Notes on power transformers for
In 2008, obtained the hundreds
of power and output transformers, and filter chokes
from a fellow who needed to move house to an apartment where
there was little
storage room. I have spare room here so he and I agreed I could
store them and
advertize them for sale, and share the proceeds. Total weight of
stocks were about
1 tonne, and perhaps I have sold about 50Kg total.
is a fact that although I have hundreds of power and
output transformers and chokes
in my stocks, most are widely different to each other, and the
chance that something
I have might suit a given project some DIY person says he wants
is remote. And after
supplying about 25 items from my stocks of hundreds during the 4
years to about 6
customers, only 1 has completed work on an audio amp project.
So I will NOT spend a
pile of time sorting out what you want unless you can convince
me you are serious about building something.
You need to tell me
about your project, and give all details of schematic of the amp
Please try to send me a schematic
which is well drawn and less
200kB in file
size, .pdf or .gif, .jpg, Or send me a link to a URL.
Please email a link to a
website which has a schematic and description of your project.
I can recommend the choice of
schematics i have elsewhere at this website.
Perhaps you'd like to study my
informative web pages at
I would always like to think
that after you have successfully built a preamp to get
some practice at building tube operated electronics, perhaps you may become
experienced enough to design and build power amp.
For those unable to fully
design any amp, I would be able to select a compatible
set of parts including a power transformer, output transformer and filter choke
and probably be able to supply a schematic suitable for almost any output
tubes you can think of between a tiny 6AQ5 up to an 833.
Should someone wish to have me
draw up a schematic and design something
special and offer information support as construction progresses, there may
be a moderate cost involved. If a DIYer purchases a complete set of iron
components for a power amp I usually can offer a free suitable schematic
to best suit their purchase.
At times some DIYers have
obtained the parts they need from myself or another
supplier, and then decide they don't have available time to construct anything,
so they ask me to do it for them. I'm usually booked solid for many months
with orders so they would have to wait. DIYers MUST REALIZE considerable
time must be spent on hobbies if a good result or any result is to be had,
so don't ask me to care about your DIYer project if you are so bone lazy
you can't get busy after working hours instead of playing computer games,
watching TV and doing
101 other trivial pursuits. Support I maybe asked to
give can be expensive
depending on what sort of workmanship a hobbyist
has achieved before he hands
his work to me to inspect, repair, adjust, modify.
I suggest all DIY hobbyists
complete all work and get their amplifier projects
basically operational before bringing it to me for any final adjustments which
might include critical damping network adjustment where NFB is applied,
because some years of experience are needed to get this right.
Where I have had someone keen who has purchased a set of
parts, I have been very helpful with schematics and advice.
I do not supply full kits of parts for amplifiers.
DIYers must be able to work
fine details, and source all minor parts such as tubes, diodes,
capacitors, solder, hookup wire, terminals, switches, chassis, LEDs, SCRs,
BJTs, nuts, bolts, screws, tag strips or anything else. There are plenty of good
suppliers online for tubes and for small parts and I suggest
http://www.wescomponents.com.au and http://www.evatco.com.au
Usually DIYers realize that if
I were to supply minor parts, they would have to
pay much more for them for me to spend time dealing with an order, working
out the order, and supplying in small quantities.
transformers for sale......
Most transformers have GOSS
double C-cores, formerly made by AEM in Sth
Australia. These low loss cores run with a low rise in operational temperature.
After inspecting each
transformer type and measuring wire gauges where
possible I have given current
ratings for each secondary winding based
on 3Amps per square millimetre
of copper section area, eg, for 1.0mm copper
dia wire the rating is 2.36 Amps.
Most transformers have carefully
layer wound wire with at least 0.15mm thick
Nomex or polyester insulation between every layer of wire. There is a bobbin
with 3mm base wall thickness with ends of wire layers all kept back 3mm
from the edge of the insulation to maximize creepage distance.
Buyers should have slow blow
fuses to all primary and secondary windings.
Fuse values should be no more
than 2 twice the expected operational
maximum RMS current.
So if a primary has 1 Amp rms
maximum of input current while charging
capacitors, the mains fuse
should be a slow blow 2 Amp type, or just above the
value where there would be occasional nuisance fuse blowings.
There are NO thermal fuses
inside the windings of these transformers.
Because I have no control over
how anyone might use the transformers being
offered, I cannot offer a warranty included if you do not
to high standards of safety and protection against bias failure or any other fault.
There are schematics elsewhere
at this website for active protection against
bias failure and excessive cathode currents. All tube amps should have such
Some transformers with E&I
laminations were made in the 1960s by A&R or
Ferguson and have been in use in other equipment but are still in excellent
Buyers should carefully design
their amp schematics with regard for anode
supply voltages and anode load values and allow the B+ winding to cope
with at least 33% more current delivery than required at the idle condition.
They should allow for some
flexibility for the anode supply voltage of say
+20% and -5% before finalizing
It is easier to use a series
resistance in the B+ circuit to the OPT input to
slightly reduce the B+ to enable the right Iadc for class A working with the
It is impossible to increase
the B+ voltage easily if the HT winding has a
voltage which was too low for the project. The best outcome for the hobbyist
is to design the amplifier and its PSU and power tranny around the output
transformers available, rather than insist that the amplifier conform to yet
for which it is impossible to find a perfectly suitable
output transformer which will always be harder to find than a suitable power
transformer. Buyers should have the iron wound parts in their possession
before proceeding to make a chassis or to purchase one so as to
arrange the parts for spacious
and well proportioned layout.
All power transformers have
nominal 240V primaries to suit Australian buyers,
or where mains voltages are between 220V and 250V.
The secondary voltages stated
are nominal working voltages with 240V
applied to the primary.
The B+ anode supply voltages are
calculated at 1.35 x Vac and for working
Idc and for capacitor input filters. Bias windings can give Vdc = 1.35 x Vac,
or 2.7 x Vac depending on rectifiers being single silicon diode, silicon diode
bridge, or doubler configuration.
For those wanting to use tube
rectifiers, the B+ Vdc at the reservoir cap will
be between about 1.0 and 1.2 x Vrms of HT winding, with the B+ being
highest factor used where Idc is small, as it may be for a preamp.
the B+ Vdc at the cap after the
choke will be approximately 0.8 x Vrms at the
working Idc, and only if the choke winding resistance is low.
The input VA rating is that of
the input winding only, and VA = Input Vrms x Irms.
This input VA rating will be
equal to the sum of all VA ratings for all windings
plus 10% winding and core heat losses. A user may find that he can extract
more current from a HT winding than the VA rating indicates but this means
he must then extract less current from other windings to keep the
under the transformer input
Some HT windings for B+ have a
higher VA rating than required for idle
conditions because one must allow for temporary higher anode currents
because of class AB working and and occasional tube bias faults.
In general, the core VA rating
for C-cores is higher than the copper winding VA.
The C-cores have a larger ratio
between winding window area and the iron centre
leg area when compared to wasteless pattern E&I laminations.
Thus winding losses in
C-core transformers are lower than when using standard
wasteless pattern E&I laminations for the same VA. The permeability of GOSS
C-cores is higher than for non oriented Si Fe cores.
Heat losses for GOSS is often
negligible because the iron permeability is very high,
usually above 7,000. GOSS Toroidal cores have the highest permeability because
there are no joins in the sheet metal strip used to wind the spiral core, so toroidal
cores run coolest of all, and this is needed because the core is
the many insulated layers
of wire and core heat cannot escape easily.
The C-cored transformers will
be supplied with mounting brackets attached, and
all supplied with full information.
For sale power transformers
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