ECC85 question

[kestrelmusic]

I'm trying to find a substitute for the ECC85 in the front end of FM receivers. THe Russian 6N1P is alleged to be a near equivalent, but given that the source of my information is an Eastern European dealer with a large stock of them, I am unconvinced. Has anyone had any experience of the Russian bottle?

I've tried a 6/30L1 in my FenMan1. It works reasonably well, though the gain is lower and it shifts the tuning by about 1 Mc/s - presumably due to different inter-electrode capacitances.

Has anyone any other ideas, other than the direct equivalents 6AQ8 and 6L12, both of which attract the same high prices as the ECC85?

[Maarten]

As far as "near equivalent" goes, the 6N1P would be closer to the ECC88 but not close enough to replace it in every application, see https://www.vanderheem.info/164-verg...cc88-6n1p.html (use a translation egine if necessary). Also see http://www.r-type.org/exhib/aag0186.htm

I haven't compared the ECC85 data myself, but that would be a good starting point.

[agardiner]

Langrex list 6N1 under ECC85, and 6N1P under ECC88, so as Maarten has said, the 6N1P is closer to the ECC88. That said, I have swapped substituted ECC85's with ECC88 on occasion, particularly if the set is a bit fussy as some are.

How much are these 6N1P's? If cheap enough then I would say worth the risk to acquire a few and try them.

[Robert Gribnau]

Originally Posted by Maarten

As far as "near equivalent" goes, the 6N1P would be closer to the ECC88 but not close enough to replace it in every application, see https://www.vanderheem.info/164-verg...cc88-6n1p.html (use a translation egine if necessary). Also see http://www.r-type.org/exhib/aag0186.htm

I haven't compared the ECC85 data myself, but that would be a good starting point.

I think that the value for Ri of the 6N1P provided in the first link is wrong. On triodes the formula μ = S x Ri applies. But S and Ri of the 6N1P are both given as 4.4 which would give a μ of only 19.4.

Since many other sources state that μ is about 35 and S is about 4.5 mA/V, I conclude that Ri must be about 7.8 K Ohm.

As a side note: In the Svetlana datasheet for the 6N1P the values for S and Ri are mixed up. See: https://frank.pocnet.net/sheets/164/6/6N1Pspec.pdf

[Gabe001]

Given how fastidious FM sets are for ecc85 valves in good working order, I would substitute an ecc85 with another ecc85. There seem to be plenty around.

[David G4EBT]

Unfortunately, ECC85s seem rather short-lived. NOS ones are starting to become quite expensive, and can cost more than some sets are worth. Watford Valves have Siemens branded ones made in the Tungsram factory in Hungary in stock at £16.00, which is as good a price as any I've seen. ('Tungsram' is etched on the anode plates). Interestingly, Watford Valves state: 'this is a super upgrade over the 6n1 and 6n1p, and comes in the Siemens orange and blue box':

https://www.watfordvalves.com/produc...il.asp?id=3825

Some sellers are asking more than that for 'used' ones. (I'm not sure who would buy a 'used' ECC85).

[vidjoman]

Leak fitted an ECC88 in their Trough Line mono tuners in place of an ECC85 when they upgraded to the stereo version. I don’t remember seeing any component changes in that front end area.

[See_Mos]

Kestrel, you have a P.M

I have 5 available.

[kestrelmusic]

Originally Posted by David G4EBT

Unfortunately, ECC85s seem rather short-lived. NOS ones are starting to become quite expensive, and can cost more than some sets are worth. Watford Valves have Siemens branded ones made in the Tungsram factory in Hungary in stock at £16.00, which is as good a price as any I've seen. ('Tungsram' is etched on the anode plates). Interestingly, Watford Valves state: 'this is a super upgrade over the 6n1 and 6n1p, and comes in the Siemens orange and blue box':

They also say: "the Tungsram has a warm and rounded performance with excellent treble detail. The item produces a very well balanced stereo image..."

What a load of cobblers!

[David G4EBT]

Originally Posted by kestrelmusic

They also say: "the Tungsram has a warm and rounded performance with excellent treble detail. The item produces a very well balanced stereo image..."

What a load of cobblers!

True, but I truncated that bit of blurb to obviate the risk of 'Audiophool' trolling

I've got form for that. On 5 October 2017 I posted a 24-word 'Audiophoolery' thread, which I though would have the lifespan of a mayfly, yet seems destined to have a longer run than 'The Mousetrap' with 3,132 posts and 242,498 views to date.

Sorry about that.

[Radio Wrangler]

Originally Posted by David G4EBT

I've got form for that. On 5 October 2017 I posted a 24-word 'Audiophoolery' thread, which I though would have the lifespan of a mayfly, yet seems destined to have a longer run than 'The Mousetrap' with 3,132 posts and 242,498 views to date.

Sorry about that.

