; As recommended to me by keen cable DIYers; Neotech UP-OCC copper headphone cable is proving a step up from stock cabling and also from my Forza Hybrid (copper/ silver). Solidly recognisable.

And finally, a few more 6J5 pics. Not used yet. Still enjoying current setup too much!




I see one of these in your future

vibration-isolation-table.jpg
 
Nov 26, 2019 at 3:22 PM Post #34,423 of 39,920
Question related to the KT66/KT88: why on the GOTL compatibility table these are marked as "non compatible"?
The voltages and currents seem in line and these are really kicking ass on the F.A. amps.

Generally these tubes are not used in OTL amplifiers because they have high plate resistance, meaning they will have a high output impedance without an output transformer, and therefore, a very low damping factor = distortion. I don't know much about the FA OTL topologies, so no idea what the output impedance would be with these tubes in those amps, but it's probably pretty darn high. If they employ negative feedback, could drop the output impedance down to a usable range with high-impedance headphones maybe? Glenn might know more about those amps.

The reason you see 6AS7G, 6080, etc. used so often in OTL amplifiers is because they have a relatively high plate current with low plate resistance, leading to a lower output impedance without the need for a transformer (with a sufficiently high resistance load).
 
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Nov 26, 2019 at 3:22 PM Post #34,424 of 39,920
Looks like a mag-lev butcher block :)

My kitchen onion dicing will NEVER interfere with my listening again!

Well multitasking right?

It's a vibration-isolation table and what is not shown are the air tanks used to pressurize the tabletop so that it floats on an air cushion. You can usually get these for about 4-6K (US), so you'd have to decide between one of those or a few more Glenn amps :).
 
Nov 26, 2019 at 5:10 PM Post #34,425 of 39,920
Question related to the KT66/KT88: why on the GOTL compatibility table these are marked as "non compatible"?
The voltages and currents seem in line and these are really kicking ass on the F.A. amps.

The main reason they will not work is. In FA amps the two half's of the 6AS7 are tied together in parallel and wired as a cathode follower.
In my amp the two half's of the 6AS7 are separate and not a cathode follower. Run as SEPP
To use these tubes a special adapter would have to be made Each KT88 wired as a triode would be hooked to each side of the 6AS7 socket.
And there internal impedance is to high to get good sound in a OTL without a output transformer. The bass would be bloated and not tight
might sound like lots of bass but not good bass.
 

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