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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 2nd Jul 2019, 8:41 am   #1
Aerodyne
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Default EF80 - anyone tried it as an audio amp?

The ubiquitous EF80 (who amongst us doesn't have a pile of these?) but unwanted for most construction tasks. My question is, has anyone attempted to use the valve as an audio amplifier and if so, what were the results?

Tony
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Old 2nd Jul 2019, 8:44 am   #2
merlinmaxwell
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Default Re: EF80 - anyone tried it as an audio amp?

It will work, just not very high power. A few in parallel push pull will make a nice room heater.
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Old 2nd Jul 2019, 8:55 am   #3
paulsherwin
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Default Re: EF80 - anyone tried it as an audio amp?

There were hobbyist designs for all sorts of things in the 60s when huge numbers of EF80 pulls became available from scrapped tellies. They're a bit noisy for low level audio use, but you can use them as output valves if you only need half a watt or so.
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Old 2nd Jul 2019, 9:01 am   #4
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Default Re: EF80 - anyone tried it as an audio amp?

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Originally Posted by paulsherwin View Post
They're a bit noisy for low level audio use, but you can use them as output valves if you only need half a watt or so.
There was at least one TV that actually did this but the model escapes me....
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Old 2nd Jul 2019, 9:11 am   #5
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Default Re: EF80 - anyone tried it as an audio amp?

I've used one as a leaky-grid detector, works fine (100kΩ anode load), not noticed any tendency to be microphonic.
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Old 2nd Jul 2019, 9:34 am   #6
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Default Re: EF80 - anyone tried it as an audio amp?

I did it a few years ago. I wasn't very impressed with the result BUT suspect that the EF80s I had weren't in the best condition.
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Old 2nd Jul 2019, 9:55 am   #7
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Default Re: EF80 - anyone tried it as an audio amp?

I've done this, they work okay, not exactly a power output valve, prolly my favorite small valve, don't tell the audio lot about them triode strapped, it'll push the prices up!
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Old 2nd Jul 2019, 11:45 am   #8
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Default Re: EF80 - anyone tried it as an audio amp?

I have been wondering how well they would work in push pull with a very small mains transformer for background audio service.
I looked at the data sheets and came up with about 2 or 3 whats.
I will follow with interest.
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Old 2nd Jul 2019, 11:59 am   #9
Peter.N.
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Default Re: EF80 - anyone tried it as an audio amp?

I also remember a TV that used an EF80 as a sound output valve, but as usual can't remember what it was.

Peter
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Old 2nd Jul 2019, 1:14 pm   #10
barrymagrec
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Default Re: EF80 - anyone tried it as an audio amp?

The Z77 (EF91) which is a B7G version of the same valve to all intents and purposes was used by EMI as 3rd and 4th stage valves in the record amplifier of the TR50 and TR51 tape machines.
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Old 2nd Jul 2019, 3:32 pm   #11
TonyDuell
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Default Re: EF80 - anyone tried it as an audio amp?

The HMV 1840 series of TVs used an EF80 as the audio output valve. The 1807 used a Z77 (similar to an EF91 I think).

It's not clear to me if the OP meant using the valve as an audio power output device (to drive a speaker via an output transformer) or an audio signal voltage amplifier. I am pretty sure the EF80 can be used for the latter (as well as obviously the former).
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Old 2nd Jul 2019, 3:48 pm   #12
GW4FRX
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Default Re: EF80 - anyone tried it as an audio amp?

When I was a lad I used one as the PA in a 144MHz AM transmitter (the modulator was an ECL80). It did manage several contacts although the output power couldn't have been much. But what a thrill...those were the days.
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Old 2nd Jul 2019, 4:59 pm   #13
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Default Re: EF80 - anyone tried it as an audio amp?

I've never used an EF80 as a power-device but _have_ used them as a low-level audio stage in the same sense as EF86.

They're cheap and ubiquitous as 'pulls' from old tellies, so why not experiment
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Old 2nd Jul 2019, 8:07 pm   #14
Leon Crampin
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Default Re: EF80 - anyone tried it as an audio amp?

The EF80 is near enough pin-compatible with the 6BW6 to operate as a plug-in replacement. In a small set such as the KB FB10, it's hard to tell any difference in performance.

Not the best of bodges - but effective in an emergency.

Leon.
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Old 3rd Jul 2019, 7:50 am   #15
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Default Re: EF80 - anyone tried it as an audio amp?

Hi All I have used EF80's in a 5-10 stereo amp in place of the EF86 and ECC83 ( the push- pull output used PL508's in place of the EL84's).
The preamp EF80 rang like a bell !! but when replaced with a frame grid EF184 it worked well. Two EF80s triode connected were used in place of the ECC83.
I call this my Tele Amp.
Keith
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Old 3rd Jul 2019, 8:02 am   #16
Ed_Dinning
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Default Re: EF80 - anyone tried it as an audio amp?

Hi Gents, there were many designs for complete amps, radios etc using EF80's and also EF50's in the magazines of the day.
It would be interesting to see the above amp using a set of nice red EF50's, possibly less micro-phonic as well !

Ed
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Old 3rd Jul 2019, 8:08 am   #17
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Default Re: EF80 - anyone tried it as an audio amp?

Quote:
Originally Posted by ctc15 View Post
... The preamp EF80 rang like a bell !! but when replaced with a frame grid EF184 it worked well ...
The Radford STA100 (a serious hi-fi amp, often used in recording studios) used a pair of EF184s as the phase-splitter.

Cheers,

GJ
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Old 3rd Jul 2019, 8:58 am   #18
Peter.N.
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Default Re: EF80 - anyone tried it as an audio amp?

The 1807 was probably the one Tony, we serviced a few of those and yes, the Z77 was to all intents and purposes an EF91, so that could have been what was used. I'm sure I did see one with an EF80 though. The valve holders on those sets gave no end of trouble.

Peter
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Old 3rd Jul 2019, 10:51 am   #19
Aerodyne
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Default Re: EF80 - anyone tried it as an audio amp?

Just for clarity, I had in mind low-intermediate AF amplifier use for the EF80 (a la EF86). Obviously it couldn't hope to compete with the EF86 directly, but it struck me that as an audio voltage amplifier it ought to work reasonably well. I'm surprised it was used as an output valve, but I shouldn't have been, knowing the 'any port in a storm' approach to TV design in the mid 20th century.
Thanks for all the replies. Some really interesting points made.

Tony
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Old 3rd Jul 2019, 11:33 am   #20
GrimJosef
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Default Re: EF80 - anyone tried it as an audio amp?

One of the features of the EF86 was its spiral-wound heater designed to reduce levels of hum in small-signal audio applications. These days it's cheap and easy to implement DC heater supplies for valves in these circuit positions so the EF80's simple 'hairpin' heater geometry wouldn't be an issue.

Cheers,

GJ
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