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48-1262 stumped - Printable Version

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48-1262 stumped - ke5yum - 05-02-2013

I am not sure what to do next, and I need some help.

I replaced the rectifiter tube to get the voltages up.

I double checked the wiring of my new electrolytic capacitors (C101 and C102) and they are correct.

I replaced R202. That gave me a whine in the audio that is removed with the volume control.

Now my C101 and C102 have blown. Smoke everywhere. I have two new caps on hand but do not want to replace them until I can figure out why they blew. Voltage rating on the blown caps were 500 volts.

I'm thinking I may have a short somewhere, and if so, how do I track that down.

Thanks, Terry

RE: 48-1262 stumped - morzh - 05-02-2013

See if your rectifier tube is shorted or very leaky.

Shorts do not make capacitors blow.
Although it is always a good idea to check for them.

RE: 48-1262 stumped - Steve Davis - 05-02-2013

Recheck the polarity of C101 and C102.

Steve

RE: 48-1262 stumped - morzh - 05-02-2013

That too of course.

Did you re-stuff the caps? Or did you use new bare caps? If you re-stuffed, are you sure you did connect + to + and - to - when sealing the cans?
When you say new capacitors, what exactly does that mean?

RE: 48-1262 stumped - ke5yum - 05-02-2013

I bought new 16 mf axial capacitors from Justradios. As for polarity, I am pretty sure that I installed them correctly.

I will get back to the project next week when an Electrical Engineer friend can help me and verify the work.

Thanks for the help.

RE: 48-1262 stumped - morzh - 05-02-2013

16 mF or uF? That makes about 1000 times the difference. You talking microfarads, right?
Axials have the "-" going to the case and the "+" insulated, as usual, plus there are usually "+" side markings.

If you are sure and you did not re-stuff anything that would be another variable.....I would

1) check my rectifier tube
2) with the rectifier out, put a meter and measure the transformer output to the rectifier. What if it is doubled? Not sure how that could happen, but.....


I am still (if you are sure of polarity) leaning towards a bad rectifier.

RE: 48-1262 stumped - Ron Ramirez - 05-02-2013

Actually, in this country, MFD = mf = mF = uF.

We used to call pF "mmfd" or "mmf" but we've standardized on "pF" these days.

We did not use the in between nanofarad or "nF" in the USA.

RE: 48-1262 stumped - morzh - 05-02-2013

Ron, have to disagree.
I cannot speak for the ham or antique radio community lingo, and the marking on the old capacitors was different from today (then again those were condensers, not caps Icon_confused) ), but in today's EE practice in the US:

uF - microfarad
mF - not used. 1000uF is what it is.
nF - nanofarad.
pF - picofarad.

In general, in engineering and physics, today:

m - always ""milli", 1/1000
u - always ""micro, 1/1000,000, from its resemblance to Greek "mu" which starts the word "Mikro".
n - always "nano", 1/1,000,000,000

RE: 48-1262 stumped - Ron Ramirez - 05-02-2013

I was speaking from the antique radio collecting perspective, and had no knowledge of which terms modern engineers use. Icon_smile

RE: 48-1262 stumped - morzh - 05-02-2013

That I have no argument with.

Just kinda hard to switch between the two systems. When it is imperial and metric - easy, they have nothing in common, no confusion there. (although Martial modules occasionally crash) Icon_smile
Or between Russian and English.

But the same system where while speaking to some folks "mF" is a microfarad and to some others - 1000 microfarads, this gets downright confusing.