[jcmjrt]

I'm not a fan of metal boxes and was thinking about making a nice wood box...maybe try something with a copper top plate. Are there any shielding issues that would crop up with a wood vice metal enclosure?

[hagtech]

Actually, it will work fine in a wood box, as long as you don't place it right next to anything spraying big fields.  The chassis is not for shielding the electronics from itself, only from various external sources.

jh

[PatOMalley]

Much wiser to use the metal case as it gives you ability to put it anywhere on the rack.

[Kegger]

I have a few questions of different tubes used on this unit.

Can inderectly heated rectifiers like the 5y3gb, 5v4, 5z4 be used?
(What is the plate voltage on the tubes also)

Can the 12BH7 be used instead of the 12AU7 as usually it's a non
issue but they do draw .6a verse .3a on the heaters?
(So a pair would draw .6a more on the heater circuit)

Thanks, Hey JC what a cowinkidink to see you here! LOL!

[hagtech]

Other octal rectifiers are fine, as long as they don't use more than 2 amps heater current.  The NOS GZ34 / 5AR4 works very well.  It's the closest match to the stock Sovtek 5Y3, which for some reason is also indirectly heated.

The 12BH7 might be workable with some other circuit modifications.  Basically, you'd have to change a bunch of resistor values to accommodate the higher currents.

jh

[Kegger]

Thanks for the reply!

That's very good to know about the rectifiers.

But I'm not a giant fan of 12au7's and every circuit that uses one where
I've swapped in the 12BH7 has worked fine and sounded much better.

The only real diference is the 12au7 has a .3a heater and the 12bh7 has
a .6a heater. Are you saying the resistors need to be changed to higher
rated watt values then what is currently used?

Thanks!

[hagtech]

I'm thinking the bias for a 12BH7 is not the same as the U7.  More to it than just heater.  You also have to change the SRPP circuit to bias the new tube for best sonics.  Likely this is a higher current too, which means you'd have to adjust power supply dropping resistors.

Is the pinout the same?  I can't remember off the top of my head.  Anyway, plug it in and it will probably work.  However, as I point out above, probably far from optimized.

jh

[Kegger]

Yes they are pin compatable and usually a drop in replacement for the 12au7.
They are a taller tube with larger plates and generally more linear then 12au7's.

I am not a designer, more a tweaker but all the info I find and when looking at
the specs from TDSL I see no circuit mods that should need to be done, except
that the heater current draw is more, other then that I can find no real difference.

Thanks for all your responses on this.

I ask these questions for 2 reasons, my friend/aquaintance JC is looking to
build this unit and I really really like the general sound of 12bh7's so I would
be interested in a preamp that utilized them. I've used them in many 12au7
circuits to where they have pretty much allways sounded better then all the
previous 12au7's and there variants I had tried, so I do feel pretty confident
that a 12au7 circuit would be optimized the same way as a 12bh7 would be.

Thanks.