Guitar tube effect box.

[ian field]

Is there some favoured property of triodes as usually used in the front end
of a tube guitar amp?

What I was planning was a "tube box" to put in front of a transistor amp,
although I can find triodes if needed I have a small stock of tetrodes. The
puzzle is, whether to wire them up as tetrodes or use them as "triode
connected" - does the screen grid give any interesting properties for
modifying the characteristics of the amplifier stage?

TIA.

 

[Rich Grise]

On Tue, 14 Jul 2009 14:07:57 +0100, ian field wrote:

Is there some favoured property of triodes as usually used in the front end
of a tube guitar amp?

What I was planning was a "tube box" to put in front of a transistor amp,
although I can find triodes if needed I have a small stock of tetrodes. The
puzzle is, whether to wire them up as tetrodes or use them as "triode
connected" - does the screen grid give any interesting properties for
modifying the characteristics of the amplifier stage?

With a tetrode, you can make a dynatron oscillator, for whatever that's

worth. ;-)

As far as toobz, I have the impression that the 12AX7 is a really good
dual triode audio amp. (12AT7 is for RF, and 12AU7 is for switching, a
la flip flops and gates) As far as linearity or distortion etc, you'd
have to get the data book and draw your own load line and stuff.

Have Fun!
Rich

 

[Rich Grise]

On Tue, 14 Jul 2009 14:07:57 +0100, ian field wrote:

Is there some favoured property of triodes as usually used in the front end
of a tube guitar amp?

What I was planning was a "tube box" to put in front of a transistor amp,
although I can find triodes if needed I have a small stock of tetrodes. The
puzzle is, whether to wire them up as tetrodes or use them as "triode
connected" - does the screen grid give any interesting properties for
modifying the characteristics of the amplifier stage?

You might even look into nuvistor toobz, if they can still be had. They

look like a tall TO-5 transistor but are immune to overloads, etc.

Good Luck!
Rich

 

[Tim Wescott]

On Tue, 14 Jul 2009 14:07:57 +0100, ian field wrote:

Is there some favoured property of triodes as usually used in the front
end of a tube guitar amp?

What I was planning was a "tube box" to put in front of a transistor
amp, although I can find triodes if needed I have a small stock of
tetrodes. The puzzle is, whether to wire them up as tetrodes or use them
as "triode connected" - does the screen grid give any interesting
properties for modifying the characteristics of the amplifier stage?

TIA.

AFAIK triodes sound better in distortion -- they have a "softer" sound
than tetrodes or pentodes.

If you absolutely positively must use up your current stock of tubes then
wire them as triodes (or better yet put in a switch...). Otherwise the
standard audio triode is the 12AX7 as Rich mentioned -- it's popular
enough that you can swing by your local guitar store and pick up as many
new ones as you'd like.

--
www.wescottdesign.com

 

[ian field]

"Rich Grise" <richgrise@example.net> wrote in message
newsan.2009.07.14.19.09.25.572995@example.net...

On Tue, 14 Jul 2009 14:07:57 +0100, ian field wrote:

Is there some favoured property of triodes as usually used in the front
end
of a tube guitar amp?

What I was planning was a "tube box" to put in front of a transistor amp,
although I can find triodes if needed I have a small stock of tetrodes.
The
puzzle is, whether to wire them up as tetrodes or use them as "triode
connected" - does the screen grid give any interesting properties for
modifying the characteristics of the amplifier stage?

You might even look into nuvistor toobz, if they can still be had. They
look like a tall TO-5 transistor but are immune to overloads, etc.

The one I have in the drawer is........I think, an 8056 low voltage type, I
rescued it from the tuner of a Sealy TV someone left in the communal bin
room at the flats.

That's sort of reserved for one day I get the lead out and build the GDO
I've always wanted.

Without digging in the shed for the box of tubes someone gave me years ago,
the only triodes I've got are E88CC scope tubes.

 

[ian field]

"Tim Wescott" <tim@seemywebsite.com> wrote in message
news:CcKdnbRkBvWaU8HXnZ2dnUVZ_gJi4p2d@web-ster.com...

On Tue, 14 Jul 2009 14:07:57 +0100, ian field wrote:

Is there some favoured property of triodes as usually used in the front
end of a tube guitar amp?

What I was planning was a "tube box" to put in front of a transistor
amp, although I can find triodes if needed I have a small stock of
tetrodes. The puzzle is, whether to wire them up as tetrodes or use them
as "triode connected" - does the screen grid give any interesting
properties for modifying the characteristics of the amplifier stage?

