Mullard yellow print on valves.

Lets face it, it doesn't really matter why some have yellow and some have white....maybe they just ran out of white paint! Incidentally I have a UL84 clearly marked Mullard but in BLUE paint. It's currently giving good service in my Bush VHF80. I have to admit it is so far the only one I've seen with blue paint.

Posted by: sideband

Incidentally I have a UL84 clearly marked Mullard but in BLUE paint. It's currently giving good service in my Bush VHF80. I have to admit it is so far the only one I've seen with blue paint.

OMG you have a blue one! That's worth thousands!......They are rare and make the yellow sound like white.... Start the rumour, reap the rewards  ? 

No I can’t say I have seen blue printing, I didn’t take much notice though, I just wanted a valve that worked with the correct number.

They were not going to stop production because a particular colour was not available, they were making millions of valves a year at Blackburn, so they would use what was available.

Posted by: Terry

It is a weird site - it insisted on capitalising every word I wrote and then refused to accept it because I hadn't provided the name of my country, but there was no such field to enter the data! This is what I wrote (decapitalised!):

Which site was this, Terry - the one in the OP? If so, I can only see two comments although it says there's four...

Yes, same site as in OP and I noticed that discrepancy too!

Posted by: sideband

Lets face it, it doesn't really matter why some have yellow and some have white....maybe they just ran out of white paint! 

You and I know that, and so does anyone else in full control of their sanity: but we're dealing with people who think silver plated wire lowers distortion (copper wire is non-linear? news to me), and who are prepared, without a blush, to pay about 40 times the bulk rate for a mains lead that someone has had connected to a load for a few hours (and not just any load, oh no: it must be the right sort of load) in the settled belief that it will do the same.  I'm sure there must be a good PhD in there somewhere for someone who wants to study the psychology of it all.

A former colleague tells a story about a vac student we had come round in the mid-seventies.  Two things were happening at the time, (i) we were going through another period of being desperate for staff, because the BBC thought it could pay in washers, and (ii) there was a fad for d.c.-coupled audio power amplifiers.  The young man seemed (and I'm being as polite as I can) very full of himself, "I'm at Imperial, you know," all that kind of thing, and banged on ad nauseam about how important it was to keep the d.c. component all the way through to the loudspeaker. (By the way, does audio have a d.c. component? Do wind players pressurise the concert hall?  That's news to me too).

My colleague, a man a good deal more patient than I, eventually invited the student to get the handbook for the studio's (broadcast quality) sound desk off the shelf in the maintenance room, and to turn to the page containing the circuit diagram of the channel card - the very first bit of electronics encountered by the signal on entering the desk. There, right at the front of the channel card, was the component found in the same place in every similar sound desk at the time, an audio-frequency transformer (broadcasting and telecomms people call them repeating, or rep coils).  Our Imperial College student was in some difficulty explaining how the d.c. component passed through that. ?

(He wasn't invited back, by the way.  His lifespan on a fraught "Top of the Pops" day would have been measured in microseconds).

Posted by: occiput

Posted by: sideband

Lets face it, it doesn't really matter why some have yellow and some have white....maybe they just ran out of white paint! 

You and I know that, and so does anyone else in full control of their sanity: 

There, right at the front of the channel card, was the component found in the same place in every similar sound desk at the time, an audio-frequency transformer (broadcasting and telecomms people call them repeating, or rep coils).  Our Imperial College student was in some difficulty explaining how the d.c. component passed through that. ?

? Love the story and comments! Excellent!

But if asymmetric waveforms exist in music, doesn't that create a DC component? 

There are asymmetric waveforms in music: the classical example is that of a bowed string, but electronic musicians can create any degree of asymmetry they choose,  I suppose.  Not all asymmetric waveforms give rise to a d.c. component: the trite example is to think of, say, a 10:1 square wave.  Provided the amplitude x time product is equal but opposite for the two parts of the wave, there is no d.c. component.

That ever reliable source, Wikipedia, says that the threshold of audibility in a young adult with normal hearing is a sound pressure level of about 20 microPascals r.m.s. (there is also a dependence on frequency).  If we say that the human dynamic range is about 140dB between sepulchral and burst eardrums, this implies that the upper limit of the system is about 200Pa r.m.s. 

Now consider pressure variations occasioned by the weather.  If we say that summer high pressures rarely exceed 1030 millibars, and winter depressions rarely fall below 970mb, this is a variation of 60mb peak to peak, hence 30mb peak or about 21mb r.m.s., and since 1000mb = 10^5 Pa, the variations due to the weather will be about 0.021 x 10^5 = about 2kPa r.m.s.  This static (or at any rate very slow-acting) change in pressure is therefore about ten times the level of sound which is likely to permanently damage an individual's hearing, yet we cannot routinely detect it [1].  This is because the human hearing system is balanced against static variations in pressure i.e. against the d.c. component.

