Transformer winding resistances

[NoobGuy]

I have recently completed a Crack build, and enjoyed it very much.

However, when I power it on without tubes or headphones in place it keeps burning the fuse. I have double and triple checked all my solders and component orientation. Everything looks good. The measured resistances according to the manual are all proper.  The diodes are not blown. After some reading on these forums I also checked transformer orientation, and its fine.

Next is to check that the transformer is okay. What resistances should I get when measuring the primary, LV secondary and HV secondaries?

Thank you

 

[fullheadofnothing]

The tubes need to be in place to do the voltage checks.

The measurements you ask for will be different depending on if it is a 120 or 240 transformer, which you did not specify.

Also posting pictures is generally helpful for locating shorts.

 

[NoobGuy]

Thank you for the reply Joshua

It is the 240V version. I have not reached the voltage check stage yet, as the fuse keeps blowing. Another post recommended measuring resistance on the transformer windings to see if it is damaged.

I am quite certain there are no shorts, and I have ensured that there are no stray pieces of wire offcuts anywhere.

I will post pictures once I have checked the transformer and there are still problems

 

[fullheadofnothing]

Primary should be about 12Ω. That may be hard for your meter to measure, and may change based on being installed. I don't know the secondary measurements, but faulty transformers are exceptionally rare. I brought up the voltage checks because you said you were blowing fuses without tubes, and there is no reason to turn on an amp without tubes. Also, since you have blown multiple fuses, you must have sourced them yourself, so what value and type are you using?

Please post pictures. Virtually every problem that gets asked about on the forum is assumed to be a faulty part, and the resolution on most involves clearing up a wiring issue.

Finally, could you please sign your posts with your real name? It's the first rule of the forum, and it helps us track down parts requests and order anomalies behind the scenes if we know who we are talking to online.

 

[Paul Birkeland]

I would suggest removing the black and red wires that feed from the power transformer to 19 and 18. Then you can measure the power transformer voltages.  (Meter set to AC, measure voltage between 1 and 2 on the power transformer, 4 and 5, 6 and 7, and 9 and 10)

For what it's worth, I think we see a defective power transformer once every 5-10 years.

The common causes of an immediately blown fuse in the Crack would be:
Wrong diode orientation.
Two diode leads touching that go to different terminals (causes a short).
Backwards capacitor.
Octal socket orientation incorrect. (Keyway faces front of panel)

-PB