Shielded cable from valve to OT

[tony.r]

Shielded cable from valve to OT

What a learning experience that has been. I solved a few problems with that
move. I found the other day I altered a few things inside my amp and all but
reduced the coupling squeal. Then a day latter when I did a few more mods
the noise came back.
Tonight I finally go it and put it right. Shielded mic cable is all I hade
and its worked.

tony.r http://www.ncable.com.au/~tony.r/

[Choky]

indeed;
first time I saw that in old movie-theater monoblocks,and since then I
always do the same ;)

--
Choky
Prodanovic Aleksandar
YU


"tony.r" > wrote in message
...
> Shielded cable from valve to OT
>
> What a learning experience that has been. I solved a few problems with
that
> move. I found the other day I altered a few things inside my amp and all
but
> reduced the coupling squeal. Then a day latter when I did a few more mods
> the noise came back.
> Tonight I finally go it and put it right. Shielded mic cable is all I hade
> and its worked.
>
> tony.r http://www.ncable.com.au/~tony.r/
>
>

[jim]

"tony.r" > wrote in message
...
> Shielded cable from valve to OT
>
> What a learning experience that has been. I solved a few problems with
that
> move. I found the other day I altered a few things inside my amp and all
but
> reduced the coupling squeal. Then a day latter when I did a few more mods
> the noise came back.
> Tonight I finally go it and put it right. Shielded mic cable is all I hade
> and its worked.
>
> tony.r http://www.ncable.com.au/~tony.r/


What are you on about ?? Send me a wrap. Shielded cables from OP valves
to OPT. ?? There's enough bounce in them buggers to frighten the B+ tranny
!!
Peace, man !!
jim

[Fred Nachbaur]

Good idea! Hmm... a good application for RG58A/U ??? And RG8 or LMR400
for the really big amps. :)

Cheers,
Fred

Choky wrote:
> indeed;
> first time I saw that in old movie-theater monoblocks,and since then I
> always do the same ;)
>
> --
> Choky
> Prodanovic Aleksandar
> YU
>
>
> "tony.r" > wrote in message
> ...
>
>>Shielded cable from valve to OT
>>
>>What a learning experience that has been. I solved a few problems with
>
> that
>
>>move. I found the other day I altered a few things inside my amp and all
>
> but
>
>>reduced the coupling squeal. Then a day latter when I did a few more mods
>>the noise came back.
>>Tonight I finally go it and put it right. Shielded mic cable is all I hade
>>and its worked.
>>
>>tony.r http://www.ncable.com.au/~tony.r/
>>
>>
>
>
>

--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects, Vacuum Tubes & other stuff: |
| http://www.dogstar.dantimax.dk |
+--------------------------------------------+

[jim]

"Choky" > wrote in message
...
> ZM spoke.
> try ,then talk;
> even if ya can hear difference,first time when you'll be in trouble and
some
> silly old rule help ya,then you will be more humble.
> ;)
>
> --
> Choky
> Prodanovic Aleksandar
> YU
>
>

Hey, got the picture now. W'ere talking about top cap valves, right ? Makes
sense now.
regards
jim

[Ian Iveson]

Humble?

Never seen this as a rule of thumb, choky. Seems more like a common
fudge.

If short of space, then you may end up radiating to sensitive input
wiring from the insensitive but high AC voltage anode connections.
If you build uncrowded amps like Jim does, and carefully route the
wires, then surely it would be better not to use screened cable
inside.

Never tried, don't seem to need to.

cheers, Ian

"Choky" > wrote in message
...
> ZM spoke.
> try ,then talk;
> even if ya can hear difference,first time when you'll be in
trouble and some
> silly old rule help ya,then you will be more humble.
> ;)
>

[Choky]

not just top cap leads;
all anode and G2 leads.
in principle ,all potentials, say, above 40 Volts.