TIA.

AFAIK triodes sound better in distortion -- they have a "softer" sound
than tetrodes or pentodes.

Didn't one of the nowadays highly prized Vox amps use a pentode front end?

If you absolutely positively must use up your current stock of tubes then
wire them as triodes (or better yet put in a switch...). Otherwise the
standard audio triode is the 12AX7 as Rich mentioned -- it's popular
enough that you can swing by your local guitar store and pick up as many
new ones as you'd like.

Is that strapped to the anode for "triode connected", and is that switched
out to "left floating" or the usual dropper with decoupling cap for a screen
grid?

The local music shop is run by a snobby git who doesn't believe in spare
parts of any description!

And his far East import cheap imitation strats are the tackiest I've ever
seen!

 

[Tim Wescott]

On Tue, 14 Jul 2009 22:00:01 +0100, ian field wrote:

"Tim Wescott" <tim@seemywebsite.com> wrote in message
news:CcKdnbRkBvWaU8HXnZ2dnUVZ_gJi4p2d@web-ster.com...
On Tue, 14 Jul 2009 14:07:57 +0100, ian field wrote:

Is there some favoured property of triodes as usually used in the
front end of a tube guitar amp?

What I was planning was a "tube box" to put in front of a transistor
amp, although I can find triodes if needed I have a small stock of
tetrodes. The puzzle is, whether to wire them up as tetrodes or use
them as "triode connected" - does the screen grid give any interesting
properties for modifying the characteristics of the amplifier stage?

TIA.

AFAIK triodes sound better in distortion -- they have a "softer" sound
than tetrodes or pentodes.

Didn't one of the nowadays highly prized Vox amps use a pentode front
end?

If you absolutely positively must use up your current stock of tubes
then wire them as triodes (or better yet put in a switch...).
Otherwise the standard audio triode is the 12AX7 as Rich mentioned --
it's popular enough that you can swing by your local guitar store and
pick up as many new ones as you'd like.

Is that strapped to the anode for "triode connected", and is that
switched out to "left floating" or the usual dropper with decoupling cap
for a screen grid?

The local music shop is run by a snobby git who doesn't believe in spare
parts of any description!

And his far East import cheap imitation strats are the tackiest I've
ever seen!

OK, _my_ local guitar store has them. My condolences on yours.

I have no real experience with guitar amps -- I listen to music, and I
got my ham license about the time that lots of perfectly good tube gear
was showing up at hamfests for really good prices, so I kinda know tubes
and have a soft spot for them.

Were I to use a switch, I'd switch the screen between the plate and
either a dropping resistor & cap or a nice stiff supply. Switch the cap
to the plate through a BIG resistor so it has about the right voltage
when you switch, or you'll get a heck of a thump, though.

--
www.wescottdesign.com

 

[greg]

ian field wrote:

What I was planning was a "tube box" to put in front of a transistor amp,
although I can find triodes if needed I have a small stock of tetrodes. The
puzzle is, whether to wire them up as tetrodes or use them as "triode
connected" - does the screen grid give any interesting properties for
modifying the characteristics of the amplifier stage?

As I understand it, the main point of the screen grid is
to reduce the effect of Miller capacitance, which is
usually only a concern at RF frequencies. So it probably
doesn't make much difference in an audio amp, although
connecting it in the usual screen grid configuration
shouldn't do any harm.

A pentode, on the other hand, can be configured to give
a much more linear relationship between grid voltage
and anode current, which can be advantageous in an
audio amp without negative feedback.

But if the point of this "tube box" is to give a soft
overload characteristic, then you actually *want* some
non-linearity, so using a pentode might be counter-
productive.

--
Greg

 

[ian field]

"Tim Wescott" <tim@seemywebsite.com> wrote in message
news:CcKdnbZkBvWUwcDXnZ2dnUVZ_gJi4p2d@web-ster.com...

On Tue, 14 Jul 2009 22:00:01 +0100, ian field wrote:

"Tim Wescott" <tim@seemywebsite.com> wrote in message
news:CcKdnbRkBvWaU8HXnZ2dnUVZ_gJi4p2d@web-ster.com...
On Tue, 14 Jul 2009 14:07:57 +0100, ian field wrote:

Is there some favoured property of triodes as usually used in the
front end of a tube guitar amp?

