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Old 14th Sep 2017, 1:23 pm   #1
Edward Huggins
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Default Audio use of the ECL80 valve.

I only know of 2 makes of portable record player that used this little triode-pentode - Champion and Masteradio. With "only" 1.2 watts of output power and the (unloved) use of a common cathode, this was overlooked in favour of the later ECL82 and ECL83. However, I have a fully restored Masteradio single player from early 1957 using an ECL80 and EZ80 amplifer (7" x 4" speaker) and have been delighted with its sweet, undistorted sound. Even on LPs this gives a surprisingly room-filling volume. Do honourable Members know if this valve was ever used in any other audio application?
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Old 14th Sep 2017, 1:38 pm   #2
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Default Re: Audio use of the ECL80 valve.

Not audio as in record players but used in many TVs with good results. Not seen any push-pull.
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Old 14th Sep 2017, 1:59 pm   #3
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Default Re: Audio use of the ECL80 valve.

Mullard themselves produced a circuit for a push-pull 3W amplifier using two ECL80's. I've not heard it, but do intend to make one, some day...
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Old 14th Sep 2017, 2:04 pm   #4
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Default Re: Audio use of the ECL80 valve.

With care, the ECL80 can give good results as an audio amplifier. It was mainly used in TV's where it gave service as audio amp, sync separator/line/field osc and in at least one set, a mixer/oscillator (though exactly why, I don't know). It also appeared in a push-pull output stage in at least one of the more expensive sets. My Ekco T45 TV uses one in the audio output stage with excellent results.

Very occasionally it was used in small radio's. I think Champion used it in one of their 'budget' sets.

Respect for one of the workhorses of the 50's TV era!
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Old 14th Sep 2017, 3:28 pm   #5
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Default Re: Audio use of the ECL80 valve.

Here is the push-pull ECL80 amplifier used in the Ferguson 991T from 1952.

...and a slightly simpler Mullard circuit from the Nation Valve Museum:-

http://www.r-type.org/adverts/adv-0280.htm
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File Type: pdf 991T Audio Amp.pdf (199.7 KB, 545 views)

Last edited by ukcol; 14th Sep 2017 at 3:35 pm.
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Old 14th Sep 2017, 3:34 pm   #6
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Default Re: Audio use of the ECL80 valve.

More info here: https://www.vintage-radio.net/forum/...ad.php?t=62813
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Old 14th Sep 2017, 4:46 pm   #7
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Default Re: Audio use of the ECL80 valve.

A good while ago there was quite a bit of discussion on the forum about push-pull circuits for this valve. It was on my to do list but I eventually binned the idea because of the complexity of the common cathodes. I originally tried to design my own circuit but had to ask the forum members for advice. I think potential instability and the risk of the whole thing turning into a push-pull oscillator was a big factor. It would be interesting to find out if anyone has built one successfully. The main reason I had an interest in building one is the fact that I had loads of NOS ECL80's in my valve store, as I am sure many other people have.
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Old 14th Sep 2017, 5:08 pm   #8
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Default Re: Audio use of the ECL80 valve.

If anybody is reluctant to wrestle with the stability issues of the common cathode, the pentode section alone makes a perfectly serviceable output valve if you don't need loads of power. The low heater consumption is a bonus.
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Old 14th Sep 2017, 7:01 pm   #9
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Default Re: Audio use of the ECL80 valve.

Two ECL80 valves were employed in push pull for audio in the TX1410U Philips TV, 1951.
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Old 14th Sep 2017, 7:07 pm   #10
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Default Re: Audio use of the ECL80 valve.

I built a stereo version of Ferguson circuit a few years ago and used 100V line transformers for the output, the 5pF capacitors from the anodes of the output valves were not required, but I did add a bit of global negative feedback.

Dave

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Old 14th Sep 2017, 8:34 pm   #11
kalee20
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Default Re: Audio use of the ECL80 valve.

Another Mullard circuit used the ECL80 (pentode section) as a phase inverter feeding a pair of PL81's in push-pull. The triode was configured as an RF oscillator, the grid-leak bias voltage developed by the oscillation was filtered and biased the PL81's, all to save losing precious HT voltage in cathode resistors in this AC/DC circuit. So the ECL80 is half used at AF.
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Old 15th Sep 2017, 1:23 am   #12
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Default Re: Audio use of the ECL80 valve.

Hello,

It would appear that Mc Michael used a pair of ECL80s in push-pull in their AC only models 154 radio and 553 radiogram.
http://www.radiomuseum.org/r/mcmichael_553.html

A single ECL80 was used in their model AC/DC model 854 radio. (This uses 0.3 amp series heaters as I think the chassis was designed to fit into a TV/Radio combination as well.)
http://www.radiomuseum.org/r/mcmichael_854.html

The ECL80 is unusual amongst output triode pentodes in having a 6.3V, 0.3A heater so it could be used in both series and parallel heater chains. I suspect that the common cathode was needed to keep the heater current down to 0.3A.

Yours, Richard
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Old 15th Sep 2017, 6:00 am   #13
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Default Re: Audio use of the ECL80 valve.

I used an ECL80 in a battery-powered portable amplifier that I built. The 6V rechargeable battery provided the heater supply and negative bias on the grids.
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Old 15th Sep 2017, 11:53 am   #14
Edward Huggins
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Default Re: Audio use of the ECL80 valve.

I did not expect my Post to elicit such an abundance of information regarding this little valve. My thanks for all the info this has yielded.
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Old 15th Sep 2017, 4:27 pm   #15
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Default Re: Audio use of the ECL80 valve.

2*ECL80 should make a passable short superhet- mixer, regen second detector, output perhaps?

An interesting grounding and biassing challenge.......
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Old 15th Sep 2017, 4:44 pm   #16
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Default Re: Audio use of the ECL80 valve.

I can remember homebrew projects for all ECL80 radios in 1960s magazines, as they became freely available as pulls from scrap 1950s TVs. There were also lots of comparable designs based on EF80s and EF91s for the same reason.
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Old 15th Sep 2017, 5:18 pm   #17
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Default Re: Audio use of the ECL80 valve.

I used a pair of ECL80 in a 'midget' 160-metre AM transmitter.

One used the triode as an xtal oscillator and the pentode as output, with a pi-tank to match it to the antenna.

The other used the pentode as modulator (with a carbon mic) and the triode as a self-biasing send-receive switch.

I used the primary of a push-pull output transformer as the modulation-transformer: HT to the centre tap, one end-winding feeding the PA the other end being to the audio pentode. From memory it ran about 3 Watts of RF up the spout. The power-supply was bigger than the transmitter!

A related transmitter used an ECL80 as xtal osc/driver feeding a 6146 as the PA.
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Old 15th Sep 2017, 8:05 pm   #18
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Default Re: Audio use of the ECL80 valve.

Probably a little bit sad, but I think the ECL80 is an attractive little valve. Ok, Ok, I know that's not normal...but I still like them.
Alan.
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Old 15th Sep 2017, 9:03 pm   #19
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Default Re: Audio use of the ECL80 valve.

I also like the ECL80. It's had a lot of bad press because of the common cathode but hey....it's economical, still plentiful and gives a good account of itself as an audio amp. Actually it's surprising just how loud 1.2 watts is.....
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Old 15th Sep 2017, 11:40 pm   #20
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Default Re: Audio use of the ECL80 valve.

I also like the ECL80, as well as using a pair in push pull audio I have built a very simple oscilloscope with the pentode section as a transitron timebase and the triode used as Y amp. The valve is also low cost

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