Another solution for the 547 HV transformer problem


Morris Odell
 

A friend of mine named Deon Vandenberg recently acquired a 547 scope and as expected, the HV transformer had the classic thermal runaway problem. The only cure for this is to replace or rewind the transformer and as Chuck Harris is not currently providing this service, we had to find an alternative solution. I say "we" because although Deon lives over 1000 miles away from me (Australia is a big country!) we we were able to collaborate by internet and phone.

Deon has managed to modify a transformer from another junked scope to provide virtually identical function to the original and the 547 is now working perfectly. He has kindly consented for me to upload his description of what he did in the hope that it will help others.

If you're interested, I have uploaded a word file to the "547 hv transformer" folder in the files section.

Comments welcome!

Morris


momemeca
 

Hello Morris,
Rick here … Is Deon back from Japan? Also, when lockdown is over, I would like to come for a visit and pick up that carcass ;-)
Cheers.

On 25 Aug 2021, at 14:49, Morris Odell <vilgotch1@gmail.com> wrote:

A friend of mine named Deon Vandenberg recently acquired a 547 scope and as expected, the HV transformer had the classic thermal runaway problem. The only cure for this is to replace or rewind the transformer and as Chuck Harris is not currently providing this service, we had to find an alternative solution. I say "we" because although Deon lives over 1000 miles away from me (Australia is a big country!) we we were able to collaborate by internet and phone.

Deon has managed to modify a transformer from another junked scope to provide virtually identical function to the original and the 547 is now working perfectly. He has kindly consented for me to upload his description of what he did in the hope that it will help others.

If you're interested, I have uploaded a word file to the "547 hv transformer" folder in the files section.

Comments welcome!

Morris





David Kuhn
 

I saw your post on Facebook; great job. Question: Are 535 transformers
easy to get? I would imagine the 535 still around have been fixed up and
restored. The 547 is a better scope than a 535, so to sacrifice on to save
a 547 may be acceptable, I donno???

On Wed, Aug 25, 2021 at 12:49 AM Morris Odell <vilgotch1@gmail.com> wrote:

A friend of mine named Deon Vandenberg recently acquired a 547 scope and
as expected, the HV transformer had the classic thermal runaway problem.
The only cure for this is to replace or rewind the transformer and as Chuck
Harris is not currently providing this service, we had to find an
alternative solution. I say "we" because although Deon lives over 1000
miles away from me (Australia is a big country!) we we were able to
collaborate by internet and phone.

Deon has managed to modify a transformer from another junked scope to
provide virtually identical function to the original and the 547 is now
working perfectly. He has kindly consented for me to upload his description
of what he did in the hope that it will help others.

If you're interested, I have uploaded a word file to the "547 hv
transformer" folder in the files section.

Comments welcome!

Morris






Dave Wise
 

Clever idea! I wonder: how about a dropping resistor in series with the tripler input? If deflection factor stays constant as you vary intensity, you don’t have to de-wind.

I salvaged a handful of HV transformers from Stan Griffiths’ estate. I sent some to Chuck; I’ll go figure out what I kept.

Dave Wise
PS – Don’t forget I published a low-tech recipe for winding your own transformer. That was 453 but it’s easily adaptable to 547. Photo album and topic, “453 HV Transformer Rewind”.

=============================================================================
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David Kuhn via groups.io
Sent: Wednesday, August 25, 2021 7:16 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Another solution for the 547 HV transformer problem

I saw your post on Facebook; great job. Question: Are 535 transformers
easy to get? I would imagine the 535 still around have been fixed up and
restored. The 547 is a better scope than a 535, so to sacrifice on to save
a 547 may be acceptable, I donno???

On Wed, Aug 25, 2021 at 12:49 AM Morris Odell <vilgotch1@gmail.com> wrote:

A friend of mine named Deon Vandenberg recently acquired a 547 scope and
as expected, the HV transformer had the classic thermal runaway problem.
The only cure for this is to replace or rewind the transformer and as Chuck
Harris is not currently providing this service, we had to find an
alternative solution. I say "we" because although Deon lives over 1000
miles away from me (Australia is a big country!) we we were able to
collaborate by internet and phone.

Deon has managed to modify a transformer from another junked scope to
provide virtually identical function to the original and the 547 is now
working perfectly. He has kindly consented for me to upload his description
of what he did in the hope that it will help others.

If you're interested, I have uploaded a word file to the "547 hv
transformer" folder in the files section.

Comments welcome!

Morris






Morris Odell
 

It's true that the 547 is the best of the 500 series single beam scopes, but I would never advocate using a good working scope as a parts donor. There must be plenty of junkers out there. Also regrettably scopes that have had all their tubes removed and would be not be economically feasible to re-tube.


Morris Odell
 

Hi Dave,

You could put a resistor in series with the anode supply but I suspect it might lead to HV variations with intensity as the beam current changes. That would affect the deflection factors and thus the calibration. I like Deon's solution of removing few turns from the overwind. This method might be amenable to other models too if the ratio of turns between the cathode and grid windings are suitable. Testing with a low voltage is a useful way to check that.

Morris