Pooh Bear wrote:

Patrick Turner wrote:

robert casey wrote:

Phil Allison wrote:


** WHY post this in a group dominated by Tube Heads ??

Don't you know Tube Heads loathe toroidal and R core transformers ??

Tube Head logic is that since toroidals did not exist in the golden era of
tubes ( 1920 to 1965 ) it is pure sacrilege to even suggest using them now.

That would also rule out those boutique and other modern capacitors as
well. Back to wax paper caps..... :-)

There are problems with toroidal OPTs used in PP amps due to easy saturation if the
DC
becomes slightly imbalanced.

That seems to me to be more of a problem with the circuitry than the transfomer. If
you'd accept ss electronics even as a servo, the bias could be dynamically adjusted
to prevent any DC component.

About 10 years ago there was an article on Electronics World which advocated the use
of a pair of differential mode opamps to adjust grid bias so that balanced dc cathode
current is maintained.
The circuit filtered out the signal from small cathode R current sensors.
Since most PP amps are class AB the cathode current in output tubes is never constant in
class AB
and the current in both tubes rise with signal, and its the balance that needs to be
maintained
and not total dc current which must be allowed to rise above the idle Ia which stays
fixed for the first few watts
of class A.
I tried this thing with discrete connected darlington pairs which worked great until i
added NFB
and then there was much LF oscillation.
Having cores with a small gap or with not extremely hig µ will allow some bias imbalance.

I usually place a bias balance pot in PP amps and the balance can be adjusted with two
leds indicating
bias balance when operating at equal brightness.
No need for the servo circuit.





Tube head DIYers don't like bloomin toroids mainly becaise they are so difficult to
use.

Eh ? What's difficult ? It's a transformer dammit. What can be difficult about that ?

I meant difficult to use in a transformer they would wind themself.
OK for RF where a few turns are involved but not with audio OPT or PT where many
turns are needed.



The last 500VA power tranny I wound by hand took 3 days with a shuttle passed
around the core
at about 1 turn per 45 seconds average.

You wind your *power* transformers ? I can understand OPTs but really !

I wind all my own iron wound components because I cannt find anyone selling trannies
wound how I like them to be wound, or they take too long, charge too much etc.



All the toroidals I have purchased for PT have been noisy even unloaded, and way
too noisy
with a rectifier connected

You've been buying the wrong ones. That's a non-existent problemas far as I'm
concerned. Crikey, I've found E-Is to be noisy for heaven's sake !

The reason I wound the toroidal 500VA was because first I unwound something I'd bought
because it was too noisy for hi-fi and then re-wound it for B= 0.85T instead of the B=
1.25T it was set up for.
I once supplied a customer with a sub woofer amp with another toroid from another
supplier
and thought myself that the toroid was barely quiet enough, and sure enough my client
objected so I replaced it with
an E&I which is usually far easier to make quiet than a toroid.
Two other toroids from a third supplier were too noisy so I gave up, and have never
bothered with buying a single tranny since.



their winding doesn't include proper baked varnish or epoxy imprgnation.

Doesn't need it if wound properly.

Rubbish.

Windings on a tranny are subject to forces shoving the winding one way then the other
depending on ac flow direction.
The windings are like those on a motor armature but have no place to go. The tension in
the polyester tape insulation
may be high but it acts like a diaphragm which gives off sound when agitated.



When i see a tube amp with all toroids in it I shudder, and usually it is a crap
product fron China.

Association like that is nuts.

The chinese how to make an amp look nice but their OPTs fail to atact me ans their PTs
are barely passable.

I never buy chinese made anything if I can avoid it. I get numerous spams from china
offering all this cheap as dirt crap
and I email them back to tell them I'd happily pay 4 times the price if the standards
were higher, then I explain what i expect.
It is like emailing a brick wall to tell it to move. They think they are such masters but
they are merely arrogant
amateurs.

You should see the hi-fi amps in the shop here selling for about usd $2,000 with a pair
of 6L6 per channel
Toroidal OPTs, PT, and they are all just toys....



But on the other hand the toroidals from Plitron are very decent, if anyone can
afford them...

I specify Toroid International.
http://www.toroid.se/

I compared Auricaps to plain cheap MKP Wimas and heard ZERO sound change.

No surprise there. For there to be any difference there would need to be a scientific
explanation why ! And there isn't. Essentially all plastic film caps perform
identically for coupling.

I would agree but the audiophiles cannot. I just work as directed, and when asked to
install
Auricaps, I just install them.

Patrick Turner.



Graham