Date   

Re: Beeswax in Transformers

Dave Wise
 

I didn't impregnate my low-tech 453 rewind. Hang on for ten more years, maybe you'll see a post titled "Dave Wise HV rewind failed" :)?

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Chuck Harris via groups.io <cfharris=erols.com@groups.io>
Sent: Friday, March 05, 2021 9:48 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Beeswax in Transformers

Hi Barry,

It isn't a coating, but rather an impregnation. The beeswax, or
epoxy is drawn into the spaces between the wires to add additional
insulation, and to keep them from moving.

If you don't add an impregnant, corona effects may eventually break
down the insulation... in my experience, *will*...

-Chuck Harris

n4buq wrote:
I'm curious why transformers (in particular, this transformer) benefit from a coating - beeswax or otherwise. Is it to damp sympathetic vibration at the operating frequency/frequencies?

Thanks,
Barry - N4BUQ






Re: Modifying W Plugin to use 6DJ8 Tubes

Dave Wise
 

Background:


Production below S/N 7000 uses a pair of 8056 Nuvistor at the input.

At 7000 they are replaced by a dual JFET.


V114 is on the A (plus) side, V214 is on the B (minus) side.??

One section is a cathode follower that bootstraps the first-stage amp anode or drain,

the other section is the top half of the second-stage hybrid transistor-tube cascode amp.


V124 is current sinks on the first-stage cathodes or sources.


Update:


I'm still investigating powering 6DJ8's, but I also experimented with a couple of common 12V tubes.


First I tried 12AT7. It's a no-go. The cascode top's grid bias is Q154's Vce. 12AT7 is only 0.5V, so Q154 doesn't work.


Then I tried 12AU7.

Like 8416, it's about 2V and Q154 is happy.


12AU7 works! Albeit with reduced 3dB bandwidth.


I see 22MHz with 12AU7, and 20ns rise time. Compare with the spec: 26MHz and 14ns.

I see a flat top on the square wave. I didn't bother adjusting amplifier HF comp. Maybe I can speed it up.

I see 33MHz with 8416.


Common-mode rejection spec is 500:1 at 500kHz; both tubes make 1000:1.

(Just for fun I tried 20MHz. Atrocious with either tube. Don't throw out your Type G.)


It's a simple mod. Unless you're a purist or a stickler for specs, I say go for it.


To modify your Type W to use 12AU7:


1) Cut off XV214 pin 9 solder tail. For assembly convenience Tek ran a component lead through it.

This 8416 pin is internal shield but for 12AU7 it's the heater center tap and must be disconnected.

To reach the solder tail to cut it, I had to lift the grounded terminal next to the socket, with a skinny right-angle #1 Phillips.

This step is backward compatible.


2) Add 1200 ohms 2W across the V114-V214-V124 heater string. I hooked one end to the chassis end of R290 and, with a wire, extended the other to XV124 pin 4 . To pass shake test, add a tie point at the flying end of the resistor.


3) Adjust DC Level. I hit spec with R280 at minimum R, i.e. full CW. (Same as 8416.)


4) Adjust amplifier HF comp. I have not done this.


Dave Wise


My signal sources were HP 8640B and HP 8601A. Using an HP 436A/8482A power meter I confirmed less than 0.5dB variation from 1MHz to 35MHz.

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Dave Wise via groups.io <david_wise=phoenix.com@groups.io>
Sent: Tuesday, February 23, 2021 9:28 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Modifying W Plugin to use 6DJ8 Tubes

In post #108873 (https://groups.io/g/TekScopes/message/108873<https://groups.io/g/TekScopes/message/108873>), David Hess suggested wiring 6DJ8's in parallel and running them off 6.3VAC from pin 13-14.

Unfortunately, that's out. Pin 13-14 is elevated to +100V and that will exceed the heater to cathode voltage rating on V124.

To recap, today I see exactly two approaches.

One, reverse a transformer. Unless you get lucky and find one with 6V and 18V windings like the 1A4's 120-0481-00, you have to wind your own, or put up with wire sized for 110V, i.e., at least 20VA even though the load is less than 4W.

