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RFT 12AU7

108.77.77.32
Posted on May 19, 2012 at 13:37:35
mike1127
Audiophile

Posts: 264
Joined: June 3, 2009
 I recently asked about bright 12AU7 tubes. I purchased one German-made RFT tube and I'm using it now in my headphone amp (the Hifiman EF5, a hybrid amp with 12AU7 gain stage and FET output stage). Maybe it's too bright, but I can hear why people like this tube. It was harsh right out of the box, but after about 75 hours of burn-in this tube has incredible treble. Incredible presence and liveliness. Makes my other amps sound dull by comparison. I wish it weren't so lean on the bottom end, but maybe more burn-in will fix that. I also think it might not be functioning optimally because the tube pins are corroded. I need to clean those.

Previously I was using a clear top RCA 12AU7. It my amp it is warm and has good bass, but when paired with my rather dark headphones (the Audeze LCD-2) it lacks sparkle.
---
"Just because I'm paranoid doesn't mean they're not out to get me."
High-end headphone system with photos.

 

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RE: RFT 12AU7, posted on May 19, 2012 at 16:23:46
starchild
Audiophile

Posts: 146
Joined: August 21, 2001
 I've tried the RCA cleartop, Mullard IEC, RFT, Tungsols and many other 12AU7 tubes over the years in my amps and pre-amp. I ultimately settled on the Cifte tube for my preamp and RCA clear tops as driver tubes in my power amps. The Cifte is very transparent with a sparkling treble. I'm sure there are better tubes out there but I find them difficult to beat for the price.

 

RE: RFT 12AU7, posted on May 19, 2012 at 18:14:22
coolhand
Audiophile

Posts: 471
Joined: June 5, 2006
 That leaned out bottom end is a characteristic of the all German & French manufactured tubes I've used (not solely the 12AU7's), whether it is why they also appear to be more lit up and project a sense of enhanced presence is a matter of opinion, but I believe it is partially responsible.

I always end up tiring of them and find alternative tubes or methods to liven up the presentation.
Having said that, it's all part of the fun of cooking with tubes, so you may only need to counter balance the diminished bass with a more bottom-end centric tube elsewhere, in the case that your circuit employs more than one tube of course ;-)

In the case of 12AU7 (almost equivalent) drop in alternatives which offer the best of both worlds, with increased resolution, superb bass and expansive refined top end, there are a couple which spring to mind IF your circuit can accommodate the increased heater current requirements, which in the case of a single tube substitute is most likely not an issue.
Another consideration is the increased height of these tubes if they are to be internally accommodated.

These are the E80CC or 12BH7 and are available in versions which err from warmer to neutral. IMHE either will handily outperform any of the 12AU7 varieties, particularly when employed as drivers. If you poke through the archives here you'll find loads of comparative user experiences, mostly positive from recollection... and these tubes are generally less costly than their 12AU7 cousins too !!

 

what are the alternatives?, posted on May 19, 2012 at 20:38:50
mike1127
Audiophile

Posts: 264
Joined: June 3, 2009

Thanks.

The amp uses just one tube, the 12AU7.

When you mention 12AU7 alternatives that require more heater current, were you referring to the E80CC and 12BH7? Or something else? Regarding the heater circuit question I can contact Hifiman customer support about that if I know the specific models to ask about.

The high-end is not just bright -- it is bright, yes -- but it conveys a lot of life and music. I can imagine a tilted-up tonal balance that doesn't have any up-side to it. So something special is going on. But I understand about tiring of it -- I might start to find it monotonous after a while. I'm not sure. I have another headphone amp that I can switch to (a modified Woo WA6-SE) which is radically different in character so I have variety available to me at all times.


---
"Just because I'm paranoid doesn't mean they're not out to get me."
High-end headphone system with photos.

 

He was referring to the E80CC & 12BH7 requiring double the heater current, posted on May 20, 2012 at 01:20:39
XLR8OR
Audiophile

Posts: 597
Location: Sydney, NSW
Joined: August 30, 2005
 No one can provide you with the definitive answer you are seeking. Sure, recommendations can be given. You need to tube roll and find out what in practice pleases you in both the short and long-term. The E80CC is my strong recommendation, if your headphone amp can obviously accommodate the extra heater current. If not, you can also try the early 1950's CBS-Hytron 5814, 5814A or 5814WA with angled and bent rectangular getter or a 7316. The latter would be more bright sounding and analytical in presentation, whereas the former in contrast will be far more warmer. Try both and more and see what pleases your ear. That's the ultimate judge in the end.

