Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Dec Fri 15, 2017 1:05 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 187 posts ]  Go to page Previous  1 ... 6, 7, 8, 9, 10  Next
Author Message
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sat 23, 2015 1:19 am 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
I changed the "vintage" BNC jack that the previous owner added. I found the connection to the jack below the BNC was broken. With no attenuator, it's still picking up stray voltage.

Here's 455 Khz just after bringing the scope back online. In other words cold. Focus is slightly right of mid scale. A little retrace.

Image

This is after it warmed up, maybe 10 minutes later. 3.3kHz and no retrace. Focus is max'd out

Image

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sat 23, 2015 1:43 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
How many DC voltmeters can you muster? You might try monitoring all the CRT pins from a cold start and watch for drift.


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sat 23, 2015 2:12 am 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
Alan Douglas wrote:
How many DC voltmeters can you muster? You might try monitoring all the CRT pins from a cold start and watch for drift.


Too many :D More meters than I have bench space, but I have a small bench. Specifically I have I have 6 or 7 but I believe only 3 or 4 have been recapped and calibrated.

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sat 23, 2015 10:04 pm 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
Alan Douglas wrote:
How many DC voltmeters can you muster? You might try monitoring all the CRT pins from a cold start and watch for drift.


Things just got interesting. I started testing various points the brute force way. Ie put the lead on when it's cold, focus the trace (1VP/P from the scope), and take an initial and final reading, log it on the sheet you see below, and turn it off. When it's cool, move the lead to a new point. The big red circle is where I thought the problem would be and it wasn't.

See the small red dot on the line from Pin 9 of 1V2 to R60? That was my next test point. I tried to take a "cheater" reading when the scope was still warm and the meter was pulsing. It varied from -200 to -400 VDC with about a 500ms period (eyeball freq meter). Very odd. Odd enough that I put a post about it down in the Tube forum.

After I typed up the Tube forum post I decided to check it again. The scope had cooled significantly. When I turned the scope on the meter was immediately slammed to the peg so I cut the scope off real quick. My Eico 249 only goes to 1500 VDC. I need to see what my Simpson 260 goes to and try that but it's not a VTVM.

Image

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sat 23, 2015 10:31 pm 
Member

Joined: Jun Sat 09, 2007 8:14 am
Posts: 3014
Location: Florida
Whatever is going on there the voltage should obviously not be hopping around. There are only a few parts involved, one of which is the power transformer. A breakdown of the CRT filament winding could do all sorts of weird things, none good. Before condemning the transformer I'd be really sure the other associated parts are good and that everything is wired correctly.

RRM


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sat 23, 2015 10:53 pm 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
Retired Radio Man wrote:
Whatever is going on there the voltage should obviously not be hopping around. There are only a few parts involved, one of which is the power transformer. A breakdown of the CRT filament winding could do all sorts of weird things, none good. Before condemning the transformer I'd be really sure the other associated parts are good and that everything is wired correctly.

RRM



The power transformer is solid at 1380 VAC (measured with a Fluke DMM). I'm letting it warm up again. Initially the rectifier output was 1,460 VDC measured with a VTVM. It's below 1300 VDC now. The focus control is almost at max.

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sat 23, 2015 11:26 pm 
Member

Joined: Jun Sat 09, 2007 8:14 am
Posts: 3014
Location: Florida
The CRT filament winding is connected to the HV. A breakdown in it's insulation gives a path to ground or one of the other windings. Let's hope this isn't the problem but it could explain the temperature effects you are seeing.

RRM


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sat 23, 2015 11:44 pm 
Member
User avatar

Joined: Apr Thu 25, 2013 9:24 am
Posts: 45
Location: South Australia
If your scope has a fault when it is hot try some pressure pack cold in the
suspected area.I had a similar problem many many yeas ago, found out it
was a heat sensitive dry joint on a Cossor scope . Cool the solder joint
fault was gone heated the solder joint with a (hair dryer) Heat gun now
fault returns.
The pressure pack cold I use was call Freeze Spray by Dick Smith here in Australia

_________________
Hello my name is Crazzzymick
I keep Buying test equipment
I have a electronic problem
I NEED HELP


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sat 23, 2015 11:47 pm 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
Retired Radio Man wrote:
The CRT filament winding is connected to the HV. A breakdown in it's insulation gives a path to ground or one of the other windings. Let's hope this isn't the problem but it could explain the temperature effects you are seeing.

RRM


Yessir, I thought it was odd that the HV from the 1V2 and the filament winding "mixed" at the 5UP1 but that's how it's drawn.