What I was planning was a "tube box" to put in front of a transistor
amp, although I can find triodes if needed I have a small stock of
tetrodes. The puzzle is, whether to wire them up as tetrodes or use
them as "triode connected" - does the screen grid give any interesting
properties for modifying the characteristics of the amplifier stage?

TIA.

AFAIK triodes sound better in distortion -- they have a "softer" sound
than tetrodes or pentodes.

Didn't one of the nowadays highly prized Vox amps use a pentode front
end?

If you absolutely positively must use up your current stock of tubes
then wire them as triodes (or better yet put in a switch...).
Otherwise the standard audio triode is the 12AX7 as Rich mentioned --
it's popular enough that you can swing by your local guitar store and
pick up as many new ones as you'd like.

Is that strapped to the anode for "triode connected", and is that
switched out to "left floating" or the usual dropper with decoupling cap
for a screen grid?

The local music shop is run by a snobby git who doesn't believe in spare
parts of any description!

And his far East import cheap imitation strats are the tackiest I've
ever seen!

OK, _my_ local guitar store has them. My condolences on yours.

I have no real experience with guitar amps -- I listen to music, and I
got my ham license about the time that lots of perfectly good tube gear
was showing up at hamfests for really good prices, so I kinda know tubes
and have a soft spot for them.

Back when I first started out on TV repair there were still an awful lot of
tube only sets in use with a rapidly growing number of hybrids appearing, so
I have a fair idea about fault finding on tube gear but I've never tried my
hand at design with them.

 

[robb]

"ian field" <gangprobing.alien@ntlworld.com> wrote in message
news:Tq%6m.9833$BS2.1550@newsfe02.ams2...

Is there some favoured property of triodes as usually used in
the front end
of a tube guitar amp?

What I was planning was a "tube box" to put in front of a
transistor amp,
although I can find triodes if needed I have a small stock of
tetrodes. The
puzzle is, whether to wire them up as tetrodes or use them as
"triode
connected" - does the screen grid give any interesting
properties for
modifying the characteristics of the amplifier stage?

TIA.

cross-posting on (alt.guitar.amps) may result in lots of
additional ideas ?

 

[ian field]

"robb" <some@where.on.net> wrote in message
news:18Sdnau7Nrnr7_XXnZ2dnUVZ_rGdnZ2d@earthlink.com...

"ian field" <gangprobing.alien@ntlworld.com> wrote in message
news:Tq%6m.9833$BS2.1550@newsfe02.ams2...

Is there some favoured property of triodes as usually used in
the front end
of a tube guitar amp?

What I was planning was a "tube box" to put in front of a
transistor amp,
although I can find triodes if needed I have a small stock of
tetrodes. The
puzzle is, whether to wire them up as tetrodes or use them as
"triode
connected" - does the screen grid give any interesting
properties for
modifying the characteristics of the amplifier stage?

TIA.

cross-posting on (alt.guitar.amps) may result in lots of
additional ideas ?

I posted essentially the same question on alt.guitar.effects and got 0
replies - AFAIK a lot of the same people use both of those groups.

 

[Jim]

I don't see your original post, so I'll throw my comments in here.

robb wrote:

"ian field" <gangprobing.alien@ntlworld.com> wrote in message
news:Tq%6m.9833$BS2.1550@newsfe02.ams2...
Is there some favoured property of triodes as usually used in
the front end
of a tube guitar amp?

Today's high gain tubes are twin triodes. It's safe to say 12AX7 is
used in over 90% of all guitar gain stages.

You might google EF86 to find comments on a commonly used pentode.

What I was planning was a "tube box" to put in front of a
transistor amp,
although I can find triodes if needed I have a small stock of
tetrodes.

But what is the gain factor? I guess it all depends on what your goal is.

In practice, I often find that a lower gain tube like 12AY7 or even
12AU7 sound better in "factory made" effects designed for 12AX7. Even
in the gain holes of many current amps.

The

puzzle is, whether to wire them up as tetrodes or use them as
"triode
connected" - does the screen grid give any interesting
properties for
modifying the characteristics of the amplifier stage?

TIA.

cross-posting on (alt.guitar.amps) may result in lots of
additional ideas ?

 

[robb]

"Jim" <jim@askmebeforeyousend.com> wrote in message
news:LdSdnc2zFO5aKvXXnZ2dnUVZ_j-dnZ2d@posted.isomediainc...

