Croft preamp - 12BH7A or 6SL7?

Hi all

I'm about to buy Glenn's latest preamp offering, the "25RS LS" which is a souped-up linestage version of the RS two box solution. The LS comes in two varieties, which as the title suggests can incorporate either a 12BH7 or an old school 6SL7 in the linestage slots (x 2).

I have a 25RS at the moment which has a single BH7 which works well for my tastes in that it's fairly lean sounding. Reading up though I haven't found a single post that doesn't extol the virtues of the 6SL7 that can be found in some of Glenn's earlier preamps. So I am a bit stuck which way to go, any opinions or thoughts based on experience would be useful.

I've never seen the LS version. But I'd be tempted with the 6SL7, it will certainly address the leanness with a bit more overall drama. There are plenty of 6SL7's to choose from too, it's great fun. :) I'm currently running x2 NOS Brimar brown bases in the line, superb!

It would be great to see a naked pic (ooer!) of the new LS version if anyone has the means.

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Originally Posted by The Black Adder

I've never seen the LS version. But I'd be tempted with the 6SL7, it will certainly address the leanness with a bit more overall drama. There are plenty of 6SL7's to choose from too, it's great fun. :) I'm currently running x2 NOS Brimar brown bases in the line, superb!

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Hi Black Adder - I see you have an Epoch which I imagine will have fairly similar characteristics to the LS with 6SL7s. I would be interested to hear what different types of 6SL7 produce in your Croft? I would be most interested in the ones that sound lean, neutral and transparent.

Hi Mathew.

Yes, I have the Epoch Elite although it's nothing like a stock one, it's been upgraded an awful lot by Glenn. :) It has dual separate PSU amongst other things. Yes, 6SL7's do have different sounds in the line stage. For a lean yet open and transparent sound then try the Russian MELZ ones. For something with a bit more body but with still lots of stage then NOS Brimar's or Raytheon's are a good choice or Sylvania WBGT's.

The Central valve also changes the sound as well as the regulator valves... it's all good fun and once your sorted with valves it's everything you would want, and more.

Marco has even more experience as he's had his longer than mine so he might pop in to elaborate.

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Originally Posted by The Black Adder

I've never seen the LS version. But I'd be tempted with the 6SL7, it will certainly address the leanness with a bit more overall drama. There are plenty of 6SL7's to choose from too, it's great fun. :) I'm currently running x2 NOS Brimar brown bases in the line, superb!

It would be great to see a naked pic (ooer!) of the new LS version if anyone has the means.

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It's not a 'new' model. It's a two box jobbie as the 25RS but line level only. It has a choice of B9a or Octal valves.

ah... righto. :) With it being called the RS LS I thought it was a new one, but I get it now.

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Originally Posted by hifi_dave

It's not a 'new' model. It's a two box jobbie as the 25RS but line level only. It has a choice of B9a or Octal valves.

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I believe it also has uprated larger output caps as well as some other bits...

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Originally Posted by hifi_dave

It's not a 'new' model. It's a two box jobbie as the 25RS but line level only. It has a choice of B9a or Octal valves.

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Hi Dave, I believe you said you sold a couple of these? Could I ask if they were B9a or Octal flavours?

Octal.

I would have thought there were a lot of other dereference between the two than just the valve. A 6sl7 is very different to a 12bh7, so I would guess the circuit is very different.

Just a couple of resistor values I would have though Nick, it is just a line stage with the gain set by feedback.

:)

Yep, but the difference in gain of the two, 60 and 10, is going to mean a lot more feedback with the 6sl7. so I would have thought the spectral output of the two would be very different. Also I assume there is a cathode or source follower on the end, there have been in the ones I have seen. Otherwise the different ra will make a difference to its load driving ability. All the Croft stages I have seen have been anode followers plus a source follower inside the feedback loop. Are there different sorts from that? The difference between the two valve would make me think you could use any dual triode with relevant anode load and feedback resistor.