--
Choky
Prodanovic Aleksandar
YU


"jim" > wrote in message
...
>
> "Choky" > wrote in message
> ...
> > ZM spoke.
> > try ,then talk;
> > even if ya can hear difference,first time when you'll be in trouble and
> some
> > silly old rule help ya,then you will be more humble.
> > ;)
> >
> > --
> > Choky
> > Prodanovic Aleksandar
> > YU
> >
> >
>
> Hey, got the picture now. W'ere talking about top cap valves, right ?
Makes
> sense now.
> regards
> jim
>
>

[Robert Casey]

tony.r wrote:

>Shielded cable from valve to OT
>I found the other day I altered a few things inside my amp and all but
>reduced the coupling squeal. Then a day latter when I did a few more mods
>the noise came back.
>Tonight I finally go it and put it right. Shielded mic cable is all I hade
>and its worked.
>
>
>
The shielding must have stopped an undesired feedback loop. Depending
on the
circuit involved, it may be a better choice to shield the high signal
level/ low
impedance (relatively speaking) then to try to shield all the low level
/high
impedance input and intermediate circuits. You might not need to use
microphone
or other shielded cable; a grounded wire twisted around the high signal
level
line might be enough. Or slip braid over wires coming from output
transformers,
though care is needed to avoid shorting the tube socket terminal to
ground with the
braid. Also this can be used to treat hum coming from the AC powerline
running to the power switch and power transformer.

Shielding can be used for both: Protecting low level input signals from
high level
signal sources, and contain high level signals from leaking into low
level inputs.

[Ian Iveson]

Doesn't the capacitance to ground blur your microtransients? Or
risk new HF squeals in feedback amps?

But seriously, this is an equation with several variables. Horses
for courses and all that. Or do you think it is always better to
screen high-amplitude signals?

Why is it better to screen the HV wiring, rather than the high gain
+ high impedance wires that it radiates to?

cheers, Ian

"Choky" > wrote in message
...
> not just top cap leads;
> all anode and G2 leads.
> in principle ,all potentials, say, above 40 Volts.
>
> --
> Choky
> Prodanovic Aleksandar
> YU

[Choky]

"Ian Iveson" > wrote in message
...
> Humble?

try with "more suspective for other approach"
or "more open to other's oppinion"
or " more interested in old and mebbe forgoten experiences"

ya know that English is not my native,so don't read what I wrote without
good will hehe.......

>
> Never seen this as a rule of thumb, choky. Seems more like a common
> fudge.

as ya wish;
that tells something about your's present wiev of ZM and his knowledge ;)
mebbe ya can reread down what I wrote earlier,so you can see that I also use
" then you may..." conditional sens
there is no absolute rule; problem is in us ,when we don't care.

>
> If short of space, then you may end up radiating to sensitive input
> wiring from the insensitive but high AC voltage anode connections.
> If you build uncrowded amps like Jim does, and carefully route the
> wires, then surely it would be better not to use screened cable
> inside.
>
> Never tried, don't seem to need to.
>
> cheers, Ian

same to ya ,
--
Choky
Prodanovic Aleksandar
YU


>
> "Choky" > wrote in message
> ...
> > ZM spoke.
> > try ,then talk;
> > even if ya can hear difference,first time when you'll be in
> trouble and some
> > silly old rule help ya,then you will be more humble.
> > ;)
> >
>
>
>

[Ian Iveson]

Well OK...but I would always try to do without screening, and as far
as possible without insulation too. But if you are dealing with an
amp that is already crowded, with preamp and ps on same chassis,
then I suppose you must do what you can.

My only guitar amp is a converted PA...same circuit as a Marshall.
There are no screened wires, BUT there is a shield between power
valves and input valves...just a sheet of aluminium sticking up from
the chassis about half way.

The screen and anode wiring to the bases is all in one plane with
the other wiring, arranged so there are ground and other
low-impedance circuits between them and the input stage wiring.

I guess combos, with tight 3-dimensional layouts, are more
problematic.

Perhaps Tony might also try screening cans on the input valves.

cheers, Ian

"Choky" > wrote in message
...
>
> "Ian Iveson" > wrote in message
> ...
> > Doesn't the capacitance to ground blur your microtransients? Or
> > risk new HF squeals in feedback amps?
>
> nope with clever arrangement of grounding
>
> >
> > But seriously, this is an equation with several variables.
Horses
> > for courses and all that. Or do you think it is always better
to
> > screen high-amplitude signals?
>
> yes,I think-especially when chassy is small,OPT is relativelly
near input
> wiring etc
> naturally-when trouble arrive,cure can be also removing of that
shielding
> and mebbe some other shielding also;
> there is not any absolute rule,remember?
> only many rules of thumb to help us in avoiding trouble.
> but sometimes ,nature (or physic laws-if you prefere) play little
games with
> us,so we must use some other approach.
> same as that there is not one absolute best grounding scheme (
plane,star
> ,bus etc) ;
> one is always better than others,but just for exact case.
>
> >
> > Why is it better to screen the HV wiring, rather than the high
gain
> > + high impedance wires that it radiates to?
> >
> screen everything if ya can;
> or screen nothing if ya can;
> what is better you choose.
> but,in any case you must have starting strategy,don't ya think?
>
> > cheers, Ian

[Ian Iveson]

"Kirk Patton" > wrote lots of good stuff!

