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Old 10th Feb 2018, 4:58 pm   #1
dragonser
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Default When did Valve heaters change from 4v to 6.3v

HI,
sorry if this is a stupid question, but does anyone know roughly when valve heaters were changed from 4 volts to 6.3 volts ?
the reason I ask is that I have an old mains transformer with the usual ht windings ( 340- 0- 340 ) , but it has two 2-0-2 heater windings and one 12v winding.
I was thinking of making a HV bench power supply with it, but out of interest I wondered how old it might be ?
I'm assuming the 12volt winding might be for a bias supply ?
I can post a picture if it would help..
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Old 10th Feb 2018, 5:22 pm   #2
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Default Re: When did Valve heaters change from 4v to 6.3v

Mid-late '30s? Some UX American types were 6.3V, then octal types generally were.

If the 2-0-2 windings are similar, all of one plus half the other will give near enough 6.3V to be OK as long as current drain is within their ratings.
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Old 10th Feb 2018, 5:32 pm   #3
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Default Re: When did Valve heaters change from 4v to 6.3v

4v is for a two-cell lead-acid battery, running alone.

6.3v is for a three-cell battery with a dynamo charging it.

The former fits users who took their accumulator along to the bicycle shop every week to get it charged. The latter fits the car radio market. Valve makers went to 6.3v heaters when they thought there was a hope of selling some for car radios in their part of the world. 4v valves had gone from direct heated to insulated cathodes when mains sets appeared.

America had the lead in 6.3v valves because the greater wealth over there meant cars were more common sooner.

Our military wanted 6..3v for mobile comms.

The move to 6.3v was not a sharp change, it spread across the later thirties and WWII hammered it home.

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Old 10th Feb 2018, 6:12 pm   #4
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Default Re: When did Valve heaters change from 4v to 6.3v

Audio amplifiers using PX4 or PX25 valves would use 2-0-2 heater windings and they were still popular after the war.

You could build a PX4 Williamson amp with 340-0-340 and use the 12 volts to run the two B65 heaters in series.

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Old 10th Feb 2018, 6:54 pm   #5
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Default Re: When did Valve heaters change from 4v to 6.3v

Hi,
this is all very useful info, thank you !
I guess the transformer might be older than I thought it would be.
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Old 10th Feb 2018, 9:25 pm   #6
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Default Re: When did Valve heaters change from 4v to 6.3v

It looks '30s ish. Not well stored either, but should be fine if it's well dried out.
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Old 13th Feb 2018, 7:46 pm   #7
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Default Re: When did Valve heaters change from 4v to 6.3v

Hi dragonser,
Way back in the 1960s, I bought a GEC AVC5 radio from a scouts jumble sale for 5 bob. It dates from 1934 and had a lineup of valves X30, W30, DH30 and N30 which all had 13 volts heaters. The rectifier was a MU14 which was 4 volts. It sounds like your transformer could have come from one of these sets.
Regarding when 6.3volt valves came into service, I suspect it happened gradually in the mid-late 1930s. Some manufacturers stuck with 4 volt valves using tried and tested designs but it all changed when American octal based valves appeared in the receivers of the day and European valve manufacturers had a range of side contact valves that also came with 6.3 volt heaters.
This might have arisen from the developing car radio market as many cars had 6 volt batteries but I could be wrong!

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Old 13th Feb 2018, 9:19 pm   #8
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Default Re: When did Valve heaters change from 4v to 6.3v

Some mid/late '30s British sets even started out with a 4V valve line-up and part-way through production changed to a 6.3V complement, e.g. the Marconi 559 here with its B7 base W42, X42, W42, DH42, KT42 line-up changed to an IO W63, X63, W63, DH63, KT63 set, the rectifier went from B4 base 4V heater U12 to IO base 5V heater U50. All of them featured a 6.3V heater Y63 magic eye though, early sets having a low-current additional transformer winding added onto the relatively beefy 4V main heater winding for the ME. Quite a few Marconi/HMV sets of this era followed this part-way change-over trend, they seemed to follow US trends closer than others with an association with RCA. I think that RCA patented the magic eye and the US makers eagerly took it up, hence even early magic eyes came with 6.3V heater (though a handful of 4V heater type MEs were produced).
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Old 13th Feb 2018, 9:22 pm   #9
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Default Re: When did Valve heaters change from 4v to 6.3v

In GEC's Osram valve catalogue for 1938-9, all the valves mentioned in #7 are in the "Replacement types, available for servicing" list. There are approximately equal numbers of 2V and 4V types, and a somewhat smaller number of Octal-based valves .

