Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Television Broadcast Gear

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #16  
Old 06-23-2016, 07:56 PM
dtvmcdonald's Avatar
dtvmcdonald dtvmcdonald is offline
VideoKarma Member
 
Join Date: Nov 2012
Posts: 785
Here is the "better" screen image, and "before recapping" pictures of the chassis.

The bending at the top of the image has been fixed by adjustment of DC levels.

"after" pics of chassis in next post.
Attached Images
File Type: jpg _MG_6211.jpg (63.9 KB, 55 views)
File Type: jpg _MG_6190.jpg (121.1 KB, 32 views)
File Type: jpg _MG_6191.jpg (81.2 KB, 26 views)
File Type: jpg _MG_6192.jpg (90.3 KB, 21 views)
File Type: jpg _MG_6181.jpg (110.5 KB, 37 views)
File Type: jpg _MG_6182.jpg (88.9 KB, 28 views)
Reply With Quote
  #17  
Old 06-23-2016, 08:04 PM
dtvmcdonald's Avatar
dtvmcdonald dtvmcdonald is offline
VideoKarma Member
 
Join Date: Nov 2012
Posts: 785
Here are the images, "after recapping" and other changes, of the chassis. Many changes are hard to see, but are there .. look at the 6X5s
for a bit of silicon.

Next is the power supply ... it needs safety covers.

Also the iconoscope. As you see, I'm lucky i'm works at all with that
opaque yellow getter rim.
Attached Images
File Type: jpg _MG_6214.jpg (111.9 KB, 40 views)
File Type: jpg _MG_6215.jpg (95.8 KB, 38 views)
File Type: jpg _MG_6216.jpg (113.2 KB, 32 views)
File Type: jpg _MG_6221.jpg (108.7 KB, 32 views)
File Type: jpg _MG_6222.jpg (146.2 KB, 43 views)
File Type: jpg _MG_6219.jpg (87.3 KB, 52 views)
Reply With Quote
  #18  
Old 10-24-2016, 05:16 AM
Aussie Bloke's Avatar
Aussie Bloke Aussie Bloke is offline
VideoKarma Member
 
Join Date: May 2004
Location: NSW, Australia
Posts: 542
Hey just wanna say it's awesome to see another one of these WWII block cameras get restored to working order and any Iconoscope camera in general, great work and look forward to seeing more on it!

I myself have built a crudely working Iconoscope camera using the same RCA 1846 tube type and driven by video/deflection circuits I made originally for a 2/3" vidicon camera, my Iconoscope camera construction log can be seen on my site starting from this page http://troysvintagevideo.0catch.com/...peproject.html .
__________________
AUSSIE AUSSIE AUSSIE!!!!! OI OI OI!!!!!
Reply With Quote
  #19  
Old 03-11-2017, 04:25 PM
dtvmcdonald's Avatar
dtvmcdonald dtvmcdonald is offline
VideoKarma Member
 
Join Date: Nov 2012
Posts: 785
Last week I noticed another 1846 for sale on the 'bay. It had
a good center of the getters, clerly visible, so I bought it.
It arrived yesterday and today I tried it.

It works identically to my other semi-working one. It runs for about 15
to 30 minutes and then the bias need raising and it loses the picture.
Turning off 10 minutes and the picture is back

Questions for those, especially the Aussie guy, who have gotten one to work indefinitely: is there a brown rim around the shiny getters or are they all shiny?

Have you experience of a tube acting like mine?

Do you think that maybe it could be an electrical fault since the two tubes
work or don't work identically? I have a similar appearing third tube
that does not produce any picture at all.
Reply With Quote
  #20  
Old 03-11-2017, 04:37 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 4,215
I have no idea about the gradual loss of picture (I have never played with one of these) except that you mentioned back bias lighting. Have you tried it? An LED flashlight, with its high blue content, might be good for a quick test.

Can you post a schematic of the first amplifier stage?
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
Audiokarma
  #21  
Old 03-11-2017, 05:33 PM
dtvmcdonald's Avatar
dtvmcdonald dtvmcdonald is offline
VideoKarma Member
 
Join Date: Nov 2012
Posts: 785
here's that part of thttp://videokarma.org/attachment.php?attachmentid=194149&stc=1&d=1489275 183he schematic
Attached Images
File Type: png CRV-59AAE_Schematic2c.png (108.8 KB, 16 views)
Reply With Quote
  #22  
Old 03-11-2017, 11:13 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 4,215
Just on general principles of poking around, have you checked R114 and R126?
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #23  
Old 03-12-2017, 10:29 AM
dtvmcdonald's Avatar
dtvmcdonald dtvmcdonald is offline
VideoKarma Member
 
Join Date: Nov 2012
Posts: 785
Quote:
Originally Posted by old_tv_nut View Post
Just on general principles of poking around, have you checked R114 and R126?
Yes, and they are new. I've checked all bias resistors. I've studied all the
bias voltages as it heats up. They do drift, but the key grid-cathode bias
voltage does not, and all drift in sync and in small amounts. The bias
in any case need far more adjustment than the drift.