Two, run a switching power supply off +225V. I will investigate this if the 12AT7 sub fails.


Re: 547 HV Transformer: Bill Schell rewind failed

Chuck Harris <cfharris@...>
 

Hi David,

Thank you for the picture.

The 561B tranny shown is in black epoxy, which isn't usually
a problem, and has turret posts, which adds to my expense.

I will probably keep the tranny open frame, and use an FR4
terminal board to handle either eyelets, or turrets... likely
eyelets.

-Chuck Harris

David Holland wrote:

I directly emailed Chuck a picture of the 561B HV Transformer from my
B19xxx. (I hope he didn't mind.)

But I'll also freely admit it is a fairly late SN'd 561B.

David

On Fri, Mar 5, 2021 at 2:50 PM Chuck Harris <cfharris@erols.com> wrote:


Re: 547 HV Transformer: Bill Schell rewind failed

David Holland
 

I directly emailed Chuck a picture of the 561B HV Transformer from my
B19xxx. (I hope he didn't mind.)

But I'll also freely admit it is a fairly late SN'd 561B.

David

On Fri, Mar 5, 2021 at 2:50 PM Chuck Harris <cfharris@erols.com> wrote:

Hi Charles,

I would imagine so, but I don't have anything that shows
what the 561B transformer looked like, nor how it mounted.

The 561A is the old style as was used in the 545 etal before
epoxy was used. It has micarta boards that fit into the
core window to insulate the filament winding from the core.

One of the family used a similar transformer, but stuffed it
into a drawn aluminum can with clear silicone RTV to insulate.

That might be more of a challenge, due to the wires all coming
out through the can's opening... High voltage, low voltage all
mingled together.

-Chuck Harris


Charles wrote:
Does that include the 561B? I need one, once you start winding again :)










Re: 547 HV Transformer: Bill Schell rewind failed

Chuck Harris <cfharris@...>
 

Hi Charles,

I would imagine so, but I don't have anything that shows
what the 561B transformer looked like, nor how it mounted.

The 561A is the old style as was used in the 545 etal before
epoxy was used. It has micarta boards that fit into the
core window to insulate the filament winding from the core.

One of the family used a similar transformer, but stuffed it
into a drawn aluminum can with clear silicone RTV to insulate.

That might be more of a challenge, due to the wires all coming
out through the can's opening... High voltage, low voltage all
mingled together.

-Chuck Harris


Charles wrote:

Does that include the 561B? I need one, once you start winding again :)






Re: 547 HV Transformer: Bill Schell rewind failed

 

Does that include the 561B? I need one, once you start winding again :)


Re: 547 HV Transformer: Bill Schell rewind failed

Chuck Harris <cfharris@...>
 

Hi Bernd,

Since the winding pattern is entirely under computer
control, I can wind anything that goes on the cardboard
former that tektronix used.

The only other issues with models other than the 547/545B,
is termination. Small wires are easy, lugs or pins are
harder.

My highest priorities are 545B/547, 647A/B, and 576.

Anything that uses the same mounting as the 545B/547/647A/B
transformers should come essentially for free.

-Chuck Harris

widgethunter via groups.io wrote:

Chuck;Am pleased to see that your ambitious undertaking is coming to fruition.I know that many Tek owners, who weren't so fortunate as to be able to keep their scopes working, are eagerly awaiting the day.We talked about this in terms of a side business, initially.If you are able to rewind other models, as well, you may be busy enough to get there, after all these years.Bernd



-----Original Message-----
From: Chuck Harris <cfharris@erols.com>
To: TekScopes@groups.io
Sent: Thu, Mar 4, 2021 4:45 pm
Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed

Hi Bernd,

All indications are that my new machine is going to
do an even better job than the best I could do with
the old manual machine.

As an example, I was able to get 2/3 of the way to a
full wind without using the rosin/alcohol mixture that
I developed to enhance the wire's friction...

Using the rosin/alcohol, I am there already.

And, I will be using beeswax.

I'm glad to hear the prototype is still soldiering
on.  Soon, I may be able to get you the winds I promised
oh so long ago...

