Hi everyone,newbie with a question or two. I'm working on my second radio a 46-1201 model 128. First was a Canadian 706a. The 706a was just a recap and refinishing the case and it was fine. This one isn't so easy. Must have been sitting in a pretty damp spot because the bottom cover was destroyed and the bottom edge of the phono had spots rusted rusted away...like where the feet screw on. So i cut the rust out and welded in some steel i cut from some brackets i got from home depot.
[Image: http://img.photobucket.com/albums/v680/t.../weld2.jpg]
[Image: http://img.photobucket.com/albums/v680/t.../weld1.jpg]
The case is pretty much done,
[Image: http://img.photobucket.com/albums/v680/t...abinet.jpg]
unfortunately couldn't find the proper grill cloth.The turntable is almost done and rebuilt the cartridge.
[Image: http://img.photobucket.com/albums/v680/t.../phono.jpg]
[Image: http://img.photobucket.com/albums/v680/t.../cart2.jpg]
This is the problem,
[Image: http://img.photobucket.com/albums/v680/t...rorcap.jpg]
I can't tell by the diagrams i have with updates if it's a capacitor or resistor. I'm not a total newb at reading schematics but i definitely could have missed something.Looking at resistor and capacitor charts(white,brown,black,brown,black) it's either a 0.0001mfd cap or 910 ohm resistor...maybe.
This is how it looked originally(the number 1),
[Image: http://img.photobucket.com/albums/v680/t...before.jpg]
and here it is now ,and the electrical tape is temporary ,
[Image: http://img.photobucket.com/albums/v680/t.../after.jpg]
The blue line is where it should be. Any ideas??
Oh, and when plugged in there is no output from the speaker and all the tubes are getting power. Thanks in advance.
That looks like a 100pF (.0001 uf) tubular caramic cap. It is an RF bypass for the detector output. The radio will work without it so its not the cause of your no output problem.
You can reinstall that existing cap. It is a ceramic capacitor, very reliable and not subject to deterioration like the paper capacitors.
Thanks Mondial, thats one down. This one i thought i had figured but now i'm not so sure.This is it here connected to pins 6 and 7 of the 50A5. The diagrams say its a cap rated 240mmf but i've never seen a cap like this and there's no cap-like markings. I just want to make sure, in case it's something different from the schematic.
I've also attached a copy of the revised photofact sheet that i just got to refer to and in case anyone else can use it. It's the closest one i've found so far.
That looks like another early style ceramic cap. It is also an RF bypass connected between the grid and cathode of the 50A5 output tube.
Again, it most likely is not the cause of your problem as the radio will work fine with it disconnected.
To troubleshoot your no audio problem, I would suggest making voltage measurements from each of the tube pins to B- supply and compare with the chart on the schematic. If any voltage reading is significantly different, it can point you to the cause of the problem.
Here is another schematic and service data with voltage measurements. Use the VTVM readings if you are using a digital multimeter.
Either pin 5 of the 7B7, or pin 4 or 7 of the 7C6 would be B- or negative power supply common.
With a power transformerless set like this, B- is isolated from chassis ground for safety reasons, so you have to sort of hunt for the common negative of the power supply, which is referred to on the schematics as B-.
Some of these have a voltage doubler circuit coming off the rectifier tube, so they are not exactly normal when it comes to B-. What code number does it say on the chassis? They had codes 121 up to 128 on the 46-1201.
Regards
Arran
Hi Arran, this is a 128. I've ordered new resistors and new tubes as i don't have a tube tester (it's on my "need to buy" list). And i'm currently trying to get my Eico 249 working. Won't read anything correctly, like it's always too low.
Another quick question, are there silver mica caps in the if/rf cans? And i'm still waiting for parts to come in for the radio and vtvm. Although i did replace all the tubes with no difference.
So i did the tests and some of the values are WAY off. Here's the Specs plus my test values.(also as an attachment in case they're not very legible) The DC were all taken from the 7B7 pin 5 and the AC from the switch on the volume control as per the schematics i uploaded.
Tig, I'm far from the brightest bulb here but I question the 7C6 readings. I wouldn't worry about pin 1, you may have set the meter wrong. Should read very low A/C voltage. I would worry about pin 2 and measure that one again. Most voltage readings are semi close for using a DVM. They are high. The plate voltage (pin 2) on the 7C6 being sky high, indicates to me that tube is not conducting. Cathode not tied appropriately or tube really bad. Need to get that plate voltage down. Item 27 a 470K is the feed and should drop the voltage across it within specified range. Check the voltage on both sides. No change then tube or cathode is not wired properly.
Jerry
A friend in need is a pest! Bill Slee ca 1970.
(This post was last modified: 11-17-2013, 06:16 PM by jerryhawthorne.)
I agree with Jerry. Something is not right with the 7C6 wiring. Pin 7 should have 0 voltage, as it should be connected to the common B- just like the 7B7 pin 5 you are measuring from. Did you disconnect any wiring and not reconnect it?
Pin 7 of the 7C6 is the cathode, and if it is left floating the tube will not conduct current, making the plate voltage high. The tube will not amplify in this condition which is probably why you have the low distorted audio.
I'll double check but i don't think i left anything off. I did check the resistance on 27 and 37 though. 27 is open, nothing going through, and 37 is 533k. Could that be it?
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