1950 Arvin Radio

[GWIZ]

Originally Posted by Whitetrash

Checked pins 5 and 7 of the 35W4 120V Ac at pin 5 almost nothing at pin 7 like 1.5 volts DC. I'm a little confused Where is the 65 + volts showing up later down stream? it would appear the tube is bad and readily available for under $8 But, what am I missing ?

You are on the right track.

35W4
as to pin 7 you likely did something wrong try it again.
check the meter probe contact.
black probe on the triangle common B-


notice pin7 to R12 to R13 to R14
That is a voltage divider network check the 3 voltages shown in the drawing.

Note C11 is three Electrolytic capacitors in one.
20uf, 40uf, 20uf.

*** Electrolytic capacitors will, can hold a charge after the unit has been turned off, there is a potential to be charged up to 120 volts (the voltage that feeds them).
in this circuit the resistor divider likely discharges the caps, BUT be Cautious any way.

[Whitetrash]

Just caught up enough to check in and read your response. I know what I did wrong on Pin7 I believe. I have had my black lead clipped to the chassis with a spring clip. I can see one thing I need to do before going much deeper. I need to get new test leads for my Fluke. I bought it years ago for electrical repairs on trucks. The probes are way too big and clumsy I feel like I'm trying to touch the pins with a "Railroad Spike" pair that with my shaky hands and it's challenging.

[Whitetrash]

I have a new set of way finer test probes coming and figuring I need to go back to step one and reestablish all my readings with a better method.

[Whitetrash]

I thought a chassis ground was fine because the tube plugs all seem to have a riveted ground to the chassis.

[Whitetrash]

Finally received delivery of my new probes for the Fluke. So, much nicer to work with. Pulled the tape off the big Cap so I could roll it out of the way a little. I have a clue honestly don't know what to make of it. I'd be lying if I said I knew what was going on. Checked voltages for the Cap using the common ground. 102, 102, 65 on the 40 MFD leg going to IF1 ?

[GWIZ]

In this case a 40uf replacing a 20uf is not all that bad, maybe that is all he had.

trying to figure out the 86 voltage being low.
one of two things the value of R14 has changed or been changed ... but more likely C11 the Cap is bad.
while you are at it checking the value of R14 (1200 ohms), check R12 (15 ohms) and R13 (120 ohms).

Resistance is always measured with the power disconnected, never feed power into the meter when set for resistance measurements.
If in doubt measure for a voltage across the items before switching to a resistance setting.

C11 can hold a charge after the power is removed but will likely be discharged due to the resistors wired across the cap. a charged Electrolytic cap can destroy a meter.

C11 will likely try to charge up from your meter and give you a bad reading, you will have to disconnect the cap to measure the resistors.

[Whitetrash]

Thanks, G I need to sort out the schematic to zero in on what I need to test. I'm fairly good with schematics. But, this one is testing me quite a bit. trying to find a "Cheatsheet" to clarify some of these symbols and circuit routing. Let's just say Truck wiring is way way simpler. I'll get it I'm just going to have to dig a bit.

[Whitetrash]

So, what resistance would be good for C11 all 3 legs are right around .537 to 715 Ohms

[GWIZ]

Resistance measurements will be all over the place because a cap tries to charge up using the meters supply voltage, creates an unstable reading.

Here is just one link testing.
http://www.learningaboutelectronics....st-a-capacitor

You can search for youtube testing a capacitor with a meter.
Also using an Analog meter.

Does your meter have a capacitance scale?
you can check if its value has changed.

[mccutter]

I got six? of these meters last year to hand out as presents after buying and testing one. Good little meter with a capacitance function so why guess? They are still selling them a year later so I suppose that is a good thing... LINK

Checking AC caps earlier this year. 0uf supposed to be 15uf, 22uf supposed to be 35uf. Local ACE Hdwr stocks these, $15-$20 each.