-Chuck Harris

widgethunter via groups.io wrote:
My memory certainly hasn't improved with age.Not much else seems to have, either...But, the beeswax thing I'd be willing to put money on - fwiw.
Incidentally, I still have not installed the 2nd wax xfrmr you made for me, but the 1st prototype continues to perform flawlessly.Bernd



-----Original Message-----
From: Chuck Harris <cfharris@erols.com>
To: TekScopes@groups.io
Sent: Thu, Mar 4, 2021 4:05 pm
Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed

Hi Bernd,

I guess the biggest indicator of a scatter wind would be
the presence of a spool.  The universal wind doesn't require
any additional support.

In addition to talking to you, I talked to Deane Kidd, and
Deane talked about Bill using beeswax, like tektronix did in
the earlier transformers.

But, like you, it has been a looong time, and I don't think
our memories are getting any better.

-Chuck Harris

widgethunter via groups.io wrote:
Hi Chuck;Assumed scatter because of the larger size of Schell rewinds.It has been a looong time, but I think I'd remember if he'd said anything about epoxy...B



-----Original Message-----
From: Chuck Harris <cfharris@erols.com>
To: TekScopes@groups.io
Sent: Wed, Mar 3, 2021 9:57 am
Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed

Hi Bernd,

There have been several discussions about Bill's transformers of
late, and there is a picture on the group, that looks very much
like epoxy varnish, or some other non wax compound.

However, it is most definitely not scatter wound.  It is a nice
looking, self supporting, universal wind.

Bill didn't use an outer tape covering on this transformer.  The
naked winding is right there for you to see.

-Chuck Harris



















Re: Looking to ID a diode in a 1S1 sampling plug-in

Jonathan Pyle
 

Hi Sean,

Since you have a very early model 1S1, you might be interested in checking out whether your vertical board uses "pellet parts." See:

https://groups.io/g/TekScopes/topic/74982135#168407
https://groups.io/g/TekScopes/topic/75088746#168713

The serial number of my 1S1 is in the 700s and I see regular discrete components on the underside of the vertical board, as in the picture snapdiode took, which suggests that maybe Tektronix gave up on the "pellet parts" idea. (Even in the photo on page 4-8 of the manual it looks like R4 and R5 are mounted in the normal fashion.)

In trying to figure out the history of embedding discrete components under the traces in a PCB, I found a site saying it was still considered a "cutting edge" practice in 2014. So if Tektronix was doing it back in 1965 I wonder if they were one of the first.


Re: To Beeswax or not to Beeswax: that is the question.

Roy Thistle
 

My first question would be, "Exactly, what is beeswax?"
--
Roy Thistle


To Beeswax or not to Beeswax: that is the question.

Roy Thistle
 

Hi All:
Yes, there are some threads about beeswax... and many more posts about beeswax, in other threads too... usually about using beeswax in/with transformers.
In this tread, I want us to try to get to the bottom of the topic.
I have a feeling, it'll be like herding a clowder... but here goes.
--
Roy Thistle


Re: Tek 492BP how to save via GPIB to a PC

 

Got it fixed.


Re: Replacing Variable Vertical Attenuator Shaft

SCMenasian
 

Several years ago, I had some fiberglass rod in my junk collection. I think it was a part of a fishing rod. I used it for just this sort of thing and I think the diameter was close to 1/8". Also, if Amazon has delrin, I would prefer it to nylon.


Re: 547 HV Transformer: Bill Schell rewind failed

widgethunter
 

Chuck;Am pleased to see that your ambitious undertaking is coming to fruition.I know that many Tek owners, who weren't so fortunate as to be able to keep their scopes working, are eagerly awaiting the day.We talked about this in terms of a side business, initially.If you are able to rewind other models, as well, you may be busy enough to get there, after all these years.Bernd

-----Original Message-----
From: Chuck Harris <cfharris@erols.com>
To: TekScopes@groups.io
Sent: Thu, Mar 4, 2021 4:45 pm
Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed

Hi Bernd,

All indications are that my new machine is going to
do an even better job than the best I could do with
the old manual machine.

