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Valve questions from a total numpty

Printed From: Graham Slee at Hifi System Components
Category: And the rest
Forum Name: Amplification
Forum Description: Share your interests or views on amplifiers, preamps, etc
URL: https://www.hifisystemcomponents.com/forum/forum_posts.asp?TID=2750
Printed Date: 19 Nov 2019 at 1:15am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com


Topic: Valve questions from a total numpty
Posted By: morris_minor
Subject: Valve questions from a total numpty
Date Posted: 01 Jan 2016 at 5:06pm
I'm getting together a little bedroom system and recently got an amplifier off eBay which did what I was after - two analogue inputs and Bluetooth connectivity.

The downside (or maybe upside!) is that this little thing has a valve pre-amp. The first time such an anachronistic device has set foot over the threshold . . Embarrassed

So my questions are:

1. Do valves wear out more quickly with being left on for long periods, or being turned on and off many times?

2. When one fails, is it a simple question of just turning the thing off and inserting a new valve? I read about setting bias, and valves having residual current (or something).

How can I prolong the life of the tubey things, and not kill myself when I need to change one? Shocked

I'll leave the issue of tube rolling to much (much) later . . . Wink




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Bob

Majestic DAC/pre-amp
Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V
Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50
2 x Proprius + Spatia/Spatia Links



Replies:
Posted By: Richardl60
Date Posted: 01 Jan 2016 at 5:17pm
Never had a valve amp but always found the early 80s Audio Research very inviting (albeit way out of price range)...

An extremely experienced and traditional audio engineer I use advised some time ago that valve gear tends to need 'tuning' it may be the bias you mention. I strongly suspect they may degrade over relatively short period.

Perhaps Graham can verify or otherwise?

Richard


Posted By: Chris Firth
Date Posted: 01 Jan 2016 at 9:23pm
You should get a relatively long life out of your preamplifier valves, typically somewhere in the order of 10,000 hours as long as the valves aren't getting a caning from poor circuit design.


Posted By: oldagetraveller
Date Posted: 01 Jan 2016 at 10:27pm
Just make sure the valves are there to carry out their intended function and not for effect!
I have seen reports that some so called valve pre amps from China have cheap valves fitted to show a nice glow but do absolutely nothing.

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Peter

P T- LPT/RB300/G1042, Pink Triangle Tarantella/Nima/Ortofon 2M Black, SL1210II, Naim CD5, NAC112, NAP150, Flatcap2, Proac SC1, GS SoloUL,GS Accession , Senn HD250 & HD540.


Posted By: Graham Slee
Date Posted: 02 Jan 2016 at 11:04pm
Thomas Alva Edison was inventing the light bulb when he by chance happened on another invention which he eventually developed into the thermionic valve (tube).

He discovered electron flow in the vacuum of the light bulb envelope was plating the inside of the glass (much as an auto bulb does when your alternator regulator packs in), because he was using DC volts (quite popular in the USA at the time - and quite dangerous!).

After much development by those following in his footsteps reliable valves became a possibility. Reliable to a degree. If we understand that what is basically metal is being very-very-slowly deposited from one place to another it will eventually fail. Therefore between first switch on and failure its characteristics are changing.

Transistors got around this problem with electrons and holes where it's all "recycled" around the circuit they're in.

The above is intentionally simplified. The people reading this are intelligent but in their own field of work. And I don't feel like writing an essay.

For the valve to work and due to its high impedances (ac resistance) it needs a HT supply. HT is high tension -- high DC voltage. Most valve preamp circuits work at 100 - 250 volts DC, which is above the (75 volt) Low Voltage Directive (not that manufacturers care).

Signal modulated voltages greater than 75 volts are found in valve amps on the output transformer primary. Like 100V line used in PA if you touch it you can "feel the music". But that's a valve amp, not a preamp.

As you will get an electric shock from the mains supply, you will get a belt off HT, but it will have the effect of making your hand tighten around the conductor, and this is why DC mains was eventually banned in the UK -- because of all the fatalities. An ac shock because it alternates gives you chance to let go.

