12AT7 Power Tube

69SG · Post by **69SG** » Mon 08/08/05 5:11 am

This may sound Dupid
But a 12AT7 Put's out 2.5 watts 10500 ohms.
Couldn't that make a neat little 2 tube PP kickaround amp.
12AX7 & 12AT7

loverocker · Post by **loverocker** » Mon 08/08/05 5:33 am

Yes it could.

Take a look at the AX84 'FireFly' (which uses a 12AU7). Plus one of the old H&K widgets (Cream Machine) used one of these as a power valve. Plus Fender amps use tham as a power valve to drive the reverb.

daschnoz · Post by **daschnoz** » Mon 08/08/05 8:49 am

During testing, I used a 12AT7 in a FireFly. It didn't sound bad. I don't exactly remember how it sounded compared to the 12AU7, but it did work. If you think about it, Fender used 12AT7's in power amps for years in their reverb drive circuits on quite a few amps.

Post by **rjgtr** » Mon 08/08/05 9:55 am

In my experience, a Firefly is cool, but not as satisfying as a larger tube single ended. The low end just isn't there. I built an amp with a firefly output into a 1U rack and it wounded Ok through a speaker in a room, but was weak when mic'd.

I'm going to create a new version with a 6V6 or EL84 single ended output. I actually built a nice little combo with a 6V6 SE output and it sounded great (it evolved into a 2 6V6 PP amp). There really isn't a lot of difference in real volume between 1.5 and 5 watts anyway.

69SG · Post by **69SG** » Mon 08/08/05 10:12 am

I can't understand why they used a 12AU7. If I'm right the It's Ra is 100k Compared to 10k for the 12AT7. I guess It doesn't matter If you can match up a OT. Seems like 10k would be the better option though.
It's amazing the way SE and PP amps sound so different. Yet they both sound great, It's the differences in character that makes It so interesting.

Brett · Post by **Brett** » Tue 08/09/05 6:38 am

Plate resistance on a 12AU7 is 7 to 8k, which is probably why it was used. 12AT7 has 10 to 12kohms plate resistance, so it would ok. Must try it in my 'fly.

DutchMarco · Post by **DutchMarco** » Wed 08/24/05 12:35 pm

How about a Moonlight? A 'proper' PP amp with LTPPI, instead of self-split PP. Some folks at AX84 who have experimented with these have gone off the self-split arrangement into either SE or PSE, or into 'proper' PP amps with PIs. They just didn't like the sound with SSPP.

HBamp · Post by **HBamp** » Wed 08/24/05 12:51 pm

Hello,

Here is another one.
http://amps.zugster.net/projects/micro/index.html

Henk,

Hbamps

DutchMarco · Post by **DutchMarco** » Fri 08/26/05 1:38 am

Henk,

Did you think the 12AU7 had not enough low end, or did you find that the Moonlight was better than the Firefly?

I've ordered parts to build a Moonlight, but so far no luck at all in receiving them. AES shipped promptly, but it's been a month since they did that and I still have not received it. I've heard about customs being a pest these days, but only with people sending stuff INTO the USA, not out of it to Europe.

Post by **zaphod_phil** » Fri 08/26/05 4:37 am

HBamp wrote:Here is another one.

Where? Did you forget to add a URL, maybe...

69SG · Post by **69SG** » Fri 08/26/05 5:47 am

daschnoz Wrote:

During testing, I used a 12AT7 in a FireFly. It didn't sound bad. I don't exactly remember how it sounded compared to the 12AU7, but it did work. If you think about it, Fender used 12AT7's in power amps for years in their reverb drive circuits on quite a few amps.

Tube type / Amplification factor
12AT7 / 60
12AX7 / 100
12AY7 / 44
12AZ7 / 60
12BH7 / 16.5
(draws twice the filament current)
12AU7 / 17

HBamp · Post by **HBamp** » Fri 08/26/05 6:52 am

Marco wrote,

Did you think the 12AU7 had not enough low end, or did you find that the Moonlight was better than the Firefly?
I build something like the Chameleon for a friend about a year ago. I think
the low end for both options is fine. After all it is a bedroom amp.
The speaker cabinet was a little oversised and closed back with one 10"
celestion Vintage. In the 6SN7 mode it was slightly warmer and more bluesy. But the 12AU7's have their own charmes also.

