EF86

[ruffrecords]

The cascode is an interesting topology. It has the pentode's advantages of high gain and wide frequency response without the poor noise performance - which explains why it was used in early VHF receiver front ends. Its downside is that its distortion is relatively high. It has been used in pro audio circuits - I think it appeared in one version of the UA 610 mic pre.

Cheers

Ian

 

[johnheath]

Thanks PRR

I will surel scan that page with all its articles =)

It is true that I am a sucker for tubes but I do not have an opinion concerning the overall 12AX7… designing and building is like a drug for me… it started with a Fender baseman (blonde) trying to copy Brian Setzers sound before I realized that that amp must be played really loud to produce anything near Brains sound… so, I started modding to get MY sound… nowdays I only play acoustic guitars and sing and it was all natural to try to get decent preamp for less bucks… like the bassman project.

I wish I didn't have to design but the market is rather short on really good preamp schematics or I might be a stupid "googler"

I tried the 12AY7 instead of the 12AX7 due to its lower mu… it resulted in two normal gain stages driving a 12AU7 as a SRPP and it gave the preamp a nice warm tube flavor that I want.

I might be way out in the forrest here but it sounds nice and is rather cheap … which is what I like… also =)

 

[PRR]

> DAMN YOU PRR!!

Not sure how I offended you? ?

> triode connected EF86 is sorta 12AY7 / 7025

I would not say they are all that similar. Mu is all over the place, as is the maximum current.

All three were promoted with some promise of low-noise.

> why 7025 was so popular with sensible condensor mike makers.

7025 was also promoted as a more-reliable type. Since condensor mike tubes are often expected to last many years, and the mikes were not cheap in those days, 7025 would be a preferred type. I suspect that after 1959, "7025" was just the better crop of 12AX7, not a separate production. You could probably "make your own 7025" by buying 100 12AX7 and weeding-out 5 or 10 that burbled or rattled.

Of course today's production is all lowest-bidder and the markings of the buyer's choice. And some of the "12AX7" on the small retail market may be the fall-out from some guitar-amp maker's weeding-out process of his boxes of 100 12AX7.

 

[johnheath]

As far as I know, after reading data sheets thoroughly, the 7025, ECC83 and 12AX7  all have the same
mu of 100 and the same plate resistance while the 12AY7 have a mu of around 40 and a different and lower plate resistance… there seems to be small differences among the 12AY7's depending on maker and brand though.!?

The designing process is also a very good way to learn and understand the behavior of different tubes (if altering)… and I must say and I guess it has been said before that noise is a matter of listening… meaning that it depends on when and where and how you use your preamp… in my case my own tube preamp is noiseless compared to a LA2A compressor or any guitar amp I have. On high gain levels it is more noisy that some OP-amp preamps that I have but on normal gain levels and… for example playing an acoustic guitar into a large condenser mike you won't hear anything from the internal noise… that mike will pickup noise from the surrounding when turned up high though.

From experience

Regards

/John

 

[ricardo]

> DAMN YOU PRR!!

Not sure how I offended you? ?

Joke PRR.  Insclutable Oliental attempt decadent Western joke.

> triode connected EF86 is sorta 12AY7 / 7025

I would not say they are all that similar. Mu is all over the place, as is the maximum current.

All three were promoted with some promise of low-noise.

For the unwashed masses .. If you look at the tech blurbs for these 'low-noise' devices when they came out, it is obvious that the makers were much more concerned with hum & microphony than hiss.  eg
http://www.r-type.org/addtext/add036.htm

 

[ln76d]

I had really good results  replacing EF86 with E80F (especially Valvo), in some preamps  including G7 microphone.

 

[gyraf]

Also note that PF86 is the same tube as EF86, but with different heater voltage. The beauty is that heater voltage (at 4.5V/300mA) is different enough that the hifi-people haven't hoarded all remaining NOS, so there is still plenty around for decent prices.

This also means that it's unlikely that you get counterfeit PF86 tubes

Last remark - I have a feeling (not scientifically tested just yet) that the PF86 in general behaves better - i.e. more of a batch are suitable - for microphone front-end use. Maybe this has to do with slightly different cathode material/structure for the different heating?

Jakob E.

 

[iprovlek]

I had really good results  replacing EF86 with E80F (especially Valvo), in some preamps  including G7 microphone.

Yes me to!
Have Valvo E80F,better than Telefunken EF86 in my G7!
E80F is super replace for EF86...