[Boatanchors] Repair Advice

[Al Klase]

A quick troubleshooting tutorial.

1)  SIGNAL TRACE to find the bad STAGE.  (Then check the tube.)

2)  Make tube-pin VOLTAGE measurements to find the bad CIRCUIT. (Plate 
circuit, screen-grid circuit, etc.)
         If you don't have a voltage chart, consult a tube manual, 
referencing the appropriate supply voltage.

3)  Turn off the power, and make RESISTANCE measurements to find the bad 
COMPONENT.


A)  In a 60-year-old device, replace all the paper and electrolytic 
capacitors before you even turn it on.

B)  Try not to mess with frequency-determining components (mica caps, 
etc.) unless you have no choice.

In a bad oscillator, that has good plate voltage, the next thing I check 
is the grid resistor.

Hope this helps,
Al

On 1/8/2013 1:57 AM, Drew P. wrote:
> Scott wrote:
>
> "I am curious of the technique or strategy that you use to resolve an oscillator issue like this where it is not oscillating at all and you have no confidence in any of the oscillator components."
>
> Hi Scott,
>
> It has been said that two of the most vexing problems in engineering are oscillators that don't and amplifiers that do.  Poorly-aged components are of no help.
>
> You stated that you "checked the oscillaor tube".  By what test?  Tube testers do not always tell the whole story.  You would do well to try substituting the tube with a known good one.
>
> You mentioned "Micamold" capacitors.  Are these real "Micamold" or are they just mica?  Mica capacitors are fairly reliable but are found occasionally to be bad.  "Micamold" capacitors are in actuality nothing more than paper capacitors in a molded case which looks like a mica capacitor.  "Micamold" capacitors are notoriously unreliable and should be shotgunned on sight.
>
> Drew
>
>
>
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/