In ,
Arny Krueger typed:

I keep hearing about this, but have never seen the problem up front
and personal. I have had RF problems but they were in the front end,
not the back end.

A while back I had an amp
that would pick up VHF taxi and police transmissions
quite clearly.

Brand - model?


Texan, circa mid-1970s

It even picked up Radio Moscow on
occasions when global MF radio propagation conditions
were favourable. Home made longitudinal chokes on the
speaker leads fixed most of this problem.

Most power amps already have chokes in series with their output
terminals.
As they should. The Texan didn't.

Jo

In article ,
says...

A while back I had an amp
that would pick up VHF taxi and police transmissions
quite clearly.

Brand - model?


Texan, circa mid-1970s

Blimey, I remember building one of those from a 'Henrys' kit..
Beefed up with a large torrodal transformer and higher power transistors
following an article I read in a mag. I imagine it sounded horrendous
but it was certainly the loudest thing on our corridor in Hall.

Allegedly designed in the bar at a conference by a bunch of Texas
Instruments engineers. Probably apochrophal though; sadly..

T.

"Tony Gartshore" wrote in message
...
In article ,
says...

A while back I had an amp
that would pick up VHF taxi and police transmissions
quite clearly.

Brand - model?


Texan, circa mid-1970s

Blimey, I remember building one of those from a 'Henrys' kit..
Beefed up with a large torrodal transformer and higher power transistors
following an article I read in a mag. I imagine it sounded horrendous
but it was certainly the loudest thing on our corridor in Hall.

Allegedly designed in the bar at a conference by a bunch of Texas
Instruments engineers. Probably apochrophal though; sadly..

T.

As I recall, it was originally designed as an article for Practically
Witless ( or was that Practical Wireless ? ) magazine. It *was* designed by
a bunch of Texas engineers at Bedford, but I'm not so sure about the " in
the bar " bit. Several of us built them from Henry's Radio kits, and I think
that for it's day, it represented pretty much state of the art for what any
of us could afford. I seem to remember that its specifications were beyond
anything that we had ever heard. A friend of mine that built one, did that
power upgrade to his, and used it to drive his quad electrostatics, and I'm
sure I recall it sounding superb. I built a 'standard' version, and used it
to drive my EMI 13 x 8's, with 6 x 4 mids ( remember those - they came as a
pair ) rounded off with an Eagle duralumin dome tweeter, and Eagle 3 way
crossover. At the time, I thought it was the dogs ...

Arfa

In ,
Arfa Daily typed:

As I recall, it was originally designed as an article for Practically
Witless ( or was that Practical Wireless ? ) magazine. It *was*
designed by a bunch of Texas engineers at Bedford, but I'm not so
sure about the " in the bar " bit. Several of us built them from
Henry's Radio kits, and I think that for it's day, it represented
pretty much state of the art for what any of us could afford. I seem
to remember that its specifications were beyond anything that we had
ever heard. A friend of mine that built one, did that power upgrade
to his, and used it to drive his quad electrostatics, and I'm sure I
recall it sounding superb. I built a 'standard' version, and used it
to drive my EMI 13 x 8's, with 6 x 4 mids ( remember those - they
came as a pair ) rounded off with an Eagle duralumin dome tweeter,
and Eagle 3 way crossover. At the time, I thought it was the dogs ...

Yes, I built my own. Drove to Bedford and bought a kit from the original
manufacturers. Freq response, THD and stuff were leading edge at the time
and it sounded great to me through my Wharfedales (which have only just
expired). My Texan still works and the only problems were worn out volume
controls which I changed around 1995. Design was quite innovative with high
slew-rate op-amps at the front end.

Jo

In article , Jo
wrote:
In , Arny Krueger
typed:


Most power amps already have chokes in series with their output
terminals.
As they should. The Texan didn't.

A snag here is that some designers feel that an output choke increases the
HF o/p impedance and degrades the sound. Classic example being the older
Naim power amp designs which just used a 0.22 Ohm resistor...

.... and then may require about 10microH of lead inductance to be stable.
:-)

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
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Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

In ,
Jim Lesurf typed:
In article , Jo
wrote:
In , Arny Krueger
typed:


Most power amps already have chokes in series with their output
terminals.
As they should. The Texan didn't.

A snag here is that some designers feel that an output choke
increases the HF o/p impedance and degrades the sound. Classic
example being the older Naim power amp designs which just used a 0.22
Ohm resistor...

... and then may require about 10microH of lead inductance to be
stable. :-)


Yes, this brings us back into the topic of "but can humans really hear the
difference ?" that occupies many threads. I wonder how much extra impedance
is added to the output circuit at audio frequencies by the addition of RF
chokes ? The formula for inductive reactance is simple and for a 100uH choke
I get:

XL=1.3K at 2MHz and 13 Ohms at 20KHz which would seem to be a significant
contribution to the impedance of an amp output circuit...

....BUT if a decent common mode type bifilar wound filter choke is used the
effective inductance in the speaker circuit would be much less than this and
so any degradation of the audio signal would be negligible....or would it
:-)

Jo