In article , David Looser
wrote:
"Jim Lesurf" wrote

That said, I did have one of my summer project students once develop a
single-ended transistor amp that used an output transformer, just to
play with. So 'SET' I guess, if T = Transistor. ;-


As used in car radios at one time. Hybid and early all-transistor car
radios mostly seemed to use a Class-A single-ended power transistor
(OC16 or similar) output stage rather than a Class-B push-pull pair. I
guess it was cheaper and the much higher power consumption of Class-A
didn't matter much in a car.

I guess designers of commercial audio amps back then were more habituated
to using transformers than nowdays. I didn't know about the above, but
recall that some early domestic transistor amps included things like
coupling transformers.

BTW Not sure if I'll be able to look at the Newmarket devices tomorrow. May
be delayed by snow! :-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

On Sun, 20 Dec 2009 12:22:40 +0000 (GMT), Jim Lesurf
wrote:

I guess designers of commercial audio amps back then were more habituated
to using transformers than nowdays. I didn't know about the above, but
recall that some early domestic transistor amps included things like
coupling transformers.

How about a current guitar practice amplifier?

http://www.soundthoughts.co.uk/look/pignose.jpg

The idea is to sound like a proper valve guitar amplifier, and it sort
of does it.

d

In article , Don Pearce
wrote:
On Sun, 20 Dec 2009 12:22:40 +0000 (GMT), Jim Lesurf
wrote:

I guess designers of commercial audio amps back then were more
habituated to using transformers than nowdays. I didn't know about the
above, but recall that some early domestic transistor amps included
things like coupling transformers.

How about a current guitar practice amplifier?

http://www.soundthoughts.co.uk/look/pignose.jpg

The idea is to sound like a proper valve guitar amplifier, and it sort
of does it.

The transformers look quite small. What's the scale of the picture?

I did once do a 'theoretical' design using two bipolars and couple of
transformers to make a SET power amp, just to work out what kind of gain,
etc, you might get. But never built it as it didn't seem worth trying to
get suitable transformers. Maybe the above did it anyway? :-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

"David Looser" wrote in
message
"Jim Lesurf" wrote

That said, I did have one of my summer project students
once develop a single-ended transistor amp that used an
output transformer, just to play with. So 'SET' I guess,
if T = Transistor. ;-

As used in car radios at one time. Hybid and early
all-transistor car radios mostly seemed to use a Class-A
single-ended power transistor (OC16 or similar) output
stage rather than a Class-B push-pull pair. I guess it
was cheaper and the much higher power consumption of
Class-A didn't matter much in a car.

Probably driven by the then-current high price of power transistors.

If memory serves, there was a period of time where most of the car radio was
built from tubes that used +12 volts for the B+, and a single power
transistor in the output stage. This eliminated the need for a vibrator and
power transformer to create more typical B+ voltages.

"Jim Lesurf"


I guess designers of commercial audio amps back then were more habituated
to using transformers than nowdays. I didn't know about the above, but
recall that some early domestic transistor amps included things like
coupling transformers.


** The use of coupling transformers disappeared by the early 70s in ( new)
domestic hi- fi amplifiers.

However, one famous British maker of "professional" audio revived the idea
in the early 80s - a massive leap backwards if there ever was one. Hill
Audio Ltd of Kent.

http://www.hill-audio.com/?page_id=4

Hill produced thousands of truly awful DX700 and DX1000 et alia models that
internally consisted simply of a TO220 style audio amp IC ( TDAxxxx )
driving a transformer and thence rows of Motorola MJ15024s - labelled
with their own number. These ugly boat anchors had huge toroidal
transformers, heatsinks that simply didn't and no fan.

The only overload / SOA protection for the MJs were DC rail fuses.

It blew up if ever it got hot, the speaker cable shorted or the driver
tranny wiggled loose on the PCB.

Most primitive power amps I ever saw.