I don't see your original post, so I'll throw my comments in
here.

robb wrote:
"ian field" <gangprobing.alien@ntlworld.com> wrote in message
news:Tq%6m.9833$BS2.1550@newsfe02.ams2...
Is there some favoured property of triodes as usually used
in
the front end
of a tube guitar amp?

Today's high gain tubes are twin triodes. It's safe to say
12AX7 is
used in over 90% of all guitar gain stages.

You might google EF86 to find comments on a commonly used
pentode.

What I was planning was a "tube box" to put in front of a
transistor amp,
although I can find triodes if needed I have a small stock
of
tetrodes.

But what is the gain factor? I guess it all depends on what
your goal is.

In practice, I often find that a lower gain tube like 12AY7 or
even
12AU7 sound better in "factory made" effects designed for
12AX7. Even
in the gain holes of many current amps.

cross-posting on (alt.guitar.amps) may result in lots of
additional ideas ?

Thanks Jim,
For the reply.
The OP was not mine but was in the message you responded to. I
only crossed it along to the (a.g.a) for potentially more
responses/opinions. My experience lurking in (a.g.a) is the group
usually produces a large number of opinions on such matters
(sometimes)
robb

 

[RS]

On Thu, 23 Jul 2009 10:26:17 -0400, "robb" <some@where.on.net> wrote:

"ian field" <gangprobing.alien@ntlworld.com> wrote in message
news:Tq%6m.9833$BS2.1550@newsfe02.ams2...

Is there some favoured property of triodes as usually used in
the front end
of a tube guitar amp?

What I was planning was a "tube box" to put in front of a
transistor amp,
although I can find triodes if needed I have a small stock of
tetrodes. The
puzzle is, whether to wire them up as tetrodes or use them as
"triode
connected" - does the screen grid give any interesting
properties for
modifying the characteristics of the amplifier stage?

TIA.

cross-posting on (alt.guitar.amps) may result in lots of
additional ideas ?

You misspelled "composted" (kidding---there are still some
knowledgable posters here in aga).

Quite a few manufacturers have taken to using tubes as a front end for
solid state amps. Some of it is pure marketing; you can often see
front panels with a special window to view the tube. I've even seen
that done in a CD player.

In hifi you wouldn't make use of distortion characteristics, but
obviously that's what you're after here. Triodes are the usual way to
go for that, and 12ax7/7025 tube preamps are the norm, as already
mentioned.

Pentodes are much less common as preamp stages, and you'll rarely find
a tetrode anywhere these days (look up 'secondary emission' for the
reasons). The EF86 is actually a pentode, and is found in some guitar
preamps, but you may want to go with triodes for this particular app.
12ax7's are easy to deal with, and you'd have a vast bank of
schematics for ideas (Fender, Marshall, just about every major amp).

Check website: http://www.schematicheaven.com for some schematics.

There were some circuits designed by B.K.Butler that used 12ax7's in
what's known as 'starved plate', with very low plate voltage. This
would simplify things for you. Starved plate circuits sometimes get a
bad rap, possibly because they're very sensitive to the type of tube
that's used. But Eric Johnson and other well known guitarists use
them. The sound is a bit different from higher voltage circuits, but
in this case it could simplify things for you.

Those circuits are used in Chandler, Tube Works, and in Butler's own
line. See: http://www.butleraudio.com/tubedriver.php

That might save you building a high voltage supply, and save us from
posting another long disclaimer about juicing the bejeezus out of
yourself. <g>

PS: You say you have a box of tetrodes. What type are they?

 

[ian field]

"RS" <RS@nonspam.com> wrote in message
news:3r6l65d46vipo0os573bvpoh0l09f224nl@4ax.com...

On Thu, 23 Jul 2009 10:26:17 -0400, "robb" <some@where.on.net> wrote:

"ian field" <gangprobing.alien@ntlworld.com> wrote in message
news:Tq%6m.9833$BS2.1550@newsfe02.ams2...

Is there some favoured property of triodes as usually used in
the front end
of a tube guitar amp?

What I was planning was a "tube box" to put in front of a
transistor amp,
although I can find triodes if needed I have a small stock of
tetrodes. The
puzzle is, whether to wire them up as tetrodes or use them as
"triode
connected" - does the screen grid give any interesting
properties for
modifying the characteristics of the amplifier stage?

TIA.

cross-posting on (alt.guitar.amps) may result in lots of
additional ideas ?

