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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 14th Oct 2019, 8:17 am   #21
kalee20
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Default Re: Why Both EAA91 and EB91?

Good point, David. In fact, why not EAA90... If it comes to that, why not EB90? After all, we have the EF80 so zero as a final digit is certainly admissible!
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Old 14th Oct 2019, 12:00 pm   #22
Maarten
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Default Re: Why Both EAA91 and EB91?

Could it be that they simply couldn't make a 'reliable for mass production' short envelope yet, when the EB91 was conceived? Melting on the base to the envelope would heat up the cathode, which was a reason for fritting on the base button in other types.
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Old 14th Oct 2019, 12:09 pm   #23
G8HQP Dave
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Default Re: Why Both EAA91 and EB91?

A different number generally means different characteristics, and in most cases the same number means the same characteristics (don't mention the EL84 vs PL84!). Hence the short 'EB91' could not be called EB92 without creating confusion. It probably should have been called EB91A, but then someone might have said that a suffix could imply improved reliability or whatever. I can imagine that a committee somewhere spent many hours debating all this; I can certainly remember that back in my days as a computer programmer we would spend a few hours designing a new feature for the software and then an equal amount of time arguing about what it should be called.
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Old 14th Oct 2019, 12:32 pm   #24
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Default Re: Why Both EAA91 and EB91?

First application for the Mullard EB91 in a TV receiver was in 1946 in the Pye B16T. Later Pye TV receivers employed the EB41.
Did Mullard go it alone with the EB91 with no Philips input?

DFWB.
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Old 14th Oct 2019, 1:19 pm   #25
FERNSEH
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Default Re: Why Both EAA91 and EB91?

After WW2 Cossor made a single diode on the B7G base. Type SD6. Dimensions similar to EB91.

http://www.r-type.org/exhib/aai0018.htm

DFWB.
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Old 14th Oct 2019, 6:04 pm   #26
ColinTheAmpMan1
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Default Re: Why Both EAA91 and EB91?

To perhaps put the cat among the pigeons, I think there are other equivalents of the EB91/6AL5, etc.. I have a number of valves that I bought as EB91 equivalents that are labelled with the Mullard logo and bear the numbers M8212 and CV4025. Are these just ruggedised or maybe special quality?
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Old 14th Oct 2019, 6:24 pm   #27
G6Tanuki
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Default Re: Why Both EAA91 and EB91?

Quote:
Originally Posted by ColinTheAmpMan1 View Post
To perhaps put the cat among the pigeons, I think there are other equivalents of the EB91/6AL5, etc.. I have a number of valves that I bought as EB91 equivalents that are labelled with the Mullard logo and bear the numbers M8212 and CV4025. Are these just ruggedised or maybe special quality?
Colin.
See here: http://www.r-type.org/exhib/abh0050.htm

They're electrically an EB91 but subject to various enhancements/more-rigorous QA, some of which is described here: http://www.r-type.org/pdfs/mull-sq.pdf
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Old 14th Oct 2019, 7:26 pm   #28
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Default Re: Why Both EAA91 and EB91?

Quote:
Originally Posted by FERNSEH View Post
First application for the Mullard EB91 in a TV receiver was in 1946 in the Pye B16T. Later Pye TV receivers employed the EB41.
Did Mullard go it alone with the EB91 with no Philips input?
Was it actually marked thusly in the set, or only in a (later) service manual?

P.S. Evidence that the EAA91 was also labeled EB91 (for the British market?): http://www.r-type.org/exhib/abn0112.htm

The Philips factory code list supports this as well. An early single digit code W for the EB91, a later code 'mirrored 2' for the EAA91 and then a double digit code R3 for EB91 and a double digit code 33 for both EAA91 and EB91 (presumably with the external dimensions of the EAA91).

Last edited by Maarten; 14th Oct 2019 at 7:38 pm.
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Old 14th Oct 2019, 9:26 pm   #29
FERNSEH
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Default Re: Why Both EAA91 and EB91?

The post-war Philips TV model 383A employed three Mullard EB91s. This set was I believe on sale in 1947.
The presentation of the 383A table model resembles the pre-war model 2405.

