Right 12AU7 and 12AX7 combination

[EWBrown]

6AV6/12AV6 is half of a 12AX7, 6AT6/12AT6 is half of a 5751, and 6C4 is half of a 12AU7. The 3V and 4V versions could be pressed into service, with a little creativity. A 6AB4 is half of a 12AT7, and 6DT8 / 12DT8 are very close to 12AT7, with a 6DJ8 style pinout.

I'm working up a 5HA7 / 6GK6 "plinkertron", at least on paper...

/ed Bee in NH

[TomMcNally]

I put an EH 12BH7 in my rev D ST-35 the other day and it sounded
kind of nasty. The 12AU7 went back in after a half hour or so.

[jeffdavison]

Found a great albeit pricey) x and u combo in my Kaye upgraded "Super It"
The "IT" uses one 12au7 and two 12ax7's
For the AU I'm using a NOS Brimar 13D5
For the AX's I'm using a NOS matched pair of Mullard CV4004's

FANTASTIC COMBO!!!


Jeff

[Marshman]

My son and I tried an RCA 12BH7 greyplate with a Sovtek 12AX7LPS and it was quite bright compared to the RCA blackplate 12AU7. I like the 12AU7 with the speakers we are using.

I have some amperex and mullard 12AX7's we might try with the 12BH7 and see if that tames it down some.

mm

[Ty_Bower]

I put an EH 12BH7 in my rev D ST-35 the other day and it sounded
kind of nasty. The 12AU7 went back in after a half hour or so.

Tom,

Do you still feel the same way about the 12BH7? I see you've got one in your most recent Rev D.

[EWBrown]

Probably was an EH problem.... I recently tried some new EH 6SN7s in my modded VA / CF Bottlehead Foreplay III linestage and they sounded kinda rough and nasty.

The cheap "generic" 6SN7 / 6H8C sounds a LOT better, as do good old USA made 6SN7GTAs. I have some Chinese made "Sino" or "Shuguang" brown base 6SN7s but haven't yet dared to tried them. At only 150VDC @ 3.5 mA, on them they shouldn't go too "pyrotechnic" on me

Maybe the EHs just need a lot of break-in time, but I'm not too willing to listen to that much nastiness for that long Yellow_Light_Colorz_PDT_09 :o

/ed B in NH

[TomMcNally]

Good question Ty ....

I need to put some hours on that amp and see how it sounds.
I built it to sell on eBay, and haven't had any luck.

... tom

[Ty_Bower]

I know that many have tried a 12BH7 in place of the 12AU7 for the concertina phase inverter. I read somewhere that nine out of ten people will say the 'BH7 is the "better" tube. I also read somewhere that the 'AU7 has lousy specs - never intended for audio use, horrible distortion specs, blah blah blah. Anyhoo, many will say they like the ‘BH7 better, and a few will say they like the ‘AU7, but no one seems to say why.

I'm trying to understand what makes a particular tube a "good" choice for the cathodyne splitter. I found a relatively simple to understand description here: http://www.freewebs.com/valvewizard/cathodyne.html

I've managed to grasp about the first four paragraphs. I'm still working on the rest. In the meantime, I've spent a lot of time swapping my JJ ECC82 with an Ei Yugo 12BH7. In general, I try to be the skeptic. I want to believe that all tubes sound the same. I've got tin ears, and all the golden ears have had a glass of wine (or three) too many. Despite my stubborn and generally pessimistic attitude, I'm afraid I'm starting to develop some strong feelings about the way the 'AU7 and the 'BH7 sound. And yes, I think they do sound different.

I think the 'AU7 gives the appearance of having more bottom end. It sounds fuller, or deeper and richer. I don't think it actually renders the lower octaves "better" - in fact, I fear it may be the opposite. It could be that it is sloppier on the bottom end, but the slop gives the bass more body in a way that sounds full and appealing. It may be doing this at the expense of the mid and upper ranges. The effect is particularly noticeable on piano, acoustic guitar, strings, and vocals. I've been listening to a lot of Natalie Merchant, Indigo Girls, Sarah McLachlan, and Lorena McKennitt recently.

