Re: ...Time to do a run of 547/545B HV transformers...


Hi Chuck , this is a slight detour ! . Would it be possible for you to remanufacture the bobbin for a 549 HV transformer . I no longer have the original core but I do have the bobbin partially stripped of the windings , I think the primary is still there . I will have to find a suitable core here in the UK - not going to be easy I know but I have been trying to find someone able to produce bi-filar wave wound windings for quite a while without success .
I feel sure that if I have a good set of windings the problem will be halved . I have original transformer drawings from Tektronix with the winding details should you need them .
best regards
Brian .

--- In, Chuck Harris <cfharris@...> wrote:

Hi Gang!

A good friend has urged me to make one of my world renowned
545B/547 replacement HV transformers for him. If I'm going to
start up the production line for one transformer, I might as well
do ten.

My transformers are a completely remanufactured replacement for
the original Tektronix 545B/547 HV transformer. They use all new
parts, with the exception of the ferrite core (which is pure
unobtanium in quantities I can support). Pictures can be found
in the album section of both the Tekscopes, and Tekscopes2 groups.

As many of you know, the original tektronix transformers, for the
545B and 547, were a technological leap that fell a little short
of the desired mark. Tektronix built a new self contained modular
HV section in a plastic box. To complement the new module, they
tried out a new epoxy varnish to protect the transformer winding.

Unfortunately, this new epoxy varnish became progressively lossier
over time, causing the HV to sag, and the CRT image to bloom
in size as the scope warmed up. Eventually, the loss would grow
so high that the HV would quit. The epoxy became lossy whether
the scope was in use, or not. This makes finding good replacement
HV transformers problematic.

My new transformers take a step back, and use the extremely reliable
beeswax/paraffin impregnating compound that tektronix used with
great results in all of the previous 500 series scopes, ranging back
to the mid 1950's. My transformers have been extensively tested,
and are completely immune to the failure mode of the epoxy varnished
transformers made by tektronix. And yes, they have been used on
hot summer days in unconditioned work spaces (Thanks Bernd!).
They are an exact drop-in replacement for the original 545B/547
transformer, and have ample room for the original 5642 filament

Because of the complexity of the winding process, it takes me
about 2 hours to build a new transformer from the ground up:

First I strip the old cores, and clean them of all epoxy residue.

Next, I CMC machine new FR4 terminal boards, and install the
terminal eyelets.

Then I build the winding termination tape strip and install it on
a new former. This tape strip gets covered with 3 wraps of Kapton
tape, and one wrap of double stick tape.

The universal wound primary comes next. And when finished is
terminated, and covered with 3 layers of Kapton tape, and another
layer of double stick tape.

The universal wound secondaries complete the windings. 733 turns
of bifilar wound #38 enamel wire, tapped appropriately, and finished
with 3 layers of Kapton tape.

The new coils are heated to 140F, and are submerged in a molten
beeswax/paraffin potting compound. While they are soaking in the
molten wax, they and are put into a Pyrex vacuum impregnation chamber
and cycled down to a mild vacuum a half dozen times to assure complete
penetration of the wax into the coils. This process requires careful
watching to avoid boiling the potting wax!

After impregnation, the coils are tested on a hipot jig to 4x normal
operating voltages, and those that pass are given a wrap of 3M fiberglass
tape, labeled and assembled with new terminal boards, and recycled cores.

Leads are attached as per tektronix specifications. I use teflon leads
to protect the wires from accidental soldering iron burns.

The finished transformers wrapped in tissue paper, and sealed into
plastic bags ready for shipping.

Because of the time and materials I put into each of these transformers,
I have to charge the following prices:

QTY 1 - $85
QTY 2-5 - $75 each
QTY 5+ - $70 each

$15 will cover FedEx shipping to anywhere in the US. Foreign shipping
will have to be extra, and will be investigated if necessary.

I cannot source cores, so you must send a set of unbroken cores with a
check for payment before I can send you a transformer. It is not
necessary, or even desirable for you to disassemble the old transformer.
[Note, good cores from any of the 500 series with plugins are suitable.]

Winding these transformers is a difficult tedious process. I am not
certain how many more I will do. I have scratched my own itch... All
of my scopes, and all of my close friend's scopes have new transformers.

If you have a 545B, or 547, that needs a new HV transformer, now is the

-Chuck Harris

OBTW, let's keep the orders off of this list. I am open to any and all
transformer questions on list.

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