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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 5th Oct 2019, 11:05 am   #1
woodchips
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Default 12E1 as amplifiers?

Just unearthed some 12E1 valves out of an old variable PSU.

Never come across these before, data book says they are specifically designed for shunt series regulated power supplies.

Why?

What is different about them that they won't make an audio amplifier?

Seem odd in that they will take 800V, 200mA, anode dissipation 35W, which does seem rather low.

Thanks
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Old 5th Oct 2019, 12:15 pm   #2
G8HQP Dave
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Default Re: 12E1 as amplifiers?

Where does it say in the datasheet that they cannot be used for audio? You can use almost any valve for almost any purpose, but it might not work too well.

For a PSU you often need high current at low voltage drop for a series regulator, so low mu triodes (or triode-connected pentodes) are used. The 12E1 appears to have mu=5 when triode-connected. This might be a disadvantage in an audio amp.

The high voltage, high current - but not both at the same time - is again typical of PSU duty (and TV line output stage duty). It gives you flexibility, in that you don't need two separate valves for the two different regimes. If you want both at the same time then you need a much bigger and so more expensve valve.

You can be sure that someone somewhere will have used a 12E1 for an audio amp.
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Old 5th Oct 2019, 1:24 pm   #3
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Default Re: 12E1 as amplifiers?

Yes, the 12E1 is mostly used in voltage regulation circuits. I remember seeing a headphone amp built with them somewhere.
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Old 5th Oct 2019, 1:46 pm   #4
GrimJosef
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Default Re: 12E1 as amplifiers?

12E1's have been used in audio amps https://www.diyaudio.com/forums/tube...-poweramp.html although not, I think, commercial ones.

Power supply valves don't need to have a very linear characteristic - they typically operate with a lot of feedback and don't have to deal with very high frequency noise. With audio amps linearity is very handy as it means you can use less feedback and still not have unacceptable levels of distortion. Less feedback is A Good Thing given that you need quite wide bandwidth and have to accommodate the phase-shift idiosyncracies of the output transformer, which can lead to stability issues, especially at high frequencies, if the feedback level is too high.

One thing which is sometimes tried with these very low impedance valves is output-transformerless operation where the valves drive the speaker directly. That comes with challenges of its own though.

Cheers,

GJ
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Old 5th Oct 2019, 2:04 pm   #5
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Default Re: 12E1 as amplifiers?

I think the 12E1 headphone amp I'm thinking of was transformerless.
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Old 6th Oct 2019, 5:36 pm   #6
woodchips
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Default Re: 12E1 as amplifiers?

Thanks for the comments.

As I said, the data book said they were for regulators, I hadn't come across any killer reason for why that was true, so ask.

Yes, the idea of a transformerless design is one I hadn't thought of, certainly saves the cost of one. I was wondering if these valves, and others like the 6050, could be cobbled together to make a cheap, 30 bits cost, valve amplifier. No idea what it would sound like but interesting to try.
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Old 6th Oct 2019, 10:17 pm   #7
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Default Re: 12E1 as amplifiers?

You can pick up something like an 807 for close to peanuts and in a conventional audio amp they might well be a better bet. Transformers and chassis can be the most expensive parts at the cheap end of the market. In the end cost can come down to what bits and pieces you already have available.

EDIT: In fact in the case of an 807 it might be trickier to find the socket than the valve !

Cheers,

GJ
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Old 7th Oct 2019, 2:03 pm   #8
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Default Re: 12E1 as amplifiers?

Given what can be done with an EBL1 to turn it into an EBL31, a similar octalisation of an 807 shouldn't be too difficult. Use the pinout for a TT21 as a guide.

Though there seem to be plenty of ceramic UX-5 bases on Ebay, anyway.
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Old 7th Oct 2019, 5:55 pm   #9
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Default Re: 12E1 as amplifiers?

The briefest of casual searches reveals that it has long been suggested as an audio power valve- if for no other reason than that anything capable of double-figure wattage anode dissipation and 300V+ capability is going to be seized on as a possible. I've long suspected that it could well have been based on a well-known power beam tetrode anyway, with an anode cap and a bit of tweakage to suit it for regulator duty.
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