I would have thought a 6072a would make a better 9pin version of the 6sl7. Or a 6sn7 as an octal replacement for the 12bh7

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Originally Posted by lurcher

Yep, but the difference in gain of the two, 60 and 10, is going to mean a lot more feedback with the 6sl7. so I would have thought the spectral output of the two would be very different. Also I assume there is a cathode or source follower on the end, there have been in the ones I have seen. Otherwise the different ra will make a difference to its load driving ability. All the Croft stages I have seen have been anode followers plus a source follower inside the feedback loop. Are there different sorts from that? The difference between the two valve would make me think you could use any dual triode with relevant anode load and feedback resistor.

I would have thought a 6072a would make a better 9pin version of the 6sl7. Or a 6sn7 as an octal replacement for the 12bh7

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From what I understand the circuit is quite different for the Octal and 12BH7.

Seems there is a 6SN7 option as well as the 6SL7 for the 25RS LS :scratch:

The 6SN7 is more neutral from what I understand so possibly the way to go - does anyone have any experience either way with 6SN7 vs 6SL7 Croft equipment?

Have you enquired / put your questions to Glenn?

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Originally Posted by vinyl

Have you enquired / put your questions to Glenn?

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I have indeed, he says he has no personal preference...

My experience with octals - I have a Charisma X pre with phono - it utilises 5 x 6SL7 in total. The phono output stage 6SL7 can be swapped with a 6SN7 to my preference (which I haven't tried). As it uses the two 6SL7 in the line stage, I can easily say it is the most sonically satisfying of any preamp I have heard - and I have heard many including high end / very expensive / call them what you will preamps in comparison with some nudging £10k. That's not to say the more expensive gear isn't good - it is very good but personally not for me.

Glenn has told me Jo's, Marco's and mine are practically the same preamp circuit wise.

Glenn is quite right as the preference in sonics between the two octals will be how you enjoy them and you won't know until you've tried. Glenn welcomes feedback and whatever you choose and then don't enjoy he'll change for you. Hope this helps.

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Originally Posted by vinyl

Glenn is quite right as the preference in sonics between the two octals will be how you enjoy them and you won't know until you've tried. Glenn welcomes feedback and whatever you choose and then don't enjoy he'll change for you. Hope this helps.

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Thanks vinyl, yes it does. I'm pushing ahead with the 6SN7 version (if only because no one else seems to have), I'll see how I get on.

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Originally Posted by mathewf

Seems there is a 6SN7 option as well as the 6SL7 for the 25RS LS :scratch:

The 6SN7 is more neutral from what I understand so possibly the way to go - does anyone have any experience either way with 6SN7 vs 6SL7 Croft equipment?

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Hello Mathew.

I have the 6SN7 version and it's really very nice indeed. Mine now runs 2x 6LN7's in the line, 1x 6SN7 as the middle and x2 6SL7s in the phono. Let me know if you need to know any other information.

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Originally Posted by mathewf

Thanks vinyl, yes it does. I'm pushing ahead with the 6SN7 version (if only because no one else seems to have), I'll see how I get on.

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I will be keeping an eye on this Mat as I would like a phono stage with 6SN7,s.

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Originally Posted by The Black Adder

I have the 6SN7 version and it's really very nice indeed. Mine now runs 2x 6LN7's in the line, 1x 6SN7 as the middle and x2 6SL7s in the phono.

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Hi Black Adder - Could I ask what do you mean by "the middle one" please? Also where you say "6LN7's in the line", do you mean 6SN7? Thanks.

lol, yes... sorry. 6SN7's

In my preamp there are 5 of the larger octal valves. So I have x3 that are 6SN7's, whilst two 6SL7's in the phono.

Actually, I have another question for you Black Adder if I may;

I asked you which 6SL7s you thought worked well in your Croft preamp when I thought I was going that way; which 6SN7s would you recommend trying?

I actually have a pair of Brimar grey plates, a pair of RCA grey glass GTs and a lone Ken-Rad waiting for a partner to try out...

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Originally Posted by The Black Adder

lol, yes... sorry. 6SN7's

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Easily done, I made a very similar mistake emailing my dealer recently ..:rolleyes:

For the line stage and the central valve I recommend NOS Brimar or Melz (OTK) and for the phono stage (6SL7's) NOS Sylvania 6SL7GTB's.

If you are going for 6SL7's in the line stage then NOS Melz.