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Old 24th Apr 2012, 1:34 pm   #1
ricard
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Default EL84 vs. UL84 and PL84

Reading through the pages on the EL84, UL84 and PL84 at the National Valve Museum website, it appears that the UL84 and PL84 are different from the EL84. The two former are described as beam tetrodes, and are designed to operate at a lower anode voltage (due to their use in AC/DC sets where no mains transformer is present) and higher anode current than the EL84. In this respect they are more like the EL86.

But isn't the convention tha the first letter just differentiates the heater voltage, when the rest of the designation is the same? ECC85 vs. UCC85 for instance etc? I know there are exceptions to this; DM71 is a subminature magic eye valve, whereas the EM71 is a much bigger loctal device, with no similarities apart from the fact that they are both magic eyes.
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Old 24th Apr 2012, 1:58 pm   #2
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Smile Re: EL84 vs. UL84 and PL84

Hi,
I think I asked a similar question on this forum a while ago. Maybe a search will unearth it. Thanks to my lousy memory, I can't remember when, or if, I posted it
Cheers, Pete
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Old 24th Apr 2012, 2:17 pm   #3
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Default Re: EL84 vs. UL84 and PL84

Perhaps you are referring to this thread. (Found in less than a second with the new search facility!)
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Old 24th Apr 2012, 2:41 pm   #4
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Default Re: EL84 vs. UL84 and PL84

All three types are shown as pentodes, in the Brimar manual no. 6.
-Tony
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Old 24th Apr 2012, 4:30 pm   #5
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Default Re: EL84 vs. UL84 and PL84

Sorry it didn't occur to me to check the archives first ... figures, someone would have asked this previously.

It appears that the Brimar manual though is in conflict with the national valve museum site regarding beam tetrode vs. pentode for UL84/PL84. Anyone else know more on that subject?
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Old 24th Apr 2012, 5:19 pm   #6
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Default Re: EL84 vs. UL84 and PL84

Mullard were owned by Philips, who originally invented the pentode and were fiercely proud of that.

Other manufacturers might have made valves that were electrically interchangeable with an [EPU]L84, but using a beam tetrode structure.
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Old 24th Apr 2012, 5:20 pm   #7
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Default Re: EL84 vs. UL84 and PL84

Quote:
Originally Posted by ricard View Post
But isn't the convention tha the first letter just differentiates the heater voltage, when the rest of the designation is the same?
Convention hasn't really been established sufficiently for this to be a reliable guide. Usually you're right, but this is an exception (and the DM71 / EM71 is another striking exception, as you point out).

As well as different heaters, the EL84, PL84, UL84 have different cathode areas, and probably different grids, for their differing gm's etc. The anode is, as far as I know, the same, so they are a bit difficult to tell apart if the markings get rubbed off.

All are true pentodes however. (Mullard/Philips decribe the ECL86 and DL92 as pentodes, but these are really BT's although Mullard/Philips didn't acknowledge that!)

Last edited by kalee20; 24th Apr 2012 at 5:22 pm. Reason: Added last para
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Old 24th Apr 2012, 5:52 pm   #8
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Default Re: EL84 vs. UL84 and PL84

Didn't Philips have a patent on Pentodes which was gotten round (and arguably bettered) by the Kinkless (or beam) Tetrodes from the GEC group?

Consequently they (Philips/Mullard) were not keen to publicise that some of their offerings were beam tetrodes rather than pentodes.....
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Old 24th Apr 2012, 6:47 pm   #9
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Default Re: EL84 vs. UL84 and PL84

I think the "E" in EL84 or ECC83 refers to the filament current, not the voltage.

Pic attached of an old ECC8n ad, which I hope is sufficiently on-topic.

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Old 24th Apr 2012, 7:12 pm   #10
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Default Re: EL84 vs. UL84 and PL84

As far as I remember E stands for 6.3v heater, P for 300ma heater and U stands for a 100ma heater. I think otherwise the characteristics are similiar.
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Old 24th Apr 2012, 7:16 pm   #11
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Default Re: EL84 vs. UL84 and PL84

Hi Gus

E series valves are all 6.3V with widely differing filament currents.

U series are all 100mA fils

P series are all 300mA fils both the later types have widely varying fil voltages.

