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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 8th Apr 2011, 1:12 pm   #1
Herald1360
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Default Mazda Octal vs International Octal.

Anyone got some dimensioned drawings of both?

In particular is the pin circle PCD different as well as the spigot size?
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Old 8th Apr 2011, 1:50 pm   #2
kalee20
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Default Re: Mazda Octal vs International Octal.

Octal and Mazda Octal. But I put the graphic files below for posterity (in case the link disappears).

It is a shame the Mazda Octal didn't become more popular. The larger spigot allowed the envelope's exhaust pump tube to sit within the spigot, so the whole glass envelope could sit much lower and closer to the base. Shorter lead lengths resulted, thus MO based valves potentially were capable of much better high-frequency performance.

Note also that the pins are not quite equidistantly spaced around the pitch circle.
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Old 8th Apr 2011, 3:18 pm   #3
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Default Re: Mazda Octal vs International Octal.

I'm afraid the larger spigot/exhaust tube story was probably Mazda hype. There are loads of IO valves with the exhaust tube fully in the spigot. Later types such as the EL34 had no pinch and were effectively shorter than anything Mazda made.

The MO base was just Mazda trying to exploit the fact that their pre-war valves out performed most IO types and they saw the chance to make a quick buck without re designing any of their old 4V B7 valves, by simply changing to a non standard base. Second sourcing was also eliminated by this practice - they even kept the 4V heaters, isolating themselves from the car radio market.

In contrast, Mullard/Philips must have lost out when their (sensibly designed) E30 series were replaced with American types, eg. EF39 -> 6K7. So many American valves were available surplus after the war that their compatibility must have made considerable inroads on replacement sales - even now we see sets in which this type of substitution was made, years ago. MOV just gave up, and re-badged most of the American octals other than output valves, so they also lost out to the availability of American surplus types.

The radio industry was rife with restrictive practices at this time, and the MO base was a good example. Much as I like Mazda valves, I'm glad that this type of restrictive practice backfired on them and they eventually lost the battle against Philips. Mazda's dogged adherence to the B8A base later on (which prevented multiple valves for VHF sets and TV), the use of 0.2A heaters and a really stupid numbering system probably finished them off.

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Old 8th Apr 2011, 10:33 pm   #4
Herald1360
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Default Re: Mazda Octal vs International Octal.

Thanks for the drawings. Question answered
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Old 8th Apr 2011, 11:18 pm   #5
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Default Re: Mazda Octal vs International Octal.

Hi.
In essence I agree with Leon, Mazda were very good at designing RF valves but were hopeless with Rectifiers especially their early TV ones. The SP41 was a super valve often forgotten about. The SP41 & 61 were used prior the the EF50 in radar, and the misconception among people is that the EF50 was the first, it wasn't it was the British Mazda, then when Philips came along with the EF50 with better performance it then took over from the Mazda valve. I wonder though what would have happened to radar if those million parts hadn't made it from Holland to the UK, would the SP41/61 have been used or would we have used the 955, 954 Acorn series from the States
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