12AV7 NOS

[deeder]

According to you, what is the best brand for 12AV7 NOS:
SYLVANIA
RCA
GE
STANDARD BRAND (?)
PHILCO

Thanks

[David Root]

This tube, and its industrial equivalent the 5965, is not much used in guitar amps as it is basically a 12AT7 with lower gain. It has become popular in audio circles though.

I have not used either myself, but for what it's worth here's my take.

I would choose in the regular 12AV7, RCA or Tung-Sol, because I consistently find that these manufacturers are as good as any and better than some. Generally, the older the better and preferably no later than 1965 or so.

In the 5965, audiotubes.com recommends the GE Five Star triple mica or the Telefunken. GE Five Star tubes were a special grade designed for broadcast use so you can expect very low microphonics and good balance triode to triode.

Philco brand was usually made by Sylvania, but there is a pair of Philco 12AV7 on EBay right now that were made by Raytheon (260 manufacturer code).

Standard Brands was a distributor so anyone could have made that one.

[deeder]

Thx David ;^)

[Stevem]

Should it matter Sylvania tubes always seem to have higher GM then the spec , RCAs are more frequency nutral and the RCAs with the two ribs on the top are Mullard made.

[tubeswell]

If you can find a whole stash cheaply then go for it. In guitar amps, they're typically not worth the risk of paying good money for singly because of issues with microphonics, but you might find a good one or two in a batch. They were designed for use as cascode stage tubes in TVs

[10thTx]

I like the 12AV7 and use them in my amps. I have used them in V1 as I would a 12AY7 (which I also have) and I especially like them in an on board active effects loop like a D'Lator where I am not really wanting any more increase in gain.

I have used them in my Tweed BluezMeister and my D'Mars ODS builds in the V1 and FX loop. The are d-inspired amps and have a clean channel going into an overdrive section by relay switching.

They sit somewhere between a 12AY7 and 12AU7 but closer to a 12AY7 in being more musical to my ears. I find the 12AT7 and the 12AU7 tubes to be the most consistently unmusical to my ears in a V1 position. 5751, 12AY7 and 12AV7 tend to be my "go to" tubes in V1 in my builds most often.

I've got perhaps 6 or 7 of them and maybe one of them has been microphonic? I have not found a particular brand to be the "best". Mine were all used and not NOS.

With respect, 10thtx

[10thTx]

There is a 12A_7 gain factor chart here:

http://www.thetubestore.com/Resources/G ... ain-Factor

The 12AY7 is 45 and the 12AV7 is 41. The 12AT7 is 60 and the 12AU7 is 19

Again, I like the tube and have had good experience with it. Having said that, I currently have the new production 12AY7 EH tube in V1 in both my amps and the 12AV7 in the effects loop of one of them.

With respect, 10thtx

[Stevem]

I have always liked a 12ay in place of a 12at for the reverb driver in amps and and depending where you use these lower gain but higher current drive tube they can make a so so sounding tone stack work great!
A lot of the JJ brand ax7s are very high in current drive.

[deeder]

Thanks again to you guys ;^)

So I bought 2 RCA's, 2 Sylvania's and 1 GE for 40 bucks, not bad

[martin manning]

Plugging a tube into a circuit that was not designed for it seems an odd practice to me. If you look at where the operating point goes for say a 12AT7 or 12AU7 when it is substituted for a 12AX7 it makes little sense, and that is probably why they don’t sound very good when used in that way. On the other hand, a 12AY7 will land on a very reasonable operating point (with Ra a little on the high side) when dropped into a 12AX7 circuit, so it’s no surprise that it sounds good.

Values of mu, ra and gm differ from the data sheet values at these odd operating points. Gain (Rk bypassed) is a function of Ra, mu, and ra, and Ra is constant when swapping tubes. For both of these reasons the actual difference in gain is not as much as the difference in data sheet mu would suggest. From a 12AU7 to a 12AX7, mu increases by a factor of six, while the in-circuit gain only increases by 3.7.

Putting a 12AX7 into a 12AT7 reverb driver circuit positions it’s load line partially above the maximum anode dissipation, and this happens much more so when substituting a 12AY7. I wouldn't recommend either of those swaps.

12AV7 is a high-current tube like 12AT7 and 12AU7, but it has ra like a 12AU7 and mu that is in-between. Note that the 12AV7 data sheet values are quoted at 150V instead of at 250V like the others. The mu is more like 35 at a similar operating point, as opposed to the value of 41 given on the data sheet.

If I were going to design a gain stage around a 12AV7, I would use a 15k anode load and a 500-ohm Rk, with a supply voltage around 325V. That gives an operating point with 200V on the anode, 8mA current, with 4V on the cathode. At that point the gain (fully-bypassed) is 27dB as compared to a 12AX7's 35dB (100k Ra/1k5 Rk, 200V Va).

[deeder]

Very interesting and instructive development. My idea is to use old tubes I have to design a simple circuit with EF806S/12AV7/6V6 in SE mode. It’s an uncommon way but I like to take side streets.
Ok, let’s see the math’s right now… Since I’m not an engineer it’s the long way which waits for me…

[martin manning]

Merlin Blencowe's Valve Wizard site has much better explanations than can be made in a few words here, so I suggest a visit. Then ask questions.

[deeder]

You read in my thoughts Martin! And to be more precise I was thinking to use an EF80 Valvo that allows a higher grid resistor. I am going to follow the advice.