Hi friends...savy here Nova Scotia with my old friend Mr princeton rev
2 that has risen from a 20 year hiatus to express it'self again. Alas
it had a cold and is right, at this hour recouporating with narry a
grumble save for a few eletronic medications:

New GE style 6L6 PTs and re bias has brought this amp up a class to
that of Fender Delux of clean headroom and middle to late onset of OD
that seems to respond to dynamic fairly well. Promises to be a gigable
amp at under 40W.
Got some bugs worked out and did a few simple mods help shake out the
tone monkies and am about to re-do the power filter stage in the great
quest for silence (the good kind...with no buzzzzzz)

So I'm now seeding the idea of an AC to DC heater conversion to try to
substantially lower the amps noise floor.

Have any of you tried subbing a 6V battery for temp heater supply to
find less noise.
Any value in refitting the standard filiment hook-up with ac/dc
converter circuit to provide steady DC and po-po the hum ?

In my heater system Ive' just removed the hum-bal pot in favor of
running 2 100 ohm R to chassis ground from each side of the pilot
light.... good move.... The 120 Hz buzz is well masked in the shroud of
60 cycle tube amp personality. I'm thinking the intended power filter
refit will deal with a portion if not the bulk of noise... back to
heater Refit... any one care to talk me down ?

Cheers, P Savy

Couple of things, in no particular order and just random thoughts.

Running a battery as a heater supply could be a good thing, but the
amount of current required for the typical 6L6 is substantial, just
below one amp/heater. So, your battery would have to have some heft to
it to provide sufficient current for any substantial length of time.
This, of course, entails size and weight.

Now that you have gotten to size and weight, you want to keep the
battery in good condition (not deep-cycled, and not run-dead either).
So, a self-limiting battery-charger may be useful. Then, the typical
lead-acid battery is ~2.2V/cell, so, you will get 6.6V at full charge,
not the 6.3V that is 'ideal' for the tubes. Not that this is much of a
problem as that will drop off almost right away... within a very few
minutes at most.

So, cutting to the chase, you could run a constant (self-limiting, of
course)trickle-charger across the battery that would maintain the
charge when the amp was not in use. If you are running two (2) 6L6s, a
6V, 20AH battery should give you enough resilience to cover an entire
evening gig without the risk of sudden-death, and allow a reasonable
charging time until the next day from a 1A trickle-charger. Such a
battery will run you ~US$40 + shipping, a charger about 2X or more for
one that is reliable and won't boil the battery dry on a bad day. That
is one option... US$150 or so, inclusive of shipping if you cannot
obtain both locally. Then the wiring involved.

Or: You will need about a 4.5V AC suppply at about 4-6 amps. Through a
10A bridge, you will get 6.363VAC, with losses, close enough. Add about
2000uF of capacitance at 30V or so, and you should be fine, and not
burn anything up during normal use. 4A @4.5V will give you about
, enough for some safety margin. But not much. If you are
heating more than just the 2 6L6s, revise all numbers and capacities
accordingly.

DO NOT attempt to rectify your present filament supply to convert it to
DC. Even if you add a zener diode (and thereby switching artifacts) to
drop the voltage, or a half-wave ILO bridge, you will either boost the
voltage way high or make enough losses that you may risk that
transformer winding. For instance: 6.3VAC through a bridge comes to
8.9Vchopped DC.

So, either a black-box that requires line-current and associated
wiring, or a battery/charger combination and associated wiring, or
clean up the existing circuit as much as possible and no boxes or
batteries at all. I have heard repeatedly that guitar-amps want to be
distorted and fuzzy and all sorts of other stuff not usually part of
the audio vocabulary, so unless you are converting this unit to
folk/classical/instrumental/jazz music reproduction and reinforcement,
I cannot see where either of the above solutions would be worthwhile.

At the same time, I have always wondered why it is that so little audio
equipment is based on pure battery power-supplies. All that I read and
hear about various power-transformer options, cryogenically treated
receptacles, thousands for one meter of line-cord... a decent 450/12/6V
lithium-ion or Lithium/metal-hydride battery pack and associated
charger should be within that sort of budget, easily. And not very
large, either.

Just my random opinions & equally random thoughts.

Peter Wieck
Wyncote, PA

wrote:
Running a battery as a heater supply could be a good thing.

Thanks for the thorough response. There are some smoking good points
made there and not least of which your suggestion of an independant
and rechargable DC araingment for the filiment heaters... I had not
even dawned on me that it might be considered a permanent solution but
rather a tempoary trial substituting for the AC system in place now...
to prove, by product of elimination, if any substantial reduction in
noise might be had by following through with an actual in-circuit
conversion to DC (bridge rectifier arrangment as mentioned).... one for
each preamp tube ??? Seems like a lot of fuss for a modest improvement
??

