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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 19th Feb 2019, 7:25 pm   #81
Dave1000
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Default Re: "Audio" Valves

Audio websites are full of suggestions about "tube-rolling", but not (so far as I recall) about swapping dissimilar valves, just brands and very near direct equivalents, such as ECC82 and 5814A, unless sanctioned by the relevant manufacturer.

Cable changers fall into two directly opposing camps - bliss or nonsense, I'll go for the latter, so long as interconnects are screened and earthed.

Cap's - I've no idea on that one, although I see no reason why markedly different cap's, which can have large differences in ESR etc., which is completely ignored by 99.99% of audio fiddlers, should not change the output of an amp'.
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Old 19th Feb 2019, 8:05 pm   #82
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Default Re: "Audio" Valves

I think that it's the pluggability of similar pin-out valves that leads to the interminable arguments over makes, print colours, date-codes etc. because it's so quick and easy to do.

Anything that involved changing valve socket pinning would uncork another can of worms- which brand of silver-loaded solder has best sonic performance, why joints have to be made at an exact temperature with a particular type of iron and bit and allowed to cool at a precise rate..... The possible fussiness is endless.
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Old 19th Feb 2019, 9:05 pm   #83
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Default Re: "Audio" Valves

My one time foray into EF80s for audio suggested that they're rather too microphonic for any low level use. I've got enough EF37As and ME1400s to last me out....
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Old 19th Feb 2019, 9:46 pm   #84
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Default Re: "Audio" Valves

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Originally Posted by G8HQP Dave View Post
Quote:
Originally Posted by Dave1000
I have never seen anyone suggest any valve swapping in audio amp's outside of what equipment manufacturers or websites such as the Valve Museum suggest, or very close equivalents with different pin-outs (which require adapters or rewiring).
Have you never visited an audio website? Some people encourage valve swapping (in audio i.e. not guitar amps) ... In a sufficiently poor circuit it might even have some effect ...
Well if you will hang around on the dodgier websites then I'm afraid you've only got yourself to blame when you bump into that sort of speculative tinkering https://www.vintage-radio.net/forum/...ad.php?t=12309 .

Cheers,

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Old 20th Feb 2019, 12:04 am   #85
Lucien Nunes
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Default Re: "Audio" Valves

These days, users of valves are increasingly unaware that they were made for any purpose besides audio, if this has been the sole commercial application during their lifetime. A young former colleague questioned the need for valves in a TV (the 1400 that I was fettling) where top-notch audio quality was unimportant. My Tektronix 555 blew him away!

Modern valve sellers may seek to foster this idea, that valves and audio were 'made for each other'. Humdrum and lo-fi applications detract from the boutique appeal. Who would get any pleasure from their record collection knowing that the heart of their preamp was once destined to monitor smoke density in a refuse incinerator flue? This might lead to a tendency to classify any vaguely industrial sources as 'defence applications', as this at least implies gallantry if not sonic finesse.
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Old 20th Feb 2019, 2:12 pm   #86
G8HQP Dave
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Default Re: "Audio" Valves

Part of the problem is that some people think that audio is a particularly difficult application of electronics so it needs special components. These are people who have never had any contact with all the other ways electronics is used (except as an ignorant end-user).

Two slightly challenging things about audio: it is somewhat wideband (three decades in frequency), it needs fairly low noise so flicker noise is a potential problem. The bandwidth is no problem for valves but the low noise is. Hence some specifically 'audio' valves were designed for low noise and hum.
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Old 20th Feb 2019, 5:19 pm   #87
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Default Re: "Audio" Valves

A little knowledge is a dangerous thing. Couple that with, sometimes staggering levels of, naivety…………

Not all can remember the telly man calling every once in a while to empty the 6d's from the wind-up box at the back, or to fiddle with and change a couple of valves, or the googlebox that took minutes to, literally, warm-up.

I am sure that that all applies to most sellers, as well as punters.

LLLLOL - I just Googled Tektronix 555
If nothing else, at least you can get to all the controls/adjustments dead easily.....
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Old 20th Feb 2019, 5:49 pm   #88
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Default Re: "Audio" Valves

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Originally Posted by G8HQP Dave View Post
Part of the problem is that some people think that audio is a particularly difficult application of electronics
Maybe so - and although not 'difficult' it does pose its unique challenges: Wide frequency range (especially tricky when transformers are used); wide dynamic range; and quite extreme uncertainty of waveforms makes recovery from overload quite a consideration.

Stray circuit inductances can almost always be ignored. Distributed strays particularly - you don't have to think transmission lines, like you do at RF. Transit time effects in valves / charge storage in transistors, can largely be ignored. But as Dave says, low noise is key. And extreme linearity - we are looking at instrumentation techniques and layout for good hi-fi performance.

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These days, users of valves are increasingly unaware that they were made for any purpose besides audio.
Yes I can believe that! Though, the same people may be only dimly aware of the other disciplines in electronics anyway.

Valves do make rather lousy switches (I did one substitute a KT66 for a switching MOSFET in an off-line forward converter SMPS). Silicon does the job much better. Even the line-output valve was consigned to history once high-voltage transistor reliability was sorted.

But a lot of valves perform, in applications well away from the 'target' application. I have heard of EF37A's being used in electrometer applications - the top-cap grid means leakage to other pins is miniscule, and the low-noise techniques mean grid current is very small. Radio amateurs have got across the world with a 6V6 - try doing that with a 2N3055! Variable-mu RF pentodes have been used in AF compandor systems, well away from their intended use.
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Old 20th Feb 2019, 5:50 pm   #89
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Default Re: "Audio" Valves

Not a question restricted to any valve in particular, but does anyone know if any company but Tungsram ever used metal date/batch tags welded to various parts of the internal metalwork?
Also one (or more) of the German factories?
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Old 20th Feb 2019, 8:30 pm   #90
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Default Re: "Audio" Valves

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Originally Posted by kalee20 View Post


I have heard of EF37A's being used in electrometer applications - the top-cap grid means leakage to other pins is miniscule, and the low-noise techniques mean grid current is very small. Radio amateurs have got across the world with a 6V6 - try doing that with a 2N3055!



That's what the ME1400 is- an EF37A dressed up for electrometer use. Possibly specially selected, but just as good for audio use.


You might just actually get round the world with a later higher Ft 2N3055 as PA.
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Old 22nd Feb 2019, 10:18 am   #91
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Default Re: "Audio" Valves

Quote:
That's what the ME1400 is- an EF37A dressed up for electrometer use. Possibly specially selected, but just as good for audio use.
I have some 6BS7's which also had a secondary use as electrometer tube. The datasheet states specially selected for this use. There is an example circuit of such use on the datasheet I have.
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