DFWB.
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Old 14th Oct 2019, 9:38 pm   #30
FERNSEH
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Default Re: Why Both EAA91 and EB91?

Maarten wrote: "Was it actually marked thusly in the set, or only in a (later) service manual?"

Never seen the EAA91 in any UK made TV set and that includes the B16T. The Pye B16T service manual valve list shows the EB91. The other double-diode employed in the set is the older octal base EB34.

DFWB.
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Old 14th Oct 2019, 10:45 pm   #31
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Default Re: Why Both EAA91 and EB91?

Quote:
Originally Posted by FERNSEH View Post
First application for the Mullard EB91 in a TV receiver was in 1946 in the Pye B16T. Later Pye TV receivers employed the EB41.
Did Mullard go it alone with the EB91 with no Philips input?
It might have been the case that Philips delegated to Mullard the task of setting up a range of B7G AC miniatures because such were needed to be competitive in the UK market for industrial purposes, and also to some extent for domestic receiver purposes. Whereas most of the European valve makers did adopt the Rimlock type for domestic applications, in the UK several did not and instead went with the B7G format for their domestic receiving ranges.

From the concurrent thread “EF91 to EF80” (https://www.vintage-radio.net/forum/...d.php?t=157399) one may see that there is at least circumstantial evidence that it was Mullard who developed the EF91, as the Philips match to the Osram Z77, etc. That resulted in the duality whereby Mullard was offering the EF42 and EF91 side-by-side for applications which Philips Netherlands was offering only the EF42. It would also appear that Mullard was also offering the EF41 and EB91 side-by-side in the UK when Philips was offering just the EB41 until it adopted the EB91, replacing the EB41, for its standard TV valve range.

The Philips B7G battery receiving range that was released more-or-less concurrently with the initial set of Rimlocks mostly had an overall length of 54 mm, the exception being the DK91 at 55 mm (why a 1 mm difference though?). The corresponding American series was 47.6 mm (1.875 inches) for the signal valves and 54 mm (2.125 inches) for the output valve. Evidently Philips to standardize on the longer of those two dimensions, and it would appear that that decision also carried across to Mullard’s putative activities on the B7G AC range, including the EB91. The EF91 was also 54 mm, although that was the same as for most of the American B7G RF pentodes such as the 6AG5, 6BA6 and 6AU6. (The 6AK5 was short at 44.5 mm (1.75 inches).)

One can find other dimensional anomalies. Mullard quoted the EBC90 and EBC91 at 54.5 mm maximum, whereas the American 6AT6 and 6AV6 from which they respectively derived were 47.6 mm (1.875 inches). On the other hand, the Philips EF95, at 45 mm, was aligned with the 6AK5. The EF95 appears to have dated from 1952, by which time the importance of dimensional matching, particularly for commercial and military business, may have been realized.


Cheers,
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Old 14th Oct 2019, 11:33 pm   #32
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Default Re: Why Both EAA91 and EB91?

Quote:
Originally Posted by kalee20 View Post
Good point, David. In fact, why not EAA90... If it comes to that, why not EB90? After all, we have the EF80 so zero as a final digit is certainly admissible!
Keeping the “91” may have been attractive as an easy way of signifying that the EAA91 was functionally the same valve as the EB91.

Regarding the allocation of numbers, some sequences appear to have started at n0, such as EF40 et seq, whilst others started at n1, such as ECH41 et seq and EF91 et seq. With different people doing the number allocation at different times, then there could have been different views as to whether zero as a final digit was valid. However, the initial Rimlock series had both 40 and 41 starts – that seems to be a “go figure” case.

Another case where the final digit may have been chosen to establish an association was with the EBF89, whose pentode was the same as the EF89. The EBF allocations were EBF80, EBF81, EBF83 and EBF89, and of those, the EBF83 (12-volt HT car radio valve) followed the EBF89. Logically the EBF89 should have been the EBF82. (The EBF8n series did not follow the EF8n series convention of even final digits for sharp cutoff and odd final digits for remote cutoff valves.) Perhaps because the EBF89 should have been the EBF82, the latter was skipped, so that EBF83 was next available for the car radio valve. Or maybe “83” was to be associated with car radio valves because the car radio triode heptode was the ECH83, which skipped the apparently available ECH82 slot. Who knows!


