The ECF82

[ColinTheAmpMan1]

Hi,
I have read that the ECF82 is the same as an EF86 and an ECC83 in the same envelope. I am disinclined to believe this, even forgetting that the ECC83 is a double-triode . Unfortunately, since the ECF82 was designed originally as a frequency changer or mixer and thus not for audio frequencies, the only data I can find for it don't give figures for audio use as is the case for the EF86 and ECC83 . Furthermore, the National Valve Museum states that the "pentode" section is actually a beam tetrode. The EF86 is a low-noise pentode intended for use at audio frequencies. Any thoughts?
Colin.

[G6Tanuki]

I've certainly seen an ECF80 used as a pentode first-amp and triode phase-splitter with the pentode being fed in 'starvation' current-voltage to get good gain [ screen-grid of pentode fed from cathode of triode]

The Radford MA15 series of audio amps used the ECF80 or ECF82 in audio front-end duty.

http://www.audiomisc.co.uk/HFN/Radfo.../circuits.html


Also see http://www.r-type.org/articles/art-097.htm


"The change to a pentode-triode was a development by Arthur Bailey and has a dramatic effect on the open loop gain of the amplifier. In effect, although the double-triode only had a flat gain bandwidth of around 15 kHz, the pentode-triode extended this to above 150kHz. As with the previous design, this flattening of the open loop response in terms of amplitude and phase made the amplifier inherently better, and allowed global feedback to provide further improvements without the amplifier oscillating on some loudspeaker loads. "


A R Bailey MSc(Eng) AMIEE, author of the second article, was one of Mr. Radford's design cow-orkers.

[Aub]

I've seen one used in a 160/80 metre AM transmitter in the late sixties. The triode section was the VFO, with the pentode section used as a buffer on 160 and a doubler on 80. Not very relevant to audio, I know, but just shows how versatile it is.

Cheers

Aub

[Synchrodyne]

It is unlikely that there is any connection between the ECF82 and the ECC83 and EF86.

The ECF82 was the European version of the 6U8. The latter, developed by Tung-Sol and released late in 1951, was specifically designed as a TV VHF frequency changer for receivers using the then-new “high” IF of 45.75 MHz. It was the second such valve, closely following the RCA 6X8. The basic requirements were for a triode that would be a robust oscillator at frequencies as high as 257 MHz, and a pentode that was as quiet as possible at Band III frequencies whilst still being a good mixer and also minimizing the various regeneration and degeneration mechanisms that could occur on the low Band I channels where the signal, oscillator and IF were fairly close to each other, particularly taking account of the fact that the mixer would be looking into a lowish-Q load that would not necessarily be an RF earth at signal and oscillator frequencies.

That design basis certainly would not disqualify such a valve from other applications. One might note that for example the 12AT7 (ECC81), originally designed as for VHF applications up to 300 MHz, was frequently used in audio circuits. In fact Philips originally included it in its TV World Series valves for use as an RF amplifier and frequency changer, and then a couple of years later it turned up as one of the “new” noval-based audio valves.

In fact TV frequency changer triode pentodes, particularly those with separate cathodes (the majority), were employed in many other applications. Mullard devoted two issues of its “Valves, Tubes & Circuits” series (#26 & 27) to alternative TV applications for the PCF80, having described its primary mission in #16. And from the start, RCA had suggested the 6X8 for use as a frequency changer for both AM and FM radio receivers. In the FM case, the pentode could be used as such or strapped as a triode (presumably in cases where the associated RF amplifier had lowish gain).

The ECC83 was the European version, allegedly with lower hum transfer, of the 12AX7, which in turn was a pair of the same triode used in the 6AV6 double diode-triode.

With a µ of 100 and a slope of 1.25 mA/V (at 100 V on the anode), the triode used in the ECC83 looks a lot different to that in the ECF82, µ 40 and slope 7.5 mA/V (at 125 anode volts).

The EF86 was the noval-based version of the EF40, both being similar to the EF37A. All were low-noise, low-microphony audio pentodes, with a slope of 2 mA/V (at 250 anode volts). In contrast the 6U8/ECF82 pentode was high slope, 5 mA/V (at 125 anode volts).

