Poor's man 12AY7 tube ..... which is a cheap substitute for this tube ?

[kagliostro]

I'm looking for cheap alternatives to the tubes we usually use in guitar amp

so I discovered tubes like

GU50 that is something like a ruggerized KT88

6005/6aq5 that is a 7 pin 6V6

6P1P that is a 9 pin 6V6

6N2P that is a 6.3v 12ax7

for EF86 the correspondent (russian) tube is 6J32P but I'm not able to find it

and for the 12AY7 the correspondent tube is the 6N4P also this not findable

Do you know if there are other tubes correspondent to the 12AY7 that are cheap and easy to be find ?

Thanks

K

[tubenit]

I use 12AV7 and it seems to be about the same as the 12AY7?  12AY7 is 45 gain factor and the 12AV7 is 41.

http://www.thetubestore.com/Resources/Guitar-Amp-Info/Gain-Factor

With respect, Tubenit

[kagliostro]

Thanks Tubenit

I'll try to find the 12av7 tube

Franco

[HotBluePlates]

I've not found anything that exactly matches a 12AY7, even the 12AV7.

Amplification Factor (Mu) is only one of the 3 main triode characteristics; the other two are Transconductance (Gm; plate current change per unit of grid voltage change) and internal Plate Resistance (rp).

You could relate the three as:
      Mu =       Gm * rp, not unlike
Voltage = Current * Resistance

To truly evaluate the tubes' characteristics directly, we need to check them at the same operating point (plate voltage, plate current, etc) which sometimes doesn't happen with the conditions listed on the data sheets.

From a 12AY7 data sheet,
Mu = 44
Gm = 1.75mA/v (= 1750 µmhos)
rp = 25kΩ

From a 12AV7 data sheet,
Mu = 41
Gm = 8.5mA/v (= 8500 µmhos)
rp = 4.8kΩ

You'll see Mu is similar, but Gm went way up and internal plate resistance went way down. To be fair, the 12AV7 data sheet condition was at an operating point with silly-high plate current which skews Gm up and rp down.

But look at the plate curves for each tube, specifically the -2v gridline. If you follow the 150v plate voltage line straight up to its intersection with the -2v gridline, the 12AY7's plate current is 2.5mA at that operating point while the 12AV7's is 10mA.

So it looks like the 12AV7 will have ~1/5th the internal plate resistance and pass about 5 times the current. This ratio will be different at different operating points, but the 12AV7 will always be a higher-current, lower-rp tube than the 12AY7. Without doing a proper design-check, I'd expect the 12AV7 to exhibit slightly more gain when plugged in the same socket, albeit with the possibility of being biased to a poor operating point for the tube.
Maybe it's worth asking why you need a 12AY7?

If you are replicating an old design to the last detail, or using the tube in an old amp, maybe you really need a 12AY7. Seems like the 12AY7 (or 6072) is your only viable option.

If you wanted a 12AY7 because it is to be used in a new design (maybe the amp in your other thread?), you may want to ask yourself if you simply need the approximate gain the 12AY7 would provide. It would be a lot easier to take the cheap 12AT7 or the omnipresent 12AX7 and knock their gain down to what a 12AY7 would give.

The tradeoff is generally that the lower-Mu tubes (12AU7, 12AY7) accept larger input signals before overload than the higher-Mu tubes (12AT7, 12AX7), along with having lower gain. Their internal plate resistance can also dictate appropriate circuit resistances, with low rp tubes leading to lower output impedance. That may matter in some applications.

[kagliostro]

Many thanks HotBluePlates

As always a very interesting explanation

If you wanted a 12AY7 because it is to be used in a new design (maybe the amp in your other thread?), you may want to ask yourself if you simply need the approximate gain the 12AY7 would provide.

The reason is double, the first as you have guessed is about the amp on my other tread that ask for a 12AY7 as V1

there I indicated 12AY7 or 12AT7 because the original schematic uses a 12AY7 with the triodes paralleled, giving a bit more gain than the single triode, so I was thinking to the 12AT7 that has a bit more gain as my version use one triode for each channel of the stereo

The other reason is because I discovered that the russian 6N4P is claimed to be a substitute for the 12AY7 tube and this will be a cheap tube to be used in circuits that are planned for the 12AY7 tube, though, unfortunately, it is hard to have those 6N4P tube, so I was wondering if there are other tubes that can be considered as substitutes

Franco

[HotBluePlates]

... I discovered that the russian 6N4P is claimed to be a substitute for the 12AY7 tube ...

Show me a data sheet first.  Russian vendors claim a lot of their products are "same as ..." which may or may not be true.

I found some links to 6N4P data sheets, but non of them worked.

... the original schematic uses a 12AY7 with the triodes paralleled, giving a bit more gain than the single triode, so I was thinking to the 12AT7 that has a bit more gain ...

With the fairly unique design in that amp, I'd prefer analyzing how the stock circuit performs, choose the proposed new tube, the re-design around the new tube to give stock-circuit performance. With 4 gain stages (one a paralleled triode, another a pentode) driving a single output tube, I can't imagine you'll need or want "more gain".

[kagliostro]

Ahem .... only cyrillic

and effectively I get the info from a russian e-shop



https://www.google.it/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0CE4QFjAF&url=http%3A%2F%2Fwww.magictubes.ru%2Fsprav%2Fpdf%2F6n4p.pdf&ei=b6heVLDaEsr3PMGcgNAB&usg=AFQjCNG75wAfvS9C2PZWSawqgP-ZQQEpEQ&bvm=bv.79189006,d.ZWU

http://elbase.ru/files/doc/9053020.pdf

Radiomuseum didn't show a datesheet but say they are close each other

http://www.radiomuseum.org/tubes/tube_6n4p.html

http://www.radiomuseum.org/tubes/tube_12ay7.html

Franco

[DummyLoad]

http://duncanamps.com/tdsl/show.php?des=12AY7


all are rare. EF86 in triode mode is remotely similar.


http://www.tubeampdoctor.com/en/shop_TAD_Premium_Tubes_TAD_Pre_Amp_Tubes_SELECTED/12AY7_6072A_TAD_Premium_Selected_396


--pete

[HotBluePlates]

Ahem .... only cyrillic

Excellent! Cyrillic is good enough!

