Yes sir thanks I was able to find some old pics of the original part

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Yes sir appears to go to

-negative terminal of capacitor

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-and the emitter of the tip31a on the right

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and a resistor

Meanwhile... experienced my first Chernobyl.

So this metronome I had removed the bridge rectifier a while back and it tested good...oh well

Put a new one in today.... thought it would be fun to hook my meter to the leads before I clipped em and read ac and DC on the different leads.

So I solder it in...crudely soldered the transformer wires back making sure I put the right ones in order.  Plug it in...I'm gathering up my meter and test leads and I hear woosh and see lots of smoke

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And liquid 

Later I was outside and thinking did I put it in backwards or something...or leave a solder bridge?  But looks like the orientation is correct and the solder reasonable (these pics are post meltdown)

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Im beyond hoping this thing will be fixed but I did want to replace that part.

Meanwhile I put it on my ugly dbt after the fact yes it was glowing.

 

Thanks G1 it's a gorgeous day today with plenty of sunshine so I'm actually fixing to take some good pics of this scope so I can put it on the auction site.  Hope is waning that the ever so coveted green trace will ever appear.
I'm happy that it's been a great learning tool but at this point I don't even know if the CRT is any good. When I first got it there was a slight glow at the small end and it gets dimmer and dimmer.
Also there are a bunch of rusty trim pots then another board has an open somewhere (at the minimum).
A 68v zener is cheap though I might need to see that localized issue settled.
Also I really like that arrow pointing at that node and a diagram of a square wave.
Would be cool to see if that is there with my other scope.
 

Quote from: saturated on April 11, 2024, 10:29:56 PMWhat it does mean is:

The circuit is open.

 

I decided to have a look at this scenario...of course I had seen it and read it in books and kind of unwillingly accepted it.

My point being...take an open circuit...add some resistors in series to the positive side...and your gonna measure the same voltage anywhere along that open series...doesn't matter....one resistor...two resistors...three resistors....there is no voltage drop. 

I had to try it.  I made up a three resistor open series circuit connected to 5v.

Well you guys know what happens and already know this.  But seeing it in practice really firmly eliminated any skepticism. 

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Obviously this is way over simplified but it still is a powerful tool when probing.

 

Quote from: saturated on April 09, 2024, 08:49:16 PMThese two ceramics are still hot enough to cook steaks on....

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At least small steaks...well done...

So I'm going out on a limb here and proposing that the 8k ohm 10w resistor is shorted to ground.  It measures 170v on one end and zero on the other.
A quick look at the schematic (a forensically enhanced version kindly provided by the Mighty Mick) to me places cross hairs directly on the zener diode.

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So I'm guessing that the zener diode is shorted...idk.

Or perhaps I'm unfairly blaming it. 

 


To be continued...the story of the zener diode that was (possibly) framed

Welcome to the forum Valleyslad

 

And I'm ready to put forth another conclusion:

If I measure xxx volts on one end of a resistor.....and ZERO volts on the other end

Guess what


 

It's time to go ISO

 

What it does mean is:

The circuit is open.

 

Today I learned:

Just because a resistor has no voltage drop across it and measures the same voltage at each end with respect to ground

Doesn't mean the resistor is shorted

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These two ceramics are still hot enough to cook steaks on....

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At least small steaks...well done...

Looks odd but oh well replaced three axial caps with radial (have you seen the price difference between axial and radial)   

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Still I had not an extra angstrom of length to spare on two of them.  On the third I clipped the lead and used the j-hook method.

Still no green phosphor....  

Meanwhile....onward through the fog.  I am still holding out hope that I can get a trace on this Heathkit oscilloscope.  I ordered the four ICs for it and now I thought I would investigate this power supply by removing caps and reinstalling if testing good.

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Unfortunately (or fortunately) I have removed two and both tested (presumably) good

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So back in they go

Except...hmmm no way here to test leakage so I checked DC ohms with my meter and I have one that charged up pretty quick to about 70 kohm but then really slowed down

So idk maybe it's leaky

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But as I type it's still creeping up in fact it's at 130 kohm now so maybe it's ok.

 

Thank you sir I am glad I did not have to touch any power tubes...in the back of my mind I had heard about tube biasing and was dreading having to do something like that.  But I looked it up and evidently preamp tubes are just plug and play...?

The two 12ax7 I switched positions were in there really tight.  To avoid broken glass and blood I put on a leather work glove.

I really appreciate everyone's help with this idk what we did but it's sounding really crazy nice it still has a little hum at low volume but I ain't touching it right now.

The guys here can help you get it running.  I would ask if you have tried it out yet but it seems like you know it has a problem..what did the seller say about it was it listed for parts or something? 

I would say plug it in and try it but I would hate to see it burn up some impossible to find outputs or something.