Octal & Loktal triodes (6SN7)

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Viitalahde

Well-known member
Joined
Nov 7, 2005
Messages
727
Location
Kuhmoinen, Finland
I plan on trying out the Aikido amplifier for a new passive EQ.

http://www.tubecad.com/2006/05/blog0064.htm

I already have a nice pair of RCA 6SN7's, but I would need more.. And boy, have they gone up in value! :shock: It doesn't seem to make a difference to buy a 12SN7 or any other heater equivalent these days, everyone seems to know the options. I don't mind putting 40 euros in tubes now, but if the trend keeps on going, I would like to be able to maintetance the thing in the future, too.

The Loktal equivalents seem to be cheap though, 7N7, 7AF7, 14N7, 14AF7.. Is the Loktal socket a good one? It was never that popular.

The single 6SN7, the 6J5 is cheap too. Maybe I should build with them and have 8 octal sockets. :razz:

Or maybe I should just give up and go Noval.
 
That's why I hate popular tubes...there are a lot of great tubes that are not so well known. Search for them.

analag
 
Using Loctals is an option. The sockets are easy to get also (from me for instance :green:). But it looks like even the 7N7 is going up in price...

Have you tried the Russian 6SN7s? They're not bad at all in my opinion - and you can get them cheap on eBay (last I checked at least). The Chinese made/makes 6SN7s also, but I have never tried those.

Best regards,

Mikkel C. Simonsen
 
Yeah, I've seen the Russian 6H8C's (=6N8S) for sale. Who knows what to think of the audiophools opinions, some praise by them, some say they're crap. They are cheap, though, The metal base ones are good..

7N7 is interesting me more and more. :wink: I think you could still find good deals for them and stock up.
 
I don't know, why go crazy with NOS tubes. The Electro-Harmonix 6SN7EH seems to be liked, and it's not obviously going to be used in a bad circuit.
 
I much prefer a DMOS working as plate load than a tube. The aikido setup looks good, but the triode represents a "soft" load.

analag
 
Yeah Rowan, I've seen you post some hybrid designs.

This is just speculation, but there seem to be a lot of nice single octal triodes (6J5, 6C5 etc) available, and they cost nothing. Maybe they could have an sand-state active load, dunno. I'm still just entering the tube world since I've started to realize they can be designed really clean sounding..
 
[quote author="Viitalahde"]but there seem to be a lot of nice single octal triodes (6J5, 6C5 etc) available[/quote]
Note that the 6C5 is often (perhaps always) not a triode - it's actually a trioded 6J7. The 6C5GT is probably a real triode, because you can see the guts :grin:

Best regards,

Mikkel C. Simonsen
 
> Is the Loktal socket a good one? It was never that popular.

It is 10 times better than wretched Mini.

A vintage Loktal socket is 10 times better than new-made Octal sockets.

If you are going to hang it upside down and drive over bad roads, Loktal is the only way to fly.

Nothing wrong with Loktal, except it could not fight RCA's Octal momentum, nor the economy of Mini. Arguably a better design, like BetaMax.

My only "???" is: if you use John's PCBs, with normal P2P Loktal sockets, you will have to cobble it together. Remember it takes force to seat a Loktal. Eight 1" long #28 wires won't do; eight minimum length #14 wires surely will.
 
[quote author="mcs"][quote author="Viitalahde"]but there seem to be a lot of nice single octal triodes (6J5, 6C5 etc) available[/quote]
Note that the 6C5 is often (perhaps always) not a triode - it's actually a trioded 6J7. The 6C5GT is probably a real triode, because you can see the guts[/quote]

have you cut a bunch open? where do you get this info? that makes no sense from a labor point of view. And the 6J5? Why not the 6SJ7 instead?
 
> where do you get this info?

http://www.mif.pg.gda.pl/homepages/frank/sheets/127/6/6C5.pdf

6C5 appears to be a triode-strapped '57. Called 6J7 on octal base.

Why do we care? The electrons don't know the difference.

> Why not the 6SJ7 instead?

The SJ lacks a top-cap, and this makes it less-kewl than the 6J7.

