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Hi Tam,

I was musing about replicating them more than seeking replacement knobs. I am in need of knobs for some restoration projects but they are months (or even years) away from starting.

Thanks all the same,

John

Apologies... two missing details... I couldn't see any obvious damage under the HV cover, (no charring or whatever), and I don't clearly remember if it's +100 volts or -100 volts that I measured on the -1850 supply for the lower beam.

Hey all,

I just acquired a 556, but it's having some fairly serious issues. Before powering it on, I checked all the supply rails for shorts with a meter, and checked the power plug for shorts as well. I then proceeded to slowly turn the scope on with a variac. Once at full voltage for a few moments, I heard a bang and smelled that something had gone wrong. Surprisingly, the main rails are all healthy (350,225,100,-150). The high voltage on the upper beam is at it's nominal voltage, but the high voltage on the lower beam is around 100 volts. Boooo.

Okay... so now I wonder... if the post-deflection acceleration (supplied by the lower beam supply only) is dead, will the CRT still light? What are the chances that I blew up the HV transformer itself and will need to wind a new one? What components are most likely to have exploded in that area?

Evan

I would say go with the X/Y capacitors and pick ones that have the highest AC and DC voltages you can find which will fit physically. Be aware of any special local and national electric codes for equipment where you live and try to comply with the latest standards where you can. There is more to snubber applications than one might think at first. The encapsulation materials used are important from the aspect of fire and smoke hazards. The same is true for AC power switch assemblies in electronic equipment. Older models may have materials that do not meet more modern standards, but of course many of them are unique to a given product at the time of manufacture. Some go the route of using power strips that can turn units on and off externally to extend the life of the internal OEM switches.
Joe

I have 2 original manuals 5A15N Amp and 5B10N Timebase. (so sad I don't have that mainframe anymore!)
Free - but postage to O/S will be about $20A
contact hugh@...

"I have now seen two 2465 PCB blocks with a burnt-out on/off switch."

"The damage is caused by the arcing across the now-separating terminals, when the machine is switched OFF."

No manual and not right now because I am AGAIN (GRR) downloading a rather large file and don't want to slow it down. Yes I got highspeed internet but it is running through about 100 feet of bookie phone cable.

Enough on that, your problem is not inductive kick. Reason ? Because that unit uses an SMPS. The AC does not go to a coil, it goes to a bridge rectifier, full wave bridge in 240 and half wave doubler in 120. How do I know that ? I had to work on one. In fact I am going to start a thread about exactly why, instead of hijacking yours.

There is a small tektronix knob on thingiverse, I haven't tried printing it
yet, but plan too as I'm in need of a knob for a 2213...

Getting the color right is always the key, but 3d prints can be painted and
the paint stays on pretty good, also I have a pretty nice beige color of
polycarbonate, I use it to make replacement HP switch covers, looks pretty
good.

--
Keith Refior
keith@...

3.

How can there be a final verdict when the problem is
not yet defined?

-Chuck Harris

M Yachad wrote:

An earler post asked about using snubbers to save the contacts of switches & relays.
Many of the same issues apply to both relay & switch contacts.

I looked into factors reducing relay contact life a while ago & there are a couple of Application Notes that I have saved.
An Application Note "Maximizing the Life Span of Your Relays" discusses relay selection, contact life & snubber systems.
This App Note has been arround for some time & a recent Keysight version is at:

An earlier Agilent version can be found at:


One factor that can dramatically reduce the life of relay contacts is the common Back EMF "Flyback" protection diode fitted across the coil.
The diode slows the relay operation making arcing far worse & that destroys the contacts.
The App Note "Coil Suppression Can Reduce Relay Life" recommends the simple addition of a Zener Diode in series with the usual diode to maximise contact life.


An article "Back EMF and snubber" has a nice short discussion.
He has a section that I find very interesting: "I have seen the diode replaced with MOV (Metal Oxide Varistor) or a bipolar TVS (Transient Voltage Suppressor) but I am not fond of that since both types of devices seem to age over multiple breakdowns and finally stop working. In the case of the MOV it shorts across its leads when the back EMF exceeds its breakdown voltage, so it is no better than the diode. The TVS keeps a fixed voltage on breakdown and the time the current flows for is reduced."


** SAFETY WARNING **

This last comment leads to a safety warning.

I once worked on a piece of equipment damaged by a close lightning strike.
I turned the item on & off a few times & then opened it up to do some voltage probing.
It had been on for a short time & I hadn't touched probes to the circuit when the Surge Suppressor / Varistor / VDR exploded & embedded shrapnel in my face.
Some of it had to be dug out.
I had not not touched the circuit with my probes so the Surge Suppressor must have been just about ready to fail - a direct short circuit I guess.

