no power

[tweedgv]

Hi guys.. 

so, i have been tinkering with the bridge rectifier mod, as well as having some issues with the power inlet.  I've been having to wiggle the power cable in place in order to get a power source to the crack.   

I recently put the bridge rectifier mod in, and when i switched the amp on, it was making a buzzing sound.  i turned the amp off and checked everything, as well as re-soldered behind the power inlet, because it has been a little dodgy as i have mentioned above.  when i turned the amp on, i don't think i'm getting any power at all as i can't get the tubes to glow.  I took the bridge rectifier mod out and reverted back to the old recifiers but the issue of power is still there. 

i would like to do some checks but my crack manual is on an old mac that has passed away.

any help would be amazing. 

[tweedgv]

I have since found a partial crack manual on line, and done the resistance checks.  all is good, apart from no readings on 7 & 9, and B3 & B6. 

The crack has the speedball upgrade... if this makes any difference.

[Tom-s]

Since it's weekend and the team will probably only be back on monday i'll try to help out.

Beware that modifying parts around the PT might kill the PT when done wrong.

See that your circuit is operating perfectly to start with, before you make any changes.

In it's current state i would not turn Crack on.

For a manual. You can ask the BH team for a new one with your original order info.

As i read it, you have 2 problems. First i'd check for normal continuity from power inlet to power transformer.

This was a problem before you made any modifications and should be addressed first.

Doublecheck all wiring and measure all. Maybe some wire is broken inside the insulation. Also, measure the powercord aswel.

Without manual, search the forums for pictures of the rectifier area and see if all is wired as it should (note direction on the diodes and beware of shorting them out).

You could also search the forum if any threads show normal resistances in the PT, to see if it hasn't burnt or anything.

Second problem is your adaptations made to the rectifying circuit. Search the forum for other Cree / Schottky diode rectifier bridges and note orientation and wiring. If all looks correct, check for correct continuity with your DMM.

[Tom-s]

As you replied while i was typing.

With the Speedball the resistance checks do change indeed.

But 7 is connected to B3, and 9 to B6. These are different with speedball.

That being said. I'd check continuity on all heater wiring (coming from the PT) and all other wires from / to the PT.

[Doc B.]

That buzzing sound was a bad sign. It meant that there was a hard short in your amp that was badly overloading the power transformer. A reasonable guess would be that you had an error in the wiring of your modification, most likely a backwards or miswired rectifier. My suggestion is to work through the amp from the power entry through the transformer and on through the power supply with a meter checking resistances and continuities. Don't plug this amp into the wall again until you have it sorted out.

First, fix that bad power inlet. Is the fuse installed correctly and intact? Check to see if the pins that the power cord contact are loose from the inlet being softened too much while soldering. Check that the wires from the inlet to the switch and power trans are properly soldered. If the inlet is damaged, replace it, as that is not safe.

Once that is fixed you will need to determine if the power transformer has been damaged. The damage would be most likely to have occurred at the high voltage secondary. Disconnect the rectifiers from the HV secondary terminals and then measure the resistance from PT terminal 11 to terminal 12. I don't recall the exact value and I am not at the lab where I could measure one, but the resistance should be low, tens to hundreds of ohms. If it reads infinity/OL/open, the transformer is dead.

[tweedgv]

ok.... thanks guys.  i'll have to get on this again tomorrow but thanks for the replies.

i did take the mod into college where the engineering lecturer tested it on the o-scope there.  he has very little interest in music/sound equipment but knew exactly what it was.  it was looking good to him, doing what it should have been doing and gave me the confidence to try it in the amp.... bit gutted now i must admit.  the chances are greater that it was a mis-wired rectifier, as i made the board myself. 

bad times, indeed.

[tweedgv]

would it be possible to get a new download for the amp build, please?  I'm not 100% sure on a few things you said and i don't want to be a pain in the ass.

[Doc B.]

You can request a replacement manual at [email protected]

Be sure to include the name and email that you used to purchase the amp from us, and the approximate date of purchase.

[tweedgv]

great... thank you