Capacitor discharge at such voltages isn't nice either, but not quite as bad as an EHT (extra high tension) discharge. You have little chance of accidentally killing yourself from EHT discharge, but you have more chance of being killed or seriously injured by the way it throws your body at high acceleration away from it. Luckily when it happened to me there was a soft sofa to reduce my impact with the wall behind it.

My thoughts on valves: I'd rather have my heart beating.

Why do I know so much about electric shock? Because I was trained in it and still have my certificate somewhere. Wink


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Posted By: morris_minor
Date Posted: 03 Jan 2016 at 9:39am
Hopefully the bed will stand in for the sofa . . . LOL

What I'd really like to know is does either frequent switching on/off or being left on for long periods have a worse effect on valve life? Or doesn't it matter?


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Bob

Majestic DAC/pre-amp
Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V
Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50
2 x Proprius + Spatia/Spatia Links


Posted By: Graham Slee
Date Posted: 03 Jan 2016 at 11:06am
Originally posted by morris_minor morris_minor wrote:

Hopefully the bed will stand in for the sofa . . . LOL

What I'd really like to know is does either frequent switching on/off or being left on for long periods have a worse effect on valve life? Or doesn't it matter?


If you leave it on then the tubes will obviously be burning like light bulbs, or to be more precise, the heater elements which are needed as a catalyst to get electrons to flow are burning just like light bulbs. The heater winding on the transformer was 6.3 volts when I was a lad, so the heaters are glowing a bit like torch bulbs in a 6 volt lantern. Some are DC and some are ac which are a bit more "hummy". I can't remember which type lasts longer and I wouldn't know what yours has. I don't know what's "trending" in valve hifi, I just know how to design using valves but I don't put it into practice.

So it's probably best to switch it off. Each time you switch it on each heater element has to go from cold to hot. Therefore it suffers a step-change. Obviously that is a designed-for occurence. But like a light bulb it has a lifetime. It's all basic physics. If you get some thin metal and keep bending it back and forth it eventually fractures. If you were to switch on and off in rapid succession the heater element would eventually fail. Valves are more subject to fatigue than solid state because they're more "mechanical".

In the case of those USSR valves which don't have a heater the above is academic.

Now, do you want me to explain how valve biasing works?


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Posted By: morris_minor
Date Posted: 03 Jan 2016 at 12:44pm
Thanks Graham.

BTW the tubes are Chinese 6n1 . . .

I think any explanation of biasing will go right over my head . . .Ermm


-------------
Bob

Majestic DAC/pre-amp
Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V
Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50
2 x Proprius + Spatia/Spatia Links


Posted By: Chris Firth
Date Posted: 03 Jan 2016 at 1:15pm
The comment about capacitor discharge brings back memories of taking a guitar amplifier head in for repair.
The repair tech carefully removed the chassis from its cabinet and placed it upside down on the bench.
He then picked up a very large and well insulated screwdriver, and contacted it on the legs of the large reservoir caps, which emitted a very loud crack on each cap.

How loud was it?
I nearly soiled my undergarments.

The guy did explain to me that he had once started to work on an amplifier and he hadn't checked that the caps were discharged, and he got a belt off one of them that threw him against a stud wall.




Posted By: morris_minor
Date Posted: 03 Jan 2016 at 1:37pm
This 1998 article from the IEEE is interesting . . .

http://spectrum.ieee.org/consumer-electronics/audiovideo/the-cool-sound-of-tubes - http://spectrum.ieee.org/consumer-electronics/audiovideo/the-cool-sound-of-tubes


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Bob

Majestic DAC/pre-amp
Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V
Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50
2 x Proprius + Spatia/Spatia Links


Posted By: Graham Slee
Date Posted: 03 Jan 2016 at 6:03pm
Originally posted by morris_minor morris_minor wrote:

This 1998 article from the IEEE is interesting . . .

http://spectrum.ieee.org/consumer-electronics/audiovideo/the-cool-sound-of-tubes - http://spectrum.ieee.org/consumer-electronics/audiovideo/the-cool-sound-of-tubes


Oh dear, another one taken away by the tube monster Sleepy

(only kidding... I hope Wink)

The IEEE claims to be the World's Largest Professional Association For The Advancement Of Technology.

