Which vintage DHt tube would be close to 6j5 ?

See link below.
The 27 was an indirectly heated 26, it appears -- and you probably already know the story from the 27, 56, 76, through to the 6J5, and then 6SN7 (and at least as well as I). If not, you can see their entries on the same website and/or look in any tube manual(s) of the proper era(s). :)

source: https://worldradiohistory.com/BOOKSHELF-ARH/RCA-Books/RCA-Receiving-Tube-Manual-1937-RC-13-OCR.pdf

all the best,
mrh

https://vinylsavor.blogspot.com/2015/05/tube-of-month-26.htm

Nothing close to mu=20, plenty of mu=8, posted on March 18, 2023 at 03:23:11
andy evans Audiophile Posts: 4382 Joined: October 20, 2000	Plenty of choice around mu=8. 26, 4P1L, 2P29L, 47, 10Y, 112A, 01A etc. I would definitely use filament bias with Rod Coleman V9 regs. The easiest above is 2P29L which should give you a worthwhile improvement. If you need more gain stick a step-up transformer in front of it. I use a Hammond 1140-LN-C in 1:4. That solves the gain problem with DHTs.

RE: Nothing close to mu=20, plenty of mu=8, posted on March 18, 2023 at 13:31:49

FlaCharlie
Audiophile

Posts: 940
Location: Gville, FL
Joined: June 1, 2003

I'll both agree and disagree with Andy on this . . .

Based on his suggestion, I've been using the Hammond 1140-LN-C as a step up in my direct coupled breadboard project that uses all DH tubes and they work great!

Bought the first pair in the US. Best price was from a Chicago dealer and they were just over $100 each shipped. I liked them so much that I ordered 6 more from KGA Enclosures in England, which Andy suggested in a post on DIY Audio. Cost, including shipping, was $45 each and they arrived in two days! THANK YOU ANDY!

But there ARE some DHTs that have mu that's similar and even higher than the 6J5. Whether or not they'll work well as subs, I don't know. Most of them are, however, "battery types" which have reputations for being microphonic. And some of their other characteristics may also be problematic, such as low transconductance. I'm not knowledgeable enough to analyze their suitability for any particular application.

One is the 2J27L, which is a sister tube to the 2P29L. It supposedly has a mu of ~16 in triode vs ~8 for the 2P29L. It's the tube used in the little Nobsound E6 preamp, which is the only mass produced preamp I've seen that uses DH tubes. I breadboarded the 2P29L a while back and started a thread about it on DIY Audio. So for $60 shipped I couldn't resist giving the 2J27L a try and I've been pleasantly surprised. The Chinese tubes that it ships with are sometimes horribly microphonic but using the Russian ones seems to solve the problem. Details in the link below . . .

Some others are the 1H6G / 1B5, which is a single DHT with a pair of diodes. Mu is 20, just like the 6J5. The 1G6G / GT is a dual DHT with a mu of 30. The 4A6G is another dual DHT with a mu of 25. And the 40 is a single DHT with a mu of 30. Unlike the others it has a 5v filament but transconductance is extremely low at 200.

So there are 5 options for you to investigate . . .

Nobsound E6 Preamp with 2J27Ls

Well, yes, some odd DHTs with higher mu, posted on March 19, 2023 at 02:53:55

andy evans
Audiophile

Posts: 4382
Joined: October 20, 2000

Thanks for the update FlaCharlie. I was aware that there were some higher mu DHTs like the 3a5 for instance, but nothing I would use. The 3a5 isn't bad if its gain suits, but it's not mu=20.

The twin triodes are nothing special - 1J6 has very unbalanced halves - I had several and only a handful were balanced in any way. Sounded OK but I wouldn't use it. 3B7 sounded quite bad.

RE: Well, yes, some odd DHTs with higher mu, posted on March 19, 2023 at 06:50:36

FlaCharlie
Audiophile

Posts: 940
Location: Gville, FL
Joined: June 1, 2003

Yes, I had forgotten about the 3A5, which is a 7 pin mini with mu of 15. I plan on trying it sometime.

I think you must mean the 1J6G as the 6J6 is indirectly heated. There is also the 1E7G, which is a dual DHP. I'm not sure what the mu is in triode. I've tried both the 1J6G and the 1E7G and they sounded good to me but I preferred others. I only used them with sections in parallel so I didn't notice any mismatch between sections. As I recall, the bass was very articulate using the 1E7G.

The 3B7 is a loctal with mu of 20. I think I have a couple but haven't tried them.

There's also a DHT triode / diode with a mu of 65 which comes in both octal and loctal bases. The octal is the 1H5G / GT, which has a top cap. The loctal is the 1LH4, which has no top cap.

And some other DHPs but I'm not sure what their mu is in triode.

A Triode wired Directly heated 47 pentode would be around mu of 20~nT, posted on March 26, 2023 at 15:04:05
Cleantimestream Audiophile Posts: 7551 Location: Kentucky Joined: June 30, 2005	~! The Mind has No Firewall~ U.S. Army War College.

Tubes Asylum

Which vintage DHt tube would be close to 6j5 ?

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