I tried checking drift of filament voltage while running by comparing
the brightness and color of the tube in the camera to that of my dead
1846 running on 60 Hz and they are rock stable. I measured
the heater voltage both by comparing the brightness to the other tube
both on 60 Hz and the other one on 60 HZ and the camera one on
15750Hz, and also by measuring the camera tube voltage with a digital
scope across the filament with the HV disabled, then calculating the
RMS voltage from the scope trace (its sort of a square wave). I can't
get the voltage up to 6.3 but is very close and does not drift enough
to cause the problem.

Of course, both tubes could be equally bad by chance. But its
odd that of three tubes that have look-alike getters one does not
work at all and two work sort-of, and the same.

I've tried swapping 6AC7s around to no effect.
Reply With Quote
  #24  
Old 03-12-2017, 11:55 AM
dtvmcdonald's Avatar
dtvmcdonald dtvmcdonald is offline
VideoKarma Member
 
Join Date: Nov 2012
Posts: 785
Oh yes, a bit off topic ... the iconoscope I just bought came with "extras".
One was a mounting block for it to display it, into which I will put my bad one.
Second was a copy of Pem Farnsworth's biography of Philo, autographed by
her in 2004 (she died at age 98!).
Reply With Quote
  #25  
Old 03-12-2017, 01:22 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 4,215
I'm running out of wild guesses. Slow onset and slow recovery seems like a thermal problem, but if the bias voltages aren't changing, what could it be?

What happens if you run it until the video disappears and then ground the collector ring with a clip lead/screwdriver? Could this be a bad ground connection charging up the second anode?
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
Audiokarma
  #26  
Old 03-12-2017, 03:35 PM
dtvmcdonald's Avatar
dtvmcdonald dtvmcdonald is offline
VideoKarma Member
 
Join Date: Nov 2012
Posts: 785
I've tried grounding the collector ring with a screwdriver. I've also
tried putting + or - 9 volts on the unused pins which attach to
the Cesium dispensers, and they don't do much if there is no
hum on them.

I've tried using a magnet to move the electron beam over to the
side where it hits beyond the edge of the silver dot area.
This generates a very strong signal which lasts a lot longer.
Its currently cooling down so I'll try that again.


It does seem thermal, but why cooling down much faster than
warming up?

Edit: a new try shows that the actual picture lasts much longer,
at any setting of the bias, at the far left of the screen.

Last edited by dtvmcdonald; 03-12-2017 at 03:57 PM.
Reply With Quote
  #27  
Old 03-12-2017, 09:56 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 4,215
Quote:
Originally Posted by dtvmcdonald View Post
...
Edit: a new try shows that the actual picture lasts much longer,
at any setting of the bias, at the far left of the screen.
...
Well, this just gets more and more puzzling.

Do you have anyone who can review the wiring with a fresh eye in case something got missed when you recapped?
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #28  
Old 03-14-2017, 09:11 AM
dtvmcdonald's Avatar
dtvmcdonald dtvmcdonald is offline
VideoKarma Member
 
Join Date: Nov 2012
Posts: 785
I discovered by accident that even if it runs 5 minutes beyond the
picture disappearing, and I then turn off all power for 5 seconds and then
back on again, as it re-warms up for a couple of seconds an excellent
picture appears, just a bit small, lasting just an instant as it gets
full size.

This would seem to be a bias drift problem.

I spoke to Schechter last night on the phone. Amazingly, he only knows
of himself, McVoy, Aussie Bloke, the Japanese genius with the perfect
transistorized picture, and me, with 1846 cameras working at all.

Do you know of more?
Reply With Quote
  #29  
Old 03-14-2017, 10:45 AM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 4,215
If my wild guesses are just annoying, tell me and and I'll shut up...

Is there more than one connection possible to the collector ring (like through the cesium depositors)? If so, can you try measuring voltage and/or grounding with a screwdriver?

Can you pull the socket partly off and measure directly on the pins?
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #30  
Old 03-14-2017, 12:33 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 4,215
Another thought is to float a VOM across the cathode and G1 so you can see any differential drift on a sensitive scale. (Just be careful to have it on an insulated surface and don't try to touch it while in operation!)
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
Audiokarma
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 07:10 PM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
ęCopyright 2012 VideoKarma.org, All rights reserved.