I don't really claim anything but what I do is to try and find, tie down and overcome all the little things nobody else seems to want to talk about because it's not sexy. For example: parasitics which modulate the music signal and to be honest that's basically all I do. Pretty boring stuff to talk about and far from glamorous I know, and completely dead boring compared to glowing tubes. No way I could ever compete.

Did I tell you about the little parasitic oscillations on the output of a linear voltage regulator and how different implementations can make a night and day difference to your music? Of course I didn't, because it's so utterly boring. Nuff said.


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Posted By: Fatmangolf
Date Posted: 03 Jan 2016 at 6:25pm
I have several guitar amps with valves in them and they sound great when used as expected. thermionic valves/vacuum tubes don't last forever and yes they should be powered down when not in use, the warmed up through standby before use.

My knowledge of valves is from repairing and modifying guitar amps. The supply voltages are pretty high so dangerous and I use discharge resistors not screwdrivers to make the chassis safe to work on!



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Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: morris_minor
Date Posted: 03 Jan 2016 at 6:48pm
Originally posted by Graham Slee Graham Slee wrote:


Oh dear, another one taken away by the tube monster Sleepy

(only kidding... I hope Wink)
You can breathe easy, Graham - I'd no more have a valve amp for quality listening than chose Bose speakers . . Shocked

In my little bedroom system the amp comes downstream from a Novo, fed directly from a Raspberry Pi "squeezebox". The amp's only driving an old pair of Sony music system speakers anyway; it just makes a "pleasant noise" . . .Wink


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Bob

Majestic DAC/pre-amp
Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V
Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50
2 x Proprius + Spatia/Spatia Links


Posted By: Graham Slee
Date Posted: 03 Jan 2016 at 7:06pm
Originally posted by morris_minor morris_minor wrote:

it just makes a "pleasant noise" . . .Wink


Of course it does Bob, just like "Cathode Ray" (RIP) explained it would in a very old issue of Wireless World.

(https://en.wikipedia.org/wiki/M._G._Scroggie)


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Posted By: Graham Slee
Date Posted: 06 Jan 2016 at 4:49pm
I take all the avove back! The amp's a charlatan!!!

Just read the description: Hybrid!

A solid state amp with valves that might be doing something but definitely not power amplification--the dead give-away being its weight: 1.7kg. Not much iron then in its two (stereo) output transformers??

Doubt if it has output transformers, and if not it'll be a little class D solid-state amp.

Thumbs Down

I'd just like to add that I respect good valve designs, but have much contempt for people using valves for marketing hype, especially when the valves are just for show, and from my discussions with my good friend Bob I took it that he really thought he'd bought a valve amp.



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Posted By: BackinBlack
Date Posted: 06 Jan 2016 at 6:34pm
To be fair, Bob did say that it had a valve preamp. 

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Just listen, if it sounds good to you, enjoy it.


Posted By: tg
Date Posted: 06 Jan 2016 at 7:22pm

Quote I'd just like to add that I respect good valve designs

That's a relief, thought I might be banned for using illicit substances for a while there Wink

Bob, small signal valves such as your hybrid uses for preamp duties have, as already noted, a fairly long life, likely years of light use such as a few hours per day.  Best not switched on and off too often or run for short periods.  A couple of times a day should be fine, leave it on for at least an hour or so when you do use it, it will usually sound better after a little warm up time anyway.

Might be worth finding out what valves it runs and getting in a set of spares.

Changing them over is not difficult, nor should they require any adjustments to be made when doing so.  A gentle rotational rocking can be helpful in removing them, when replacing them a careful inspection of the socket and the valve base will show the correct orientation.

Bias adjustment (on amps that do require it) is usually only for power valves not preamp valves.



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Tony G


Posted By: morris_minor
Date Posted: 06 Jan 2016 at 7:34pm
Thanks Tony.

Whether or not these valves do anything, is, for me immaterial. I didn't buy it wanting a "tube sound". I wanted a bluetooth enabled amp with two inputs. This fitted the bill and I got it cheap.

