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I've seen these tubes mentioned a few times, but never in a dedicated thread. These are some of my favorite tubes. I'll post up some pictures and technical info the next few days. To start with here are two pairs of ECC31's. I use these in my Woo WA22 with an adapter. Here is the first set:
 

 

 

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Second set. Notice the difference:
 

 

 

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Some technical details of the ECC31:
 

The CV1285 was previously called the NR73 before the CV register was established in 1941. The prototype for the design was the ECC31.

Type CV1285 and its other commercial equivalent the 6N7, is by no means a general-purpose double triode since it has a powerful heater, a common cathode, and is designed to operate in push-pull Class B2 with zero grid bias or quiescent push-pull. The anode to anode load is given as 8,000 Ohm.

It is specifically an audio power valve capable of 10 W per pair.

The classic envelope is 42 mm in diameter and, excluding the IO base pins is 82 mm tall.

References: Datasheet & ¹⁰⁴³. Type CV1285 was first introduced in 1937.

http://www.r-type.org/exhib/aac0112.htm
 

The ECC31 is a medium μ double triode with a common cathode. The CV1285 (formerly NR73) was based on the ECC31. The 6N7G has the same base connections but a much higher anode current rating and was designed for use as a Quiescent Push-Pull output stage.

http://www.r-type.org/exhib/aaa1556.htm
 
 

The ECC31 is a twin triode audio output valve. Imbued with a powerful heater and a common cathode cage these hallmarks belies it’s true purpose as an audio power valve capable of 10W dissipation when operating push-pull.

Often confused for the legendary ECC32 small signal triode as it shares a similar envelope, the key is in it’s totally different pin out and the half screened envelope.
http://www.mullardmagic.co.uk/ecc31-6n7g-nr73-cv1285-cv1956-twin-triode-various-manufacturers

 

[Mechans1]

I am quite surprised to see so little being written about these fabled tubes.  I have only had ECC32s for a couple of years and ECC33s for less time than that.  I use them in spots where a 6SN7 would be called for.   The guy that solded me the ECC32s I think felt some guilt about them, they were sold as NIB NOS but there was a run of Russian made ECC32s in the 1980s.  After careful exam,ination of thr getter I think these are British but not truly NOS as it seems most "NOS" tubes they were used even if with some care and limited application.  I think he was also a bit concerned about them in 6SN7 duty, repeatedly telling me that the filament draw was high.  All that said they still sound wonderful to me.  I have 3 they anything but cheap.
The ECC33s were an Ebay purchase with the seller telling all that these were used tuvbes with less than "new" emissions and transconductance but well within the good range.   So I got them at a good price because so many want to hear BS about NOS this and if it has a box NIB NOS all the while with well used tubes.  Heavily used may be a problem but used is fine by me if they make good music.  I have a pair of B309 Marconi (British) 12AT7s.  These tubes test on the edge of throw em out, I would except they make such beautiful sound.  There are things that tests don't always measure.
I wonder if anyone will ever read this or will it lie here for years to come and unceremoniously erased.

 

[leftside]

I kind of prefer none NOS when it comes to these tubes. I have some NOS, and I didn't even want to open their boxes let alone play them.

 

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On to the ECC32.
 
Sensibly equivalent to:
13D2 6SN7GT B65 CV181
 
The ECC32 is a clear predecessor of the ECC82 instrumentation double triode. In octal terms the later and smaller 6SN7GT and its variants were better known, but were equally designed for the same range of activities. Mullard describe the ECC32 as a double triode with separate cathodes for use as a papaphase AF amplifier and in phase inverters, multi-vibrators, etc. The low impedance triodes are the workhorse of instruments such as oscilloscopes etc.
The classic envelope is 43 mm in diameter and, excluding the IO base pins, is 86 mm tall.
http://www.r-type.org/exhib/aad0139.htm
 
http://www.mullardmagic.co.uk/ecc32-cv181-cv1988-13d2-b65-6sn7gt-twin-triode
 
Here are some Triotrons (rebranded Mullards) from 1954:
 

 

 

 

 

[Oskari]

I've seen these tubes mentioned a few times, but never in a dedicated thread.

There are these:

• http://www.head-fi.org/t/536785/ecc32-tube-addicts
• http://www.head-fi.org/t/558352/ecc33-ecc35-tube-addicts

 

[leftside]

Thanks for the links. They don't seem too active though. Might get more responses if the ECC31 - ECC35 tubes are rolled up into one thread?

 

[Oskari]

That could well be the case.

 

[abvolt]

My favorite driver tubes for my wa22 no doubt ecc35's also have 2 pair of the ecc31's awesome sounding..

 

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Here are two different Mullard ECC32's:
 

 

 

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ECC33
 
The ECC33 is a low impedance double triode with high gain. It featured separate cathodes and was designed for use as AF voltage amplifiers, phase splitters.  Many affectionados prefer this valve to the more common ECC32  variants because of the lower impedance and the curiously smaller and very rigid para-ellipsoid electrode cage which makes for a very stable, low noise base floor non microphonic dry incisive sound.   The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 62 mm tall.
 
Mullard, in 1949, describe the ECC33 as a high slope, low impedance double triode with low heater consumption, primarily intended for use in flip-flop, scaling and computer circuits. The electrode assembly is considerably smaller than other double triodes of the period.
The wide glass tube envelope is 30 mm in diameter and, excluding the IO base pins, is 67 mm tall.
References: Datasheet & 1040. Type ECC33 was first introduced in 1949.
http://www.r-type.org/exhib/aaa0474.htm

 

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Triotron 1955 Black Base:
 

 

 

 

 

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Mullard ECC33 (brown base):
 

 

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Mullard ECC33 1961 Black Base: