Additional Preamp Tubes

+1 on the Mulllard CV4003.

My favorite 12AU7 variant.

  You have nice gear and premium tubes. My experience with 12AU7’s in a line stage pre brought me to Telefunkens. I’ve tried a few American tubes , the German stuff and regular nos Mullard 12AU7’s. The Seimens Nickle were too bright and the Mullard sounded like a blanket over my stereo. I ran Tungsram’s long ago and they were somewhat relaxed. If the CV 4003 is above the standard nos Mullard , that might be good. NOS Tung Sol’s are nice. The nos Tesla is similar to Tekefunken but a pinch more relaxed. FWIT people absolutely rave about the Mazda’s. I’d suggest asking PS directly and Andy at Vintage Tube. Also Brent Jesse’s site is still up and the descriptions are very accurate. Happy Hunting , Mike B. 

@mofimadness Thanks, I will probably try them. If I knew I could trust Valve Tubes out of the UK, it would be a done deal. 
@buellrider97 Thank you. I agree, the Siemens are bright. Tele’s are a little forward. i don’t think a blanket would be good, but I do want warmth. ChatGPT once described my ref 3’s as ‘brutally honest”.  My tubes are the only tuning in my perhaps analytical system. 
I believe the CV4003 variants (both Brimar & Mullard) are military spec. Thank you for the advice. 

BTW, ChatGPT (not the end all be all… but interesting) ranked them as follows: 

Overall

1. Brimar CV4003 ⭐⭐⭐⭐⭐

Your benchmark.

2. Mullard CV4003 ⭐⭐⭐⭐⭐

If you want maximum warmth and romance.

3. Amperex Bugle Boy ⭐⭐⭐⭐½

More lively, still musical.

4. Mazda/Cifte ⭐⭐⭐⭐½

The connoisseur’s choice.

5. Telefunken Medical ⭐⭐⭐⭐

More neutral and precise.

6. Siemens Nickel Plate ⭐⭐⭐⭐

Fast, open, less warmth

Maybe investigate the nos Tesla ecc802’s . They have less treble and more mid and bass compared to the Telefunkens. I have a pair of Hammond labeled 12AU7 Mullards. PM me if you want to try them I can mail them to you. Cheers , Mike B. 

On Ebay, I recommend this tube seller.     He’s one of the few who allows returns.  Most don’t.  I returned a pair once – no problem at all.    Probably best to narrow down your choice first.

My DAC uses the 12AU7 (or 5814A, 6189, etc).   IME, I have yet to find a warm variant.  The only exception was the Mullard 12AU7.  My observations were the same as @buellrider97.    Dull and lifeless.  Very unimpressed.   No experience with the CV4003.

The Amperex 7316 is a very nice possibility – relatively neutral with excellent resolution.  On the pricey side.

- - - 

Another approach. If you have Synergistic Research dealer nearby, ask if they’ll lend you a pair of upper-tier IC’s or a digital cable with the Red tuning module(s).   The Red warms up the SQ w/o sacrificing resolution.   Good luck!

Recently, I worked with a tube vendor who had a good sense of which tube manufacturer (and which era for each company) had a certain kind of sound. Emphasis on detail (Telefunken, for example), or a sense of warmth (Mullards). When I described what I had, and how I wanted the sound to change, he suggest 1960's RCA's. So, I tried a set of four for my phono preamp - that was the Goldilocks tube for me. I placed them in my three Zesto components  - phono, pre amp, and power amp. I had tried both Telefunken and Mullard in these components, and for me, my room, my ears, these have been a very good thing. 

Your experience may differ, of course...

David

Mullards are the quintessential warm tube for 12AU7, 12AX7, EL34, etc. In general, Mullards are warmer than Brimars. Unlikely you’ll find warmer tubes than Mullards. No doubt AI ripped off a plethora of posts recommending them, for that reason. The 4003 "box plates" in particular, because it was produced in large quantities all the way into the 80s for military production. Upscale Audio in particular sold them for quite a while. But don’t sleep on the Mullard 12AU7 with standard ladder plates, though they may be more costly. RCA black plates (NOT the "clear tops") have been known as warm too. Sometimes RCAs are VERY good, though I've had some duds too. 

