Traynor - Bias feed on Suppressor Grid?
jwaterfield
brief article on it over at Tone Lizard (http://tone-lizard.com/
Marshall_Myths.htm down at the bottom). Basically (for those who
don't know or remember), the bias feed is tied to pin 1 of the EL34,
instead of simply tying it to ground (via pin 8) as normal. This is
supposed to make the tube more efficient or linear, or something.
All the posts regarding this Suppressor Grid application seem to
debate whether or not it actually does what it's "supposed" to do
(increase efficiency, etc). I'm not particularly interested in what
this application does or doesn't do in the technical sense. As far as
I've seen, nobody's come out and said "NO, don't do this!!", so I'm
fairly certain it won't do any damage if I were to try it out. All
that interestes me is how it SOUNDS.
Anybody have experience with it, or tried it on their own EL34 amps?
Does it make the amp cleaner/dirtier? Brighter/darker? Louder? Any
difference at all?
boardjunkie
It certainly won't hurt anything to try it. LV stated some time back
that it sounded like ass, but try for yourself and see.
Its not for tone reasons that it was done, but safety reasons. And,
the bias feed doesn't get the suppressor, the raw pre adjustment bias
supply does. The idea being that in the event of a bias failure at the
tube's control grid pin/socket, the negative voltage on the suppressor
will limit current through the tube avoiding catastrphic tube
meltdown. Don't know how well it works....never tried it.
I have several Traynors from the very early 70s, but none have this
setup so I can't comment on any sonic fingerprint it puts on the
signal. Seems to me you'd need to bias a little hotter (voltage wise)
to overcome the effect of a negative suppressor and get the same
desired idle curent....
It's that Guy again...
>Anybody have experience with it, or tried it on their own EL34 amps?
>Does it make the amp cleaner/dirtier? Brighter/darker? Louder? Any
>difference at all?
Said trick (which has pros/cons about being worth the effort)
only (!!!!!) works with REAL EL34s (some newer made ones
have a internal tie between the two points), and the socket
CANNOT have hard wire connection between the 2 points.
Also, the -bias value on that pin doesn't matter like
how - bias to set current. All it does is place a -V
on that grid. There is a wide range of what the value
can be, with no real diff one way or another. Using
the raw - bias V works just fine. No trim pot needed.
I remember years ago, making the whole deal switch able
on a almost trashed (cab) Traynor. Sound was a little
'harsher' with the -bias trick then connecting it to ground.
The concept is 'mostly' a 'Great White North' concept,
I don't remember seeing anyone else use it. It is
claimed to extend the life of the tube, I'm not sure.
Others have compared it to change the sound, much
like the 'Ultra Lin' tranz concept, but far far far more
people like Traynor sound the UL connected amps.
Leave it and enjoy the Traynor sound... :')
JJTj
I said..Hey Hey baby
let me ride in yer car machine..
I said..Hey Hey baby
let me ride in yer car machine..
I said you got a good carburetor..
But hey, you running bad gasoline..
I said look it baby
you can't drive no more at night
you got a crack in ya cylinder head
..and a short is in ya lights
I said..Hey Hey baby
let me ride in yer car machine..
I said you got a good carburetor..
Hey, you running bad gasoline..
I said..face it baby..
you know it's time to go.
I won't write you no letter gal..
IF you drive real slow.
I said..Hey Hey baby
let me ride in yer car machine..
I said you got a good carburetor..
Hey, you running bad gasoline..
You know, I hate to see it, baby..
..that evening sun go down.
Ain't it awesome lonesome..
..yeah, you going around..
I said..Hey Hey baby
let me ride in yer car machine..
I said you got a good carburetor..
Hey, you running bad gasoline..
Lord Valve
I tried it years ago. Sounds like ass.
LV
jwaterfield
> > on a almost trashed (cab) Traynor. Sound was a little
> > 'harsher' with the -bias trick then connecting it to ground.
