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Old 19th April 2015, 02:00 PM   #1
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Default EL91 Max ratings ? help

I know data sheets say maximun 250 volt but also data sheets say pretty low B+

on 6v6 as many run them over 400 volts. Does anyone have experience with

EL91's, I suspect would run ok at higher than 250 volts.

billyoung606060 at gmail dot com
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Old 19th April 2015, 05:40 PM   #2
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If you wind up the juice too much on such tiny valves they will just give up and die.

I posted a whole load of stuff about the 6V6 family yesterday, the upshot being, you can get away abusing the daylights out of the octal ones.

Most of the smaller clones were made for car radios and other wimpy budget devices, and weren't supposed to get a caning anyhow.
It was all "marketing!"

Horses for courses!
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Old 20th April 2015, 05:09 PM   #3
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I think it was Tubelab that found out in his usual way that the small 7 pin outputs don't respond well to spec busting. The glass is so close to the anode that when you experience a hotspot, the glass facing the hotspot will quickly melt and implode.
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Old 20th April 2015, 07:07 PM   #4
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Anyone that somehow believes they're onto a winner with a British 7pin output valve, must be crazy.
These were designed for el-cheapo budget table top radios.

It was typical of the Dutch and British (phillips-mullard combo) to be selling this sort of junk to joe-public, then 50yrs later it all gets fashionable again as that age group come up to retirement, - (just like the old 60s British sports cars are to the same white haired generation also).

You need to be very conservative with ratings for anything to stand any chance of working how it should.

Eg.
6L6 max 360V
6V6 max 295V
EL84 250V
EL34 400V (800V was always a joke, it might work for a few hrs before melting!)

And EL91/95 220V

A lot of the myths about Mullard being a quality manufacturer need to be debunked.
I still can't get it how people ever imagine the EL84 or EL34 as a quality product.
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Old 21st April 2015, 08:49 AM   #5
DF96 is offline DF96  England
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Quote:
Originally Posted by mullered
Anyone that somehow believes they're onto a winner with a British 7pin output valve, must be crazy.
These were designed for el-cheapo budget table top radios.
EL91 = 6AM5 - I suspect it was actually an American design. They used miniature valves before Europe.

Quote:
A lot of the myths about Mullard being a quality manufacturer need to be debunked.
Then debunk them. We are waiting for evidence. Should we order popcorn?

Quote:
I still can't get it how people ever imagine the EL84 or EL34 as a quality product.
That could be construed in two ways:
1. a statement of your inability to "get it"
2. a statement claiming poor quality for EL84 and EL34
If the EL84 was so poor a design, why did the Russians copy it?
Why did RFT in East Germany produce so many EL34, still highly regarded as NOS?
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Old 21st April 2015, 09:49 AM   #6
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EL91 by all accounts was European Philips stuff, - a scaled down 6V6 intended for car radios and the like.
I don't think the Americans were ever keen on those silly little 7 pin, 6.3v things with pins that were easy to wreck, and had bad contacts.

I think the USA preferred octal & noval right up to the end, while the Germans made their own high quality sockets.
Look at the quality of a German radio from Grundig or the like, compared with the rubbish from the UK at the time.

Isn't anecdotal evidence from people who actually worked at the factory good enough?
The epic EL34 failures at Mullard, were a standing joke amongst their own workforce at the time.

Also, you may notice the Russians as usual copied only western consumer goods, such as the Leica camera (Zorki), Fiat (LADA), the Volga (based on an old GM design).
Their consumer end stuff were soviet jokes of the time it was so bad, only Honnecker's Germany DDR made worse stuff.

The rest such as the fridges, radios, cars of any quality, were almost invariably made elsewhere in the USSR (Eg.Riga Latvia) or (Czech) Skoda.

If you are talking about proper Russian valves with no western equivalents, they invariably were specially made and ordered for the military.
Don't you remember those times or anything?

Last edited by mullered; 21st April 2015 at 10:17 AM.
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Old 21st April 2015, 10:45 AM   #7
DF96 is offline DF96  England
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Quote:
Originally Posted by mullered
EL91 by all accounts was European Philips stuff, - a scaled down 6V6 intended for car radios and the like.
Evidence? The EL91 is nothing like a 6V6. The 7-pin '6V6' is the EL90/6AQ5.

Quote:
I don't think the Americans were ever keen on those silly little 7 pin, 6.3v things with pins that were easy to wreck, and had bad contacts.
By all accounts it was the Americans who invented those silly little 7 pin 6.3V things which we now know as B7G or miniature. Do you have evidence to the contrary?

Quote:
I think the USA preferred octal & noval right up to the end, while the Germans made their own high quality sockets.
No, Americans usually preferred B7G - it was Europe who prefered noval (9-pin miniature).

Quote:
Isn't anecdotal evidence from people who actually worked at the factory good enough?
The epic EL34 failures at Mullard, were a standing joke amongst their own workforce at the time.
Evidence? Even just a link to an anecdote?

Quote:
Also, you may notice the Russians as usual copied only western consumer goods, such as the Leica camera (Zorki), Fiat (LADA), the Volga (based on an old GM design).
I understand that there were Russian clones of Western mini-computers such as the PDP-11 - clearly not just consumer goods, but industrial/military too. There was even the famous Russian clone of Concorde; it was reported that the plans stolen/leaked to them contained deliberate errors so the clone did not fly very well.

