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Today's topics:

* Slightly odd output stage configuration. Thoughts ? - 2 messages, 2 authors
http://groups.google.com/group/sci.electronics.repair/t/2588a3ac4e8b297d?hl=en
* Proxy to open blocked sites - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/a790210194504e40?hl=en
* Timberland shoes <free shipping paypal payment>( http://www.cntrade88.com/ )
- 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/c639df6a14c2eba8?hl=en
* Looking For Usable Multimeter - Cheap - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/e1a0542b17d8b08d?hl=en

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TOPIC: Slightly odd output stage configuration. Thoughts ?
http://groups.google.com/group/sci.electronics.repair/t/2588a3ac4e8b297d?hl=en
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== 1 of 2 ==
Date: Fri, Feb 25 2011 10:31 pm
From: David Nebenzahl

On 2/25/2011 4:12 PM Phil Allison spake thus:

> Also, the power output will of course drop in triode mode and each EL84 will
> dissipate more heat under overdrive. Combined with their use of a
> "concertina" phase splitter, I suspect that overdrive clipping will not be
> symmetrical.

If you wouldn't mind indulging my relative ignorance for a minute, that
"concertina" stage business got my curiosity up. So I found the two
triode (12AX7) stages before the EL84s, and it looks to me like the
first stage (V3A) is a phase inverter, with the other triode acting as
*another* phase inverter cascaded from the first stage, presumably with
unity gain. Is that correct?

So it seems this setup would be quite problem-prone, with possible phase
distortion and phase imbalance (or crossover distortion) effects. So why
would anyone use such a phase inverter, when there are much better ones
available?

--
The phrase "jump the shark" itself jumped the shark about a decade ago.

- Usenet

== 2 of 2 ==
Date: Fri, Feb 25 2011 11:29 pm
From: "Phil Allison"

"David Nebenzahl"
Phil Allison spake thus:
>
>> Also, the power output will of course drop in triode mode and each EL84
>> will dissipate more heat under overdrive. Combined with their use of a
>> "concertina" phase splitter, I suspect that overdrive clipping will not
>> be symmetrical.
>
> If you wouldn't mind indulging my relative ignorance for a minute, that
> "concertina" stage business got my curiosity up. So I found the two triode
> (12AX7) stages before the EL84s, and it looks to me like the first stage
> (V3A) is a phase inverter,

** With an imagination like that - you should be writing fiction for a
living.

A " phase inverter" ( or phase splitter) has equal and opposite polarity
outputs.

> with the other triode acting as *another* phase inverter cascaded from the
> first stage, presumably with unity gain. Is that correct?

** Nope.

V3A is a voltage amplifier ( gain of about 50 before NFB) while V3B is the
"concertina" phase inverter. Concertina circuits always have equal plate and
cathode resistors and in operation, the voltage between the plate and
cathode grows and falls with audio drive like a concertina being pumped in
and out.

The cathode of V3A acts as a negative ( opposite phase) input for feedback
from the output transformer secondary.

Because of the easy drive requirements of an EL84, such a concertina circuit
is able to send them deep into overdrive - while maintaining good symmetry.
Not so for 6L6GC or EL34 stages which need several times more drive voltage.

.... Phil

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TOPIC: Proxy to open blocked sites
http://groups.google.com/group/sci.electronics.repair/t/a790210194504e40?hl=en
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== 1 of 1 ==
Date: Sat, Feb 26 2011 12:55 am
From: Ahmed Ragab

Proxy to open blocked sites

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OR

http://pronet.4mtm.net

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http://groups.google.com/group/sci.electronics.repair/t/c639df6a14c2eba8?hl=en
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== 1 of 1 ==
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TOPIC: Looking For Usable Multimeter - Cheap
http://groups.google.com/group/sci.electronics.repair/t/e1a0542b17d8b08d?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Feb 26 2011 1:45 am
From: "Dave Plowman (News)"

In article <V9SdnShGi7c67PXQnZ2dnUVZ_sidnZ2d@earthlink.com>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:

> "Dave Plowman (News)" wrote:
> >
> > In article <ipCdnVVbGqQnmvXQnZ2dnUVZ_hudnZ2d@earthlink.com>,
> > Michael A. Terrell <mike.terrell@earthlink.net> wrote:
> > > > > I agree. I use mine all the time, but the contacts inside are
> > > > > wearing out. Where would you find an inexpensive new analog
> > > > > meter? Do they even make them anymore?
> > > >
> > > > A half decent DVM will have a a bargraph to mimic a needle
> > > > movement.
> >
> > > A decent DVM won't have a bargraph to annoy you.
> >
> > It's there to inform. Of course information may well annoy you. And I
> > consider my Fluke quite decent.

> When you're at a bench with over 30 pieces of test equipment,
> including four or more identical DVMs the bargraph is just more visual
> noise.

Thought the question was about the spec for a basic DVM?

As regards a bargraph being 'visual noise' that's the whole point. It
draws your attention to the direction and rate of change. If you're using
'30 pieces of test equipment' at once, you can't possibly read them all
accurately at any one point in time - so a bargraph sounds to me even more
useful here.

--
*The statement above is false

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

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