Audio Research LS15 preamp tube positions

[BillWojo]

Picked up a nice LS15 preamp from BarterTown for my Mac system. It came with JJ tubes, 4 pcs of 6DJ8. Does anyone have experience with tube rolling in one of these?
I have some nice NOS Tungsram 6922 tubes that I bought from Eduarsan1, should I just put them in all 4 positions or is there a method to the madness?
I know several folks on the forum have had this preamp over the years, figured maybe someone could offer there experience.

BillWojo

 

[E-Stat]

Audio Research frequently uses unity gain cathode followers at the output. If there's any preference, I would try placing the *better* tubes in the positions closer to the rear of the cabinet as those are most likely responsible for gain. I think those are V1-V3.

The ones closest to the Infinity coupling caps at the front will be the followers.

 

[heyraz]

Bill,
I spent a small fortune on 6DJ8/6922/7308 tubes earlier this year on my LS7 until I was satisfied.
I hope this thread helps...
http://audiokarma.org/forums/index.php?threads/system-synergy-boy-do-i-love-my-preamp.834543/

 

[a_retent]

Picked up a nice LS15 preamp from BarterTown for my Mac system. It came with JJ tubes, 4 pcs of 6DJ8. Does anyone have experience with tube rolling in one of these?
I have some nice NOS Tungsram 6299 tubes that I bought from Eduarsan1, should I just put them in all 4 positions or is there a method to the madness?
I know several folks on the forum have had this preamp over the years, figured maybe someone could offer there experience.

BillWojo

I'll be interested to hear your thoughts on the Tungsram tubes.

I bought amperex 6DJ8 bugle boys to replace the 6922 Sovteks that were weak in the phono stage of my ARC SP-15 pre. Reeeeaally liked the sound I got from them but apparently the SP-15 doesn't like 6DJ8 equivalents because I keep blowing the 1/4 amp fuse in the power supply box. I tried 2 completely different sets and same problem. The second set only lasted 5 hours before "poof" no sound. I put a set of 6922 JAN Phillips in for 6 weeks now and no blown fuse, they sound okay but even the weak Sovteks sound a bit better.

The local tube shop I've been working with on this issue have been EXTREMELY cool about tube sets for my little issue. Tomorrow I'm going to return the 6DJ8 set and was going to try a set of 7308 until I read what @heyraz posted in his thread. So it now looks like I might have to bite the bullet and get a set of Amperex 6922 PQ gold pins, way more than I would like to spend.

 

[peterh]

Picked up a nice LS15 preamp from BarterTown for my Mac system. It came with JJ tubes, 4 pcs of 6DJ8. Does anyone have experience with tube rolling in one of these?
I have some nice NOS Tungsram 6299 tubes that I bought from Eduarsan1, should I just put them in all 4 positions or is there a method to the madness?
I know several folks on the forum have had this preamp over the years, figured maybe someone could offer there experience.

BillWojo

6299 won't do at all. In fact they don't even look the same and won't fit the sockets.

https://frank.pocnet.net/sheets/142/6/6299.pdf

 

[a_retent]

6299 won't do at all. In fact they don't even look the same and won't fit the sockets.

Good catch!
He'll want to use 6922 to replace the 6DJ8.

Perhaps in his euphoria, Bill got a bit dyslexic when typing with fat fingers.

 

[BillWojo]

Yup, was going from memory. Way to many tube types out there. I edited my original post. Thanks for the suggestions so far.

BillWojo

 

[heyraz]

There are so many choices.

Keep trying till you find the combination that sounds best on your system.
Edit: Removed 12au7 variants and replaced image of 6DJ8/6922/7308

 

[dogscanskate]

I own an LS 15, I also have Tungsram E88CC tubes in my stash. This is one of the best kept secrets, it's a fantastic tube. I don't think they made 6922's but Tungsram are easy to identify, they all have a tag (numbered) . They are just as good as the Siemens, Philips I have at a much lower cost. Put your 2 best tubes in the rear as was previously mentioned at position V1 and V2 (V3 and V4 are the front tubes). Pictures of the Tungsram would be helpful as I've said they made ECC88 and E88cc. In the LS 15 AR recommends 6922 or its european variant the E88cc. If they are Tungsram tubes, you should be in for a treat, they are really good.

 

[BillWojo]

https://4.bp.blogspot.com/-Gvgsq_a0ry4/VjrLrz2ZvDI/AAAAAAAAAuM/w25HrPozpgU/s1600/100_8034.JPG

https://2.bp.blogspot.com/-mjFJDRM2-cU/VjrLtjl2wVI/AAAAAAAAAuY/wePxssxnnmE/s1600/100_8036.JPG

These were labeled Dumont, sold as manufactured in England but ultimately turned out to be relabeled Tungsrams. Purchased 6 pcs from eduarsan1 from BarterTown several years ago.

Here is the discussion about these tubes.

https://audiokarma.org/forums/index.php?threads/nos-dumont-6922-ecc88-6dj8-tubes.687258/

BillWojo

 

[heyraz]

This is a tube made in West Germany Branded for RCA.
You can see the "badge" mentioned by dogscanskate

 

[dogscanskate]

From your pictures, it looks like a Tungsram. On your 2nd photo, the tag seems to be on the right next to the grey plates, if you see that tag, it would confirm the authenticity. The tags on mine are next to the grey plates. Mine are made in Hungary with non corrosive alloy pins (not gold). ,

 

[BillWojo]

Yep, mine have the tags as well and the pins are nice and shiny, like they were just made. I'll try a pair in the back two positions, V1 and V2 as dogscanskate mentioned.
Thanks for the info.