Some of the double triodes like the ECC83 have a Ct fil so that they can be used on 12.6 or 6.3

Sorry crossed with Simon

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Old 24th Apr 2012, 7:21 pm   #12
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Default Re: EL84 vs. UL84 and PL84

Hi.
"E" valves are generically 6.3v and the current doesn't come into the equation. "P" valves are generically 300ma heaters and are as a rule used in TV receivers with a 300ma chain. The "U" series have a 100ma heater and again used mostly in Radios with 100ma series fed heaters.
Mazda would have 6*** equivalent to the E Valves, 30*** equivalent to the "P" Valves & 10*** equivalent to the "U" valves.
There are though some rare exceptions.
Back OT the three valves in question do have different characteristics, dissecting the valves nothing is obvious.
Snag is today there is little reliable first hand info, the last old Mullard contact I had (a few years ago now) was in the early stages of dementia and his info was not reliable and sadly he passed away about four years ago.

Crossed with the previous posters!
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Old 24th Apr 2012, 7:40 pm   #13
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Default Re: EL84 vs. UL84 and PL84

I wonder why the ECC81, 82 and 83 series which are the equivilents of the 12.6V series 12AT7, U7 and X7 were not labelled HCC81 etc.

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Old 24th Apr 2012, 7:57 pm   #14
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Default Re: EL84 vs. UL84 and PL84

The H series were 150M/a types not generally used very much as as far as I can remember. The ECC series were used on a 6.3v circuit at .3amp and were widely used in 405 television receivers. I suppose the correct sequence should have been EHCC81/2/3.
The PL84 was used as a frame output valve in a number of 1960 series. The PCL85 followed a year later. The PL84 suffered from slow heating and self oscillation causing a 'tram line' effect across the picture. For some reason The UL84 seemed to run into grid current at the slightest excuse, similar to the UCL83. J.
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Old 25th Apr 2012, 9:22 am   #15
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Default Re: EL84 vs. UL84 and PL84

EHCC81 etc would be a strange designation, it's only the first letter that signifies heater type. EHCC would be a 6.3V heptode with double triode! (think of ECH81).

I would think the main reason for choosing E as the heater designation even though it can be run at both 6.3V and 12.6V and also in a 300mA (or 150mA) heater chain, would be familiarity. Engineers were familiar with the E series as the standard basic series of valves, and from there on also U and P for series connected heaters. Introducing a new valve at the time as HCC81 would probably have caused many engineers to miss it as few would be using H valves in the rest of the design.
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Old 25th Apr 2012, 2:38 pm   #16
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Default Re: EL84 vs. UL84 and PL84

Quote:
Originally Posted by Heatercathodeshort View Post
For some reason The UL84 seemed to run into grid current at the slightest excuse, similar to the UCL83. J.
I remember replacing a proportionally higher percentage of U-valves than P & E versions.
They just didn't last for long.
Today I would never consider building something with U-valves.

rgds,

/tri-comp
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Old 25th Apr 2012, 8:04 pm   #17
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Default Re: EL84 vs. UL84 and PL84

Could it be that the filaments are thinner due to the higher resistance needed to only pass 100mA and so are more prone to damage?

I suppose these days, when there is no DC mains anywhere, it would be possible to rewire a set to operate with E valves instead of U valves, adding a separate filament transformer. Many radios suppose would not have the space for one though.
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Old 25th Apr 2012, 8:21 pm   #18
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Default Re: EL84 vs. UL84 and PL84

Hi Gents, I have modified a white DAC90A to run on an auto transformer to prevent heat cracking of the cabinet due to the dropper.
This was actually a standard mod on these chassis as it was also fitted into other Bush sets. The chassis even had suitable holes under the dropper to fix the transformer to.

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Old 25th Apr 2012, 8:49 pm   #19
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Default Re: EL84 vs. UL84 and PL84

Quote:
Originally Posted by ricard View Post
Could it be that the filaments are thinner due to the higher resistance needed to only pass 100mA and so are more prone to damage?

I suppose these days, when there is no DC mains anywhere,

Hi Ricard,

I agree with the thinner wire = shorter life thing.

No DC mains anywhere? Not that many years ago I was designing a rack-mount frame for modular instruments, some of which were to go onto American aircraft carriers. Those particular ones needed to be designed for DC mains. As the boats are still in service, I think there are a few DC supplies stil on the go.

Cheers
David

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Old 25th Apr 2012, 11:27 pm   #20
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Default Re: EL84 vs. UL84 and PL84

There was never much DC mains about anyway; certainly not enough to justify so many "AC/DC" sets. It's my personal persuasion that the use of series-wired heaters and dropper resistors was more about a low initial purchase price than about compatibility with DC mains. Otherwise the clock radios of the time, needing AC for the clock motor, would have had power transformers.

I guess that's also why they didn't make 75 mA or 50 mA valves, which would have wasted less power in the dropper or even worked straight from the mains without a dropper, as in the "All American Five" sets; the filaments would have had to have been dangerously thin.
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