Quote:
If you are talking about proper Russian valves with no western equivalents, they invariably were specially made and ordered for the military.
No, I was speaking of what we now know as the 6P14P - which is virtually a clone of the EL84. Many Russian small-signal valves were surprisingly similar to Western designs.

Quote:
Don't you remember those times or anything?
I was alive during the Cold War. So what?

So far, your assertions in areas where I have some knowledge have turned out to be false. Could you at least try to back up your assertions in other areas with some evidence - or should I assume that they are false too?
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Old 21st April 2015, 10:54 AM   #8
316a is offline 316a  England
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What is this nonsense about Mullard being a poor manufacturer ? Lot of misconceptions and misinformation in this thread , like the 'fact' that EL91 is a scaled down 6V6 . EL90 was the scaled down version...

316a
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Old 21st April 2015, 11:09 AM   #9
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The Americans copied European valves, the Europeans copied American valves. The Russians copied both. What is the big deal here ??

However the Russians both produced some of the best quality valves and some outstanding designs of their own.

Shoog

Last edited by Shoog; 21st April 2015 at 11:11 AM.
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Old 21st April 2015, 11:50 AM   #10
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Totally agree with the last poster, and then of course there was all this patent nonsense for decades.

Don't forget Philips is Dutch, and they are not known for being generous, which is how they made fortunes out of yet another dire and dreadful product,- the compact cassette.
In any large scale industrial production facility turning out over 1 000 000 valves a week there are going to be economies of scale, and efforts to bring the quality down to a level which is JUST passable for the punter.
That is capitalism, which of course the Russians with their centrally planned economy don't have to this day.

The sheer quantity of raw material dictates these economies of scale, and lets not forget the UK had dire industrial relations, riven through with class issues, throughout the 50s right into the nightmare late 70s.
(I grew up there!)

A member of my family worked at Mitcham before he went off to work in nuclear particle accelerators.
As kids we were surrounded by buckshee bits of Mullard stuff, and could more or less help ourselves to those (POS) EL34s.

We had lots of fun making all kinds of projects and the 6V6 based home made record player, we thought sounded great, -but it WAS mono after all.

Philips were an arrogant predatorial bunch, so they refused to admit anyone else made better stuff and more or less denied the existence of the KT stuff from "shock horror" M-O-V, a direct competitor.
(A KT88 is a hard valve to melt, an EL34 is a kamikaze valve as soon as you get the G2 close to the limit)

None of this should come as any sort of suprise to a seasoned British industrial archeologist.

The coal mines were run on feudal lines, the motor & motorcycle industry slid into an abyss, the shipyards went on strike until they hit the rocks, the aviation industry struggled to survive the shock of the cancellation of the TSR2, and the railways were being closed, and the entire machine tools industry was using worn out stuff from pre-world war 1.
One of them British TIMKEN was still using that stuff until the factory caught fire in the 90s and was finally close!

The whole idea that an industry in terminal decline like Mullard was right through the 60s and 70s, should be motivated to produce top class products for crap ,*** produced TV sets, while soon competing like the rest of industry with much better made japanese stuff is a nonsense.

Of course quality control is gonna go down the pan.
I mentioned something like these a few days about "every decade sees a pinnacle of technology".
The radio valve's pinnacle in the EEC as it was then was about 1955-1971.

Today you can do repeatability with CAD, CNC & robotics, but sure as anything the quantities are not there to be able to reject a batch of 50 000 valves that fails QC in a week.
It AIN'T gonna happen especially in China or the far east!

Mullard keeled over well before the last sell by date in 1983-4, which was like the British motor industry, living in the past and reflecting on past "glories", propagating myths to all and sundry.

It makes me laugh when people claim they detect the sonic differences between what is simply PRODUCTION SPREAD, in a what is an unacceptably wide tolerance product, something you would never ever accept in something mission critical.

Look what happened to HUBBLE when they got that wrong!

You cite the Russians copying concorde.
You don't really have a clue there.
Even in aviation they got used to living on the ragged edge to try prove something, as the world headed towards another pinnacle of technology (civilian supersonic air transport).

The TU144 although loosely based on Concorde was a totally different plane with a totally unrelated internal construction, the wrong engines and landing gear, which of course is why it was a total failure, nothing to do with the popular myths.
The current TU160 is an awesome plane based on some of the very best USSR technology (1981/7, modernised in Nov 2014). It's the world's fastest nuclear bomber.

How do you explain that?
They copied it off the British or Americans?
What about Buran?
Copied from the USA too?

In fact if you carry on repeating popular myths, there's little point in continuing.
You are not on the same planet.

Read some of this:-
This is much more like the Mitcham Mullard my dad described, complete with the melting EL34s in the PA that wouldn't last more than a week...

Fascinating stuff.

Mullard valves questions - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum
Mullard valve answers - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum
How many valves did Mullard ever make? - UK Vintage Radio Repair and Restoration Discussion Forum

Last edited by mullered; 21st April 2015 at 12:17 PM.
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