5718/EC71 vs 5703/6S6B

[OneRoomStudio]

I already asked this in one of the M49 threads, but wasn't able to get a response. Has anyone had a chance to compare these two types head-to-head? Now that 6S6B-V stocks have been depleted and prices have gone crazy, it would be even more helpful to know how the 5718/EC71 (or EC72 for that matter) compare. I already built a mic with a 5718 and was happy with the result, but I've never used a 6S6B, so I have no point of comparison.

 

[LevinGuitar]

I would recommend a EC70 tube or EF762 over any 5718 or 5703. I don't like that much the 6s6b, it have too big midrange boost that works quite ok with voice but not with other sources, it's anything but flat. With a bright tube as the 5718 or 5703 are you can add a deemphasis to your circuit, but how you deal with a pre set midrange curve?

The EC70 have low gain but the curve is soo nice! EF762 is a bit different, but still very nice. I have no idea about reliability or consistency, I just have some samples of each

 

[Purplenoise]

I would recommend a EC70 tube or EF762 over any 5718 or 5703. I don't like that much the 6s6b, it have too big midrange boost that works quite ok with voice but not with other sources, it's anything but flat. With a bright tube as the 5718 or 5703 are you can add a deemphasis to your circuit, but how you deal with a pre set midrange curve?

The EC70 have low gain but the curve is soo nice! EF762 is a bit different, but still very nice. I have no idea about reliability or consistency, I just have some samples of each

I thought ec70 is interchangeable with 5718.
I haven’t found the 5718 to be bright..5840 is much brighter to my ears. The 49 clone I built around a 5718 and original k47 capsule sounded very similar to a vintage m49c I compared it to. The vintage was a little fuller in low mids but that could be a capsule difference.

 

[granger.frederic]

EF762 is the same as 5840 : https://frank.pocnet.net/sheets/082/e/EF762.pdf

 

[LevinGuitar]

They are not, nor they do sound similar. I tried both as well as many more in the same microphone with the same biasing

They sound way closer to a TFK EF86, just a bit less low end, but still plenty enough. No coloration, no noise, no bright top end.

 

[granger.frederic]

re-read the technical sheet, top right: "ahnlich 5840"
You can translate: "similar to 5840".
Anyway, both can be used in microphones, like many other tubes, without drastic difference in sound, as long as their specifications are within the same range: internal resistance, mu, transconductance...
And you have to find the right amount of underheating for each...

 

[OneRoomStudio]

I thought ec70 is interchangeable with 5718.

Both Radio Museum and Valve Museum list EC71 as the equivalent to the 5718, but Tube Depot and a number of eBay auctions refer to EC70 as “5718A,” so it’s a bit confusing. The data sheet specifies the EC70 as a VHF/UHF amplifier tube, whereas the EC71 and 5718 are specified as medium-mu triodes good up to 500Mhz.

 

[Delta Sigma]

Both Radio Museum and Valve Museum list EC71 as the equivalent to the 5718, but Tube Depot and a number of eBay auctions refer to EC70 as “5718A,” so it’s a bit confusing. The data sheet specifies the EC70 as a VHF/UHF amplifier tube, whereas the EC71 and 5718 are specified as medium-mu triodes good up to 500Mhz.

That's UHF.

 

[OneRoomStudio]

That's UHF.

The difference being that a tube specified for VHF/UHF isn’t necessarily tested at audio frequencies - just ~30MHz and up. By comparison, “up to 500MHz” implies operation tested at lower (audio) frequencies as well.

 

[RuudNL]

I often read that a certain tube produces 'a different sound'.
But it is questionable if that is caused by the tube itself, or by a mismatch in the circuit...
(IMHO tubes don't have a frequency dependent amplification, but when they are not properly matched to the circuit, the frequency response can suffer.)

 

[LevinGuitar]

There is not many things you can do in a traditional simply circuit and I'm not sure if any really could change the response in a significant way (besides feedback).

Anode voltage and the resistor
Biasing type and voltage
Grid resistor
Output capacitor value
Transformer size and ratio

For my tests I was using a SP T3 microphone with 120v on B+, 100k in anode, (12:1 original transformer), 1uf output cap and tried different biasings:
-22uf/47uf on cathode with 1.15v and 1.6v,
-C12 style with grounded cathode with -1.15v and -1.6v on grid
-Grid leak without grid resistor (sounds quite interesting too).

With some tubes the difference in the biasing type was bigger than others, I had the impression that the AC701 did not change that much, but some others did.

As a first conclusion I end up that a good EF86 (as it's cheap and easily aviable) is no worse than a AC701 for any practical purpose, just a bit different and of course, bigger.
So why not doing a M49 with it or a similar pentode in a somewhat bigger body and same headbasket? Flea used that idea for a simplier circuit construction in the 49 Next mic. Also there are a MXL 920 mic that should work.

 

[RuudNL]

As a first conclusion I end up that a good EF86 (as it's cheap and easily aviable) is no worse than a AC701

There you say something: a good EF86... But it seems good low noise EF86 tubes are hard to find nowadays.
Unfortunately the quality of currently produced tubes is not what it used to be in the past.
The worst experience I have had was with the JJ Electronic tubes. They seem to only last for a couple of months and then start to become noisy, or produce loud crackling. Electro Harmonix is better IMHO, with usually pretty low noise. But for a microphone you have to test them first for noise. With the so called 'New Old Stock' tubes it is just Russian Roulette...

 

[LevinGuitar]

Well, I almost only use old Telefunken ones, there are still a lot of them nos at reasonably price, but there are a other brands very well made EF86 too. But the point is to take in count that for the best high quality and affordable M49 sounding clone you may get away from subminiatures

 

[gyraf]

Dont forget the PF86 for this application, this one seem to take underheating really well. And is cheap and plentiful, as the hifiers hasnt hoarded it (yet)

 

[OneRoomStudio]

I take it from the above responses that not many people have had the opportunity to try a 5718 or compare it to a 6s6b or 5703?

 

[LevinGuitar]

I take it from the above responses that not many people have had the opportunity to try a 5718 or compare it to a 6s6b or 5703?

Between them I would choose 5718

 

[Purplenoise]

I take it from the above responses that not many people have had the opportunity to try a 5718 or compare it to a 6s6b or 5703?

If it helps I have tried 5718, 5840 and phaedrus ac701. The best one to my ears in a 49 cirquit with 7:1 bv11 was the 5718.

 

[terry setter]

Oliver Archut used to say that the 5718 was indistinguishable from the AC701.

 

[doqmemory]

I made three M269c microphones using 5840W, 5703WB, and 5718, each with Moby's excellent Bv12 transformers and 797 Audio K67, Neumann K67, and Neuman K87 (respectively). They all sound great, but the 5718 is my favorite of the three.

I plan to use another 5718 in my next M49 build.

 

[Cqwet Dbdfte]

The difference being that a tube specified for VHF/UHF isn’t necessarily tested at audio frequencies - just ~30MHz and up. By comparison, “up to 500MHz” implies operation tested at lower (audio) frequencies as well.

Every tube is an audio tube.
These parts work with simple physics, no quantum effects or internal impedance pre-matching.
Some tubes were targeted for AF as their high internal capacitances precluded RF work.
Av different issue is noise, and special care, i.e. quality assurance, would have to be used in production. Is the noise effect in tubes a random event, or how is it controlled? Cathode mixture composition, eveness of application, thickness? I'm sure much of the art is lost, likely mfg proprietary process stuff.
Time to break out the scanning electron mucroscope, or just get some JFET's.
Just because a tube is not marketed towards AF does not mean it would not do a great job.