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Old 15th Apr 2019, 1:05 pm   #1
Edward Huggins
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Default Mullard AF Pentodes.

Split from this thread:-

https://www.vintage-radio.net/forum/...d.php?t=155690
.

Re: Mullard AF pentodes, first came the EF37, then the EF37A, then the EF40 and finally the EF86. So given your comment n Post #1, what would be a better AF Pentode? I have always tend to assume that these were the ultimate.
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Old 15th Apr 2019, 1:49 pm   #2
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Default Re: EF86's.

This short article explains the history: http://www.r-type.org/addtext/add008.htm
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Old 15th Apr 2019, 5:35 pm   #3
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Default Re: EF86's.

Quote:
Originally Posted by Edward Huggins View Post
Re: Mullard AF pentodes, first came the EF37, then the EF37A, then the EF40 and finally the EF86. So given your comment n Post #1, what would be a better AF Pentode? I have always tend to assume that these were the ultimate.
Even before the EF37 was the EF36 from which it was developed - in non critical circuits there is no discernable difference.

You would expect the EF86 to be the ultimate but back in 1952 when EMI produced the BTR2 tape machine they used the EF37A for the play back amplifier. The EF40 was available and they would have been aware of the imminent arrival of the EF86 (Z729) so the improvement may have been slight.

Personally I have always detested the EF86 but that may be connected with the fact that it was one of the few valves to actually fail when I was playing with such things in my early teens.
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Old 15th Apr 2019, 5:58 pm   #4
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Default Re: EF86's.

Then there was the ME1400, better than the EF37A.
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Old 15th Apr 2019, 6:08 pm   #5
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Default Re: EF86's.

Quote:
Originally Posted by Edward Huggins View Post
So given your comment n Post #1, what would be a better AF Pentode? I have always tend to assume that these were the ultimate.
a better quality of the EF86 is the SQ type E80F
I use them in some testinstruments. For example: Grundig RV3
E80F is not a SQ type from EF80, this is the EF800
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Old 15th Apr 2019, 6:33 pm   #6
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Default Re: EF86's.

Among other things I've heard it argued that the larger pin spacing in the octal valves and, in particular, the fact that the grid is connected via the top cap allows the grid wiring to be kept more distant from the heater, thereby making hum pickup easier to control. Of course these days it's very easy to run low noise valves with DC heaters which eliminates the problem at source.

Cheers,

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Old 15th Apr 2019, 6:57 pm   #7
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Default Re: EF86's.

Quote:
Originally Posted by Edward Huggins View Post
Re: Mullard AF pentodes, first came the EF37, then the EF37A, then the EF40 and finally the EF86. So given your comment n Post #1, what would be a better AF Pentode? I have always tend to assume that these were the ultimate.
I have some EF804's which I bought very cheaply. Although not the ultimate 'S' version I understand they are very good and better than the EF86,, although the pinout is different to the '86
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Old 16th Apr 2019, 2:22 am   #8
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Default Re: Mullard Af Pentodes.

6BR7 is better than EF86. Different pinout
CV4006 is better than 6BR7 and has same pinout.
I have never done much with octal pentode valves as they are extremely rare in Aus

Joe
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Old 16th Apr 2019, 2:15 pm   #9
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Default Re: Mullard AF Pentodes.

Did Mullard ever have an equivalent to Brimar's 6BS7?

http://www.r-type.org/exhib/aab0164.htm

In times-past I built an instrumentation-amplifier which needed response "Down to DC and better" as one of my colleagues described it. A 6BS7 fitted in a small diecast box, with only the top-cap poking out through a hole, Mercury-batteries to provide the filament- and HT-power, and the whole thing fitted inside a larger steel box (to provide magnetic screening) did the job wonderfully.
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Old 16th Apr 2019, 5:21 pm   #10
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Default Re: Mullard AF Pentodes.

Quote:
Originally Posted by G6Tanuki View Post
Did Mullard ever have an equivalent to Brimar's 6BS7?