I had noticed that SOME manufacturers cover the Surge Suppressor with heatshrink or even fibreglass sleeving but didn't think anything about it.
After that incident I always fitted heatshrink (a thicker type) to every Surge Suppressor that wasn't already covered before I powered up with covers off.

I did see one piece of equipment where part of an exploded Surge Suppressor penetrated a large electrolytic capacitor beside it but the heatshrink appeared to have stopped any major damage to a couple of other items I saw with exploded Surge Suppressors.

It is known that Surge Suppressors eventually fail & some of them have internal fuses but it appears that some do not have internal fuses or that protection is not always effective.
Take care & protect yourself against a possible shrapnel risk.

Regards,
Brian.

Hello John,
could you send us a few photos or even lend us such a knob? I am pretty sure Sir OConnell can do something for you!

Tam
---
With best regards
Tam HANNA (emailing on a BlackBerry PRIV)

Enjoy electronics? Join 11k other followers by visiting the Crazy Electronics Lab at

So what's the final verdict?
1 or 2?

Mounted across the switch terminals, EITHER

1. A 10nF DC rated capacitor up to about 3000VDC

OR

2. A 10nF AC Class X/Y capacitor rated to about 500VAC

??

After about two and a half years I was wondering if you have made any progress.

Well, it's all good, as they say.? Nice to learn a new phrase.
Thanks!
Jim


Sent from my Verizon, Samsung Galaxy smartphone

On 07/31/2018 03:31 PM, Jim Ford wrote:

Tam, I take it you mean EDM,

No, FDM corresponds to the 3D printing he mentioned -- Fused deposition modeling == FDM == makerbot, etc.

Tam, I take it you mean EDM, Electric Discharge Machining.? A way to fabricate items not easily made using conventional milling and drilling.? I only know a very little bit about EDM because I worked at a wire bonder manufacturer for a few years.
Jim


Sent from my Verizon, Samsung Galaxy smartphone

Esteemed Quorum,

please forgive me for "soliciting my wares" - but I recently met an expert on FDM and CNC machining. He found an interesting space to spend spare time in my barely used heavy machine room.


Now, we wanted to ask what type of parts would interesting. We live in Slovakia, our time is cheap: if you make it worth our while, we will gladly help.


We can immediately 3D print buttons and can probably start machining small aluminum blades in a week. So, challenge us - a fully paid licence of AutoCad is on hand!


With compliments

Tam

Thank you, gentlemen;

From this discussion, I now have a much greater appreciation for my venerable Pace unsoldering system. You have provided some additional thoughts for maintenance procedures. The fellow I bought it from could not locate the manual for it, so I have just been going from my observations and what I had learned when at the NASA Reliable Electrical Connections School at the George C. Marshall Space Flight Center in Huntsville, Alabama, many years back.

Ralph, Latte Land, Washington

Just curious, has anyone ever tried 3D printing replacement knobs? My Tek equipment is all intact but I could use a few HP knobs as well as a couple of Genrad. That might be a nice little sideline for someone to help justify the cost of a good quality printer. Getting the color bang on would be an issue and a 4th axis to rotate the knob as it's being made might be necessary for really good authenticity. Still, worth exploring?

MOV's are a rather blunt instrument. They have two
voltages that are important, the first is their sustained
voltage, and the second is their transient voltage.

The sustained voltage must be higher than the highest
sustained voltage that could be applied (with current),
and the transient voltage is the maximum transient that
can pass through.

A 120V MOV could be expected to allow a KV transient
to pass.

MOV's are also a consumable device. each transient chips
away at the container that holds the magic smoke inside of
their packages. Enough, and big enough transients, and
the magic smoke will be released.

A snubber can be carefully crafted to allow the back EMF
to be snubbed to any value you wish. The only down side
is the more the back EMF is snubbed, the more power is
eaten by the snubber's resistor, and wasted.

-Chuck Harris

Mark wrote:

If you check my original post, you will see I used NTC.
my later use of PTC was a typo on my part.

Capacitors behave as short circuits to transient pulses.
Because the snubber capacitor is there, the back EMF
voltage never rises to the potential it would were it absent.

The capacitor voltage rating should be about double the
quiescent voltage it could achieve. In the case of a
snubber for 120V, 2 x 1.414 x mains rms voltage would suffice.

-Chuck Harris

M Yachad wrote: