Hi All,

I'm thinking about winding an OTP. Is there any reason why I
shouldn't make a single winding (like an Autotransformer) output
transformer?

C.W.

Casino wrote:

Hi All,

I'm thinking about winding an OTP. Is there any reason why I
shouldn't make a single winding (like an Autotransformer) output
transformer?

C.W.


Apart from the safety isolation feature of a separate winding
and the prevention of DC across your speakers.....no.

Regards
Mark Harriss

Just say NO!!! to Phil Allison

None at all, there is only one provisio though, you have lost any
isolation from the HT in the amp, to things connected to the amp, in
this case your loudspeakers.

if the common connection at the 'bottom' or common end of the tranny
was to become disconnected, you would have full ht on your speakers.
could be kind of messy.

If you are keen on this arrangement, try parafeeding.

kind regards.

bill ramsay


On 3 Oct 2003 15:50:31 -0700, (Casino)
wrote:

Hi All,

I'm thinking about winding an OTP. Is there any reason why I
shouldn't make a single winding (like an Autotransformer) output
transformer?

C.W.

Casino wrote:

Hi All,

I'm thinking about winding an OTP. Is there any reason why I
shouldn't make a single winding (like an Autotransformer) output
transformer?

C.W.

There has to be two windings on most OPTs because one winding
is at anode supply potential, and the other is at ground potential.
Interleaving still has to be done with say 4 primary sections, and 5
secondaries,
and the lower winding losses with an auto tranny are insignificant
when the turns ratio is a typical 25:1 btween P and S windings,
for a typical impedance match of 5k to 8 ohms.

About the only use I see for an auto transformer is for
the use of low Ra tubes, which are used as cathode followers,
such as 6AS7, EL509, to get some sort of load match
which is better than an OTL design, unless one uses mosfets,
where an auto tranny is a good idea, if the load value to be matched is
real low.

Patrick Turner.

Bill Ramsay wrote:

None at all, there is only one provisio though, you have lost any
isolation from the HT in the amp, to things connected to the amp, in
this case your loudspeakers.

if the common connection at the 'bottom' or common end of the tranny
was to become disconnected, you would have full ht on your speakers.
could be kind of messy.

If you are keen on this arrangement, try parafeeding.

kind regards.

bill ramsay

Indeed, I forgot the parafeed amp.
With a PP amp, the choke feed to the opv anodes can be a large
choke with CT to B+.
Then the OPT can have its secondaries in series with the 1/2 primaries.
There are slightly less winding losses.
The OPT secondary can have a CT, and be grounded, to permit
class AB operation, as an ungrounded secondary
only allows class A operation.

The parafeed is not necessary for PP amps, and is rarely used,
and conveys little if any sonic or measured advantages.
Perhaps it makes sense if a large SE amp is built using
say an 833, and where a ready made OPT for PP operation
can be used with parafeed, couple to the large triode anode with
20 uF HV caps, and having a couple of large 20H air gapped chokes
in series to supply the B+ anode current.
Thus the problems of relying on insulation in the OPT
to isolate the high anode supply voltage from the earthy secondary are
avoided.
The insulation of the drive caps have to be good, but at least if a cap
shorts out,
its a cheap fix.

Patrick Turner.



On 3 Oct 2003 15:50:31 -0700, (Casino)
wrote:

Hi All,

I'm thinking about winding an OTP. Is there any reason why I
shouldn't make a single winding (like an Autotransformer) output
transformer?

C.W.

Casino wrote:

Hi All,

I'm thinking about winding an OTP. Is there any reason why I
shouldn't make a single winding (like an Autotransformer) output
transformer?

C.W.


I used an autoformer that used to be a vertical output autotransformer
in a tube
TV set like this. The turns ratio was 14 to 1, and I connected the tap to
B+ so the speaker winding and speaker wouldn't see any DC current.
However, the speaker's voice coil is at B+ voltage. This isn't an issue in
my application (an AM table radio), but would be in an amp with external
speakers. Also, any negative feedback loops from the speaker would
get more complicated, especially considering that hum/ripple on the B+
would get passed along as well as the audio in the loop.

Obviously a vertical output autoformer isn't a hifi output transformer, but
still sounded fine for an AM table radio. The vertical output in a TV set
looks like a current sawtooth wave at 59.94Hz. Which is rich with harmonics
mostly in the audio frequency spectrum. Which is why I used it in the
radio.
I see no advantage in purposely building an audio output transformer this
way, I just used what I had on hand.

In addition to all of the other replies, I will add that the secondary of a
transformer is wound in a heavier guage or wire than the primary. Using the
same guage would increase overall losses in the transformer, raise the
output impedance of the amplifier, and lower the power output. If you were
to use a different (larger) guage of wire for the "tap" part of the the
primary, why not just wind it as a secondary and give isolation from B+ ?

Max

"Casino" wrote in message
om...
Hi All,

I'm thinking about winding an OTP. Is there any reason why I
shouldn't make a single winding (like an Autotransformer) output
transformer?

C.W.

Hi All,

Thanks for all your replies. So a single winding OPT isn't a good idea after all.

C.W.

(Casino) wrote in message . com...
Hi All,

I'm thinking about winding an OTP. Is there any reason why I
shouldn't make a single winding (like an Autotransformer) output
transformer?

C.W.