 

The 7316 is expensive ...but worth it., posted on May 20, 2012 at 12:47:07
Mechans
Audiophile

Posts: 1068
Location: East Coast
Joined: May 23, 2004
Contributor
  Since: May 6, 2012
 They are a little tough to find at a reasonable price but if you have the daily search function from e-bay sending you e-mails you might catch a sleeper. They are often labled as H/P Hewlett Packard or other computer/business machine names, these used to be a lot less money than the straight Amperex label but not much anymore. The word seems to have spread about there value in audio. I think they have the best extension of all 12AU7 types, not the richest tube and yes perhaps a tad analytical.

Steve

 

RE: RFT 12AU7 I am surprised no one said Telefunken, posted on May 21, 2012 at 17:31:11
Mechans
Audiophile

Posts: 1068
Location: East Coast
Joined: May 23, 2004
Contributor
  Since: May 6, 2012
 Or other West German tubes. They are pretty crisp and alive on top and may be better on the bass than the RFT German tubes. I have used Telefunken I am pretty sure but forget as I have been fixated on my Amperex favorite for quite some time now. I can't compare it to the RFT as I don'r recall ever owning RFT 12AU7s.

Steve

 

Any way to assess heater current supply?, posted on May 21, 2012 at 21:38:39
mike1127
Audiophile

Posts: 264
Joined: June 3, 2009
 I contacted Hifiman technical support to ask about subbing the 12BH7, and I got what is essentially a form letter telling me to never use any tube other than the 12AU7. So I doubt the person even understood my question. Any ideas about how I could go about getting the real answer? I don't know if this is a clue, but the Hifiman is separated into a power supply and the main unit, and the power is delivered via an umbilical with just two lines, so presumably that is ground plus some fixed voltage V. Everything in the main module either runs at V, or there are regulators in there to get lower voltages. I don't know if that gives any clue..

Mike
---
"Just because I'm paranoid doesn't mean they're not out to get me."
High-end headphone system with photos.

 

RE: Any way to assess heater current supply?, posted on May 21, 2012 at 23:16:25
Nunki
Audiophile

Posts: 130
Joined: November 27, 2010
 mike,

what variant of RFT 12AU7 is your favourite you reported about? the one with halo getter or that version with so called foil getter? the foil getter type is quite hard to find but said to be superior to halo type. them both. have you ever compared them in audition?

Nunki
The times, they are changing...

 

getter, posted on May 22, 2012 at 17:09:46
mike1127
Audiophile

Posts: 264
Joined: June 3, 2009
 I am not sure what a "getter" is, but looking inside there is a ring at the top of the bottle which, yes, looks like a "halo".

Mike

---
"Just because I'm paranoid doesn't mean they're not out to get me."
High-end headphone system with photos.

 

RE: RFT 12AU7 I am surprised no one said Telefunken, posted on May 22, 2012 at 18:08:38
nick-seattle
Audiophile

Posts: 13
Location: Seattle
Joined: May 20, 2012
 Cifte or regular, non-military Mazda tubes are great for a beautiful top end. The best buy right now is GE made in France by Mazda. A fantastic tube and cheaper than Cifte.

 

RE: getter, posted on May 23, 2012 at 10:13:17
Nunki
Audiophile

Posts: 130
Joined: November 27, 2010
 yes, that ring or "halo" under the bulbīs top you mentioned is the getter. some tubes have a plate instead of ring there. the RTF 12AU7 plate type getter looks more like a foil and this variation is highly recommended.

N.
The times, they are changing...

 

RE: RFT 12AU7, posted on May 30, 2012 at 17:24:06
tvr2500m
Audiophile

Posts: 1519
Location: Boston
Joined: February 2, 2003
 I like the RFT ECC82 a lot, whichever subvariant. I encountered this tube as the OE linestage tube in the Conrad-Johnson PV-12A that's been my frontline preamp for a while. It's a wonderful tube. Sounds good, if sometimes perhaps, maybe a bit clinical depending on what the system is like around it, typically has excellent tested Gm section balance, and is long lived and reliable. And the prices are sure right. I think it is sounds a lot like the short plate Ctx type 7316.

- SJ

 

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