UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

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.

Reply
 
Thread Tools
Old 16th Oct 2019, 9:18 am   #41
Restoration73
Octode
 
Restoration73's Avatar
 
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 1,710
Default Re: Why Both EAA91 and EB91?

I have a later 6AL5 which is only 31mm in height.
Restoration73 is offline   Reply With Quote
Old 20th Oct 2019, 7:11 pm   #42
Heatercathodeshort
Dekatron
 
Heatercathodeshort's Avatar
 
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 6,904
Default Re: Why Both EAA91 and EB91?

Interesting. Checking service manuals the Brimar 8D3 appeared in the first post war KB television receivers from 1947, the CV40. HMV did not employ the Z77 until the release of the 1805 in 1949 as did GEC.
Vidor used the EF42 in 1947 but most large manufacturers went straight to the EF91 from the EF50 in 1949. We will never know! Regards, John.
Heatercathodeshort is offline   Reply With Quote
Old 20th Oct 2019, 7:17 pm   #43
Pieter H
Tetrode
 
Join Date: Sep 2017
Location: Waalre, Netherlands
Posts: 59
Default Re: Why Both EAA91 and EB91?

Hi all,

to give a slightly different twist to this story:
To start the EB91 was introduced within Philips/Mullard in 1946. The two TV sets designed that year (the 363A and 563A, where the middle 6 indicated the design year 1946) both used the EB91. See the full story here.
As already suggested and discussed, the 90-series seems to have originated from the UK Mullard valve design group, first order for local UK marketing only.

As to the valve naming, and knowing the Philips way of thinking from the inside, I'm pretty sure there was a kind of rule "keep the valve name as short as possible given the available coding scheme". So a double diode was B, with the EB91 succeeding the EB4. Because there were no codes for triple diodes the triple diode-triode had to be the EABC80.

But then all of sudden around 1950 other companies (Telefunken?) introduce a double diode as EAA91, although the specs were roughly identical. Strictly spoken not a violation of the coding system, but clearly not in line with the Philips coding methodology. Because the Philips Radio Valves division had the policy to offer all main valves sold in their markets, they required an answer to this EAA91. One option was to start a campaign explaining that the EAA91 and EB91 were identical, but the EB91 the best of the two. A pragmatic alternative was to relabel the EB91 also to EAA91, and offer both in parallel. Although there was also the corporate rule not to issue unnecessary product codes (every code cost money for administration), in this case having both codes was probably deemed the most cost effective one.

With the result that both the EAA91 and EB91 co-existed, although as far as I can see no EAA91s were used in Philips sets, only the EB91.

Cheers, Pieter
Pieter H is offline   Reply With Quote
Old 20th Oct 2019, 7:31 pm   #44
Maarten
Nonode
 
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 2,607
Default Re: Why Both EAA91 and EB91?

What you didn't address is that in this case is, according to the codes, they seem to have existed in parallel as different (not relabeled) valves. Only after some unspecified amount of time, EB91 and EAA91 became the same valve, presumably using the envelope specs of the EAA91.
Maarten is offline   Reply With Quote
Old 22nd Oct 2019, 2:38 am   #45
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Mt. Maunganui, New Zealand
Posts: 2,449
Default Re: Why Both EAA91 and EB91?

Thanks, Pieter, for the background.

It looks then as if the EAA91 was an unexpected complication as far as Philips/Mullard was concerned.

Presumably the third party (possibly/probably)Telefunken wanted to introduce an exact copy, physically and electrically, of the American 6AL5. Given that the EB91 designation was already taken by Philips/Mullard for a valve that was electrically similar to but physically different from the 6AL5, that third party felt that it needed a different designation, and for whatever reason it picked EAA91.

As a sidebar, I think that Telefunken may also have been the originator of the ECC85, with Philips being the follower in that case. Philips Book IIIB, which covered the FM-AM radio valves, did not mention the ECC85. Rather the EC92/UC92 was the Philips VHF radio (single) triode at that time.


Cheers,
Synchrodyne is offline   Reply With Quote
Old 22nd Oct 2019, 8:32 am   #46
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 5,141
Default Re: Why Both EAA91 and EB91?

Quote:
Originally Posted by Synchrodyne View Post
Presumably the third party (possibly/probably)Telefunken wanted to introduce an exact copy, physically and electrically, of the American 6AL5. Given that the EB91 designation was already taken by Philips/Mullard for a valve that was electrically similar to but physically different from the 6AL5, that third party felt that it needed a different designation, and for whatever reason it picked EAA91.
"Whatever reason" is probably the operative phrase... personally I would have gone for EB92! But I guess we will never know now.
kalee20 is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 8:54 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.