You misspelled "composted" (kidding---there are still some
knowledgable posters here in aga).

Quite a few manufacturers have taken to using tubes as a front end for
solid state amps. Some of it is pure marketing; you can often see
front panels with a special window to view the tube. I've even seen
that done in a CD player.

In hifi you wouldn't make use of distortion characteristics, but
obviously that's what you're after here. Triodes are the usual way to
go for that, and 12ax7/7025 tube preamps are the norm, as already
mentioned.

Pentodes are much less common as preamp stages, and you'll rarely find
a tetrode anywhere these days (look up 'secondary emission' for the
reasons). The EF86 is actually a pentode, and is found in some guitar
preamps, but you may want to go with triodes for this particular app.
12ax7's are easy to deal with, and you'd have a vast bank of
schematics for ideas (Fender, Marshall, just about every major amp).

Check website: http://www.schematicheaven.com for some schematics.

There were some circuits designed by B.K.Butler that used 12ax7's in
what's known as 'starved plate', with very low plate voltage. This
would simplify things for you. Starved plate circuits sometimes get a
bad rap, possibly because they're very sensitive to the type of tube
that's used. But Eric Johnson and other well known guitarists use
them. The sound is a bit different from higher voltage circuits, but
in this case it could simplify things for you.

Those circuits are used in Chandler, Tube Works, and in Butler's own
line. See: http://www.butleraudio.com/tubedriver.php

That might save you building a high voltage supply, and save us from
posting another long disclaimer about juicing the bejeezus out of
yourself. <g

All tube TV's were still very common back in the days when I started out as
a service engineer, so I have the appropriate respect for high voltages.

PS: You say you have a box of tetrodes. What type are they?

The tetrodes are 6CY5 liberated from a communal antenna distribution
amplifier for VHF TV, the nearest I have to double triodes is E88CC scope
tubes (high precision versions of the ECC88). The EU equivalents of the US
guitar amp tubes are ECC82 & ECC83.

 

[RS]

On Sat, 25 Jul 2009 15:58:31 +0100, "ian field"
<gangprobing.alien@ntlworld.com> wrote:

"RS" <RS@nonspam.com> wrote in message

There were some circuits designed by B.K.Butler that used 12ax7's in
what's known as 'starved plate', with very low plate voltage. This
would simplify things for you
...

That might save you building a high voltage supply, and save us from
posting another long disclaimer about juicing the bejeezus out of
yourself. <g

All tube TV's were still very common back in the days when I started out as
a service engineer, so I have the appropriate respect for high voltages.

That's a welcome change. The usual high-voltage warning gets tedious
to repeat, but it's necessary.

PS: You say you have a box of tetrodes. What type are they?

The tetrodes are 6CY5 liberated from a communal antenna distribution
amplifier for VHF TV, the nearest I have to double triodes is E88CC scope
tubes (high precision versions of the ECC88). The EU equivalents of the US
guitar amp tubes are ECC82 & ECC83.

The American 6DJ8 is the equivalent to your ECC88. It's a high
transconductance, low plate resistance amp. Limited plate voltage.
There is a higher voltage version called the 6922, but it still won't
tolerate as high a plate voltage as the 12ax7 family.

I don't remember ever seeing that tube in a guitar amp, but it's been
used in lots of hifi and high end studio gear, including Avalon mic
preamps. One of my friends claims to have got some good guitar sounds
out of it in a prototype circuit, but I never got to hear that.

Of the tubes you have, that would probably be your best bet, but I
still advise going with 12ax7 family. They're not expensive, and you
can swap in other tubes in the 12a-7 family (12at7, 12au7), as they
all have the same pinout and filament voltage requirements. Not so
with the ECC88.

 

[ian field]

"RS" <RS@nonspam.com> wrote in message
news:01im65dbca0ockmupig7trn1u2toc1q0rs@4ax.com...

On Sat, 25 Jul 2009 15:58:31 +0100, "ian field"
gangprobing.alien@ntlworld.com> wrote:


"RS" <RS@nonspam.com> wrote in message

There were some circuits designed by B.K.Butler that used 12ax7's in
what's known as 'starved plate', with very low plate voltage. This
would simplify things for you
...

That might save you building a high voltage supply, and save us from
posting another long disclaimer about juicing the bejeezus out of
yourself. <g

All tube TV's were still very common back in the days when I started out
as
a service engineer, so I have the appropriate respect for high voltages.