Harsher on the powertube breakup, or harsher overall? Was it a
frequency response thing, like too many highs/mids/lows taking over?
> I tried it years ago. Sounds like ass.
> LV
Define "ass" - what was so different about it, compared to the normal
configuration of tying the Suppressor Grid to ground?
Lord Valve
Ass: DGDevin, RichL, TPS, Repair Gay, RS, Tony Elka, etc., or any other
no-blower/poser/wannabee.
As in - no tone, no chops, no soul, desafinado, etc.
Tell me - some reason why you can't just whip out
your soldering iron and rewire your sockets? It's
not rocket science, dude...try it and let everyone
know what you thought of it.
LV
jwaterfield
> Tell me - some reason why you can't just whip out
> your soldering iron and rewire your sockets? It's
> not rocket science, dude...try it and let everyone
> know what you thought of it.
>
> LV
I plan to, but I thought I'd ask first and see what everybody else
thought. Sometimes it helps to have some sort of expectations, however
vague, when going into a new project. It helps me quantify the things
I'm hearing.
The timing's perfect, since it's the long weekend and I've got nothing
important to do. I'll fire up the iron over the next couple of days,
and post back once I've put the amp through it's paces.
Luigi Vercotti
>The timing's perfect, since it's the long weekend and I've got nothing
>important to do. I'll fire up the iron over the next couple of days,
>and post back once I've put the amp through it's paces.
You will have to re-bias the amp slightly after you do it,
I remember that. Also, make damn sure you solder
connections are tight. While your at it, since they BETTER be
real EL34 designs, you could also try the 'fake' triode trick.
Either a 100 ohm resistor tied to the plate (better be 5+ watt)
or tied before the input resistor to the tube. That one can be 1wt.
Both can be done with or without involving the screens.
I for one don't like either designs, yet the screen to the plate and
the S/grid to the input was interesting, a combo of the two. Expect
a power loss (about 25% or more) but some folks like the sound.
JJTj
God Bless us, because we is funky...
Making our own rules, no matter the price..
and you best believe...we NEVER think twice...
Morris Slutsky
Well, I've done that, my main amp is wired like that. I really chose
it because I was going for lowered power (a 30W design, not a 50W -
basically 2xEL34 with iron that could just have easily used 4xEL84),
and it works well with the PPMV I had in there by providing a
convenient tie point for a backup (680K resistor) bias feed in the
event of an open PPMV pot wiper.
I have not had access to the equipment to take proper characteristic
curves of an EL34 in this setup. I understand there will be some
variability between tube types. My amp currently has the much-
maligned, but physically robust EL34BSTRs in there. I had 'real'
Sovtek EL34s in there earlier, which tended to bias quite a bit colder
under the same conditions.
Here is an observation that I made - in general, a tube with the
suppressor grid nailed to the bias supply will pull LESS current than
a tube with the suppressor grid up at ground. The suppressor grid is,
to be basic, a grid. It has 'mu'. If you hold all the other
electrodes at steady voltages and wiggle the suppressor grid up and
down, the current through the tube will be modulated. Now, the
suppressor grid doesn't have a whole LOT of mu in this setup! It's
the furthest grid away from the cathode, it offers the least
electrostatic shielding to the cathode. But it has SOME. So if you
put a negative voltage on the suppressor, you WILL decrease current.
So let's talk about power - power is the product of voltage swing and
current swing. You can't have less current through a tube than zero,
so the swing for a tube is equal to it's max current. Guitar amps do
not use driver stages capable of providing grid current (class AB2) so
your max current is the current with the grid at 0 volts (cathode
potential). You've cut the maximum current. This cuts output power.
How does this sound? It sounds 'dirtier'. A 100W Marshall isn't much
louder than a 50W Marshall, it's simply felt as a 'cleaner' amp for
example.
