bent neck CRT pins...

[Sparkey55]

Re: bent neck CRT pins...

I tried passing 5.6VDC with a LM317T regulator. Current started around 134mA but went down to 125mA and is still slowly going down, then again regular light bulbs do this too. I tested for 2 minutes....

Good test. did you see the heater glow? Hard to tell by looking from the side of crt may try looking at the end of neck where the pins come out.

Next test for heater to cathode short while filament is hot ( powered up). Be sure that the cathode is not connected internally to the filament pins. Measure for heater voltage across the filament and cathode. Their should not be any voltage showing if good. Again no connection to the scope wiring for this test.

[Sparkey55]

Re: bent neck CRT pins...

If the above test passes then the next test would be to see if the focus voltage holds up under the crt connection. any flashing or arching inside the tube from the focus terminal would mean the tube has some air inside. Using an external power source for the focus would be preferred, if not then connect the HVPS. Do not connect the HV anode to the crt while doing this test.

[eccerr0r]

Re: bent neck CRT pins...

I'd not really say that test passes, how long should it take before it settles down? It kept on going down for those 2 minutes. An incandescent bulb, granted it burns hotter, settles much faster.

I also measured ~16.2 ohms after heating 2 minutes and then letting it cool back down. Compare that to the previous reading I had, this is not a good sign.

I could not see the heater glow, the pins area is actually opaque. The fill nipple should be there but it's probably underneath that opaque plastic cap...

---

Turned on heater again and measured K to heater resistance... it's still open.

Current now dropped to 122 mA.

Very bad.

[stj]

Re: bent neck CRT pins...

if it's not open, i wouldnt worry.

[Sparkey55]

Re: bent neck CRT pins...

I'd not really say that test passes, how long should it take before it settles down? It kept on going down for those 2 minutes. An incandescent bulb, granted it burns hotter, settles much faster.

I also measured ~16.2 ohms after heating 2 minutes and then letting it cool back down. Compare that to the previous reading I had, this is not a good sign.

I could not see the heater glow, the pins area is actually opaque. The fill nipple should be there but it's probably underneath that opaque plastic cap...

---

Turned on heater again and measured K to heater resistance... it's still open.

Current now dropped to 122 mA.

Very bad.

Cathode to heater resistance should be very high value; if not infinity; cold or warm crt filament. Cathode to heater short would load the heater winding on the ferite core. The question is the heater winding isolated from the HV winding or is it connected internally to the HV coil? Most heater windings consist of one or two turns on the lower half of the flyback core using thick HV rated cable. Either way does not matter if a short from the filament to any other circuit exsists it would load down the flyback and lower other voltages or stop oscillation entirely.

If all of these tests are good then the HV anode of the crt could be leaking voltage to ground by virtue of bad crt with just enough air to conduct the high voltage anode thru the guns metal structure to ground. Another crt known to be good would be helpful here.
Any white looking getter in the tube is a bad sign. It means that air has gotten inside the crt.

[eccerr0r]

Re: bent neck CRT pins...

Yeah, I think I ended up with that conclusion a few posts ago, and just wanted to entertain a few questions. I guess the recent experiments seem to have simply reiterated the conclusion. I think at this point it's just a cleanup and figure what's salvageable and what's broken beyond repair.

Anyway yes, the heater winding is separate from the HV winding - they're isolated windings. The heater winding is on its own bobbin. I would imagine a H-K short wouldn't do much except put a bit of noise on the cathode, which may or may not affect things much.

I just hope that since this uses electrostatic deflection, what other collateral damage could have happened with air in the tube, damaged multiplier, damaged deflection circuitry,... and whether or not it's worth to continue on with this project buying another tube/psu.

[redwire]

Re: bent neck CRT pins...

I found Tektronic 2465 uses CRT 154-0850-00, P31 phosphor; Same CRT in 2430, 2445
Photos of that scope's CRT here and others show getter on the neck.

[stj]

Re: bent neck CRT pins...

what's the spec on this scope?

[eccerr0r]

Re: bent neck CRT pins...

Yeah that picture seemingly looks better than the status of mine right now. Again, this is a guess from looking at the spot at an extreme angle (there's a opaque metal shield that surrounds the tube.
I've found that the 2430 and 2440 though similar will need mods to get it to "fit". Perhaps the screen that was placed in this scope was from a 2430/2440 initially (or the tube was inserted sloppily into the shield). I think the 2430/2440 method of hookup is "better" but I'd have to retrofit them to use them on the 2445/2465 which should match.

[TechGeek]

Re: bent neck CRT pins...

Please REMOVE THE SHIELD and run the heater test!!!!!!!!!!!!!!!!!!!!!!! That would really help. And the heater may be good, you may not be able to see it because of the extreme viewing angles.

[eccerr0r]

Re: bent neck CRT pins...

Don't worry about the heater. Based on electrical observations, it's clear that it's slowly killing itself with air in the tube. The question is whether I should burn money on fixing this (new tube and new psu) or buy a LCD scope...

Or both...

Or neither (my ol' dual trace 20MHz scope is still working...)

[TechGeek]

Re: bent neck CRT pins...

If the tube's slowly toasting itself, hit the anode with mains AC, neutral connected to everything at the pin base. Watch the chaos. >

[eccerr0r]

Re: bent neck CRT pins...

Eh... what would that do? The anode is virtually open at line voltages, just looks like a very small capacitor.

[eccerr0r]

Re: bent neck CRT pins...

At this point I think the only dead part is the CRT. The HV PSU I think is still alive... I guess the tube will be the only piece on my shopping list if I end up deciding to get it...

I suppose most of the current that flows through a CRT should be from cathode to anode. If any current goes from cathode to focus or screen grid, something is wrong. The PSU may just be shorting out and shutting down because of these issues due to the air.

At least I'm a bit confused now, I thought I tried disconnecting both the end socket and the anode and the PSU shorted out, but the last test without those connected, it seems to be OK now - no short... Perhaps I forgot to test with both connectors disconnected that time I still saw a short.

Using my Eico with the 5KV range I measured the cathode voltage while not connected to the faulty CRT... -1900 volts on the dot! Now I have no way to measure the anode voltage but assume that since it's not actually shorting out now and I felt static before, this is also probably OK.

[stj]

Re: bent neck CRT pins...

this site may give you an idea of tube prices
http://www.askjanfirst.com/eindex.htm

[eccerr0r]

Re: bent neck CRT pins...

I figure all the tubes now will be used, no more NOS tubes any more. Now the other issue is that these things are extremely fragile...

[TechGeek]

Re: bent neck CRT pins...

Take line and neutral and put those on the pin base. Instant chaos.

[eccerr0r]

Re: bent neck CRT pins...

It's dead, Jim.

[TechGeek]

Re: bent neck CRT pins...

You did it!?

[eccerr0r]

Re: bent neck CRT pins...

I guess I was wrong about the shield... the shield is part of the chassis; had to remove the tube from the chassis to separate it from the shield.

Now for a replacement...