Keith G wrote:
"Rob" wrote in message
...
I'm fiddling about[1] trying to use 1 pair of speakers, with the option to
switch between power amps - one SS, one valve. This:


Rob



The danger with two amps and one pair of speakers is if ever the amps 'see'
each other, one (or both) will die of shock!


Ah!

Any switch used in this situation must be of the 'break before make' variety
and the disconnected amp should default PDQ to a dummy load. To discourage
quick and clumsy switching, I've always thought a system of wired sockets
and a couple of pairs of banana plug L & R 'patch leads' would make a an
easy and interesting DIY project. Otherwise relays should be used instead of
switches I gather?? (I know SFA about it) Also I understand the dummy loads
can exist permanently on both sets of the wires to the amps and connecting
the speakers 'over them' renders them 'invisible'?? (Or am I typing out of
my arse...?? :-)


It strikes me that the valve amp is the problem here - SS amps don't
need a dummy load. Really, your suggestion is fine. I'm just trying to
factor in certain extreme scenarios - say, someone else using the stereo.

While I'm on, have you seen these?

http://www.reel-multimedia.co.uk/

Looks mighty interesting and very versatile, but I suspect they aren't much
different to a suitably configured PC....???


Looks very neat indeed - 6 month waiting list for some of them! I'm
coming to the conclusion, having tried a few of these things, that a
PC/Mac directly hard wired is the best way to go with what I want -
playback and recording of a variety of video and music files. These
wireless server things just can't cope with either high data rates or
out-of-spec file types.

It's almost ironic that this digital age (is that where we're at?!) has
produced a stream of incompatible, unreliable, expensive and (in quite a
few cases) poorer quality media storage/playback/recording devices than
we had 25 years ago.

Rob

Rob wrote:


It strikes me that the valve amp is the problem here - SS amps don't
need a dummy load. Really, your suggestion is fine. I'm just trying to
factor in certain extreme scenarios - say, someone else using the stereo.



Don't bother if the amp has triodes on the output, its only Pentodes
that will get upset with no load.

--
Nick

In article , Nick Gorham
wrote:
Rob wrote:


It strikes me that the valve amp is the problem here - SS amps don't
need a dummy load. Really, your suggestion is fine. I'm just trying to
factor in certain extreme scenarios - say, someone else using the
stereo.



Don't bother if the amp has triodes on the output, its only Pentodes
that will get upset with no load.

Can you explain why? Afraid I don't know why an amp built with triodes
would be inherently incapable of becoming unstable when unloaded.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Jim Lesurf wrote:
In article , Nick Gorham
wrote:

Rob wrote:


It strikes me that the valve amp is the problem here - SS amps don't
need a dummy load. Really, your suggestion is fine. I'm just trying to
factor in certain extreme scenarios - say, someone else using the
stereo.




Don't bother if the amp has triodes on the output, its only Pentodes
that will get upset with no load.


Can you explain why? Afraid I don't know why an amp built with triodes
would be inherently incapable of becoming unstable when unloaded.


No reason why it shouldn't become unstable, but the fact remains that a
triode is happy with a choke load, which the transformer (ignoring
OTL's) will become when unloaded. The pentode will not however like that
load and you can end up with high dv/dt that could cause problems in the
output TX.

--
Nick

Nick Gorham wrote:
Jim Lesurf wrote:
In article , Nick Gorham
wrote:

Rob wrote:


It strikes me that the valve amp is the problem here - SS amps don't
need a dummy load. Really, your suggestion is fine. I'm just trying to
factor in certain extreme scenarios - say, someone else using the
stereo.




Don't bother if the amp has triodes on the output, its only Pentodes
that will get upset with no load.


Can you explain why? Afraid I don't know why an amp built with triodes
would be inherently incapable of becoming unstable when unloaded.


No reason why it shouldn't become unstable, but the fact remains that a
triode is happy with a choke load, which the transformer (ignoring
OTL's) will become when unloaded. The pentode will not however like that
load and you can end up with high dv/dt that could cause problems in the
output TX.


Phew! Sorry Nick/Jim, didn't get much of that. Do you think this amp:

http://www.beardaudio.com/p100-505broc.pdf

(the power amp only, obviously) would be safe switched on and not
connected to speakers?

Thanks, Rob

wrote in message
ups.com...

Nick Gorham wrote:
Jim Lesurf wrote:
In article , Nick Gorham
wrote:

Rob wrote:


It strikes me that the valve amp is the problem here - SS amps don't
need a dummy load. Really, your suggestion is fine. I'm just trying to
factor in certain extreme scenarios - say, someone else using the
stereo.




Don't bother if the amp has triodes on the output, its only Pentodes
that will get upset with no load.


Can you explain why? Afraid I don't know why an amp built with triodes
would be inherently incapable of becoming unstable when unloaded.


No reason why it shouldn't become unstable, but the fact remains that a
triode is happy with a choke load, which the transformer (ignoring
OTL's) will become when unloaded. The pentode will not however like that
load and you can end up with high dv/dt that could cause problems in the
output TX.


Phew! Sorry Nick/Jim, didn't get much of that. Do you think this amp:

http://www.beardaudio.com/p100-505broc.pdf

(the power amp only, obviously) would be safe switched on and not
connected to speakers?


Possibly, but I wouldn't do it!!

:-)

Keith G wrote:
wrote in message
ups.com...

Nick Gorham wrote:

Jim Lesurf wrote:

In article , Nick Gorham
wrote:


Rob wrote:


It strikes me that the valve amp is the problem here - SS amps don't
need a dummy load. Really, your suggestion is fine. I'm just trying to
factor in certain extreme scenarios - say, someone else using the
stereo.




Don't bother if the amp has triodes on the output, its only Pentodes
that will get upset with no load.


Can you explain why? Afraid I don't know why an amp built with triodes
would be inherently incapable of becoming unstable when unloaded.


No reason why it shouldn't become unstable, but the fact remains that a
triode is happy with a choke load, which the transformer (ignoring
OTL's) will become when unloaded. The pentode will not however like that
load and you can end up with high dv/dt that could cause problems in the
output TX.


Phew! Sorry Nick/Jim, didn't get much of that. Do you think this amp:

http://www.beardaudio.com/p100-505broc.pdf

(the power amp only, obviously) would be safe switched on and not
connected to speakers?


No, I would not trust that without a load, I would guess its a pentode
or UL output stage.

--
Nick

In article , Nick Gorham
wrote:
Jim Lesurf wrote:
In article , Nick Gorham
wrote:

Rob wrote:


It strikes me that the valve amp is the problem here - SS amps don't
need a dummy load.


Don't bother if the amp has triodes on the output, its only Pentodes
that will get upset with no load.


Can you explain why? Afraid I don't know why an amp built with triodes
would be inherently incapable of becoming unstable when unloaded.


No reason why it shouldn't become unstable,

OK...

but the fact remains that a triode is happy with a choke load, which the
transformer (ignoring OTL's) will become when unloaded. The pentode will
not however like that load and you can end up with high dv/dt that could
cause problems in the output TX.

Again, I am not sure I understand. I'd expect a real valve power amplifier
not to consist of just a triode or a pentode, and may well have global
and/or local feedback. Hence I'd expect either kind of design to perhaps
show instability with an output o/c. I'd also expect in either case that
this - if it occurs - might lead to some kind of failure or other problem.
Thus I'd assume this is a matter of the detail of design and construction,
for both a design using triodes and one using pentodes. Is this not the
case?

My curiousity is to why we can assume if the amp uses triodes, and know
nothing else about it, we can assume it has no o/c load problems, but a
pentode based design might.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Jim Lesurf wrote:
In article , Nick Gorham
wrote:

Jim Lesurf wrote:

In article , Nick Gorham
wrote:


Rob wrote:


It strikes me that the valve amp is the problem here - SS amps don't
need a dummy load.


Don't bother if the amp has triodes on the output, its only Pentodes
that will get upset with no load.


Can you explain why? Afraid I don't know why an amp built with triodes
would be inherently incapable of becoming unstable when unloaded.



No reason why it shouldn't become unstable,


OK...


but the fact remains that a triode is happy with a choke load, which the
transformer (ignoring OTL's) will become when unloaded. The pentode will
not however like that load and you can end up with high dv/dt that could
cause problems in the output TX.


Again, I am not sure I understand. I'd expect a real valve power amplifier
not to consist of just a triode or a pentode, and may well have global
and/or local feedback. Hence I'd expect either kind of design to perhaps
show instability with an output o/c. I'd also expect in either case that
this - if it occurs - might lead to some kind of failure or other problem.
Thus I'd assume this is a matter of the detail of design and construction,
for both a design using triodes and one using pentodes. Is this not the
case?

OK, so we start by assuming the design is of good quality, and that its
not going to break just because its being asked to deliver full power
output (which I would suggest is the worst case that instability could
provide). Given that, my point was purly that a triode is happy working
into a high load impedance, a horizontal load line, in fact its at its
best in some ways like this, whereas a pentode will be far less happy in
these conditions and more likely to result in problems.

At the end of the day, its just a view, I won't be looseing sleep if I
am wrong, and in reality (other than debating points on a newsgroup), I
would be happy to bet that what I say was functionally correct.


My curiousity is to why we can assume if the amp uses triodes, and know
nothing else about it, we can assume it has no o/c load problems, but a
pentode based design might.


Note that I am talking about the output devices, not if the voltage
amplifier is a triode or pentode.

--
Nick

"Rob" wrote

http://www.reel-multimedia.co.uk/

Looks mighty interesting and very versatile, but I suspect they aren't
much different to a suitably configured PC....???


Looks very neat indeed - 6 month waiting list for some of them! I'm coming
to the conclusion, having tried a few of these things, that a PC/Mac
directly hard wired is the best way to go with what I want - playback and
recording of a variety of video and music files. These wireless server
things just can't cope with either high data rates or out-of-spec file
types.

It's almost ironic that this digital age (is that where we're at?!) has
produced a stream of incompatible, unreliable, expensive and (in quite a
few cases) poorer quality media storage/playback/recording devices than we
had 25 years ago.


With technology evolving as fast as it is, I don't suppose all this
incompatability can be avoided. Soon there will be the BluRay vs. HD-DVD
Wars and when that's over (2 years, tops?) Holographic DVD will knock it all
into touch:

http://www.betanews.com/article/Holo...tes/1133197797

(All edging closer to the solid state 'Star Trek' storage blocks I mentioned
on this group *years* ago!! ;-)

Thankfully, it is all happening *globally* in mankind's chosen 'competetive'
culture and market forces will soon have the hardware on the shelves at
Tescos....