In times-past I built an instrumentation-amplifier which needed response "Down to DC and better" as one of my colleagues described it. A 6BS7 fitted in a small diecast box, with only the top-cap poking out through a hole, Mercury-batteries to provide the filament- and HT-power, and the whole thing fitted inside a larger steel box (to provide magnetic screening) did the job wonderfully.
I have some of the Brimar 6bS7, but have not seen an equivalent. I have lashed up a circuit using their recommended 5V (mine with stabilised DC) for the filament (electrometer application on datasheet) and 60V supply with a constant current cathode load (cathode follower) which has enabled me to measure voltages across a string of 10Mohm resistors with no apparent loading. I am now looking at encapsulating the circuit, as I need it for difficult measurement. Your idea of the hole for the top cap sounds good so worth a thought. Thank you.
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Old 17th Apr 2019, 7:23 am   #11
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Default Re: Mullard AF Pentodes.

"So given your comment n Post #1, what would be a better AF Pentode?" Wondered when someone would pull me up on that. I did a few tests a while back testing mainly for N but also THD, I found the EF37A better, though as you it's essentially the same device.

In some tests the 6BR7 came out tops as did the 6BS7 with very little grid leakage noted, but the pentode that came out best was the 6AU6 sharp cut off pentode. Run on DC htr's, triode strapped with a CCS as anode load it takes some beating.

However, these were limited tests of only a few valves of each type, so my statement may not be true as written. What I should have written and makes more sense is "that there are cheaper pentodes that do as good a job as a low signal, low noise valve"

Hope that clarifies things, Andy.
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Old 17th Apr 2019, 8:33 am   #12
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Default Re: Mullard AF Pentodes.

What "better" are we talking about here? - gain?, noise?, distortion?, overload handling? - it`s a bit horses for courses, surely.
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Old 17th Apr 2019, 10:04 am   #13
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Default Re: EF86's.

Quote:
Originally Posted by winston_1 View Post
Then there was the ME1400, better than the EF37A.
I understood that the ME1400 simply was an EF37A, but run at a lower heater voltage in its intended application?
Were they selected from the EF37A production for particular characteristics?

Andy
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Old 17th Apr 2019, 10:19 am   #14
Diabolical Artificer
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Default Re: Mullard AF Pentodes.

"What "better" are we talking about here?" Tried to qualify that in post #11.

Blurb here on the ME1400 - http://www.r-type.org/exhib/aaa1451.htm like the 6BS7 I guess it was made to have a very low g1 leakage current, or valves were selected to have this and other charateristics so as to be suitable in metering circuits.

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Old 17th Apr 2019, 10:34 am   #15
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Default Re: Mullard AF Pentodes.

I have noted that although 6267 is equivalent to EF86, some Japanese 6267's seemed
less noisy.
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Old 17th Apr 2019, 11:27 am   #16
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Default Re: Mullard AF Pentodes.

In Australia the 6AU6 was very popular in audio. NOT so much in phono or tape head stages, but as input high gain stages for power amps, AND as phase spltters for smaller push pull amps. My little 6BW6 stereo amp that I listen to daily uses them as described above. Input stage to power amp, then as phase splitter driving a pair of 6BW6 output pentodes run in pentode mode.
They are absolutely quiet and I didnt bother to select "pairs" or matched examples.
Thes are driven in turn by a pentode phono stage, with passive RIAA filter and thence to a simple voltage amplifier of half a 12AU7 to volume control to the first 6AU6.
The pentode input stage I designed around an EF86, (pentode mode) but that proved to be quite noisy especially as it constantly played "wind in the willows".
I subsequently changed the front end to 6BR7's which was a major improvement, especially regarding the rushing surf sound. I then swapped out the 6BR7's and replaced them with Brimar CV4006's with another LARGE reduction in noise. The phono stage ( pentode of described varieties, with single triode voltage amp) is DC heated, BUT on the same chassis as the power amp. I still have a little audible hum with the volume control flat out. At "normal" listening levels there is no "evident" noise.

Sorry about the long winded rave.

Joe
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Old 17th Apr 2019, 12:27 pm   #17
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Default Re: Mullard AF Pentodes.

I was never very impressed with the EF86 as they are the wind in the willows as Joe says, so I changed them for RCA's 5879 in all of my audio gear's front ends, including my current audio system. I first discovered these in the front ends of Seeburg Juke box amplifiers and was very impressed with them.
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