I have not MEASURED this, but I'd guess that the suppressor grid will
be a tad more 'efficient' in preventing secondary electrons from the
plate hitting the screen grid. This means that you'll get a tiny bit
more voltage swing because the 'knee' of the pentode's current
characteristic will shift to a slightly lower voltage. This will
slightly increase maximum power, but this effect will be totally
overwhelmed by the lower maximum current.
BOTH the lowered current swing and the slightly increased voltage
swing will increase the optimal load impedance! For a rough
approximation, the new ideal plate-to-plate load will be the old Zload
* (Iold/Inew) where Iold is the old plate current with 0V on the
control grid, and Inew is the new plate current with 0V on the control
grid.
Probably you won't account for this, most people wouldn't bother - so
if you keep the same load as you otherwise would, you'll be using a
downwardly mismatched load. This will cut maximum power slightly more
than it would if you accounted for it - again, 'crunch' versus
'headroom', 'mush' versus 'boom'. This also will affect clipping
characteristics. A perfectly matched load, by definition, runs out of
voltage swing and current swing at the same time. A downwardly-
mismatched load will run out of current swing first - so clipping will
happen when the power tube grid rises above 0 Volts and begins to draw
current. This will cause bias shifts and give you more of a 'touch-
sensitive' clipping, less of a hard 'crunch', and runs the risk of
'farting out' if you don't put appropriate series resistors on the
grids. If you put a higher-mismatched load on, you'd of course get
the opposite - a harder 'crunch' as the tubes run out of voltage swing
while the grid is still negative, without these bias shifts
happening.
Damping factor - this would take some sophisticated measurements of
the tube's 'composite characteristics' with the negative volts on the
suppressor. I'd guess that a given change of plate voltage would
cause less change of current in the negative-suppressor situation,
giving the amp less damping. More 'presence' and more 'resonance',
less of a 'tight' sound - 'looser' feel.
So in conclusion - less headroom than the original configuration.
More 'dirt', more 'touch-sensitivity', more of a 'loose' feel.
As JJTj suggests, this could be combined with the triode-strapping mod
for the screen grid. This mod also cuts power, but will give a higher
damping factor - a 'tight' feel instead of a 'loose' one, less
'presence' and 'resonance' but more of a 'tight bass'. And with the
added power cut, even more 'dirt'.
This is just my speculation here. I do have an amp that works like
this, though. Its pretty dirty and touch sensitive and someone loose
in feel, that's the sound I kind of like which works for me. Still,
it often ends up not able to fully exercise it's power stage due to
people always, always, always, telling me to 'turn it down'! Your
mileage may vary.
jwaterfield
to make sure I got everything straight...
> You will have to re-bias the amp slightly after you do it,
> I remember that. Also, make damn sure you solder
> connections are tight. While your at it, since they BETTER be
> real EL34 designs, you could also try the 'fake' triode trick.
>
> Either a 100 ohm resistor tied to the plate (better be 5+ watt)
> or tied before the input resistor to the tube. That one can be 1wt.
This is the age-old "half power mod", where the screens are tied to
the plate....correct?
So I'd be linking:
a) pin 4 (screen) to pin 3 (plate) = triode-strapping
b) pin 1 (S-grid) to pin 5 (grid) = Suppressor at -ve voltage
> As JJTj suggests, this could be combined with the triode-strapping mod
> for the screen grid. This mod also cuts power, but will give a higher
> damping factor - a 'tight' feel instead of a 'loose' one, less
> 'presence' and 'resonance' but more of a 'tight bass'. And with the
> added power cut, even more 'dirt'.
Basically you're saying the triode-strapping arrangement will stiffen
up the sound a bit, after the looseness induced by the Suppressor Grid
being at -ve voltage? Sounds like a good thing, if that's the case.
> So in conclusion - less headroom than the original configuration.
> More 'dirt', more 'touch-sensitivity', more of a 'loose' feel.
I'm not crazy about MORE dirt from this amp (the preamp is pretty
dirty), but who knows...maybe I'll like it. Either way, I'll give it a
shot in both configurations and see how things go.
