I'm not telling guys this

[Randall]

about how I cobbled in a PT to check for shorts in a blues Jr whilst awaiting the replacement. Two hours trying to chase down why current draw on the variac was too high even after disconnecting everything except the BR. Replaced all the diodes in desperation, kicked and cursed, etc. Then realized I had the CT of the secondary HV grounded on a SS rectified amp. Not EXACTLY sure why this is bad, only realize it is. New PT came in today, hooked it up and all is well.... except for the couple of parts I compromised effing around with the wrong transformer and oversight.

[xtian]

And I am definitely not laughing at you.

[J M Fahey]

Please draw how you actually wired the temporary transformer to the amp power supply.

Do it today where the mistake is still fresh or youŽll repeat it time and again, over and over.

Draw both what you did and the original circuit, side by side.

[Randall]

Here is the power supply of the Blues Jr as it should be. What I did was connect my replacement red secondaries to C12 and C13, with CT to chassis, green filament winding to C10 and C18 with CT to chassis, and omitted the brown winding at C16 and C17. Pretty dumb.

[J M Fahey]

Here is the power supply of the Blues Jr as it should be. What I did was connect my replacement red secondaries to C12 and C13, with CT to chassis, green filament winding to C10 and C18 with CT to chassis, and omitted the brown winding at C16 and C17. Pretty dumb.

Not dumb but lazy, because what IŽm telling you verbally wonŽt "click" until you *see* it and for that youŽll have to draw it:

1) original transformer, meant for a 4 diode bridge rectifier, has a single Red-to-Red 233VAC winding , to get +329VDC.
No ground connection whatsoever.

2) your temporary substitution, meant for a 2 diode full wave rectifier , has two 233VAC windings in series, so twice as much, so 466VAC, which will get you +658VDC .
What do you think will happen inside that poor Blues Jr?

3) but you were "lucky" , grounding the center tap shorts each half secondary to ground, through the wrongly biased diode in the bridge, which shorts the transformer and blows main fuse
Or shows a short if you slowly rise the Variac or brightly shines the series lightbulb, any of 3 indicating a massive short.

To really grab this, you have to draw it, including involved voltages and looking where current goes and which diodes get forward biased, which reverse biased ... or wrongly forward biased.
As they say, an image is worth 1000 words

4) just as the icing on the cake, you did not feed the +/- 15V rails, but thatŽs a relatively minor problem.