However, 75 *8* 1, as Meat has now corrected this to, and 6L6, same pinouts
Don't bother, Gareth is a pedantic pisswit playing some kind of
That sounds an odd configuration. Fixed positive bias on the control grids
Yeh somewhat similar. Here have a look for yourself.
Wheeee ! That really *is* an odd configuration, and one that I don't recall
First of all the Laney AOR 50 absolutely screams with the Fender iron
The philosophy is to lightly fuse the B+
I suppose the design hasYep I'd like to be educated on this desing too. Don't like repairing
I can see how they might be using that sort of drive arrangement to ensureOn Wed, 2 Sep 2009 01:51:40 +0100, "Arfa Daily"
arfa.daily@ntlworld.com>wrote:
That sounds an odd configuration. Fixed positive bias on the control
grids
(pin 5) and driven cathodes (pin 8) ? Screen grids to (taps on ?? ) the
output tranny ? Presumably, the anodes (pin 3) also go to the tranny ?
There
is a configuration called 'ultra linear' where the screen grids are fed
from
taps some distance down each limb of the OPT primary.
http://web.telia.com/~u43200663/blocks/ulaudioamps.htm
Some variation of that, maybe ?
Arfa
Yeh somewhat similar. Here have a look for yourself.
http://www.ampix.org/albums/userpics/10003/PV_MX_VTX.pdf
I've owned Peavey amps for 30 years. First was an Artist 115 and I
still own it albeit I've recapped it and fixed a couple problems
caused by age. It has a more traditional final stage similar to Fender
100 watt finals. Second Peavey I owned was a 130 watt SS 1x12 which
looks identical to this MX. I used to play through both direct in
bypassing the tone stack using a Peavey Tube Fex. Blew the Scorpion 12
in the SS amp and bought a replacement on Ebay. The Black Widow12 in
the MX is indestructible however it is not the most versatile speaker
sound-wise. I have a Peavey 4x12 cabinet loaded with 4 JBL's that has
a better response range. Going to be working on my Laney AOR Pro Tube
50 today. I've fitted it with a new Fender audio tranny I had ordered
as a spare. Wont have the impedence taps as the original did but it
will do the job at 4ohms.
Wheeee ! That really *is* an odd configuration, and one that I don't
recall
ever having seen before ... With the screen grids tapped down the tranny
below the anodes, I guess that it has got to be a variant of the basic
'Ultra Linear' scheme, but why do two of the tubes have a bloody great
power
resistor in series with the screen, and two not ? Cathodes are commoned,
as
are the control grids, so you would expect the operating conditions of all
of the tubes to be the same, except that they won't be (quite) with those
resistors there. I suppose that the actual physical circuit really is like
that ? Not just that the schematic has been drawn wrongly, and the
resistors
should be shown north and south of the screen grid junction points, so
each
one feeding both screens of one tube pair ?
First of all the Laney AOR 50 absolutely screams with the Fender iron
at the output. Two Sovtek EL34's at 400vdc plate and biased around
-39vdc. I used my Fender Twin as a speaker cabinet since it is back in
my work area and has two Weber Californian vintage style 12s. I swear
the Laney is just as loud as the 100 Twin amp.
Back to the Peavey MX VTX. Yes the schematic is correct. I didn't take
any voltage measurements since there were very few on the print. But I
did verify the plate and the 15vdc and whatever else was in the drive
stage per the print.
The drive scheme is also odd. With +15v on the grids, the cathodes must be
up at what ? +50v maybe ? Can't remember what the typical bias level for a
6L6 in AB is, but around -35v I would guess ? So why use a low Z cathode
drive, I wonder ? Seems a complicated way of going about what is a
fundamentally a straightforward task, when tackled textbook, like in a Vox
or Fender or Marshall, or just about any other two or four tube tetrode /
pentode output stage. I can quite see how a failed or leaky transistor
such
as you had, would lead to a massive shift in the bias in totally the wrong
(well, undesirable, anyway) direction, driving a tube pair to full
saturation. That alone makes it a questionable design to me, but I'm sure
we
must be missing some clever bit of design philosophy here.
The philosophy is to lightly fuse the B+
something to do with the fact that the low power setting drops just
the plates to 262vdc so anything besides linear or cathode biasing
wouldn't track the drop from 525 to 262 unlike placing a variac at the
mains where everything drops.
Anyone else got any thoughts or insights into the reasoning behind this
odd
design ?
Arfa
Yep I'd like to be educated on this desing too. Don't like repairing
things that I haven't a clue as to the operation.