..... Phil

"Jim Lesurf" wrote in message
...
In article , Don Pearce
wrote:
On Sun, 20 Dec 2009 12:22:40 +0000 (GMT), Jim Lesurf
wrote:

I guess designers of commercial audio amps back then were more
habituated to using transformers than nowdays. I didn't know about the
above, but recall that some early domestic transistor amps included
things like coupling transformers.

How about a current guitar practice amplifier?

http://www.soundthoughts.co.uk/look/pignose.jpg

The idea is to sound like a proper valve guitar amplifier, and it sort
of does it.

The transformers look quite small. What's the scale of the picture?

They do, compare with the size of the screw-heads.

I did once do a 'theoretical' design using two bipolars and couple of
transformers to make a SET power amp, just to work out what kind of gain,
etc, you might get. But never built it as it didn't seem worth trying to
get suitable transformers. Maybe the above did it anyway? :-)


That looks like a push-pull amp to me. Aren't those a pair of TO220
transistors either side of the larger transformer?

avid.

In article ,
David Looser wrote:
"Jim Lesurf" wrote in message
...
In article , Don Pearce
wrote:
On Sun, 20 Dec 2009 12:22:40 +0000 (GMT), Jim Lesurf
wrote:

I guess designers of commercial audio amps back then were more
habituated to using transformers than nowdays. I didn't know about the
above, but recall that some early domestic transistor amps included
things like coupling transformers.

How about a current guitar practice amplifier?

http://www.soundthoughts.co.uk/look/pignose.jpg

The idea is to sound like a proper valve guitar amplifier, and it sort
of does it.

The transformers look quite small. What's the scale of the picture?

They do, compare with the size of the screw-heads.

I did once do a 'theoretical' design using two bipolars and couple of
transformers to make a SET power amp, just to work out what kind of
gain, etc, you might get. But never built it as it didn't seem worth
trying to get suitable transformers. Maybe the above did it anyway?
:-)


That looks like a push-pull amp to me. Aren't those a pair of TO220
transistors either side of the larger transformer?

The size of the output transformer looks more suited to 1 watt types.

--
*Can atheists get insurance for acts of God? *

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
David Looser wrote:


That looks like a push-pull amp to me. Aren't those a pair of TO220
transistors either side of the larger transformer?

The size of the output transformer looks more suited to 1 watt types.


I don't dispute that for a moment, but they *do* look like a pair of TO220
devices! There are no heatsinks so they are probably well under-run.

David.

mick wrote:
On Tue, 15 Dec 2009 12:18:39 +0000, Jim Lesurf wrote:

In article , David Looser
wrote:
"Ian Bell" wrote
I had some of those too. There were also green spot rf ones. I still
have a red spot one. Must be worth a fortune now ;-)


If they are worth a fortune I'm sitting on a gold-mine here!
I think I have some old 'Newmarket' (if that was the name) transistors.
Maybe if these kinds of things are now 'historic relics' I should dig
some of them out... :-) IIRC they are still in the corrugated
cardboard in the boxes in which they were bought.



Would those be the ones in the flat cans with yellow & green spots for
audio and a red spot for RF, Jim?

Interesting page for flat cans:
http://homepages.nildram.co.uk/~wylie/NKT/newmarket.htm

Another for "top hat" cans:
http://homepages.nildram.co.uk/~wyli...an/Ediswan.htm

That is an interesting site, takes me back to being an apprentice lad at
RRE. I think that I have an STC "Crystal triode" kicking around somewhere,

"Jim Lesurf" wrote in message


I guess designers of commercial audio amps back then were
more habituated to using transformers than nowdays. I
didn't know about the above, but recall that some early
domestic transistor amps included things like coupling
transformers.

Driver transformers were last used in US built hifi amps, probably in the
origional Acoustic Research amplifier and receiver. Probably early 1970s.
It did not appear that they hindered performance all that much. It was a
pretty passable solution for building a SS amp in the days when
complementary transistors were expensive or simply unavailable.

http://www.hifiengine.com/manuals/ac...receiver.shtml .