Also 6SJ7 was in production far into the declining years of tube factories, while nearly all 6J7s are OLD, from days when tube production was cutting-edge technology and the workers really cared.

I love my genuine Ken-Rad 6J7s, but if you like 1970s stuff (or think "S" pinout is somehow better), use 6SJ7.

For this jujitsu-amp work, you might wonder if a twin-triode will lever better than an odd couple of single tubes. Twin-match is not always great, but at least you know both sides were made the same week in the same place.
 
Kewl factor is an issue. :green:

I think I want to try single triodes as the Aikido input stage. John Broskie sheds some light on the subject here: http://www.tubecad.com/2004/blog0013.htm

You'll need to calculate the RA and RC for each tube, but no biggie. I think experimenting with this circuit would be a nice way to start with tube calculations, just two resistors to think about. 6SN7 on the output, or maybe a 6080wc/6AS7 (which would require a lower B+).

2C22 seems cool, and should be about an equivalent for a single half of a 6SN7.

http://www.radiomuseum.org/tubes/tube_2c22.html
http://www.mif.pg.gda.pl/homepages/frank/sheets/049/2/2C22.pdf

EDIT: Oh, such a configuration will also be easy to change into something Sismofyt has posted. That one has an SRPP output stage. All P2P, half an hour of work and a new sound at hand.
 
[quote author="PRR"]> where do you get this info?

http://www.mif.pg.gda.pl/homepages/frank/sheets/127/6/6C5.pdf

6C5 appears to be a triode-strapped '57. Called 6J7 on octal base.

Why do we care? The electrons don't know the difference.

> Why not the 6SJ7 instead?

The SJ lacks a top-cap, and this makes it less-kewl than the 6J7.

Also 6SJ7 was in production far into the declining years of tube factories, while nearly all 6J7s are OLD, from days when tube production was cutting-edge technology and the workers really cared.

I love my genuine Ken-Rad 6J7s, but if you like 1970s stuff (or think "S" pinout is somehow better), use 6SJ7.
[/quote]

I think you misinterpret my commentary. I'm saying where is the proof that the 6C5 is actually pentode construction, strapped internally, as alluded to by mcs. No data sheet I've ever seen says this; that one certainly doesn't. Pentode construction makes no sense from a manufacturing standpoint.

If it was, then you'd use guts from the 6SJ7 line, being pre-constructed for base grid connection versus grid cap connection. You'd never use the 6J7 guts and rework the grid connection. Maybe 6J7 and 6SJ7 are the same production line except for a few fine points; it'd still be referred to as a 6SJ7 in regards to the 6C5.

I have a lot of original broadcast 6J7 preamps, some with 6C5's as output stage. I know them well. I sold one batch of 6J7 triode /6C5 preamps to a guy who insisted the 6C5 was so superior sounding, he planned to rework the 6J7 sockets for 6C5's. These were preamps I'd completely restored, right down to new tube sockets.

It's been awhile since I've eyeballed a glass 6C5, but I recall them having an internal shield that blocks almost all of the view. I'll go smash a few later.
 
oh yeah, I like loctals, and have intended to try using some in a build. Think I have some in a Webster or Webcor portable rig. Collins used loctal rectifiers in several portable broadcast amps with 7 and 9 pin tubes.
 
[quote author="emrr"]I think you misinterpret my commentary. I'm saying where is the proof that the 6C5 is actually pentode construction, strapped internally, as alluded to by mcs.[/quote]
I have no proof. But I have read it in different articles and books. One source is "Tube Lore" by Ludwell Sibley.

Pentode construction makes no sense from a manufacturing standpoint.
According to what I've read (I wasn't born back then...), pentodes were "in style" in the 30's and medium-mu triodes were not. So if they made a lot of 6J7s and not so many 6C5s it makes a lot of sense to combine the production.

If it was, then you'd use guts from the 6SJ7 line, being pre-constructed for base grid connection versus grid cap connection. You'd never use the 6J7 guts and rework the grid connection.
The 6SJ7 wasn't made back then. The 6C5 and the 6J7 were both parts of the original RCA metal tube line-up. The 6SJ7 came later.

Best regards,

Mikkel C. Simonsen
 
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