6SL7 is higher Mu and another good thing to try in the type of circuits 12AY7 would normally be used for.
There is no specific "equivalent". While 12AY7 is kin to many others, its precise characteristics were scaled to someone's idea of "good audio preamp".
There is no specific "equivalent". While 12AY7 is kin to many others, its precise characteristics were scaled to someone's idea of "good audio preamp".
Yeah I had kinda come to that same thought. I had looked at 7F8 or 7F8W as being close. But that tube looks like it's more for RF service NOT audio.
Page 15 on this link http://bit.ly/2VP5nUY
I was looking at the Preamp circuit shown there.
Page 15 on this link http://bit.ly/2VP5nUY
I was looking at the Preamp circuit shown there.
7F8(G) _IS_ two 6J5, which is an excellent low-gain audio tube.
OK, why??
It is a mike preamp. There is no place in a Hi-Fi rig for this much flat gain (60dB!) or low input impedance (500r).
The internal output impedance is like 5KXXX 15K, but the 0.05uFd output cap will suck bass driving even 200K load.
It needs (we didn't know) a higher-gain tube than 6SN7 or 7F8. Mu=20 will give hardly-any NFB.
The bias on the 2nd stage is just grid-leak. This works OK even good for very small signals, but at the end of a HIGH gain amplifier we expect BIG signals. The bias is uncertain and so is the headroom. In any case this bias scheme wants high-Mu triodes. The 6J5 and kin barely qualify.
Frankly the idea here is to sell transformers.
Whatever your "preamp" needs, you can do better.
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OK, well good to know. That page is what follows the UTC W-20 & W-10 amplifier. They simply advertised it as "Auxiliary High Fidelity Equipment" A variable Equalizer and the Pre-amplifier. I had assumed they intended these two circuits to be on the front end of the Williamson amp.
The 12AY7 was specifically designed for audio. It did not have a 'larger bottle' precursor.
See Radio News, March 1949 - page 15.
See Radio News, March 1949 - page 15.
If you are intending on using as diff pairs , the octal 6N7GT is fairly close .
316a
Oh, how I like those old magazines 🙂! Have a look at this ad for a TV construction kit! Unbelievable, isn't it?
But I don't find any 12AY7 related stuff at page 15?!?
Best regards!
I think it had two page 15s, perhaps because it had an industry news insert. Search for 12AY7 and you should find it.
I remember Eric Barbour, who used to write for Glass Audio magazine, considered the 7F8 as one of the best sounding voltage amp tubes.
https://www.americanradiohistory.com/Archive-Poptronics/50s/55/Pop-1955-11.pdf
12ay7
see page 87
Making an Etched Preamp
12ay7
see page 87
Making an Etched Preamp
I too was momentarily confused, but after scrolling down found the article and read it with interest. It opened my eyes a lot and I like the way people in those days very clearly described what they were doing so that someone with limited knowledge wasn't put off by too technical or incomplete passages where the writer might presume a level of knowledge on the readers part. I guess the nature of the magazine promoted that. I expect that was a pretty exciting time for amateurs.
It was particularly interesting to me as the Webster amp that I'm working on has a pair of those valves.
Regards John L.
It was particularly interesting to me as the Webster amp that I'm working on has a pair of those valves.
Regards John L.
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