How many SQ B9A wideband pentodes did Mullard make, and why ?

[GrimJosef]

I'm aware that Mullard made the D3a, E180F, E186F, E280F, E282F and E810F special quality wideband long-life (typically 10,000hr ?) pin-compatible VHF pentodes. I also understand that their characteristics aren't all the same, although some aren't too far apart. But why were there so many of this rather specific type of valve and did Mullard or Philips or anyone else ever issue a document comparing and contrasting their respective strengths and weaknesses ?

And have I missed any ?

Cheers,

GJ

[pmmunro]

I can't offer much information on these particular valve types but around 1963 my father was responsible for various items of plant in an engineering works. One of these items was a boiler whose burner control included a Brimar B9A valve - I don't remember the type. This valve had a very short life and need frequent replacement at considerable cost and inconvenience.

I suggested trying a Brimar "Special Quality" equivalent which seemed to solve the problem which was probably due to a combination of heat and vibration. It certainly more than justified the higher cost of the special valve.

PMM

[Robert Gribnau]

My guess is that the types mentioned were not all introduced at the same time and that later types had more favourable characteristics for RF and wide band applications, like lower "Equivalent noise resistance" and higher "Quality factor", than the earlier ones.

On page 9 of this Philips document from 1962 there's a comparison between the E810F and the older 6AK5W and E180F on some of their characteristics.

[GrimJosef]

Thanks for the link Robert. Yes, it is clear that there is a range of different detailed parameters and the E180F and E810F are perhaps at the two extremes of the range. The former has an advertised gm of 16.5mA/V and the latter of 50mA/V.

There would have been some spread of release dates too. I don't know the numbers for all the valves, however the valve museum says that three - the E280F (gm=26mA/V), the D3a (gm=35mA/V) and the E810F were all released in the same year, 1958. So there seems to have been a profusion of slightly different types all coming onto the market at much the same time.

Another curiosity is what these valves are special quality versions of. With other valves e.g. the standard ECC82, there were a number of special quality versions - the E82CC (resistant to shock and vibration), the ECC186 (optimised for computer applications), the M8136 (tested against a selection of military criteria). But they all have the same basic electrical characteristics as the 'ordinary' ECC82. It isn't clear what the ordinary valve(s) corresponding to the above pentodes are though. Their pin-out is different from the EF80 and EF184.

Cheers,

GJ

[Robert Gribnau]

Yes, you are right about the D3a, E280F and the E810F. So my guess doesn't make much sense.

About the other curiosity: I think that most SQ valves don't have a 'standard' counterpart, like: E1C, E80CC, E90CC, E92CC, E180CC, E181CC, E182CC, E288CC, E3F/E13F, E80F, E83F, E55L, E80L, E81L, E130L, E235L (very close to EL36, but without top connection), E82M, E1T, E4T, E80T. Besides these types with Mullard/Philips designations, there are many other SQ valves for which the same seems to be true.

[woodchips]

In my experience they all seem to be used in test equipment. Wide band amplifiers mostly, where a doubling of gain from 25mA/V to 50mA/V means a significant increase in bandwidth. Look at the Solartron 1210 and 1220, also the Hartley and others I can't remember. If they wanted a cathode follower an ECC88 was used, lots of anode current.

Similarly with oscillators, bridges and similar. They seemed to have valves far beyond what you would expect. Also all the special quality ordinary types used by Tek, HP, Solartron, Muirhead and many others.

Even the early scopes, Cossor, used pretty meaty valves for amplifiers and timebases, all that was around in the 50's until these newer types emerged. Whilst there were many different types, how many of each were actually made?

[David Simpson]

Some info on the E282F - see my thread post "Testing high slope pentodes" back on the 7th Nov. Regards, David