Kustom 200 question

[Wes]

I'm not getting any power in to this amp; the hot isn't getting across
this small black part that I'm assuming is some sort of fuse. It doesn't
have a normal glass encased filament in a holder, it's just a black part
with the brand BUSS printed on it- glued to the chassis next to the
death cap and the power switch...

I've looked at the schematics provided in other threads, but the tranny
and mains in isn't on them..

Any help is greatly appreciated!

.....here's a picture complete with the weird leads coming off the terminals.
Is it possible a fuse was soldered on these two leads?

http://www.flickr.com/photos/kwad/3651930651/sizes/l/

[Enzo]

That black thing is what's left of a fuse HOLDER. What you see there are just two terminal posts. The bare wires sticking out are what's left of a pigtail fuse. A new pigtail fuse would be soldered across it.

Or you could replace it with a regular fuse clip and use a regular glass fuse.

But check clearance, I am not sure in the photo if there ios room for a clip with end terminals to clear the switch.

[Wes]

Thanks, Enzo. I was assuming that was what's going on.

Any idea what rating of fuse should go back in the amp?

[52 Bill]

Thanks, Enzo. I was assuming that was what's going on.

Any idea what rating of fuse should go back in the amp?

3 Amp Fast Blow

[Wes]

Cool, thanks, Bill!

Now to fire this thing back up and see if anything else is wrong....

[Enzo]

This would be a good place to try a "light bulb limiter" before applying power directly.

DO a search for it.

[Wes]

Good point Enzo.....I have read about them and their use....it's now
the appropriate time for me to put one together!

[Wes]

I haven't had a chance to put together the lightbulb tester, but I did
take out the rectifier and I figured it was done for. I set meter for
diode check and got readings from all but one direction. I went ahead
and built a bridge from 1n4007's and tried to power up again and it
blew another fuse. After that I tested the transformer leads and every-
thing seemed fine testing for resistance in the primary and secondary.
Then with all leads disconnected I powered up the transformer and got
the proper 120 on the primaries and the secondaries read ~60V, 30V@ ct.

My question here is- should I be able to hook up the secondaries to the
rectifier and be able to read the B+ from the - and + that is being supplied?
I've tried to do this and the transformer connected to the rectifier blows
the fuse.

Are there other tests that can be performed to determine the health of
the transformer? Should I just go ahead and build the current limiter or
get a variac and test that way?

[Enzo]

Have you checked the output tranasistors for shorted yet?

[Wes]

What, specifically, should one look for concerning shorts?

I checked to make sure no leads were bent, there weren't, and noticed
just how dirty and grimey everything was around the four 36892s. I dis-
assembled everything and cleaned everything. From the bolts, nuts,
spacers, insulating plastic, to the aluminum chassis/heatsink where they
mount. I tested the four transistors as far as diode checking E to B to C
and they looked ok. I then put some heatsink grease down and put every-
thing back together.

The thing is that after having the fuse blow once everything was back to-
gether I disconnected the transformer leads and started testing there. As
soon as I add a rectifier the fuse blows.....not even connecting the filter
supply or the rest of the circuit....

[Enzo]

Consider this. If you test a transistor as if it were two diodes connected from the base, one to E and one to C, you can test them with a meter. The one from B-E is OK, and hte one from B-C is OK. Now what of E is shorted to C? That puts the two good "diodes" in parallel. They will still measure OK, in fact you would be measuring the same thing on both paths. But the E-C short would kill the transistor in a circuit. I am not sure from your description you did that. Did you?

I am also unsure what your test conditions are. If your secondaries are producing AC, then a properly wired rectifier circuit should put no stress on it. It makes me think your rectifier is either defective or not wired correctly.

Please describe exactly what you mean by "add a rectifier." Connecting to a bridge? COnnecting to a diode, a pair of diodes? FOur diodes in bridge? You mentioned making abridge earlier. Are you sure you put the AC on the correct opposite corners?

[Wes]

Consider this. If you test a transistor as if it were two diodes connected from the base, one to E and one to C, you can test them with a meter. The one from B-E is OK, and hte one from B-C is OK. Now what of E is shorted to C? That puts the two good "diodes" in parallel. They will still measure OK, in fact you would be measuring the same thing on both paths. But the E-C short would kill the transistor in a circuit. I am not sure from your description you did that. Did you?

I am also unsure what your test conditions are. If your secondaries are producing AC, then a properly wired rectifier circuit should put no stress on it. It makes me think your rectifier is either defective or not wired correctly.

Please describe exactly what you mean by "add a rectifier." Connecting to a bridge? COnnecting to a diode, a pair of diodes? FOur diodes in bridge? You mentioned making abridge earlier. Are you sure you put the AC on the correct opposite corners?

Ok, I finally had some time today to work on this amp again.

Firstly, thank you, Enzo, for helping me out on this and I am sorry that
I may not be so clear in what I'm describing.....

I did replace the rectifier, I just built it out of diodes I had lying around....
full bridge....

Ok, everything powers up now. I just don't get any sound. Time to
troubleshoot for that. Whew! The chassis gets super hot around the
power transistors.... You can't touch the amp there it gets so hot....

I get a big loud POP when the amp comes on, just nothing from the inputs.

[Enzo]

So is there DC voltage on the output? if so, get rid of the speaker until that is cured.

1N4007 are 1 amp rated diodes. That is not much for a whole amplifier. All the power for the speakers comes from that power supply. And 1 amp through an 8 ohms speaker is about 8 watts. You try to draw more than 8 watts from this amp and you will exceed the ratings of those diodes. That is why they used the block bridge.

The 1N4007 might be OK to verify the rest of the amp functions, but it sure won;t hold up in use.

Are you connecting the AC wires to two corners of your bridge and NOTHING else is connected to it? Not ground, not a wire to somewhere, just hanging there in mid air? ( I often sit subassemblies on a magazine to insulate them) Are you sure the diodes are all pointing in their proper directions? Are you sure none of the diodes has failed or been damaged? Are you sure you are connected to the correct corners of the bridge?

A proper bridge - alone - connected to an AC winding at its AC corners will produce DC across the opposite corners. And draw no current from the transformer while doing so.

If your transformer makes AC of more or less proper voltage, then it is fine. There is nothing that goes wrong with transformers that would only show up when rectified.

[Wes]

The rectifier is good to go. I took out the 1n4007s and installed
ones (I forget their #) that are 3 amp each. Do you think those
are strong enough?

Again, the amp fires up now, I just need to troubleshoot the lack of signal.

I haven't checked for DC on the outputs aside from hearing the big
boomy pop I get when turning on the amp....I'll look into all this next.

Thanks again, Enzo!

[52 Bill]

The rectifier is good to go. I took out the 1n4007s and installed ones (I forget their #) that are 3 amp each. Do you think those
are strong enough?

The original bridge was rated at 5 Amps.

Are the outputs still getting hot?