@steakster @buellrider97 @mulveling @dtorc Thank you for your recommendations. I have added RCA ‘50’s blackplates to my list. They happen to be available from steakster’s recommended seller. Buellrider97, thank you for the offer. 
I have the UK vender checking to see if the CV4003 Mullards were manufactured in Blackburn. Also, need to consider all the duty / tariff fees. Thanks 

Mullards as a Mil Spec in the models discussed, are the antithesis of a typical Amperex equivalent. That noticeable difference in the sonic trait does not make the Mullard a warm, rich Valve. 

The Amperex can in certain circuits be similar in the end sound produced to resemble cleaning a Blackboard with one's nails.

The Mullard is a much more desirable implement selected to clean the Blackboard.

Certain circuits with Copper used in Cap's and without metal films in use, might give up the Valves inclusion as being with added depth to the sonic.  

The ones in the Link are readily available.

The pair are 60 years vintage and comes with measurements.

The Valves are not M8137, and these Mil Spec Valves do have the edge, as quality selection was the overriding precedent for them during production. 

I have a purchase method you might want to propose if additional support is easily achieved.

I inform the vendor of my intention to have the Valves remeasured when received, and that if the new measurement taken does not match the readings shown with the Advert. A full refund is to be sought, and valves are to be returned.  

https://www.ebay.co.uk/itm/287430489477?itmmeta=01KWS2CWYZ5APGJREV1J3QQ5A6&hash=item42ec313585:g:OzQAAeSwUypqRLD7

 I owned the BHK pre when it first came out. At the time, the actual BHK - Bascom King - seemed to believe that the very best tubes for his creation were Tungsran PCC88's. I remember that Upscale Audio had a bunch they were selling to BHK owners. The tubes required that you changed a jumper inside the chassis. I bought a pair, and it wasn't my cup of tea. But that's what the guy who made the product thought at the time...

David

@signaforce ,

I’ve used about 20 different brand 12au7’s and variants through the years.

Amperex, Telefunken red tips, Mullard, Westinghouse, Cifte, RCA black plates, CBS Hytron to name a few. Hands down my favorite are Amperex 7316 pq’s.

If ChatGPT didn’t mention them, it used very incomplete references.

They are pricey! If you go with Mullard cv4003, get the m8136 version.

The Amperex 7316 gives you the clarity of a Telefunken with the warmth of the Mullard. Best of both worlds.

What about the Amperex 7316?

Or the RT/RTC/Mazda/Belvu 12AU7?  Not the chrome plates.

I find that they still provide a high level of detail, just in a smoother fashion, if that makes any sense.

For a very affordable option, try the East German RFT, which is often labeled as National.

@pindac @thecarpathian @bbroussard @dtorc Thank you for your recommendations.
Early on I read of the favs of King’s for the BHK. Not sure why, but never considered them. 

2 for the Amperex 7316, & strong praise. Added. 
The CV4003 Mullards I am considering are the M8136 version. What does that mean?
BTW, the nice thing about tubes is even expensive ones are cheap compared to components or even cables & can have a profound effect on your sound. Thanks!

Got the answer on the additional designation. 

• CV4003 = British military designation.
• M8136 = a higher-grade military/industrial specification, typically requiring tighter tolerances, lower noise, and longer life.

If they are Blackburn manufactured M8136 (B-code) buying them. If Mitcham Manufactured M8136 (R-code) maybe not  Will find out tomorrow. Thanks 

I went and looked at my tube collection, and forget that I have a pair of RCA JRC 6189/12AU7WA dated 8/62. These are a ruggedized tripple mica black plate tube. I had them in my Rogue RP-1, but went on to the Tekefunken G73-R’s as they were what I was looking for. But in retrospect of this conversion and peoples suggestions, I thought I’d mention them. My pair came in pristine condition from “ The Tube Museum “. Here’s the AI sound description-  Warm , articulate with a punchy midrange and a tightly defined low end compared to standard 12AU7’s. Regards, Mike B. 

The M8137 valves you are interested in are ones I own, where all retained Valves from purchases made, have all been tested and are comfortably within factory specification.

I did not achieve this simply by purchasing valves and relying on the measurements provided by vendors. I only proceeded with purchases when sellers agreed to the testing criteria outlined in my previous post. For clarity, all measurements were taken using a calibrated AVO valve tester.

Over several months, I purchased more than 12 valves sold as matched pairs. The advertisements included attractive measurement data for each valve and half valve section.

