12DW7 Brown Deluxe

[Jammin'John]

I got a humbucker guitar and am looking for some clean headroom in the 'ole Brown Deluxe.
I put 12AY7's in v1 & v2 and a 12DW7 in v3.
The DW has a gain factor of 100 on one side and 20 on the other.
Will this hurt anything ?
It sounds good and is a lot cleaner.

JJ

[Jana]

Using a 12dw7 in a long tail pair phase inverter is about the worst possible place to put it. If you want lower gain try an AT7 in the phase inverter. And/or try an AU7 in the first stage.

[collinsamps]

Concur with Jana, get that thing out of your PI slot. Something else to consider is the plate impedance of all the swappable preamp tubes. If you want max signal transfer and minimum impedance mismatch go with something closer to what you are replacing. IE 12ax7= 5751 vice 12AT7.

[Jammin'John]

What about v1,12ay7 v2,12ay7 v3,12ay7
12ay7 12ay7 5751
12ay7 12ay7 12ax7

So I have a long tailed pair. I need a matched tube.


So can I just use a low gain tube in the first 2 slots & then a 12at7 or 5751 or 12ax7 for the PI ?

Is a 12ay7 OK as a PI ?
JJ

[M Fowler]

You can use a non matched tube in the PI and other tube sockets but the 12DW7 is and always has been an odd ball tube that we used to convert older amps to use the 12ax7 family instead.

There are matched 12ax7 family of tubes and there are regular 12ax7 tubes not matched. It would be good to use a match tube in the phase inverter (PI) but not necessary.

You can use 12ax7(7025)(ecc83), 5751, 12ay7, 12au7, 12at7(ecc81) if you like but not the 12DW7.

Mark

[Structo]

I tried the same thing in my Hammond conversion.

I didn't have any lower gain 12a*7 tubes but I had a ECC 832 which is the equivalent to a 12dw7 in the phase inverter.

It actually sounded pretty good and lowered the overall gain quite nicely but I knew what it was and didn't keep there for long.

The 12DW7 is a strange, oddball tube in that the first half section is pins 6,7, & 8 is the equivalent of a 12AU7 and section 2, pins 1, 2 & 3 is like a 12AX7.

So to use it effectively you would wire it so the first stage would be pins 6,7 & 8 so it cascades into the higher mu side.

So totally different gain triodes in one bottle.

[Phil_S]

What is it about this amp you don't like so much and what would you rather it do better?

Here's the thing, the gain factor isn't the only characteristic of the tube. The other major factor is plate resistance. 12AU7 and 12AT7 have low plate resistance and the result of using those is that you lose a lot of drive (oomph injected into the signal that isn't really gain). 12AY7 has plate resistance in the middle, but high enough to logically be grouped with 5751 and 12AX7. The 5751 (a real 5751 and not some Russian or Chinese relabeled 12AX7) is very close to the 12AX7 in plate load, so you get the benefits of the 12AX7 with less gain. Higher plate resistance adds more drive.

Let's talk about gain for a minute. The gain you derive from the tube is always less than the potential gain or the spec'd gain factor. Just because a tube has a mu or gain factor of 100 doesn't mean you actually get 100! Often you are only getting 35 or so. Don't be suckered by the gain factor.

So here are some specs (mu=gain rating, Ra=plate (anode) resistance:

12AU7, mu=17, Ra = 7,700
12AT7, mu=60, Ra= 11,000
12AY7, mu =44, Ra= 25,000
5751, mu=70, Ra= 58,000
12AX7, mu=100, Ra= 62,500

So, even though the 12AY7 has a lower mu, the plate resistance more than makes up for it by providing drive. Remember, you aren't getting the full amplification or gain factor for which the tube is rated...that's a bit of a sucker number as a result.

If you want to clean up, try 5751 in various positions. It is a great sub for the 12AX7 and it's lower mu will be noticeable immediately without sucking so much tone. You might even end up with 3 5751's and that's actually a pretty good tube to choose, as it deviates so slightly from the intended tube that the circuit really is well suited for it. As you go down the line from there, I think you'll start to sterilize the amp. A pair of 12AU7's with a 12AX7 in the PI (v3) will turn this stallion of an amp into a gelding.

See if you can wrap your mind around this and then see if you are willing to acquire tubes to fool around with. There is no promise of good results. BTW, that 12DW7 isn't really a very good choice for the amp because the 12AU7 half is just not what this amp needs.

Good luck and try to have some fun with this!

[Jammin'John]

I have a lot of "pulls".
American 12ax7,5751,12ay7(6072),12au7.
I LOVE this old amp.
I got it in '83.It's a '61.
Up until now my guitars were(are) single coils.
The G&L's are hotter.
The amp pretty much handled them in the normal channel with a 5751 in v1.
The new guitar has a Seth Lover (humbucker) and a P-Rail (P90&'bucker).
I am using the bright channel for this darker sounding guitar.
Does v1 just do the normal channel ?
I could go with all 12ay7's.
AY's in 1 & 2 and 5751 PI.
Ay,5751,5751.
What does v1 do ?
what does v2 do ?
I have the earliest Brownie with the normal channel on the left,bright in the middle.
http://www.ampwares.com/schematics/deluxe_6g3.pdf

Thanks,
JJ

[Structo]

V1 is the preamp tube for normal and bright channel.

The second half of V2 does the tremolo duty and V3 is your phase inverter.

[Phil_S]

The tremolo needs the high plate resistance to operate correctly. I don't think the 12AY7 @ 25K has enough Ra to oscillate. For this reason, you will probably do best by limiting your choices for V2 to 5751 or 12AX7.

[Jammin'John]

So v1 sets the gain for both channels.
I rarely use the tremolo.
I messed around before I read these posts and ended up with 12ay7,12ay7,12ax7.
Tomorrow I'll try 5751 in v2 with the ax7 PI.

I'll also try 12ay7,5751,5751.
Would that be the cleanest setting that makes electronic sense ?

Thanks,
JJ

[Jammin'John]

So half of v2 affects BOTH channels ?

JJ

[jimipage]

Using a 12dw7 in a long tail pair phase inverter is about the worst possible place to put it. If you want lower gain try an AT7 in the phase inverter. And/or try an AU7 in the first stage.

well, yes and no. A direct replacement will sound lousy, but with some modification the 12DW7 can be a screamer. Check out the schems and clips here:

http://www.retrodyne1.com/29Wamp.html

[Jana]

That schematic shows a split load phase inverter, quite a bit different than a long tail pair. With the proper design, yes, a 12DW7 would work well in a split load. The high gain section does the amplification and the low gain section does the driving. Show me a schematic that uses a 12DW7 in a long tailed pair and I will eat my shorts.

[jimipage]

Show me a schematic that uses a 12DW7 in a long tailed pair and I will eat my shorts.

heh!