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(10-12-2016, 09:35 PM)Radioroslyn Wrote: https://en.wikipedia.org/wiki/Potentiometer
Yours is a dual pot, it has two sections. Can't seem to find the resistance for each section. One section shorts the ant to the chassis at low volume and the other section controls the gain of the rf amp stages.
Sorry I misspoke the model 77 uses a dual volume like the model 70. The model 87 uses a single volume control @ 10,000 ohms (10K)
I was going be the Post Subject line and assumed that we where still addressing the model 77. If you would be so kind to start a new thread when you asking question about a different chassis it would relive this confusion.
On your 87 filter caps don't use electrolytic caps. They are small in size and inexpensive but they can't sustain the ripple current and will short after a brief period of time. What you what to use is mylar or film capacitors. They are much larger than the e caps but way smaller that the original that reside in the can.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
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(01-10-2017, 11:03 PM)flatheadjr Wrote: Well the thread started out with a 77, but the field coil was bad on the speaker and so far I have been unsuccessful in finding a replacement. I found an excellent buy on this 87...
...so next time, please start a different thread if you're starting on a different project in order to not confuse people. I have split your 77 thread into a new 87 thread. Thanks.
--
Ron Ramirez
Ferdinand IN
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Found the rest of the thread, didn't see it was moved to its own for the model 87 I'm working on.
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So I'm back on this unit again and have it mostly done, for some reason I missed my quantities when ordering capacitors, I missed one 1mfd capacitor so I'll have to take care of that one later. I did the capacitors the way I wanted with all of them neatly tucked under the chassis. Capacitor block is fully intact and no mess was made. However I have 2 problems, first is that I have no volume control, I can turn the knob back a forth and nothing, it's fixed at one setting. Something wrong with the potentiometer? What readings should it deliver? The second is it seems the voltage is a little higher than I'd like on the #26 filaments. The schematic says 1.5 volts, I'm reading 5.8 volts.
(This post was last modified: 01-21-2017, 06:51 PM by flatheadjr.)
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100v maybe a little low. I'd go with 200 or higher. There is some voltage there as this is how the filament on the 26's are biased.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
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Are you measuring the voltage on the 26 tube from filament pin to filament pin or from filament pin to chassis ground?
Across the two pins should be 1.5 V AC, but from either filament pin to ground there will be a DC voltage of around 5 to 10 V.
If you were referring to using the 100 V rated caps as the filament bypass, I don't think its a problem. There is only the bias voltage across the caps to ground, which is less than 10 Vdc.
(This post was last modified: 01-21-2017, 08:48 PM by Mondial.)
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I was measuring from the chassis to the filament pin that's were I was getting the 5.8 volts from, but for some reason my meter won't read that low of AC voltage when going across the pins. As for the volume control what do I need to look for there?
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Not quite sure what your question is but it's a 10K pot. To check it you'll need to disconnect the wire on center terminal as the coil it's connected to has a much low resistance and will effect your reading. No voltage on it.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 135
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City: Idaho Falls, Idaho
I haven't tried to disconnect the wire from the coil yet, but I was able to get a reading off of it. With the volume turned down all the way I was at 13k, and with the volume fully up it was at 3.5k or around there. The problem with my volume is that it doesn't work at all, I can tune in stations, but some come in really loud and I can't control their volume.
(This post was last modified: 01-21-2017, 11:57 PM by flatheadjr.)
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OK Turn the set off. Measure the resistance from the wiper (the wire that goes to the coil ) to the chassis with the volume full up. Should see a low resistance like a few ohms. If it is much higher like several thousand ohms then your primary on the coil is bad (open) or you have a bad ground connection where the primary winding this ground to the chassis.
If the coil is open...
That part of the coil is somewhat noncritical in terms of it's inductance as it's used transferring or coupling the rf signal to the secondary which is a tuned circuit. Take the coil out and this winding will be the small one near the bottom. Rewind with suitable ga magnet wire. You can guess or approximate by counting them. The phasing or direction doesn't matter on this winding.
If the coil measures a low resistance..,
Then you have a bad ground connection at the volume control or a dirty control.
Me I'm betting on the open coil. It's easier to troubleshoot w/the coil disconnected from the pot as their resistances interact. Also you didn't say whether you where measured the pot, across the pot or from the chassis to the terminal on the pot. This adds another factor into the equation
GL
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 01-22-2017, 06:27 AM by Radioroslyn.)
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Okay so what I did was disconnect the center tap wire of the controller off of the coil so I could isolate the coil and the volume control. There are only 2 connections on that coil that sit up inside the can. When I measure that it reads 3.2 ohms. If I measure the control with the volume up all the way up, from the wire I disconnected I get a measurement of 10.5k and that's only the controller.
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Coil resistance is good so we can rule it out. There are only two connection as the other two are solder to the coils bracket hence grounded. If you measure the resistance from wiper to chassis does it vary smoothly with the rotation from 0 to 10k with wire still disconnected?
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 135
Threads: 14
Joined: Mar 2016
City: Idaho Falls, Idaho
It does vary from 10k all the way open, and as you turn down the volume it goes to about 12 ohms at the bottom. I hooked the wire back up and there is no response on the resistance on the volume control again. I measured the resistance turning the knob back and forth and it was constant at 2.7 ohms with no change.
(This post was last modified: 01-22-2017, 08:10 PM by flatheadjr.)
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(01-22-2017, 02:48 PM)flatheadjr Wrote: It does vary from 10k all the way open, and as you turn down the volume it goes to about 12 ohms at the bottom...
Ok this is good and you are measuring the resistance from the wiper to the chassis and not from the wiper to the other end of the pot? ? Or another way to measure it is with the coil wire disconnected measure the resistance from the chassis to each end of the pot. One side should be 10k and the other 0.
Quote:I hooked the wire back up and there is no response on the resistance on the volume control again.
This how it should be. The coil is a much lower resistance than the pot. To the meter it's just seeing the coil because it looks like a short by comparison to the pot.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 135
Threads: 14
Joined: Mar 2016
City: Idaho Falls, Idaho
Okay so now oddly enough after I soldered the wire back it appears to be working now. I also found out whatever the other control is (it looks like a tuning capacitor ) affects volume control as well. Also can this unit be aligned, it appears to be off a little. I still also seem to have some obnoxious static coming through along with a slight hum, any way to get rid of those? I still need to find a 1mfd capacitor, any vlue where I could get one rather than place another order, I have no supply stores in my area.
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