As an example, I was able to get 2/3 of the way to a
full wind without using the rosin/alcohol mixture that
I developed to enhance the wire's friction...

Using the rosin/alcohol, I am there already.

And, I will be using beeswax.

I'm glad to hear the prototype is still soldiering
on.  Soon, I may be able to get you the winds I promised
oh so long ago...

-Chuck Harris

widgethunter via groups.io wrote:
My memory certainly hasn't improved with age.Not much else seems to have, either...But, the beeswax thing I'd be willing to put money on - fwiw.
Incidentally, I still have not installed the 2nd wax xfrmr you made for me, but the 1st prototype continues to perform flawlessly.Bernd



-----Original Message-----
From: Chuck Harris <cfharris@erols.com>
To: TekScopes@groups.io
Sent: Thu, Mar 4, 2021 4:05 pm
Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed

Hi Bernd,

I guess the biggest indicator of a scatter wind would be
the presence of a spool.  The universal wind doesn't require
any additional support.

In addition to talking to you, I talked to Deane Kidd, and
Deane talked about Bill using beeswax, like tektronix did in
the earlier transformers.

But, like you, it has been a looong time, and I don't think
our memories are getting any better.

-Chuck Harris

widgethunter via groups.io wrote:
Hi Chuck;Assumed scatter because of the larger size of Schell rewinds.It has been a looong time, but I think I'd remember if he'd said anything about epoxy...B



-----Original Message-----
From: Chuck Harris <cfharris@erols.com>
To: TekScopes@groups.io
Sent: Wed, Mar 3, 2021 9:57 am
Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed

Hi Bernd,

There have been several discussions about Bill's transformers of
late, and there is a picture on the group, that looks very much
like epoxy varnish, or some other non wax compound.

However, it is most definitely not scatter wound.  It is a nice
looking, self supporting, universal wind.

Bill didn't use an outer tape covering on this transformer.  The
naked winding is right there for you to see.

-Chuck Harris










Re: Tektronix 2230 - no readout

oneenaht@...
 

Hi Bert,

I also have a Salae clone. Used it once to reverse engineer a display of a VHF radio, a Motorola MC Micro.
The story is on my blog (in Dutch): https://www.blogger.com/blog/post/edit/6705259174852751554/8643191421757783562
As there are not many countries where they speak Dutch: I live in Belgium, Flanders, not so far from the Northsea.
Aha Michigan, so Dr. Pol is one of you neighbours ;-) Your a bit to far away to visit...

I have been doing some more research today.
Sorry for all the Tek lovers, but this scope is not very service friendy. You have to unscrew several things, isolate the PCB's with cardboard and/or newspaper to be able to measure on certain boards and be lucky not to provoke shorts.
BTW:I found out you can test the scope without the GPIB option if you put P9107 (located 5B in schematic 10) in the other position, that way the reset from the GPIB board is inactive.
One thing I did not check previously: the 5V ref A and B, as well as the +5V on the vector and I/O board are OK.
Also checked point by point the flat cable between these boards, as well as the ribbon cable to the motherboard.
There is no activity on the X and Y vector pins going to the multiplexer 4053.
I am a bit running out of idea's. Do you have any more?

greetings, Harry


Re: Beeswax in Transformers

Chuck Harris <cfharris@...>
 

Hi Barry,

It isn't a coating, but rather an impregnation. The beeswax, or
epoxy is drawn into the spaces between the wires to add additional
insulation, and to keep them from moving.

If you don't add an impregnant, corona effects may eventually break
down the insulation... in my experience, *will*...

-Chuck Harris

n4buq wrote:

I'm curious why transformers (in particular, this transformer) benefit from a coating - beeswax or otherwise. Is it to damp sympathetic vibration at the operating frequency/frequencies?