My questions were about looking after the valves, since if they fail I suspect the amp will fail too. If it still works, then the light show is just that - a light show. Embarrassed

Whether or not the company is trying to pull a fast one is something that irks, (and certainly irks Graham!), but TBH I don't really care from a practical point of view, and my money didn't go to the company . . . I only considered it after figuring out that a Novo upstream would provide excellent listening, with the speakers used for TV sound and occasional casual music - most likely from Spotify via my phone and bluetooth. So a quality amp would be wasted. Wink


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Bob

Majestic DAC/pre-amp
Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V
Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50
2 x Proprius + Spatia/Spatia Links


Posted By: Fatmangolf
Date Posted: 07 Jan 2016 at 6:39pm
TBF it is quite pretty to look at...

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Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: morris_minor
Date Posted: 08 Jan 2016 at 8:10am
Originally posted by Fatmangolf Fatmangolf wrote:

TBF it is quite pretty to look at...
Yes, the bling factor outdoes the audio performance . . . LOL

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Bob

Majestic DAC/pre-amp
Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V
Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50
2 x Proprius + Spatia/Spatia Links


Posted By: morris_minor
Date Posted: 22 Jan 2016 at 11:07am
Will this work in my amp?




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Bob

Majestic DAC/pre-amp
Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V
Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50
2 x Proprius + Spatia/Spatia Links


Posted By: Ash
Date Posted: 22 Jan 2016 at 11:56am
Who needs valves when you can mimic their behaviour with solid state...


Posted By: Graham Slee
Date Posted: 22 Jan 2016 at 4:16pm
Originally posted by morris_minor morris_minor wrote:

Will this work in my amp?




Funny, I can't think of one innuendo right now... Wink

I'm sure other members can! WinkWinkWinkWinkWink



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Posted By: oldagetraveller
Date Posted: 22 Jan 2016 at 4:21pm
Originally posted by morris_minor morris_minor wrote:

Will this work in my amp?




Which, the woman wearing the hat?
"Don't worry sir, we don't have to insert it too far for a prostate examination."


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Peter

P T- LPT/RB300/G1042, Pink Triangle Tarantella/Nima/Ortofon 2M Black, SL1210II, Naim CD5, NAC112, NAP150, Flatcap2, Proac SC1, GS SoloUL,GS Accession , Senn HD250 & HD540.


Posted By: BAK
Date Posted: 23 Jan 2016 at 12:03am
Originally posted by oldagetraveller oldagetraveller wrote:

Originally posted by morris_minor morris_minor wrote:

Will this work in my amp?




Which, the woman wearing the hat?
"Don't worry sir, we don't have to insert it too far for a prostate examination."

OUCH !


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Bruce
AT-14SA, Pickering XV-15/625, Technics SL-1600MK2, Reflex M, Lautus, Technics SH-8066, Dynaco ST120a, Eminence Beta 8A in custom cabs;; Using Majestic DAC
Enjoy Life Your Way!


Posted By: ServerBaboon
Date Posted: 24 Jan 2016 at 10:26am
Originally posted by morris_minor morris_minor wrote:

Will this work in my amp?



.yes but you will feel slight initial pressure pressure as it is inserted.



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Steve

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Various bits of GSP Kit ..well two so far, unless you count the cables that is.


Posted By: Graham Slee
Date Posted: 24 Jan 2016 at 12:04pm
Originally posted by morris_minor morris_minor wrote:

Will this work in my amp?




Sorry Bob, no it won't, and here's why...

This is a still taken from an early pilot of the BBC's Tommorow's World from 1963, and the lady in the photo is a veterinary nurse. The device is for artificial insemination of cattle!

(hence the slightly embarrased grin on her face...)

Wink


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Posted By: BackinBlack
Date Posted: 24 Jan 2016 at 2:23pm
And there was me thinking it was a Roentgen tube....

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Just listen, if it sounds good to you, enjoy it.


Posted By: Drewan77
Date Posted: 24 Jan 2016 at 2:35pm
Originally posted by Graham Slee Graham Slee wrote:

Originally posted by morris_minor morris_minor wrote:

Will this work in my amp?


...The device is for artificial insemination of cattle!...

It won't work in Bobs' amp but it might still produce moo-sick, ouch Shocked


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Older than I once was, younger than I'll be
.............................
Andrew


Posted By: Graham Slee
Date Posted: 24 Jan 2016 at 4:15pm
Originally posted by BackinBlack BackinBlack wrote:

And there was me thinking it was a Roentgen tube....


