DIY adapter to compare modern tubes with the EF12k.

[rock soderstrom]

HI, I bought an old microphone preamplifier with 2x EF12k, I guess it will arrive tomorrow with the DHL lady.

After a small restoration this mic preamp will be a good testbed for a tube comparison.

Everyone against everyone, first EF12 from Western Europe against the guys from the East, then old against young.

I've always wanted to compare the EF12 with its successor, the EF804s, and my EF86 pearls.

So today I built adapters, quick and dirty. Maybe tomorrow I'll build some for the 6J7/1620 US boys?

 

[rock soderstrom]

Conversion chart EF804s, EF86 to EF12

 

[paulcheeba]

How is this going?

 

[peterc]

This is an excellent idea. Be great to observe your experiences. Thank

 

[rock soderstrom]

How is this going?

This is an ongoing project and has worked well so far. I think more people will have to get involved with it in the near future.

Why? Because at the same time, I checked the market here in Germany for affordable EF12k and the result was depressing. I bought 11 such tubes, all with 100% emission measurements. They were intended for the V1 position in my test amp but also for a repair project for a friend whose EF12 U47 clone had too much noise.

The times when you could buy a NOS EF12k for 20€ are definitely over and the quality is getting worse and worse. We had a horror cabinet of tube problems here. Noise, crackling, poping, extreme microphonics and oscillation, all there, really depressing.( a NOS RFT EF12k was really quite during testing, after a short moment of joy it quickly became clear why, it simply died during testing )

In the end, one tube was barely useable for a microphone! In my Gates SA70 inspired EF12 mic amp the situation was slightly better. The EF12k chapter is over for me, I wouldn't design another DIY project for it.

As for the adapter, it works without any technical problems, the only challenge is the height, especially with the EF804s. But even the EF86 is difficult to fit into a microphone, for example, with an adapter. It looks better for microphone amplifiers with more space.

I wrote to a Chinese ebay seller to see if he can offer an adapter like the one pictured for the EF12, but so far I haven't gotten any real feedback. An adapter with minimal height would be ideal.

EF86 for 6SJ7 adapter in comparison:

A totally rebuilt Funkwerk MVT4050M, which is now a Gates SA70 style amp with EF12k.

Here with the measurement "tin can" connected to terminate the input for measurements.

The whole thing is an ongoing project and will be continued...

 

[paulcheeba]

Wow cool adaptation!