Blog posts tagged with 'valve'


A number of customers are now showing interest in B7G miniature battery valves so I thought I would do today’s blog on these marvelous little devices.  These first came to the fore in the early 1940s when they were utilized in personal radios particularly Stateside where they did duty in the likes of the Sonora Candid and the RCA BPA 10. As is usual, we didn’t catch up this side of the pond until the immediate postwar period with such designs as the Marconiphone P17B and Ever Ready Personal B. Let’s also not forget how these devices also saw duty throughout WW2 in a variety of man pack radios for the military.

The first B7G devices were produced by Sarnoff’s RCA and commercially distributed during 1939 and the line up comprised of the 1R5 – Heptode Frequency Changer; 1T4 – IF/RF amplifier; 1S5 – Detector Diode and AF amplifier all of these having 50mA 1.4V filaments but there was the; 1S4 Beam tetrode which had a 100mA filament and of course a version of the 1S4 with a 50mA + 50ma Centre tap filament capable of working as either a 3V 50mA series and 1.5V 100mA parallel. Mullard/Philips and Mazda/Adzam licensed copies of these contemporaneously and in 1953 launched their take which was the DK96. DF96, DAF96 and DL96 with improved construction which meant these had 25mA 1.4V filaments except the DL96 which is 50mA, or 25mA + 25ma centre tap.

To help with equivalent identification, I have prepared the following convenient equivalents listing: -

Heptode Frequency Changer 1R5 = DK91 = VT-171 = X17 = 1C1 = 1L6 = CV782
Heptode Frequency Changer 1AB3 = DK96 = VT-171 = X25 = 1C3

Enhanced Frequency Changer 1AC6 = DK92 = 1AC6 = X18 = X20 = 1C2 = CV5172

RF/IF Amplifier IT4 = DF91 = W17 = 1K2 = 1F31
RF/IF Amplifier IAJ4 = DF96 = W25 = 1F1

VHF RF/IF Amplifier IAN5 = DF97

Detector Diode/AF Preamplifier 1S4 = DL91 = 1S4 = CV783
Detector Diode/AF Preamplifier 1AH5 = 1AF33 = ZD25 = 1FD1 = DAF96

Detector Diode/AF Preamplifier (CT) 1S4 = DL912= 3S4 = N17 = 2P2 = 1P10 = CV820 = VT-174

Beam Tetrode DL93 = 3A4 = 2P3 = CV807
Beam Tetrode DL94 = 3V4 = N19 = 1P11 = CV1633
Beam Tetrode DL95 = 3Q4 = N18 = CV818
Beam Tetrode DL96 = 3C4 = N25 = 1P1

With the above information, the B7G affectionado will be able to number cross reference and match devices from various manufacturers and hopefully achieve thermionic nirvana!





Today's Mullard archive photograph shows a Mullard Whyteleafe Valve Assembly Department operator removing an electrode cage from one of the dustproof boxes in which valve components were stored when not undergoing manufacturing operations.  As you can see, the operator's right hand holds a pair of welding tweezers with which she is about to weld a getter bar onto a selected electrode cage. 

The BBC European Service Science Correspondent in 1953 was CL Boltz and he had much to say about the valve assembly operations but that is a subject for another day and another blog entry.


Hi peeps, well, in response to another valve related query, this time about 'JAN codes', I thought I would pen a little information nuggett here today. I shall be doing a further more detailed blog entry on military coding history and types soon but for now here's a quick info - bite.

The JAN code is of course the US Military Joint Army Navy coding introduced in 1942 in which the code for a particular valve type comprises of an alphanumeric code, for example VT-114 and additionally a three digit alpha code. I will deal with the former in more detail later, but the alpha code is a manufacturer code. Here is a short listing of the most commonly seen codes with their corresponding manufacturers:-

CHS – Sylvania

CHY – Hytron or CBS-Hytron

CKR – KenRad



CRP – Raytheon

There have been multiple USN numbering systems in use over the years.

The initial numbering system was introduced in 1912 with the first of two letters signifying the device manufacturer followed by a sequentially assigned number to indicate valve type.

A replacement system was introduced in 1932 in which the two letter device manufacturer code continued but the numerical part was augmented into a 5 digit number in which the first two designated the valve classification and the successive three the specific type number.

This system was replaced in 1942 using the Joint Army Navy (JAN) system due to a larger range of valve types used in war materiel requiring classification.



 As some of you may be aware, Stephen Fry and myself are chums from our university days. You may not know that Stephen has been very busy writing the screenplay for a remake of the Dambusters which will be distributed on release by Universal Pictures & Studio Canal. I am pleased to report that due to my connection with Stephen, Mullard Magic has been asked to help with the radio installation in the Lancaster mock up that has being used for filming.

I have taken Stephen to task for his meddling in renaming Guy Gibson's beloved pet, why should we rewrite history for the sake of political correctness - history is inviolate! Anyhow, we were fortunate enough to meet one of the stars of the new film when we were fitting out the R1155/T1154 station. Remember, you saw it here first, direct from the Boreham Wood studios, I bring you this picture of Tigger, Guy Gibson's beloved cat gambolling inside a T1154 casing.



 As we all know, Mullard valves are blessed with that special sound – some call it Mullard magic – just like our website title. Bit what is it about these thermionic devices that provide this sound. Is it the Jablonski shift that occurs as the electrons rushing from the cathode electrons flip from one energy state to the next lower one emitting hv as a purple shift – could that be it? 

So the Mullard electrons are purple huh – that explains why that great swing standard Deep Purple sounds so good on a Mullard equipped amplifier. Does your Mullard 3-3 rock when you play Smoke on the Water (………. by Deep Purple). Does your bass boogaloo through your EL37 as Prince riffs along in… Purple Rain. How about on large scale choral musicals such as Colour Purple? Perhaps your Leak presents a lush soundstage so sonically superb that superlatives surpass the sensuous sound???? OMG, I'm beginning to sound just like one of those hifi comics you find in the newsagents.

Am I just being silly, shall we place this myth iof special Mullard electrons 'in the file box' along with wood capacitors, CD felt tip pens, solid silver mains leads plaited by virgin Cuban nymphs specially selected for the tightness of their (ooo-eer) cigar rolling... and other audiophillic pseudo scientific quackery.

Actually, I’ll let you into a secret, the real reason is that Mullard had been making valves for a long time even before they started manufacturing the sonic stalwarts we all crave today – the AC044, AC042, EL84, EL37. EL34, ECC 81, 82, 83, EZ80 81, GZ 30 32, 34, 37. But hey, this was also the case for other big ticket manufacturers such as Telefunken, Valvo, National Union, Sylvania, RCA, Osram, GEC, Brimar and Cossor – they might have each used differing techniques and materials but their manufacturing ethos was the same. Accordingly, during production, each device was subject to strict production controls where quality assurance was built in and end product quality control batch testing meant the product performance and consistency were second to none - inter and intra batch for any given type. And the result of this is very evident - you don't need two heads to tell the difference between these beautifully engineered devices and some of the lesser modern offerings.

And consistency in manufacture is the key to performance and longevity, many a tube affectionado had cause to lament the lack of both of these properties in recent Chinese production valves. Indeed in very recent history,,a new British manufacturer fell by the wayside as they produced a number of interesting high performance small signal audio valves yet they were unable to consistently achieve the nominal specifications as originally stated by Mullard which led to manufacturing hold ups and their eventual demise.

So it’s up to the large scale manufacturers of yesteryear – of which Mullard is only just one – to provide us with our fix of exceptional thermionic devices for a myriad of uses today. Hopefully you will find suitable specimens of tested suitable devices here for sale on our website.