Difference between EM85 and EM81 - UK Vintage Radio Repair and Restoration Discussion Forum

ricard · 20th Mar 2020, 1:20 am

A question came up in one of the threads in the Tape Recording section, what is the real difference between the EM81 and EM85 ? They are both "fan" type magic eye valves, same form factor, same display (as opposed to the EM80 which has a 'fan' which widens with increasing signal level as opposed to the EM81/EM85 which has a gap that closes with increasing signal level). Comparing the technical specs they are slightly different but not much. The pin connections are different though, but that seems to be the main difference.

Different manufacturers trying to grab their share of the market? Just seems a bit odd for such a valve as an indicator valve in that case, as it would have limited use, compared to for instance a triode or pentode.

G8UWM-MildMartin · 20th Mar 2020, 3:24 am

The triode section of the EM85 could be used as an audio amplifier stage, but usually was not.

Chris55000 · 25th Mar 2020, 7:48 pm

Hi!

I'm not entirely sure why the EM85 came out in the form it did – this indicator is identical in pinout and characteristics to the more common EM84 – it has, as mentioned, completely separate triode and indicator sections, only the heater/cathode being common!

This valve was not noted for having long–lived phosphors, like the Mullard EM80/EM81, they decayed very badly after a few hundred hours of use!

There was a Brimar/Cossor equivalent to this valve, the 65ME, I think the H.M.V. 523 used it and also a number of Murphy sets had it as well!

The M.O.V. 1965–66 Valve Data book recommended using an EM84 and masking down the aperture to suit.

This valve is invariably atrociously expensive when you do find it, and if you need a fan–shaped indicator, then I'd rewire the base to suit the Soviet 6E1N!

Chris Williams

20th Mar 2020, 1:20 am	#1
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Difference between EM85 and EM81 A question came up in one of the threads in the Tape Recording section, what is the real difference between the EM81 and EM85 ? They are both "fan" type magic eye valves, same form factor, same display (as opposed to the EM80 which has a 'fan' which widens with increasing signal level as opposed to the EM81/EM85 which has a gap that closes with increasing signal level). Comparing the technical specs they are slightly different but not much. The pin connections are different though, but that seems to be the main difference. Different manufacturers trying to grab their share of the market? Just seems a bit odd for such a valve as an indicator valve in that case, as it would have limited use, compared to for instance a triode or pentode.

20th Mar 2020, 3:24 am	#2
G8UWM-MildMartin Heptode Join Date: Jan 2004 Location: Stockport, Greater Manchester, UK. Posts: 827	Re: Difference between EM85 and EM81 The triode section of the EM85 could be used as an audio amplifier stage, but usually was not.

25th Mar 2020, 7:48 pm	#3
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,868	Re: Difference between EM85 and EM81 Hi! I'm not entirely sure why the EM85 came out in the form it did – this indicator is identical in pinout and characteristics to the more common EM84 – it has, as mentioned, completely separate triode and indicator sections, only the heater/cathode being common! This valve was not noted for having long–lived phosphors, like the Mullard EM80/EM81, they decayed very badly after a few hundred hours of use! There was a Brimar/Cossor equivalent to this valve, the 65ME, I think the H.M.V. 523 used it and also a number of Murphy sets had it as well! The M.O.V. 1965–66 Valve Data book recommended using an EM84 and masking down the aperture to suit. This valve is invariably atrociously expensive when you do find it, and if you need a fan–shaped indicator, then I'd rewire the base to suit the Soviet 6E1N! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!