American octal steel tubes in LDC microphones?

[emrr]

Every time I've tried to pile up vintage parts to do any sort of short run, the parts value appreciates past the finished product selling price.....

 

[rmburrow]

Yes, noise is always a challenge in this position.

That's what I thought too, the isolated grid on the top really makes sense here! I'm curious to see if I can get this to work.

6SN7 is a top tube. Is it also available in the steel version? I like their (single triode) predecessors 6C5 and 6J5 very much. Absolutely recommended for those who don't have them yet. I have a lot of them and they are still very good and inexpensive to get, which unfortunately can no longer be said of the 1620. They are becoming really rare, at least on my side of the pond.

6F5 has a grid cap, is high mu, and metal octal based..those were used in the Ampex 601 tape recorder preamp...

 

[emrr]

6F5 has a grid cap, is high mu, and metal octal based..those were used in the Ampex 601 tape recorder preamp...

I’ve never heard a quiet 6F5!

 

[rock soderstrom]

6F5 has a grid cap, is high mu, and metal octal based..those were used in the Ampex 601 tape recorder preamp...

Interesting, seems to be some kind of a half 12AX7 for octal sockets. I think I saw one in an early Gibson Amp.

I’ve never heard a quiet 6F5!

Bummer!

 

[terry setter]

Relative to which American Steel Octal tubes might be worthy of use in a microphone, I'd just like to offer that I spent way too much time trying to make a good mic using a 5693. I had such high hopes (it was even red!). But all the ones I tested were noisy, microphonic, and no schematic or accompanying parts I came up with made them sound good enough to bother with. Subsequently, I've spoken with two other designer/builders who had the same experience with the 5693.

Hopefully, this might save folks some time, money, and frustration.

 

[Recording Engineer]

Sad, to say the least, as I had such high hopes of the 5693 in an RFT CM-7151 circuit! Doh!

 

[rock soderstrom]

Thanks for the warning Terry! This reduces my hope of finding a suitable 6j7 or even 6c5 that is quiet enough for use in a microphone. The 5693 is considered the long life SQ version of the 6SJ7, which in turn is the more modern successor to the 6j7.

Today comes my new test body (MXL2006 in silver) which I will extend with an aluminium tube. Diameter is 50mm, which is a standard dimension and easier to obtain than the dimensions of the other testbodies I have.

I'm not giving up yet, my US steel tube experiment continues. (...the title theme of Rocky I is playing in the background)

 

[terry setter]

OK... for you, a tip. EF184 (sorry, not metal). 190-210V on the plate resistor, 1.5 or higher mA on plate. Heat it at 5.2v and consider a Cinemag NiCo output transformer. Avoid fakes of these tubes (I know of a box of 300 tubes marked EF184 but they measured like they were from Mars). I have an extraordinary one which has a dark glass envelope. It's marked "Zenith".