Lord Valve
> So I'd be linking:
> a) pin 4 (screen) to pin 3 (plate) = triode-strapping
You need a series resistor to limit screen current if you do this.
Or a whole shitload of power tubes.
Lord Valve
Expert (please obsess)
greas...@hotmail.com
Ass....Darvon singing in the shower...ass!
greas...@hotmail.com
Put a switch on it...
greas...@hotmail.com
Real EL 34 - ohm out between the pins 1 & 2 to find out?
jwaterfield
> Or a whole shitload of power tubes.
Right, I knew that. I tried it a long time ago, but didn't like the
results. The amp felt WAY too stiff.
So I went ahead and wired the Grids to the Suppressors. I didn't crank
it yet (I live in an apartment), but I did notice a change in the
clean tone so far - it's quite a bit darker, but in an unusual way.
It's not like the amp became bassier or anything...it just sounds like
the treble has been chopped on the very top end. It's almost like
switching from Vintage 30 speakers to Greenbacks...almost.
Now that's not necessarily a bad thing, but I'll have to play it loud
before I pass the final judgement. My band's got rehearsal tonight, so
I'll let it rip at the studio and report back tomorrow.
I'm rethinking the whole triode-strapping route. That arrangement cuts
too much treble as it is, and coupled with the Suppressor Grid mod
will probably make the amp way too dark. I'll still probably try it
out for fun, but I think I know what to expect.
jwaterfield
so the amp hasn't had an oppertunity to stretch it's legs.
On another note, I lowered the values of the bypass caps on V1's
cathodes, to see if I could brighten things up from the front-end. It
worked to an extent, but it still feels like the very top of the
treble range is chopped off. I don't like an overly bright and
sparkling amp anyways, so I shouldn't complain. Nonetheless, it feels
a little strange under my fingers....but I can't say exactly why.
Morris Slutsky
> > You need a series resistor to limit screen current if you do this.
> > Or a whole shitload of power tubes.
>
> Right, I knew that. I tried it a long time ago, but didn't like the
> results. The amp felt WAY too stiff.
>
> So I went ahead and wired the Grids to the Suppressors.
You mean the bias supply to the suppressors, right, not actually
suppressor-to-grid connection? I wouldn't recommend tying the control
and suppressor grids together. You'd get at a minimum some crazy
capacitance eating all your sparkle.
jwaterfield
> suppressor-to-grid connection? I wouldn't recommend tying the control
> and suppressor grids together. You'd get at a minimum some crazy
> capacitance eating all your sparkle.
Holy crap, you're right. I DID wire the suppressors to the grids, not
the bias supply. What the hell was I thinking?
I'll make the correction tonight and test again. Hopefuly, there's no
harm done (I doubt there would be...).
jwaterfield
some observations, if anybody's still interested.
The amp definately sounded quite different. First of all, it doesn't
"roar" like before. Also, there's a distinct disconnect between how
the amp sounds, and how it feels to play. It's hard to describe, but
I'll try my best....
The amp definately has a more compressed sound - slightly more spongy.
It sounds a lot looser too, almost like the NFB loop had it's resistor
increased (more poweramp gain).
Overall, I'd have to say it feels very unnatural - the feel of the amp
from the guitar and the sound from the speakers don't reconcile, in my
mind. It's almost like the feeling I get when playing a digital amp. I
don't think it sounded like total ass, as per Lord Valve, but it's
definately not my cup of tea.
I'm going back to grounding the suppressor grids, as per the tried-and-
true tradition. Oh well.....it was a good experiment!
Lord Valve
> Overall, I'd have to say it feels very unnatural - the feel of the amp
> from the guitar and the sound from the speakers don't reconcile, in my
> mind. It's almost like the feeling I get when playing a digital amp. I
> don't think it sounded like total ass, as per Lord Valve, but it's
> definately not my cup of tea.
OK, so it sounds half-assed...