Possibly the right answer but x-rays aren't as much fun! Wink


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Posted By: BackinBlack
Date Posted: 24 Jan 2016 at 6:04pm
Not got a clue about AI, but each to his own....
As for X-rays not being fun, remember those machines in shoe shops where you stood with your toes in an aperture and looked down into a screen to see your feet (bones) within your shoes?


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Just listen, if it sounds good to you, enjoy it.


Posted By: Martin1
Date Posted: 24 Jan 2016 at 7:03pm
Yes I do ,which shows both our ages . They still got my size wrong so was not exactly fool proof
still wondering why the nurse is smiling ,must be my natural innocence .






Martin

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Novo Solo SRGII PSU1 Cusat 50 Senn:250 Senn: 540II & Big Wish List


Posted By: Fatmangolf
Date Posted: 24 Jan 2016 at 9:10pm
When I last logged in we were talking about anodes and cathodes. I come back and it's bovine gynaecology and proctology . Yes it's good to share experiences but I thought we'd be onto cathode bypass caps or something similar!



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Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: Graham Slee
Date Posted: 25 Jan 2016 at 7:04am
Originally posted by Fatmangolf Fatmangolf wrote:

When I last logged in we were talking about anodes and cathodes. I come back and it's bovine gynaecology and proctology . Yes it's good to share experiences but I thought we'd be onto cathode bypass caps or something similar!



Yes, it has gotten out of hand a little and I must admit my sense of humour got the better of me, but the question was asked LOL

Now, cathode bypass caps are an interesting subject too: They're there to couple the cathode to ground for ac signals. At DC the resistor is required to lift the cathode voltage which makes the grid voltage negative with respect to the cathode. This biases the anode to somewhere between HT and ground. Just the right amount of voltage cathode to grid will bias the anode at half HT voltage allowing it to swing the full ac signal between HT and ground.

If the bypass capacitor weren't there the gain would be reduced and would be the ratio of anode and cathode resistors (given a proper HT rail which many "new" designs don't), so for maximum gain from the valve, the cathode bypass capacitor is required.

It needs to be large enough to do the lowest bass frequency expected and the formula F=1/2pi.RC is used for that. Rearrange to give C = 1/2pi.FR

This particular bypass capacitor is where a lot of tweakers spend a lot of effort on. They seem to try lots of different types of capacitors and often bypass the bypass cap with all sorts of wonderful schemes.

Instead, why not just put a high voltage GP 85 degree electrolytic there? 63V to 100V should work really well. Just ensure it's given sufficient ventilation to keep it cool. Beats Blackgates IMO!


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Posted By: Graham Slee
Date Posted: 25 Jan 2016 at 8:22am
The "story" of the valve (tube) is related quite well here:

http://www.allaboutcircuits.com/textbook/semiconductors/chpt-13/the-triode/
http://www.allaboutcircuits.com/textbook/semiconductors/chpt-13/the-tetrode/
http://www.allaboutcircuits.com/textbook/semiconductors/chpt-13/beam-power-tubes/
http://www.allaboutcircuits.com/textbook/semiconductors/chpt-13/the-pentode/
keep clicking next page for more in-depth stuff.

The very first page shows that valves have the same problems as transistors... capacitance.

However, the Tetrode and Pentodes came into being to "solve" the problem whereas different techniques are used with transistors.

Those techniques do not work for high powered high frequency circuits (like some radio transmitter power amps) where valves hold the monopoly.

A good page for determining bias and gain of valves is: http://sound.westhost.com/valves/bias-gain.html


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Posted By: morris_minor
Date Posted: 25 Jan 2016 at 8:24am
This thread has turned out to be more educational than I'd hoped . . . Ermm

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Bob

Majestic DAC/pre-amp
Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V
Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50
2 x Proprius + Spatia/Spatia Links


Posted By: Graham Slee
Date Posted: 25 Jan 2016 at 8:26am
Originally posted by morris_minor morris_minor wrote:

This thread has turned out to be more educational than I'd hoped . . . Ermm


Blame Jon Wink


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Not simple enough for Google-Bot to understand...


Posted By: Fatmangolf
Date Posted: 26 Jan 2016 at 6:35pm
Sorry chaps.

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Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.



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