I think the 'BH7 really brings out the detail in the mids and highs, but the bottom nearly suffers. It loses some of the richness that it had with the 'AU7. I'm guessing the 'BH7 is more "accurate", and overall I prefer to have the detail. But, I can't help but miss what I'll call the warmth of the 'AU7.

Am I completely off base? Have I had a glass of wine (or three) too many? Has anyone else felt the same way as I about these two tubes?

[jarre]

Ed,

I put a pair of the red base chinese 6SN7s in a Golden Tube Audio SE-40 and they were amazingly good. Somewhat bright for the first 50 hours or so but settle down a bit after that... but they'll never be red base military RCAs, or the sylvanias they replaced.

I have a preamp that uses two 12AU7s -- one for gain, the other for output buffering. So far the best buffer tubes have been a 12FQ7, a Raytheon double mica 5814WA, a CBS/Hytron 5814WA (which now seem to have disappeared from the planet), and an early 60s Mullard. In the gain stage, the same mullard, the CBS/Hytron were both very good but a late 50s Amperex Bugle Boy takes the cake.

I'm a little surprised that nobody seems to be trying any of the 5814s in the phase splitter on the Rev. D board. When mine is done that's probably what I'll start with. The Raytheons are the bomb, but getting harder and more expensive to get, but the Sylvanias are good too.

-- JR

[RuralUrban]

Ed,

I put a pair of the red base chinese 6SN7s in a Golden Tube Audio SE-40 and they were amazingly good. Somewhat bright for the first 50 hours or so but settle down a bit after that... but they'll never be red base military RCAs, or the sylvanias they replaced.

I have a preamp that uses two 12AU7s -- one for gain, the other for output buffering. So far the best buffer tubes have been a 12FQ7, a Raytheon double mica 5814WA, a CBS/Hytron 5814WA (which now seem to have disappeared from the planet), and an early 60s Mullard. In the gain stage, the same mullard, the CBS/Hytron were both very good but a late 50s Amperex Bugle Boy takes the cake.

I'm a little surprised that nobody seems to be trying any of the 5814s in the phase splitter on the Rev. D board. When mine is done that's probably what I'll start with. The Raytheons are the bomb, but getting harder and more expensive to get, but the Sylvanias are good too.

-- JR

I am currently using a Motorola branded 5814A in the phase splitter on my Rev D ST-35, compared to the JJ12AU and EH12AU I've tried so far, I like this better than both - warm and smooth.

[Ty_Bower]

Based on recent (?) suggestions in this thread, tonight I'm trying a Sylvania 7025 with a Raytheon 5814A in my DIY ST-35. Wow! Almost immediately, it sounded really good. Really, really good. Everything just seems to be in the right place. It's clear and detailed, focused and smooth. The bottom end has a full, solid, tangibility to it that is just so nice. The mids are flawless, and the highs are sparkling without a trace of shrillness. Norah Jones is sounding lovely tonight...

[EWBrown]

Recently I replaced the 12AX7 and 12AU7 in my" premium" ST-35 with NOS RCA 5751 and 12BH7A and I like the results better than the old used but still good Tele 12AX7 and RCA cleartop 12AU7. It will take a lot more listening time and musical variety to see if this combo holds up as the better one.

/ed B

[Ty_Bower]

Always in search of new and interesting driver/splitter combos for the ST35, I picked up a bunch of cheap 12AV7 tubes. I've spotted a couple of posts here and there that suggest they are decent subs for the 12AU7. Any comments?

[EWBrown]

If you reconnect the filament wiring to pins 4 and 5 only (no pin 9) then 6CG7, 6FQ7 or 6GU7 could be used in place of teh 12AU7.

In addition to 5814As, try the GE 5963s, they make nice 12AU7 replacements, I've used these and the 5814s in the original Bottlehead "Foreplay II" 12AU7-based line. The GEs were NOS, the 5814As were used "pulls". THe 7025 is a 12AX7 equivalent, some say these are a noticeable improvement.

There are also 12AX7 and 12AU7 equivalents in the "668X" industrial / computer tube series. Never have tried them, so YMMV, etc...

/ed B