It's been running for a while and the rectifier output is down to 1340 VDC from a cold start of 1460 VDC.

Also, the voltage pulses that I saw DID NOT come from the 1V2. I misread a resistor... or saw what I wanted to, which I guess is the same. My guess is that the rectifier is doing it's job. Not sure about the 120VDC drop after things warm up though.

crazzzymick wrote:
If your scope has a fault when it is hot try some pressure pack cold in the
suspected area.I had a similar problem many many yeas ago, found out it
was a heat sensitive dry joint on a Cossor scope . Cool the solder joint
fault was gone heated the solder joint with a (hair dryer) Heat gun now
fault returns.
The pressure pack cold I use was call Freeze Spray by Dick Smith here in Australia


I've used an upside down can of air to try to find a bad resistor.

I'm starting wonder if I have yet another wiring error... time to look over some pictures.

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sat 23, 2015 11:56 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 17978
Location: Warner Robins, GA
The reason the HV is on the CRT heater is so the maximum heater cathode voltage is not exceeded.


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sun 24, 2015 12:45 am 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
Tube Radio wrote:
The reason the HV is on the CRT heater is so the maximum heater cathode voltage is not exceeded.



Wanna know what happens when you don't wire it that way? Read the last 1/2 of this thread. :oops:

Somewhere out there someone is going to read this post and say THANK GOD! He finally fixed that thing! :mrgreen:

So... if you look at the schematic, there is a resistor between pin 1 and pin 2 of the CRT. The high voltage comes to pin 1 as does one of the filament wires. There is also a wire from pin 2 to the Z-axis connection (via a cap that's on the circuit board).

I had the resistor inline with the HV and pin 1 and no HV on pin 2. I am absolutely impressed that Knight was able to build something that survived my mistakes. Focus works perfectly. Intensity works perfectly. Ya just gotta wire things right.

HV is higher than I can read with the Eico.

She's smiling. This is the built in 1V P/P but I've also put 455kHz Sine, square, and sawtooth waves in and they looked fine (considering). Higher frequencies cause a little bit of retrace but that's fine with me.

Image

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sun 24, 2015 2:11 am 
Member
User avatar

Joined: Dec Sun 21, 2014 6:37 am
Posts: 1269
Location: Portland, TN, USA
I LOVE stories with a happy ending! :D

Just look at all you - and we - would not have learned if you hadn't endured and overcome the obstacles along the way. Even self-inflicted challenges can be a learning experience, and the older I get the more I'm having of this kind of experiences. Some days I REALLY don't like working with me. :lol:

Great job all around, Sir!

_________________
Chuck K4CCW
Want Hallicrafters S-76 with good cosmetics; Can fix electronics issues.


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sun 24, 2015 2:19 am 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
Hey Chuck :) I figure that some day someone will overhaul one of these, read this thread, and think to themselves- I need to triple check my wiring :)

It's really nice to see it working again. Especially considering that it went from basket case to working

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sun 24, 2015 4:22 am 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
For anyone that wonders why I put so much effort into this thing (in addition to fixing my screwups :D ) here's the deal. I'm pretty sure I talked about this in the early part of this thread but it's probably lost in all of the fluff...

I bought this scope years ago. I'm not sure exactly how long ago. My mother was alive, my boys were in high school. The oldest is going to be 32 this year so 15 - 16 years ago? Something like that. I had just got my ticket and a fellow Ham asked if I would look at the "estate" of a friend of his. The SK's daughter was clearing out her dad's place and she didn't know what to do with the stuff. I didn't either to be honest. I bought it, just because I couldn't tell her that her dad's accumulations weren't worth fooling with. I stuck it all in boxes and pretty much forgot about it. In between then and now my mom got sick, we moved close to her to help take care of her, a few months later she passed (cancer is an evil disease), and we moved back here. My boys did most of the heavy moving and they piled the boxes down in the barn. Fast forward to today and my interest in all things tube rekindled and I started hauling things up from the barn, found this site, and dove in full steam ahead.

I feel like I should get as much as the SK's items back up and running. I would want that... As I gain experience I'll tackle some of the more complicated stuff. Miss Piggy is probably the worst of the lot but it's been fun. We'll see how it goes with the rest of it...

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sun 24, 2015 4:35 am 
Member

Joined: Jun Sat 09, 2007 8:14 am
Posts: 3014
Location: Florida
Mike6158 wrote:
Hey Chuck :) I figure that some day someone will overhaul one of these, read this thread, and think to themselves- I need to triple check my wiring :)

It's really nice to see it working again. Especially considering that it went from basket case to working


Along the lines of helping others, you might consider contributing the schematic to BAMA.