However, when I had the valves tested, some of the valves' actual measurements differed significantly from those stated in the ad.

Following a number of returns and further purchases, I eventually assembled a set of six valves that are effectively interchangeable, closely matched, and all meet or exceed factory specifications on both half valve measurements.

Note: A valve specialist who is visited to carry out independent testing, explained that most valves will still function and produce sound even when their performance is well below factory specifications. He also noted that many valve owners do not know their valve's condition regarding factory spec and continue to use low spec valves without concern.

The advice I received was that a valve's published test results shown in an ad are just as important as the photographs used for the ad showing the valve's physical condition. A buyer may decide not to purchase a valve that appears to be in poor condition, and they may also reasonably question the asking price if independent testing shows that the valve's actual performance differs materially from the specifications advertised. In my arrangements, I do not negotiate the asking price when the spec is proven to be concerning; I already reserve the right to return a valve. 

@pindac Great advise & process! 
@buellrider97 Mike! I should have known. This gentleman was kind enough, (a few years ago when I was brand new to this hobby), to loan me several sets of tubes to try. Other than meeting on Audiogon, I was a complete stranger & he shipped me a couple $K worth of tubes (Mullard, Siemens, RCA, Tele’s), not trying to sell them, but to try in my RP1. I ended up buying my Siemens & Tele’s from another source as a result of Mike. What a gentleman! Thank you again Mike! 

buellrider97,

8/62 seems pretty late for a triple mica blackplate tube.   I think both GE and RCA phased this design out around 1958 or 1959.  It might have been stored without printing or possibly re-printed at the time.  Regardless, it is a very good tube, although not in the same class of some of the others mentioned above, IMHO.  Just for the record, my opinion doesn’t count.  Plug them in and see how YOU like them.  Best of luck.

@bbroussard , I’m not an expert but they shipped in their original box’s. They are not rca logos but a light brown military JRC box with the production date below the other info. The tabs fell off the second time I opened them. I did try them then went on to 5-6 other pairs settling on  the black coated Tekefunkens. Regards , Mike B. @signaforce , Ha Ha , I still have the RP-1, I aquired a Rogue Hera and a pair of M-180’s that I had upgraded to Dark. Got ‘em done last fall and it’s all in the closet until I wall mount a yet to purchase TV, new rack built and a loom of balanced IC’s. Hopefully in the new couple months. Happy Hunting. 

It was not uncommon for the military to re-test and re-package tubes with then-current dates.  They are significantly better than actual 1962 production.

FWIW , RF Parts company in San Marcos, Ca has nos RCA 6189’s black plates for $34.91. Sorry I wasn’t able to post the link with my iPhone. 

Don't rule out 6V tubes. There is a jumper to change inside the chassis. When I had a BHK pre I liked 6 volt tubes best, though I don't remember which tubes in particular. But a problem I had with 6V in my unit was noise. But I think that was not universal.

@buellrider97 ,

Mike, that's right! You're the one with the legendary Telefunkens!

Man, what a score...

@thecarpathian , Ha Ha , I should have bought Microsoft when it first was available. The guy had 10 of those tubes at $125 each , bought 4 should have bought them all. It’s sad what’s happened to nos tubes in the last 10 years. 

Checking my stash, I have 5 Mullard cv4003’s, of which 2 are 8136’s and all kinds of others.

All Mullards from Upscale Audio and been just sitting in their little boxes for years. Think it’s time to thin the herd.

@buellrider97 , you and me both!

Also Apple, Google, and Amazon!

Wow, $125 each.

At least you got four. Could have bought just two!

@markmuse Thanks, I looked at 6v and almost bought a pair of 6v Amperex a little while back. As I understand it, noise can be an issue. 

Just ordered the Premium Matched Pair CV4003/M8136 NOS Mullard tubes. They are Markham manufactured, so while less warm than the Blackburn’s they may in fact be a perfect fit. 

Mitcham was Mullard’s specialized plant for military, industrial, and high-reliability tubes. Consequently, their CV4003s often sound slightly more linear, detailed, and open than their Blackburn siblings. You still get that beautiful liquid midrange, but with a touch more top-end extension, a slightly faster transient response, and a tighter bass grip.

We shall see. Thank you for your advice. 

