Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Early B&W and Projection TV

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #46  
Old 01-30-2019, 09:47 PM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,506
V15, V16, and V17 are done. Ratio Detector, AF Amp, and Audio Output. I replaced all the single conductor shielded wire. Some minor stuff to do then onto the IF section, then onto the controls.



Reply With Quote
  #47  
Old 01-31-2019, 10:50 PM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,506
Reworked V5, V6, V7, and V8. The 4 IF stages. This pretty much completes the bottom of the chassis. There are still a few odds and ends to deal with, but over all it is finished.

Next up will be the front panel controls.



Reply With Quote
  #48  
Old 01-31-2019, 10:59 PM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,506
I was looking at the schematic and in a dotted square is M7. Looks like a coil, caps, and resistor. I'm guessing it is the video detector. What is the chances the diode is good/bad? Is there a modern day equivalent? There is a cover on the topside that comes off and there is the diode.



Reply With Quote
  #49  
Old 02-01-2019, 10:47 AM
Notimetolooz's Avatar
Notimetolooz Notimetolooz is offline
VideoKarma Member
 
Join Date: Mar 2014
Location: Dallas, TX
Posts: 547
It is a germanium diode for sure. Getting hard to find. 1N60 is similar as are a few others. 1N34 are more common, good for crystal radios and other uses, but I don't know well they would work here.
Reply With Quote
  #50  
Old 02-01-2019, 11:01 AM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
Some are fine some are not... I generally see if the set works before I consider changing it. It is above chassis so it should be easy to change post assembly.
__________________
Tom C.

Zenith: The quality stays in EVEN after the name falls off!
What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
Reply With Quote
Audiokarma
  #51  
Old 02-01-2019, 12:42 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is online now
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 7,184
It appears the choice of a particular germanium diode type will produce only a small difference in detector efficiency:
http://www.rfcafe.com/references/rad...ruary-1952.htm

(scroll down to figure 7)
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #52  
Old 02-01-2019, 03:26 PM
Gleb's Avatar
Gleb Gleb is offline
VideoKarma Member
 
Join Date: Mar 2015
Location: Russia
Posts: 66
This is an early type germanium diode. You can use a digital multimeter with a diode check function to test whether it is functional. A good germanium diode shows a forward voltage drop of about 150...400mV, and doesn't conduct at all in the reverse direction (infinity reading).

Even though there are some special "video detector diodes", I've never seen any difference replacing them with random germanium point contact types I had on hands; you shouldn't either. If the original diode tests bad, just replace it with any germanium point contact diode. I am not good in Western types of diodes, but I think 1N34, 1N60, NTE-109 and many others should be OK.
__________________
To understand a bygone era, you should use things from it

Last edited by Gleb; 02-01-2019 at 03:58 PM.
Reply With Quote
  #53  
Old 02-01-2019, 09:18 PM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 2,541
I've always found germanium diodes to show signifigant reverse leakage when checked with an ohmmeter (compared to a Si diode's zero reverse leakage). Yet the Ge diodes always worked normally in service.
Reply With Quote
  #54  
Old 02-01-2019, 09:21 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is online now
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 7,184
Quote:
Originally Posted by old_coot88 View Post
I've always found germanium diodes to show signifigant reverse leakage when checked with an ohmmeter (compared to a Si diode's zero reverse leakage). Yet the Ge diodes always worked normally.
It may depend on what voltage your ohmmeter applies.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #55  
Old 02-01-2019, 11:48 PM
irext's Avatar
irext irext is offline
VideoKarma Member
 
Join Date: Dec 2016
Posts: 69
I've never tried it but what about a Schottky diode. They have a quite low forward bias voltage. Just a thought.
Reply With Quote
Audiokarma
  #56  
Old 02-03-2019, 10:14 PM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,506
Thanks guys for the suggestions. I have some 1N60 and some 1N914. I'll try them once I get the set working.
Reply With Quote
  #57  
Old 02-03-2019, 10:29 PM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,506
I changed some resistors that were in some if the IF cans and in M7. Basically, they were 5% and each one was 10-11% out-of-tolerance.

Here is the schematic of the 2 IF cans that had resistors. L32 and L33. Both in the 1st IF stage. Each of these 2 cans had capacitors along with M7. And each can used different types of capacitors. I'll show some pics.



Here is L32. The 22K resistor was 10% out-of-tolerance and was replaced with a 1W 22K 5% carbon film resistor. The caps were disc.



Here is L33. The 4.7K resistor was 11% out-of-tolerance and was replaced with a 1W 4.7K carbon film resistor. The 2 caps were a dual mica cap. This cap used mica film just like a trimmer cap. I tested the 100pf side and got 102pf. I couldn't test the 13pf side due to my checker doesn't go down that low.







And finally M7. See schematic in a few previous posts. The 8.2K 5% resistor was 7% out-of-tolerance and was replaced with a 1W 8.2K carbon film resistor. Both Riders and Sams schematics showed M7 using a 10K resistor. I decided to use what was actually used. The caps in this unit were like "dogbone" type. Again all 3 cans used different types of caps.

Reply With Quote
  #58  
Old 02-04-2019, 10:07 PM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,506
Working on getting the chassis all cleaned up. I scrubbed and wire brushed the chassis and then shot some primer over the pitted areas from the mouse pee. Once the primer was dry, I used some Bondo Glazing putty to fill in the pits. Tomorrow I'll sand the putty and then primer and paint the chassis.

Reply With Quote
  #59  
Old 02-05-2019, 09:10 AM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,506
The glazing putty has been sanded and now on to the primer.

Reply With Quote
  #60  
Old 02-05-2019, 11:32 PM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,506
While the paint on the chassis dries I turned my attention to the tuner.
I cleaned it up and used DeOxit on the wafer switches. I also replaced all if the resistors. There were 12 of them. 9 were clearly out-of-tolerance. Some as much as 47%, while 3 were in tolerance. They were replaced with 1W Carbon Film resistors.







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 02:54 PM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.