No need to apologise. It serves multiple purposes of letting people vent steam, provides a degree of entertainment along the lines of "Look what they're doing now!" and lets people take a poke at the ones littering the world with de-valved radiograms while shoving the prices of certain valves through the roof..

David

[Katar83]

Langrex sells these valves for £18 delivered. That surely isn't too bad?

[Synchrodyne]

Originally Posted by vidjoman

Leak fitted an ECC88 in their Trough Line mono tuners in place of an ECC85 when they upgraded to the stereo version. I don’t remember seeing any component changes in that front end area.

Perhaps not quite so.

The Troughline II used an ECC84 cascode RF amplifier, followed by a half ECC85 as mixer, the other half being the AFC reactance valve. (The local oscillator was the triode section of an ECF80, the pentode section serving as 1st IF amplifier.)

In the Troughline Stereo, the ECC84 was replaced by the frame grid ECC88, ostensibly for higher gain and/or lower noise, but the ECC85 was retained for the mixer/AFC function. I think that there were some resistor changes around the RF stage, as well, to suit the higher slope, very sharp cutoff ECC88.

The original Troughline had used an EF80 RF amplifier with aperiodic input, followed by an ECF80 as pentode mixer and triode AFC valve. The Troughline II et seq had a tuned input, i.e. three-gang. It appears that Leak used the cascode RF stage more to offset the extra noise of the tuned input than to improve sensitivity; I think it claimed about the same quieting performance.

The ECC85 looks to have been a European development (Telefunken?) to facilitate the single-valve FM front end (for economy or parsimony?) There had been some use of the 12AT7 (ECC81) in the USA for this purpose, but mostly it was used as originally intended, as a mixer-oscillator preceded by a separate RF amplifier. The single-valve front end did eventually find favour in the USA in the later 1950s, though. The 6AQ8 was the ECC85. The 6DT8 was basically the 12AT7 with an internal shield, and with its split heater, had the advantage that one valve could serve both the 6.3 volt and 150 milliamp heater applications. Whereas Europe stayed with the ECC85, in the USA there were subsequent developments, in part brought about by the advent of stereo FM. These included triple triodes, allowing for an AFC valve, or alternatively deployed as a mixer-oscillator-AFC combination, although AFC triodes were soon replaced by AFC solid-state diodes. Then there were double triodes with one being a frame grid (for the RF amplifier side), pentode-triodes, with pentode as RF amplifier (GE in particular seemed to prefer the pentode RF amplifier), and double tetrodes.

The fact that the European setmakers stayed with the ECC85 from c.1953 until the move to transistors effectively limited the choice of valve types for the role, although some circuits might work with alternative double triodes. By the time the UK setmakers had to address FM, the ECC85 was well-established, so an obvious choice. Its first use in the UK might have been by Chapman in 1953 for its first FM tuner, the FM81. (But Chapman switched to a pentode RF amplifier for the FM81 Mk II, and stayed with that until the end of valved tuner production.) I suppose that the ECC85 was more suited to the setmaker level than to hi-fi tuners. Even so, Radford used it on its first FM tuner, possibly because it had to buy in a front end, and not much else was available. On the other hand, Dynatron used an ECC85 on its T10, but fairly soon changed to a two-valve FM front end on the T10A.

The use of ECC85 in AF circuits might have been simply a matter of convenience. Armstrong did that in some of its later 1950s/early 1950s lower-level tuner-amplifier chassis. Given that these already used the ECC85 as the FM front end, it made sense to use the same valve in non-critical AF circuits. That was not fundamentally different to using the ECC81 for AF purposes, given that it was primarily an RF valve suitable for use up to 300 MHz. Of course, in those days, the circuit designers endeavoured to minimize the distorting (in a broad sense) effects of their chosen active devices, such that normal production (and make-to-make) variations were rendered insignificant or at least relatively unintrusive. It would seem to be otherwise today…..


Cheers,

[Synchrodyne]

Originally Posted by Synchrodyne

The 6DT8 was basically the 12AT7 with an internal shield, and with its split heater, had the advantage that one valve could serve both the 6.3 volt and 150 milliamp heater applications.

NO, that was wrong. The 12AT7 had a split heater. But the 6DT8 gave that up to allow a pinout for the shield. So, the 12DT8 was required for the 150 mA series-string heater case.


Cheers,

[vidjoman]

Originally Posted by Synchrodyne

Perhaps not quite so.

The Troughline II used an ECC84 cascode RF amplifier, followed by a half ECC85 as mixer, the other half being the AFC reactance valve. (The local oscillator was the triode section of an ECF80, the pentode section serving as 1st IF amplifier.)

In the Troughline Stereo, the ECC84 was replaced by the frame grid ECC88, ostensibly for higher gain and/or lower noise, but the ECC85 was retained for the mixer/AFC function. I think that there were some resistor changes around the RF stage, as well, to suit the higher slope, very sharp cutoff ECC88.

Apologies as I got it wrong - thinking back it was the ECC84 that changed. I got the number wrong.