Cheers,
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Old 15th Oct 2019, 4:57 pm   #33
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Default Re: Why Both EAA91 and EB91?

I have often wondered if the 'EF91' or rather the Mazda version of it the 6F12 was actually designed by Mazda themselves rather than the Mullard version.

The 6F12 appears in a number of post war television receivers including the 1947 Ultra W470. The actual Mullard EF91 does not seem to appear until 1949, an early user being Ferguson with their 941T.

I think the 1946 PYE D16T must be the earliest use of the EB91 in the UK. I have seen tiny squat versions of the EB91 with the same bulb size as the EF95. John.
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Old 15th Oct 2019, 5:39 pm   #34
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Default Re: Why Both EAA91 and EB91?

The Radiomuseum lists an EB40 double diode. Might have been intended for use as a VHF or UHF mixer. Note that only the active pins are present on the Rimlock base. https://www.radiomuseum.org/tubes/tube_eb40.html
The pre-war EB4: https://www.radiomuseum.org/tubes/tube_eb4.html
All these 6.3volt double-diodes are designated as EBxx and not EAAxx

DFWB.
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Old 15th Oct 2019, 6:15 pm   #35
kalee20
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Default Re: Why Both EAA91 and EB91?

Quote:
Originally Posted by FERNSEH View Post
The Radiomuseum lists an EB40 double diode....

The pre-war EB4:https://www.radiomuseum.org/tubes/tube_eb4.html
All these 6.3volt double-diodes are designated as EBxx and not EAAxx

DFWB.
Super find! The EB4 has separate anodes, separate cathodes. There is also an EB2, which has common cathodes.

Which seems to indicate that presence or absence of a common electrode does not steer between 'B' or 'AA' mumbering.
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Old 15th Oct 2019, 6:20 pm   #36
TonyDuell
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Default Re: Why Both EAA91 and EB91?

Are there any other double diodes with the 'AA' (rather than 'B') number?
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Old 15th Oct 2019, 6:30 pm   #37
FERNSEH
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Default Re: Why Both EAA91 and EB91?

From the Radiomuseum, the TFK EAA11.

https://www.radiomuseum.org/tubes/tube_eaa11.html

Also UAA91: https://www.radiomuseum.org/tubes/tube_uaa91.html

= UB91 was there such a valve? and Mazda 10D2 .

DFWB.
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Old 15th Oct 2019, 6:37 pm   #38
FERNSEH
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Default Re: Why Both EAA91 and EB91?

Kalee20 wrote: "There is also an EB2, which has common cathodes."

And also EB1 which has the ct5 base, same as MW6-2 CRT.

https://www.radiomuseum.org/tubes/tube_eb1.html

DFWB.
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Old 16th Oct 2019, 12:45 am   #39
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Default Re: Why Both EAA91 and EB91?

Quote:
Originally Posted by Heatercathodeshort View Post
I have often wondered if the 'EF91' or rather the Mazda version of it the 6F12 was actually designed by Mazda themselves rather than the Mullard version.

The 6F12 appears in a number of post war television receivers including the 1947 Ultra W470. The actual Mullard EF91 does not seem to appear until 1949, an early user being Ferguson with their 941T.

I think the 1946 PYE D16T must be the earliest use of the EB91 in the UK.
Who first developed the EF91/Z77/6F12/8D3 valve is an open question. My best estimate is that the Osram Z77 was the parent valve, see: https://www.vintage-radio.net/forum/...1&postcount=60.


Cheers,
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Old 16th Oct 2019, 1:23 am   #40
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Default Re: Why Both EAA91 and EB91?

Here is an excerpt from Vade Mecum 1994 with the entry for the 6AL5 and most, perhaps all of its derivatives, including the EAA91 and EB91. It addresses the "what", but not the "when", why" and "by whom" aspects.


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