That's a welcome change. The usual high-voltage warning gets tedious
to repeat, but it's necessary.

PS: You say you have a box of tetrodes. What type are they?

The tetrodes are 6CY5 liberated from a communal antenna distribution
amplifier for VHF TV, the nearest I have to double triodes is E88CC scope
tubes (high precision versions of the ECC88). The EU equivalents of the US
guitar amp tubes are ECC82 & ECC83.

The American 6DJ8 is the equivalent to your ECC88. It's a high
transconductance, low plate resistance amp. Limited plate voltage.
There is a higher voltage version called the 6922, but it still won't
tolerate as high a plate voltage as the 12ax7 family.

I don't remember ever seeing that tube in a guitar amp, but it's been
used in lots of hifi and high end studio gear, including Avalon mic
preamps. One of my friends claims to have got some good guitar sounds
out of it in a prototype circuit, but I never got to hear that.

Of the tubes you have, that would probably be your best bet, but I
still advise going with 12ax7 family. They're not expensive, and you
can swap in other tubes in the 12a-7 family (12at7, 12au7), as they
all have the same pinout and filament voltage requirements. Not so
with the ECC88.

Apparently the ECC88 was designed for use as the cascode pair in the front
end of BandII FM radios, it might well have been used in TV tuners but I
suspect BandI only TVs were obsolete by the time this tube appeared and a
variety of frame grid triodes were specifically developed for BandIII and
UHF tuners.

But then the tetrodes I was thinking of using are VHF types.

 

[RS]

On Sat, 25 Jul 2009 21:22:29 +0100, "ian field"
<gangprobing.alien@ntlworld.com> wrote:

"RS" <RS@nonspam.com> wrote in message
[re 6DJ8 / ECC88]
Of the tubes you have, that would probably be your best bet, but I
still advise going with 12ax7 family. They're not expensive, and you
can swap in other tubes in the 12a-7 family (12at7, 12au7), as they
all have the same pinout and filament voltage requirements. Not so
with the ECC88.

Apparently the ECC88 was designed for use as the cascode pair in the front
end of BandII FM radios, it might well have been used in TV tuners but I
suspect BandI only TVs were obsolete by the time this tube appeared and a
variety of frame grid triodes were specifically developed for BandIII and
UHF tuners.

But then the tetrodes I was thinking of using are VHF types.

The ECC88 was widely adopted for audio designs, just not for guitar
amps (at least any that I can recall). They work very well, or
companies like Avalon would not be using them.

Tetrodes: Not likely to work well there due to the kink in the curves.

Re battery-op: Ancient radios used to run on 1.5v A supplies, with B
supplies ranging from 22.5v to 90v. Separate batteries for those. You
might be able to find those old tubes at Antique Electronic Supply,
http://www.tubesandmore.com if you're determined to do that. The
novelty might wear off after the first few tube battery swaps though.

Re crosstalk: It sounds like you must already know the basics there;
keeping circuit impedances low, bypassing supplies with films and disc
caps in parallel with electrolytics, etc. But good luck with keeping
the spikes out of the audio circuits. Not easy.

 

[Jim]

but you may want to go with triodes for this particular app.

12ax7's are easy to deal with, and you'd have a vast bank of
schematics for ideas (Fender, Marshall, just about every major amp).

Check website: http://www.schematicheaven.com for some schematics.

OP: Also check: http://www.dogstar.dantimax.dk/tubestuf/mctube.htm I
haven't built one.

 

[RS]

On Sat, 25 Jul 2009 16:19:43 -0700, Jim <jim@askmebeforeyousend.com>
wrote:

but you may want to go with triodes for this particular app.
12ax7's are easy to deal with, and you'd have a vast bank of
schematics for ideas (Fender, Marshall, just about every major amp).

Check website: http://www.schematicheaven.com for some schematics.

OP: Also check: http://www.dogstar.dantimax.dk/tubestuf/mctube.htm I
haven't built one.

Cool project. B+ is much higher than the Butler-designed starved
plate circuits, so I'd expect much less sensitivity to the brand of
tube used. That would be a good thing.

Might be good to roll off extreme highs after the last OD stage in
that circuit. Most Tubescreamer and Marshall (diode-based) overdrive
boxes have surprisingly low corner frequencies on their post-filters,
but it does allow boosting of treble on the amp without getting harsh
top from the overdrive.