Yes, that sheet shows close-enough Gm and Mu, so it appears the 6N4P is a close equivalent to the 12AY7.

The only downside seems you have to look hard to find them. Maybe they are being re-branded and sold as new-production 12AY7's from places like EH.

I also just noticed that you plan for using the 12AT7 will likely use only a single triode, with a single tube dedicated to both channels. I'd still like to run through and see the end result is similar... The Aviatrix is very gainy judging from the sound-clip the designer posted.

[kagliostro]

EF86 in triode mode is remotely similar.

EF86 = 6J32P = difficult to be found 

Ciao Pete

a pair of years ago I payd 30€ for a pair of used (good condition) 12AY7 ...............

---

About the Aviatrix stereo, I too was considering that the added 12AY7 tube can be a bit too much, so on my schematic I put a second

jack to bypass the first tube

Please tell me if I'm wrong
the gain stages of the circuit are 3 (in my view)
V1=12ay7 + V2=6N2P + V3=6ak5, the following tube V4=6N2P has "no" gain as it is a CF (also if bootstrapped)


I was thinking to use a 12at7 triode for each channel and connect a third jack as linked input if both channels are to be used with the same guitar


Franco

[HotBluePlates]

the gain stages of the circuit are 3 (in my view)
V1=12ay7 + V2=6N2P + V3=6ak5, the following tube V4=6N2P has "no" gain as it is a CF

This is true. But the cathode follower also reduces the loss imposed by the tone circuit, so overall signal level is probably increased by using the cathode follower.

Additionally, the bootstrapping of the cathode follower would increase the gain of the pentode stage, though there is also attenuation built in, in the split plate load resistor and voltage divider running into the cathode follower grid. So, a lot of moving parts to study...

[kagliostro]

Oh, stupid question .... I've a lot of 12AU7 tubes ...... but a 16 gain tube as V1 may be is too low, I've seen 12AU7 as V1 only in some HiFi (DIY) circuit


Franco

[kagliostro]

Talking about gain, the 6J6 (ecc91) has a 38 that is a bit less than the 45 of 12ay7 and the 41 of 12av7


Franco

[jojokeo]

Maybe it's worth asking why you need a 12AY7?

If you are replicating an old design to the last detail, or using the tube in an old amp, maybe you really need a 12AY7. Seems like the 12AY7 (or 6072) is your only viable option.

If you wanted a 12AY7 because it is to be used in a new design (maybe the amp in your other thread?), you may want to ask yourself if you simply need the approximate gain the 12AY7 would provide. It would be a lot easier to take the cheap 12AT7 or the omnipresent 12AX7 and knock their gain down to what a 12AY7 would give.

The tradeoff is generally that the lower-Mu tubes (12AU7, 12AY7) accept larger input signals before overload than the higher-Mu tubes (12AT7, 12AX7), along with having lower gain. Their internal plate resistance can also dictate appropriate circuit resistances, with low rp tubes leading to lower output impedance. That may matter in some applications.

Our forum friend & terrific resource HBP has explained this before and in even better detail in a prior thread.
I just finished up rebuilding an old amp out of a 5E3 Tweed which cascades the two triodes using a gain pot between triodes w/ the tone stack afterwards (to give an idea of the use & subsequent gain achieved I'm referencing here). Even after lowering gain from V1a 32% it still has more than plenty ultimately driving either 6V6s or 5881s (depending on venue). Using a 12AY7 w/ a 12AT7 for pi is simply MAGIC (for me)! I can get different & better gain territory by either using a 12AX7 in the 1st V1 position still using the 12AT7 in the pi OR leave the 12AY7 in V1 and use the 12AX7 in the pi which both combinations sound very good. Using two 12AX7s is just over the top. BUT none gives the MAGIC combo like the 12AY7 w/ the 12AT7 - for this amp & the way I like to play it.

My point is that there's two other very important factors that goes along with tube choice besides just considering the gain of the tube and that's bandwidth and frequency response! These two things are not to be forgotten and what plays such an important role which can be responsible for the personal "magic" we are all striving for in our builds. Maybe we just find the magic by experimenting & being lucky but this helps us to better understand the reasons behind it giving us a better foundation to know why for future builds or needs?!

Here's something taken from that all-inspiring thread by HBP to illustrate, "tubes with LOW rp values (and thus circuits with LOW rp’ values) will have greater BW and frequency response and proportionately less loss-of-gain (ie: mu’) than tubes with HIGH rp values. Substituting a 12AY7 for a 12AX7 reduces circuit gain by almost half (45%) but nearly doubles the BW. And, remember, the greater the BW, the more “sparkle” and “chime” we’re likely to perceive."

[HotBluePlates]

Yeah, what Jojo said... 

[SoundmasterG]

I like using the 12AY7 in place of the 12AX7 in some circuits because it sounds better.....a more natural compression and distortion than the spikiness of the 12AX7. The one that EH sells sounds pretty good, though not even in the same ballpark when compared to vintage ones. I've tried the 12AV7 but they are often too high of a current draw and don't sound nearly as nice. Good 12AY7's are quite hard to find so you are smart to try to find subs....too bad there aren't many good ones that are close out there...


Greg