The 6U8 was described by Tung-Sol as a triode-pentode, so the pentode part was probably exactly that. In American practice there did not seem to be any disguising of beam tetrodes as pentodes, whereas Philips did do that at times, but not always. It is not impossible that some makers may have chosen to do the ECF82 pentode part as a beam tetrode with the same characteristics. Given that in this case the suppressor grid was internally connected to the pentode cathode, exactly the same pinout could have been used, with no-one any the wiser.

Cheers,

[ColinTheAmpMan1]

Thanks, Guys,
This is pretty much as I thought , but it's really good to have some knowledge. I read the statement about the ECF82 in a great (if rather expensive and only available in the USA) book entitled "Vox Amplifiers - The JMI Years" written by Jim Elyea. Despite the fact that Arthur Radford used it as a phase-splitter in audio amplifiers to good effect (I had not seen that arrangement before), the above book also informs us that Alan Harding of Vox wasn't impressed by the ECF82, calling it "a horrible valve".
Colin.

[Valvepower]

Colin,

Don’t know if it helps but Scott used the 6U8 (ECF82) in the LK72 amplifier.

The pentode is used a voltage amplifier and triode as a concertina phase splitter.

V3 in the attached circuit

Regards
Terry

[ColinTheAmpMan1]

Now that looks a whole lot more conventional to me . My old brain-cell(s) are more used to that sort of arrangement!
It seems that not everyone shared Alan Harding's view on the ECF82.
Colin.

[daviddeakin]

The ECF82 is nothing like the ECC83 or EF86, but some triode-pentodes did indeed contain the same triode as other double-triode bottles, such as:
ECF80 contains half an ECC82 (I think)
ECL82 contain half an ECC81
ECL86 contain half an ECC83

I don't recall any triode-pentodes having the same characteristics as the EF86, although I suppose one might exist.

[G8HQP Dave]

30PL13 contains half a 6/30L2.

The ECF80 triode is something like a whole ECC82 i.e. both triodes strapped in parallel.

The ECL82 triode is not half an ECC81. It could be regarded (roughly) as half or one third of of an ECC81 triode, as despite its physical size it draws much less current than an ECC81 triode.

[Peter.N.]

They were originally used as mixer/oscillators in TV tuners, although they were generally PCF80's but the '82 seemed to work just as well, that's the only application I have come across although the characteristics seem to lend them to other uses, but then I have seen an EF80 used as an audio output valve.

Peter

[daviddeakin]

Originally Posted by G8HQP Dave

The ECL82 triode is not half an ECC81. It could be regarded (roughly) as half or one third of of an ECC81 triode, as despite its physical size it draws much less current than an ECC81 triode.

You're right- I never noticed that before! It's sort of like a souped up ECC83... One would think it rather inefficient of these companies to make so many different variants of triode, especially the ones just for audio use. So you're making a new triode/power-pentode? Just stick in half a triode we already make and save time!

[Valvepower]

Hi,

Other pentode and triode in a single envelope are:

Brimar 6BR8 – see this thread and post #15 https://www.vintage-radio.net/forum/...ad.php?t=60549

RCA 7199 – Used in the Dynaco ST70 – see attached

Terry.

[G8HQP Dave]

Yes, it is puzzling that existing designs were not simply re-used for the triode in a triode-pentode - especially for audio. The idea seems to have been adopted only late in the valve era. Yet they did do this for earlier twin triodes (e.g. an ECC82 is two EC90) and others (e.g. the EBC90/6AT6 is a 5751 with a couple of diodes added, and is just a miniature version of the 6Q7).

[FERNSEH]

The ECF82 shown in the Radiomuseum has those beam forming plates.

http://www.radiomuseum.org/tubes/tube_ecf82.html

I believe the developer was SEL Lorenz.

DFWB.

[G6Tanuki]

I have always considered the ECF82 as being a decade-late European follow-the-leader version of the American 6U8 [and their better controlled-cathode-heating version the 6U8A] .

To me it's always been a pentode.