Amperex 7316 are my favorite, 1950s if you can ever find a matched pair/quad, but most likely 1960s.....these are easier to find and slightly more affordable, and are brilliant. 

I had the BHK preamp for a while and used the tubes mentioned previously, i.e., Brimar, Mullard and RCA.  I tend to like a warmer rather than analytical sound.  I purchased the Mullards when it was easy to deal with the UK.  It was when I stumbled upon and tried RCA black plate triple mica that I was happiest.  It provided warmth, clarity and bounce, allowed the highs to come through but nice and round in the mids and bass, much to my liking.  And, it was around half the price of the others.

I changed my system completely since then, and found the Amperex was a good match after the change.  The good news is there are options, but it's your ears that need to be happy.

If anybody is still listening, you might consider some new production tubes. Ray's Select 12au7 are nicely balanced tubes. I also tried new production Mullards. Currently I am using PSVane Horizons (GASP!) in my Backert Labs Rhythm. If you want a more controlled sound with lots of depth, give them a try. At 65$ pair from Amazon (Gasp again!!) not much to lose. 

+1 on Psvane!  I've had terrific luck with Psvane tubes.  For new production tubes, they come pretty damn close to NOS, (and sometimes better).  Highly recommended.

Still listening. My BHK pre came preloaded with PSVane tubes. Since I already had my current tubes from my Rouge RP1 that matched my BHK (part of the reason I bought the BHK), I changed them out pretty quickly. 
Most modern tubes are Russian, and refuse to buy Russian, even if they were the best… and IMHO they are not. 
My NOS Mullards arrive from the UK on or about the 22nd. I look forward to trying them. Thanks

Slava Ukraini! 🇺🇦

I have the same preamp and after trying several tubes, I ended up using some NOS RCA Cleartops. I even bought extra when I heard that Brent Jessie was closing. Having said that, I have never gone wrong with Amperex NOS.

All the best.

@curiousjim You have a fantastic system. I think your (& my) tube selection is more driven by our speakers. AI describes your G5’s as …substantially larger, deeper scale of sound with an incredibly lifelike midrange and a more forgiving, lush acoustic character. My Ref 3’s: hyper-analytic, modern presentation where pinpoint acoustic accuracy, phase coherence, and a ruler-flat frequency response are your top priorities.
As I stated ar the outset, those were my priorities, but now I want to warm things up without changing my speakers.
AI thinks more revealing tubes (your RCA cleartops or Amperex or my Siemens or Tele’s)) are perfect for your G5’s. Warmer (My Brimar’s or Mullard) for the Ref 3’s. Ergo, the Mullards. Thanks! 

I am without a recollection of Brimar Valves used in a line up when Valve Rolling and making selections for a Phonostage and DAC, as well as Input tubes for a Power Amp where the power amp's design is using a half valve only for the Input Tubes.

I am convinced there is nothing extra to be discovered with the Phon' and DAC, but do believe there is still synergy to be discovered with the upstream Input Valves on the Power Amp, which has resulted in Valve Rolling sessions over a few years.

Up until late 2025, I was confident the KR VT231 Black Glass was the most attractive I could have in use. During a new arranged Valve Rolling session in late 2025, I was introduced to vintage 6SN7's that I was not familiar with and compared these to Valves I was very familiar with. The result being all of my owned Valves were shown to not be the best interface, and a new, improved synergy was discovered.

The Valves that superseded the KR's and proven able to produce this new improvement to the system's end sound are a RCA model from the 1950's and a Brimar model from the early 60's. Subsequently, the RCA's are purchased and are a second-best option. The Brimar's are the better option, but are very expensive and not yet found at an asking price I want to pay.

With new speakers added to the system in very early 2026, the revisit to the Valves will once more occur in 2026. There are also newly purchased Linlai Elites in 2026 to add to the 6SN7 lineup. Outcomes of comparisons might once more take a new direction with the new speakers in use.

@signaforce 

That’s exactly why I traded in my Reference 5’s.

My Ref 3’s: hyper-analytic, modern presentation.

@curiousjim Too much money… too much weight. System in upstairs bonus room,  

I can’t even imagine getting your Ref 5’s or G5’s up my stairs. Bribed 2 young neighbors with Macallan just to get the Ref 3’s up the stairs. 😏

Trying to avoid it. We shall see.