Glad you got it working.

RRM


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sun 24, 2015 4:40 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 17978
Location: Warner Robins, GA
Very nice.

Now you have a scope you can use on tube circuitry without worrying about damaging your better scopes.

I'd suggest trying the scope clock just to see how the display looks. If it is fine then that is good. If it is not let me know and I'll send you the firmware I was given which allows for an adjustible rerfresh rate, although that requires the serial connection to be used. When you get to using the clock board, if you need help let me know. Will be a couple weeks though as I need to replace the DAC on mine.

Word of caution. Don't short the outputs to ground. Will damage the DAC.

If you plan on connecting this to different things it may be wise to use a dual OP-AMP with a gain of one wired as a buffer. That way there won't be any damage to the clock board if the outputs are shorted.


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sun 24, 2015 4:59 pm 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
Tube Radio wrote:
Very nice.

Now you have a scope you can use on tube circuitry without worrying about damaging your better scopes.

I'd suggest trying the scope clock just to see how the display looks. If it is fine then that is good. If it is not let me know and I'll send you the firmware I was given which allows for an adjustible rerfresh rate, although that requires the serial connection to be used. When you get to using the clock board, if you need help let me know. Will be a couple weeks though as I need to replace the DAC on mine.

Word of caution. Don't short the outputs to ground. Will damage the DAC.

If you plan on connecting this to different things it may be wise to use a dual OP-AMP with a gain of one wired as a buffer. That way there won't be any damage to the clock board if the outputs are shorted.


The first thing I need to say is that I appreciate all of the help that you and others have given me on this project. The suggestions that were made prodded me to keep working on it.

I plan to try the clock board. Today or tomorrow I hope. Sounds odd but I didn't think about using it on tube radios. I suppose it would work pretty good for that wouldn't it.

Thanks for the heads up. I'm pretty sure I have a few dual op amps laying around. I'll put one of them to work.

Thanks again!

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sun 24, 2015 6:33 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 17978
Location: Warner Robins, GA
You're welcome.

If you do get a dual op amp to work properly will you PM me a schematic? I'd like to do the same to mine.

Best to try the op amp idea on a known good scope that properly displays the clock first.

I have two DuMont scopes that I use on vacuum tube equipment mainly when checking amplifier stages or anything with B+ over 100Vdc as I can connect the scope directly to the HV without worrying about damaging anything.


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Mon 25, 2015 3:16 am 
Member
User avatar

Joined: Mar Tue 31, 2015 3:59 am
Posts: 40
What a great thread! Glad to see your success Mike! I have a real soft spot for anything with a CRT in it (as you well know) There is something about using old equipment, that just makes the repair better. (well, feel better anyways) :D

Take care
Paul

_________________
My youtube channel : https://youtu.be/qqmegXoB7lA


Top
 Profile  
 
 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: Aug Wed 24, 2016 3:50 pm 
New Member

Joined: Aug Wed 24, 2016 6:25 am
Posts: 3
Retired Radio Man wrote:

Along the lines of helping others, you might consider contributing the schematic to BAMA.

Glad you got it working.

RRM


I could have certainly used a copy. But good news, I got my own and scanned it in for the next generation. I've submitted it to BAMA, but it looks like its updates are less frequent. Hopefully the full manual will be available, but until then please be satisfied with the schematic.

I have also submitted the manual to K04BB and EBAMAN per another users suggestion.

Image

Manual Supplement Information Changes (not reflected in schematic)
R-28 = 6.7K 5%
R-44 = 8.2K 1-watt
R-48 = 100K 5%
R-69 = 2.3 meg
C-17 = 30 MMFD Mica Capacitor
C-18 = 400 MMFD Mica Capacitor
C-19 = 5000 MMFD (.005 MFD) Mylar Capacitor
C-20 = .05 MFD Mylar Capacitor
C-21 = .33 MFD Mylar Capacitor

Paul, funny running into you here as well! Your recent YouTube restoration is the reason I had to go hunting for a schematic in the first place.


Last edited by KG630Brandon on Aug Thu 25, 2016 4:29 pm, edited 1 time in total.

Top
 Profile  
 
Post New Topic Post Reply  [ 187 posts ]  Go to page Previous  1 ... 6, 7, 8, 9, 10  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: Old Tube, Yahoo [Bot] and 11 guests



Search for:
Jump to:  


















Privacy Policy :: Powered by phpBB