I would only consider this for the pre section and leave thwe power
tubes on there oun seperate AC as there doesn't seem to be much induced
noise there ... most reactive noise seems to be in the pre amp early
stages. here and there up to the 3rd tube (last before PI). I've
actually been poking around at various wires with my finger tip as a
noise dectector to discover several signal carrying wires (in
particular those closest to the first stage of input) would react with
more noise as I hovered near or tap on the wire casing (they are all
non shielded and for sure the nastiest ones translate noise in to
neighbouring leads as well as components such as coulping caps all
combining a few different harmonic resonance distortions and most
likely being the main contributer to the overall noise floor. Where did
I put that coax cable I hacked up last year ?

Yes sir I'm now leaning towards Lead Dress as being a very important
issue.

A bit of proper lead dress and shielding key preamp wires (which was
next to absent) now seems to be the ticked as I've been able to locate
and pinpoint several trouble spots right to the wire (using my
finger-o-matic noise probe) and now have a plan to change them out to
better dress. Beyond that I'm not sure what might be reasonable to do.
I guess at some point after addressing the sick amplifier symtoms my
question might remain : would the heater DC idea provide much more
benifit ?

I do appreciate the tube amp's character but having gone from the old
6v6 early onset of OD to apparently more clean headroom with the 6L6's
....I've got clean on the brain...
I know how to make it dirty again and likely will but a healthy amp
comes first nest pas ?

Oh and Peter, you did seem pretty firm on not rectifing the AC but
rather use a stand alone DC supply. In your opionion would that be the
only way you'd go ?

Thanks

Not rectifying the _EXISTING_ filament supply, yes. Not that way.
First, by the time you bridge it and increase the RMS voltage, then cut
that voltage to the proper level for the filaments, you will have
dropped the available current dangerously low, at least. However, if
you build an outboard supply with a separate transformer, then your
load is limited only by the size of the transformer and the rating of
the bridge.

Remember ACV x 1.414 = DCV using a bridge rectifier. So a 6.3VAC
filament supply rectified to DC will bring you 8.9VDC (chopped).

Peter Wieck
Wyncote, PA

Well thanks Peter, That gives me somethings good thoughts to ponder as
I continue as I continue to discover the universe with Tb. pwr.
Gotta go .. solder (or a reasonable fac.)

Will no doubt return for an update once I've had more of a go this
dressing. No kidding though y'all... that does turn out to be quite a
key thing in reducing hum.

Cheers, savy

I say replace the filter caps in the power supply first,that should get
rid of a fair amount of buzz.
If it's still too noisy,you can try going to DC heaters,mainly on the
small signal input tubes..DC on the 6L6 filaments probably won't make
much of a difference,but I could be wrong.

Lead dressing!
Twist any AC wires together (like the 120Vac lines,and the 6.3Vac
filament wires,etc) to help cancel out any induced noise..and tuck them
into the corners of the chassis.Try to keep AC wires away from the
signal wiring (input jack,input stages,etc.)

With a bit of fiddling you could probably kill almost all the noise and
buzz.



Savy wrote:
Hi friends...savy here Nova Scotia with my old friend Mr princeton rev
2 that has risen from a 20 year hiatus to express it'self again. Alas
it had a cold and is right, at this hour recouporating with narry a
grumble save for a few eletronic medications:

New GE style 6L6 PTs and re bias has brought this amp up a class to
that of Fender Delux of clean headroom and middle to late onset of OD
that seems to respond to dynamic fairly well. Promises to be a gigable
amp at under 40W.
Got some bugs worked out and did a few simple mods help shake out the
tone monkies and am about to re-do the power filter stage in the great
quest for silence (the good kind...with no buzzzzzz)

So I'm now seeding the idea of an AC to DC heater conversion to try to
substantially lower the amps noise floor.

Have any of you tried subbing a 6V battery for temp heater supply to
find less noise.
Any value in refitting the standard filiment hook-up with ac/dc
converter circuit to provide steady DC and po-po the hum ?

In my heater system Ive' just removed the hum-bal pot in favor of
running 2 100 ohm R to chassis ground from each side of the pilot
light.... good move.... The 120 Hz buzz is well masked in the shroud of
60 cycle tube amp personality. I'm thinking the intended power filter
refit will deal with a portion if not the bulk of noise... back to
heater Refit... any one care to talk me down ?

Cheers, P Savy

kooal !