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  #46  
Old 01-30-2019, 09:47 PM
Crist Rigott Crist Rigott is offline
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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.



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  #47  
Old 01-31-2019, 10:50 PM
Crist Rigott Crist Rigott is offline
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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.



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  #48  
Old 01-31-2019, 10:59 PM
Crist Rigott Crist Rigott is offline
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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.



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  #49  
Old 02-01-2019, 10:47 AM
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Notimetolooz Notimetolooz is offline
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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.
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  #50  
Old 02-01-2019, 11:01 AM
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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.
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  #51  
Old 02-01-2019, 12:42 PM
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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)
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  #52  
Old 02-01-2019, 03:26 PM
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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.
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Last edited by Gleb; 02-01-2019 at 03:58 PM.
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  #53  
Old 02-01-2019, 09:18 PM
old_coot88 old_coot88 is offline
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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.
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  #54  
Old 02-01-2019, 09:21 PM
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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.
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  #55  
Old 02-01-2019, 11:48 PM
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I've never tried it but what about a Schottky diode. They have a quite low forward bias voltage. Just a thought.
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  #56  
Old 02-03-2019, 10:14 PM
Crist Rigott Crist Rigott is offline
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Thanks guys for the suggestions. I have some 1N60 and some 1N914. I'll try them once I get the set working.
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  #57  
Old 02-03-2019, 10:29 PM
Crist Rigott Crist Rigott is offline
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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.

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  #58  
Old 02-04-2019, 10:07 PM
Crist Rigott Crist Rigott is offline
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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.

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  #59  
Old 02-05-2019, 09:10 AM
Crist Rigott Crist Rigott is offline
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The glazing putty has been sanded and now on to the primer.

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  #60  
Old 02-05-2019, 11:32 PM
Crist Rigott Crist Rigott is offline
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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.







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