Most of the Octal types have 6.3V heaters, but various ones have 26V (KT32, U31), 26V/13V (KT33), and 5V (U50, U52) heaters. The data sheet for the KT33 says "By usingthe heater centre tap, the valve becomes suitable for operation from a 12 - 13 volt Low Tension supply, such as a Car Battery." This is the only reference the catalogue has to car use.
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Old 13th Feb 2018, 11:08 pm   #10
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Default Re: When did Valve heaters change from 4v to 6.3v

I can understand the change from 4V to 6.3V. I guess it's largely coincidence that it happened at the same time as the general adoption of the International Octal base.

But why the move from 4V to 5V for rectifiers, eg 5Z4 (IO based)? And yet there's the AZ31 (also IO based, but 4V)? Whereas the EZ35 is 6.3V - this at least makes sense as its heater is insulated well enough to share the same LT as other valves, so it has to have the same voltage.
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Old 14th Feb 2018, 12:07 am   #11
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Default Re: When did Valve heaters change from 4v to 6.3v

I wonder if the 4V to 5V rectifier trend was more a case of following US practice for commercial reasons than any particularly technical motive? As mentioned upstream, a pre-war trend that rapidly became a general theme as the US became the Allies' industrial power-house and innumerable 5Z4 etc. were available, perhaps. The US adoption of 2.5V and 5V filaments/heaters for many valves before 6.3V became widespread is worthy of questions itself though.... My understanding of the 6X5/EZ35 early adoption of 6.3V and isolated heater/cathode was for car radio power pack use- but that's both hazy and tenuous!
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Old 14th Feb 2018, 5:38 am   #12
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Default Re: When did Valve heaters change from 4v to 6.3v

Its a great question, not stupid at all.
The history answers we get from the guys is fascinating.
Thanks for asking.
Mike
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Old 14th Feb 2018, 5:45 am   #13
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Default Re: When did Valve heaters change from 4v to 6.3v

Quote:
Originally Posted by turretslug View Post
My understanding of the 6X5/EZ35 early adoption of 6.3V and isolated heater/cathode was for car radio power pack use- but that's both hazy and tenuous!
There’s evidence to place that assertion in the probable or very probable class, namely this excerpt from the article “Miniature Tubes in War and Peace” in RCA Review for 1947 June (available at AmericanRadioHistory.com):

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At that time, miniature rectifiers were not offered for use in for use in AC mains-operated domestic receivers, but were offered for auto radios (the 6X5) and for AC-DC and three-way portable receivers.

An interesting facet is that when the US auto industry made a general change from 6-volt to 12-volt electrical systems in the early 1950s, there was also a change from 6.3 volt to 12.6-volt heater valves doe auto radios. Many such valves already existed; for example, quite a few of the 150-mA series-string heater small-signal miniatures happened to have 12.6-volt heaters. But as required, there were new issues starting from late in 1952 or thereabouts.

Returning to the 4-volt case, there were post-WWII new equipment designs that used them. The Dynatron T69 and associated range comes to mind; it used Mazda 4-volt valves. Dynatron switched to Osram miniatures for small-signal functions circa 1951 with the T99 and associated.

There were also one or two post-WWII new-issue 4-volt valves. The Philips AZ41 comes to mind, from its initial Rimlock series. It was a directly-heated, 70 mA full-wave rectifier.


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Old 14th Feb 2018, 2:59 pm   #14
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Default Re: When did Valve heaters change from 4v to 6.3v

Hello,

Early American mains valves were usually 2.5V heaters but this changed to 6.3V with UX or UY bases in the early 30s and then with octal bases in the mid 30s.

In Europe Philips brought out 6.3V valves (EK1, EL1, EZ1 etc) in 1934 but Mullard did not introduce later versions of these in the UK until about 1938. Octal versions of these became available between 1938 to 1940.

In the UK Marconi-Osram produced 6.3V versions of its 4V valves with octal bases in 1937-8. At the same time its high current rectifiers (U50 and U52) changed to 5V with an octal base but its low current rectifier the U10 with a 4V heater and B4 base carried on till the early 1950s.

Mazda brought out its Mazda-octal based valves (TH41, Pen45 etc) in 1938 but they retained 4V heaters and again carried on till the late 1940s to early 1950s. During the war Mazda did bring out some 6.3V versions of its 4V valves (SP61, P61 etc) for military use.
Mazda did bring out the Pen/DD61, a 6V version of the AC2/PenDD for Philco circa 1936.

Yours, Richard
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