Phill wrote,
Where? Did you forget to add a URL, maybe...
Sorry for that it was very late again. It is there now.

Henk

couchjammer · Post by **couchjammer** » Sat 10/29/05 2:58 am

I was checking out the tubes in my Maz 18 non reverb head and it doesn't have the 12 AT7 as recommended by Z. The tube selection is supposed to be two 12AX7's and 1 - 12AT7. I was wondering if this is why the amp doesn't have much headroom?

I've ordered a Mullard 12 AT7 from Mojotone so I guess I'll find out when it gets here. I'm assuming that the 12 AT7 belongs first in line after the output EL 84's .

69SG · Post by **69SG** » Sat 10/29/05 6:52 am

Where is it?
In the phase inverter?
*****************************
Tube type Amplification factor
12AT7 60
12AX7 100
12AY7 44
12AZ7 60
12BH7 16.5
(draws twice the filament current)
12BZ7 100
(draws twice the filament current)
12DM7 100
12DW7 100/17
12DT7 100
12AU7 17
12AV7 41

couchjammer · Post by **couchjammer** » Sat 10/29/05 12:41 pm

69SG wrote:Where is it?
In the phase inverter?
*****************************
Tube type Amplification factor
12AT7 60
12AX7 100
12AY7 44
12AZ7 60
12BH7 16.5
(draws twice the filament current)
12BZ7 100
(draws twice the filament current)
12DM7 100
12DW7 100/17
12DT7 100
12AU7 17
12AV7 41

It doesn't have a 12AT7. I'm not sure where in line it's supposed to be. I think first in line closest to the pair of EL 84's but I probably should email Dr Z and ask just to make sure.

I know this sounds stupid, but what is a phase inverter?

The tube I ordered is a 12AT7WA, NOS Mullartd (CV4024).

lastwinj · Post by **lastwinj** » Sat 10/29/05 3:33 pm

a 12at7 will have earlier distortion than a 12au7, in an output stage. sounds quite nice IMO.

germ

69SG · Post by **69SG** » Sat 10/29/05 4:08 pm

couchjammer wrote:
I know this sounds stupid, but what is a phase inverter?

The tube I ordered is a 12AT7WA, NOS Mullartd (CV4024).

If you are familiar with transistor power amps NPN & PNP(push Pull)
A Phase inverter is the stage just before the Power section of a Valve Amp.
It performs a similar function as the NPN & PNP transistors
But instead It splits the signal Into 2 signals 180 degrees apart
feeding the OT.
Look at it like a machine gun with red and blue bullets (Every other one)
Firing a red-blue-red-blue-red-blue-.
Red leftside of the OT---blue right side of the OT
And funeled to the speaker
******************************
This sounds stupider than the question

couchjammer · Post by **couchjammer** » Sun 10/30/05 3:09 am

69SG wrote:
couchjammer wrote:
I know this sounds stupid, but what is a phase inverter?

The tube I ordered is a 12AT7WA, NOS Mullartd (CV4024).
If you are familiar with transistor power amps NPN & PNP(push Pull)
A Phase inverter is the stage just before the Power section of a Valve Amp.
It performs a similar function as the NPN & PNP transistors
But instead It splits the signal Into 2 signals 180 degrees apart
feeding the OT.
Look at it like a machine gun with red and blue bullets (Every other one)
Firing a red-blue-red-blue-red-blue-.
Red leftside of the OT---blue right side of the OT
And funeled to the speaker
******************************
This sounds stupider than the question

Thanks for explainig that. It all sounds pretty greek to me. As it turns out, it looks like I jumped the gun by ordering that 12AT7. I emailed the Dr and he said that 12AT7 goes into the REVERB model, not the higher gain Non Reverb model.

I don't know, I thinking something ain't right. This amp had more headroom when I first got it. I was playing with a slide one night and all of the sudden it got real real dirty sounding. I changed out the tubes and it helped but now it breaks up way too early for my liking. Even with single coils and at a low volume I can can hear it breaking up.

Z said the the non reverb model is a higher gain amp than the reverb model.. I like clean,sparkly clean and I figure that I can get all the dirt I'll ever need with a pedal. I may sell this one and get something with more headroom.

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