BillWojo

 

[onemug]

should I just put them in all 4 positions or is there a method to the madness?

figured maybe someone could offer there experience.

My LS7 is similar to your 15 in that it uses 4 6922's, 2 are for l/r gain, other 2 are for the cathode follower. With some guidance from knowledgeable friends and, most important, my own ears...this is what I'm learning: the l/r gain choices have the most effect, cf's... not so much, but can still affect the overall sound. The cf's would be like adding a little cream or sugar to your coffee...changes it a little, allows you dial it in for your best taste.

Lately I've been doing some rolling with the 7. After looking through my stash and finding several "pairs" of some popular brands, I found a "quad" of Amperex 7308's, all testing great. They gave me great sound. Experimenting with mixed 'pairs', so far, I came up with Amperex Bugle Boys for the l/r and used a pair of nos/grey plate Sovteks for the cf. Result, best yet! I could live with this sound for a long time. Still have pairs of Siemens, orange and white label Amperex's, etc. to try in the l/r stage but I'm very please 'as is'.

 

[heyraz]

My LS7 is similar to your 15 in that it uses 4 6922's, 2 are for l/r gain, other 2 are for the cathode follower.

I'm not sure about that. I think the LS7 and LS15 are two different animals.
The LS7 has single ended outputs while the LS15 has balanced outputs.

6DJ8/6922/7308 is a dual triode tube (2 channels in one tube).

For the LS7 I see V4 serving as a single cathode follower for both channels (1/2 V4 Left Channel, 1/2 V4 Right Channel).
I can't find a schematic for the LS15 but the physical layout of the board suggests mirror image discrete left and right channels that don't share tubes. Without a schematic, I can't tell if the LS15 utilizes cathode followers.
LS7 schematic:

LS7 Physical layout: (LS7 has single ended outputs). Single tube at top of image is cathode follower for left and right channel

LS15 Physical Layout: (LS15 has balanced outputs) Output tubes at top of image

 

[onemug]

LS7 Physical layout: (LS7 has single ended outputs). Single tube at top of image is cathode follower for left and right channel

You may be right. When I asked some tech friends about tube rolling in the 7, they said to concentrate on the front 2 (bottom of your picture, V1 & V2) as they were the gain stages. Not sure what V3 is exactly for, I'm far from a tech.

In your opinion, how much effect to the sound does V3 and/or V4 have in the LS7?

 

[heyraz]

When I asked some tech friends about tube rolling in the 7, they said to concentrate on the front 2 (bottom of your picture, V1 & V2) as they were the gain stages

I'm not 100% sure how this circuit operates, so I created a thread in this forum"Can Someone Please Explain This Preamp Circuit (ARC LS7) in this Tube Audio Section.

In your opinion, how much effect to the sound does V3 and/or V4 have in the LS7?

V3 definitely had a great effect for me. Telefunken tube's aren't my favorite, but in V3 a Tele brought up the midrange and gave more "character" to the sound. The Siemen's tube sounded similar. 6922 and 7308 were clear but "blander" by comparison. Not bad....just not as exciting.
V1 and V2 definitely need to be as clear a possible, they handle the input. A couple of Amperex USA 6299's (White Label 'PQ") sounded the best to my ears. Amperex 7308 in V1/V2 were clear and nice, but I preferred the White Label Amperex Made in USA 6922's. The tubes I used were made for the US Navy. I preferred the white label "PQ" over the orange label "PQ" tubes.
The cathode follower (V4) does more than simply add "finish" or "polish" to the sound. V4 also provides negative feedback to pin 7 of V1 and (pin 2 of V2), so the importance of the cathode follower (V4) shouldn't be underestimated.

In all cases, the Bugle Boy versions were my least favorite.

Keep an eye on the new thread I posted.....I'm sure someone more knowledgeable than myself will provide a detailed explanation.

There were a couple of internal construction variations I noted. I had some very nice labeled for HP Amperex 6922's. The getter structure looked very stable and these tubes are keepers.

A different getter structure:

 

[onemug]

the importance of the cathode follower (V4) shouldn't be underestimated.

Appreciate your well worded response and I will keep an eye on the new thread you started.

In the meantime, would I be right in assuming that:

1. V1 and V2 should be of the same brand and
2. V3 and V4 could each be a different brand

I'm looking forward to some tube rolling. I was quite surprised by the Bugle Boy/Sovtec pairing. First up will be a pair of while label Amperex's and I'll keep the Soveks as is in V3/4.

 

[heyraz]

1. V1 and V2 should be of the same brand and
2. V3 and V4 could each be a different brand

Yes

 

[BillWojo]

Well this past weekend I opened it up and the tubes turned out to be EH6922. I installed the Tungsram's in the back two positions. There was not a real noticeable difference. I'd like to add some warmth, anyone have suggestions?

On Edit: Does anyone have a schematic for a LS15? I'd like some discussion on the circuit as well.

Thanks

BillWojo