Excellent Kirk, thanks for the most credible advice I've ever had
about anything. Could have done with a lawyer like you. You are
immortalised in my library. Thanks too for the links.

Setting off for Hull, UK, where I believe the boy might be
found...perhaps this time there will be traffic on the bridge, so I
won't be too scared to cross on my own.

While I'm thinking of rack-mount valve amps, it is important to use
good PS transformers that won't vibrate. A rack cabinet can make a
very effective sound-box for a humming transformer.

cheers, Ian

> Hi Ian,
>
> This sounds like what I usually call a "pin-1 problem" . . . named
after the
> ground pin on an XLR connector . . . it is way too common in
> commercially-produced gear. Basically, what happens is that
different
> stages inside a given piece of equipment are grounded in different
places,
> and when current flows from pin 1 of one XLR to pin 1 of another
XLR, the
> accumulated resistance in connectors, wires, and P.C. board traces
is
> sufficient to allow a small AC voltage to develop, and if an
amplifying
> stage's input is referenced to the wrong part of the ground trace,
then the
> AC voltage is amplified as humm.
>
> The reason for the ground current flowing in the first place is
leakage
> current onto the chassis from the power transformer's
primary-to-secondary
> reactances. I'm assuming two pieces of audio equipment here -- a
synth
> sound module and a tube amp, the tube amp has a grounded cord and
the synth
> doesn't, and there is an unbalanced audio connection between the
two pieces.
> The symptom as described is that there is no hum present in the
system,
> until there is a very low-resistance (rack flange) connection made
between
> the chassis of the synth and the chassis of the tube amp.
>
> So here are some of my guesses as to the problem:
> 1 - Internal grounding mistake in the design of the synth sound
module.
> Wouldn't surprise me a whole lot . . . PC board designers have off
days too
> . . .
> 2 - Less likely: Your input stage/phase splitter star ground point
has a
> lower impedance to the chassis than the one that has the mains
cable. In
> this case, the ground current from the synth chassis would flow
through the
> rack, to the amp chassis, to the input star ground, through the
wire that
> connects the two star points together, and to mains ground. The
resistance
> of the wire between the two star points would cause a voltage to
appear on
> the grids of the output tubes. Only problem is, that it would be
mainly
> common mode (though not perfectly balanced) and would also be
bypassing the
> higher (voltage) gain stages in the amp. Hmmmmm.
> 3 - More likely than #2: Your input jack isn't isolated from the
chassis,
> and is actually making a better connection to the synth's chassis
than your
> star points, from the point of view of the rack (grounded to front
panel
> with rack ears, while other star point is at the back of the
chassis?) In
> this case, the ground current from the synth chassis would flow to
the input
> jack, to the first star ground, (and then maybe to the second star
ground
> via either the wire or the chassis), and to the mains cable
ground. The
> resistance of the input jack ground to the first star point in
this case
> would be the primary mechanism, resulting in a hum voltage
directly on the
> input.
> 4 - Humm is a side-effect of an oscillation. Maybe not terribly
likely;
> adding a grid-stopper resistor on the input tube may be a good
idea if there
> isn't already one there.
>
> If the situation is as I described it, then I would lift the
chassis ground
> on the second star-point, and ground the mains cable to its own
point, with
> a low impedance to the rack mounting ears. I would also isolate
the input
> jack, and make sure that there is a separate, low impedance ground
from your
> first star point to the rack ears/front faceplate as well.
>
> also, check out:
>
> http://www.jensentransformers.com/an/an004.pdf
>
> http://www.jensentransformers.com/as/as032.pdf
>
> for insights into these types of hum mechanisms.
>
> Hope this at least gets you pointed in the right direction,
>
> Kirk Patton
>
>