The Telarc recording of the 1812 claims to have a component at 6Hz when the cannons fire.  If we take the lower 3dB point of a cooking hi-fi system as 20Hz, this is only about 2 octaves under, and it is therefore likely that the system will still have significant output at this frequency: indeed, I understand that when the recording was originally released on vinyl, there was a sleeve note cautioning against the possibility of loudspeaker overtravel. Nevertheless, the effect is felt rather than heard.

[1] Some individuals claim to be sensitive to absolute barometric pressure, but there is no reliable evidence to suggest that the hearing system is the mechanism for this sensitivity.

Equally - where does the DC component arise from a magnetic pickup cartridge?

It's bunkum, of course. I always understood the vogue for DC coupling in audio amplifiers was (i) to minimise phase shift and (ii) to increase the damping on the loudspeaker. It does of course mean that more than ever, switch-on thump suppression was needed along with protection for that delicate voice coil were a transistor to get tired of life and turn itself from semi-conductor to conductor (full time).

Posted by: Cathovisor

Equally - where does the DC component arise from a magnetic pickup cartridge?

 

...or, indeed, any component relying on magnetic induction to work, so dynamic microphones are out, as well.

Some types of transducer are, however, capable of generating a d.c. output: the obvious example, if you ignore the weeny issue of telling the difference between millivolts of signal and 50V of phantom, is a capacitor microphone.  It seems sacrilege to mention carbon microphones and hi-fi in the same breath, but they do too (pace the same issue with the polarising supply).  If you had an all-digital signal path between there and your DC-300A, you could do it, I suppose...

... and it would still be a complete waste of time, essentially for the reasons explained above.

If l.f. phase shift is bothersome, fit bigger Cs.  That won't do any good either, by the way.  If loudspeaker damping is a problem (and assuming your power amplifier isn't completely toytown) the thing you ought to be concerned about is not whether the signal path works at d.c., but the resistance of your speaker cables and, if you are using a passive crossover, the inductors in that.

I may be being wholly unfair to my ex-colleagues in what I'm about to say, and if that's thought to be the case I apologise right readily, but I am moderately certain that, if I'd stood up in a Supervisory Engineers' meeting and announced that fitting selected NE5532s in my studio's sound desk had make the output "wide and fat", the consensus view would be that I'd fallen over the edge at last, and perhaps ought to try putting more water in whatever I was taking at night.   ?  ?  ? 

Amazing how a bit of trivia about print colour on valves can spark such a varied and interesting discussion.  ? 

Posted by: sideband

Lets face it, it doesn't really matter why some have yellow and some have white....maybe they just ran out of white paint! Incidentally I have a UL84 clearly marked Mullard but in BLUE paint. It's currently giving good service in my Bush VHF80. I have to admit it is so far the only one I've seen with blue paint.

I have seen valves with blue print, but I couldn't say if they were Mullard or otherwise. However, I'd bet there are many times fewer valves, of any make, with blue print than yellow.

Oh aye, and red, and green print too!

One thing is for sure....I bet you'll never see a valve with the print on the inside, regardless of colour.  ? 

I have seen yellow print valves being sold for silly money too.

I have seen green print on some non Mullard valves too especially USA brands.

I’ve just pulled a yellow UCH81 from a VHF81, the others are yellow too ... I have a limited stock of spare valves but I did have a UCH81, and luckily for me it’s also yellow, phew. 

The pulled valve is available for the right price 😉

John

I have a box full of 100 Mazda PL504 with blue markings, Malc.

Drat, I have no Mullard valves with yellow markings, what am I going to do, how will I survive.  ? 

Anyone remember the Toshiba valves with the green ring around the glass near the base. We bought them from CPC, came in a red box with no markings, I presume CPC transferred them from bulk to single boxes. I bought mainly line output valves, perhaps boost diodes as well. I  had to obtain what as available, Toshiba were good valves.

My friend, the late and very knowledgeable Alan Stepney worked at Mullard during the "Yellow Paint" period(s).

He gave lectures on valves in his retirement (one of which I attended) and was always at pains to point out that, as stated, the yellow paint was just a cheaper version of the originally specified gold for the jubilee.

However, they ordered a lot of it, and for many, many years afterwards would dig out stocks for the production line if the white had temporarily run out.

As far as he was concerned, it was a non-story, and definitely nothing to do with special quality valves!

Jeremy

Hi.

I've lots of valves with no markings at all. They live in a box narked take you pick,  by looking at the structure 80% of the time I get it right. Im not saying what happens when I get it wrong though.