Thanks,
Barry - N4BUQ






Re: Replacing Variable Vertical Attenuator Shaft

John Bennett
 

Dick,
I don't have advice for 485 access, but I found that 1/8" Nylon 6/6 Round Rod (available in 5' lengths from Amazon at https://www.amazon.com/gp/product/B0070ZEW7K) did the trick for replacing the shaft (in a 2465B). I used 7/16" OD tygon tubing drilled and tapped for set screws as my coupler.
John, AE0AM


Re: 547 HV Transformer: Bill Schell rewind failed

Chuck Harris <cfharris@...>
 

Hi Tom,

Moisture is definitely a factor, but the problem is not
really reversible.

Yes, you can gain an improvement by cooking, or vacuum
drying, a tektronix epoxy transformer, but it will return
to its failed condition in a much shorter time than it did
originally.

My guess is the brownish/red coloration to the epoxy is
because tektronix added a fire retardant to the epoxy...
most everyone did back then, resulting in a lot of failures
over the years. One place you hear quite a lot about it is
in red doorknob style epoxy molded HV capacitors.

Time has showed that the bromine, and other fire retardants,
have failed in a variety of ways everywhere industry used
them.

Fire retardant plywood loses its structural integrity after
about 10 years, causing roofs to collapse. Fire retardant
added to plastic computer and monitor enclosures caused
them to turn brown over time... and let's not forget about
tris added to kid's pajamas!

-Chuck Harris



fiftythreebuick wrote:

Hi Dave-

I'm sorry to hear that you're having trouble with that HV XFMR....

I did a lot of testing and evaluation for Bill Schell over the years and I don't remember him every testing a transformer with any epoxy in it at all. He and I both felt that we oughta get as far away from that as possible. He first wound them without sealing them and I have never had one of those fail. Then when he started treating them with beeswax and a vacuum chamber, it seemed like he had found quite a good process. So far, I have never had one of his fail, of any description.

Just saw your later post and I'm glad that yours is improving! A friend of mine has restored an original xfmr by putting it in a vacuum chamber and keeping it in a deep vacuum for a while. Don't remember how long he left it in there.

I hope yours comes out alright. It really does seem like the moisture is the major factor.

Tom






Beeswax in Transformers

n4buq
 

I'm curious why transformers (in particular, this transformer) benefit from a coating - beeswax or otherwise. Is it to damp sympathetic vibration at the operating frequency/frequencies?

Thanks,
Barry - N4BUQ


Re: Tek 492BP how to save via GPIB to a PC

 

Got the NI installed but I got another error now it said: ibert error no listener. I do have both switches talk only and listen only open in the 492BP. What can I do.


Re: Tektronix 2230 - no readout

Bert Haskins
 

On 3/5/2021 10:45 AM, oneenaht@gmail.com wrote:
Hi Bert,

thanks for reply.
strange coincidence: about a week before I got the 2230, I bought a digital scope (Hanmatek DOS1102,
I have a Hantek DSO5102P and several "pocket" scopes beyond my dozen+ Teks.
same as OWON) during an action at Ama***n, at almost half the normal price. I could not resist that bargain!
My purpose for it is to be able to see fast and slow things like I2C communication.
I use a saleae and/or one of it's ( many many ) clones for things like that.
My workhorse is a 20MHz Hameg HM205 or so, but unsuited for that.

Now for the 2230:
I have removed the GPIB option (+memory) to take a look fot loose connectors hidden behind the mounting plate and under de CRT.
Without this option, the scope looks to be working analog only, do you need to jumper some cables?
Anyhow, I found nothing suspicious.
Also, I tried the Kernel isolation, and looking at the pins of U9112 and U9114.
All looks similar as in the service manual, except for pins 16/17/18/19 of U9114. There is a nice pulsetrain, but not as displayed on figure 6-3.
It looks they are all the same, but no pins are shorted.
A thing I have never came across before: Have you ever experienced bad EPROMS
Not in any of my Tek scopes, but I have certainly improved my bank balance by restoring eproms in failed factory systems.

It's amazing how many things are still running on old vintage micros.

? Ans if so, where could I find hexdumps?
I checked for this in https://w140.com/tekwiki/wiki/2230 and didn't find any, maybe I should fix that.


best greetings, Harry
Where are you located?

I'm in west Michigan near the lake.

 Bert




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