JCM 800 2204 NO SOUND

[wawa]

Hi Guys,

I hoping someone can give insight as to whats wrong. i had my JCM800 clone working nice and wanted to try a different opt over my hammond.

The wiring was different between them and I some how wired it wrong.
When i turned the amp on there was a loud pop than silence! NOT GOOD.
I checked fuses and nothing blew. So i pulled out thr OPT and re-installed the old hammond again (correctly). However i still have NO SOUND. something let go? ideas..

there is no burnt parts, or traces, tubes are good & light up. Any suggestion on where to look. maybe my choke is gone.

[stoo]

Got a mutimeter? I'd check al the high voltages ect.
Stew

[paulster]

Pull the tubes and make sure you're getting high voltage to everywhere you should. Make sure also that you're seeing it at the output tube sockets on the plate and screen grid pins (3 and 4) so you know it's passing through the OT primary and the screen resistors.

If you have 1ohm bias resistors tied between pins 1 and 8 and the chassis then check that these are intact too, as an overload situation could have taken them out.

[Richie]

When i turned the amp on there was a loud pop than silence! NOT GOOD

check the speaker first..maybe it was the thing that popped. If speaker is ok.. need to do as others posted. maybe blew a rectifier or cap..

[stoo]

When i turned the amp on there was a loud pop than silence! NOT GOOD

check the speaker first..maybe it was the thing that popped. If speaker is ok.. need to do as others posted. maybe blew a rectifier or cap..

Good point! if the tranny was miswired there might have been a good chunk of DC going to the speakers
Stew

[Structo]

Could also have been a filter cap go if you had the polarities wrong.

Lots of possibilities, but most of them should be pretty obvious by the look of them.

[wawa]

Great replies everyone and thank you!

The first thing I did was check speakers, thier good. Phew!

I do have the 1 ohm to ground and they looked ok., but I will re-check.
I'm going to open it up tonight and take some readings.

I will look at the pins closer on the tube sockets.

cheers.

[Structo]

Be sure to discharge the filter caps before going inside the chassis.

Was this OT the type with the funky secondary wiring?

[wawa]

it looks like the powert trans let go. no secodary voltage.
I have orderd a new one. wait and see.

[Structo]

Does this amp have an HT fuse?

Be sure to correct whatever was wrong that blew it up if it is indeed dead.

[roadkingbluzs]

It seems odd you tubes light up but no Hv output. Just an observation.

[roadkingbluzs]

Hi Guys,

I hoping someone can give insight as to whats wrong. i had my JCM800 clone working nice and wanted to try a different opt over my hammond.

The wiring was different between them and I some how wired it wrong.
When i turned the amp on there was a loud pop than silence! NOT GOOD.
I checked fuses and nothing blew. So i pulled out thr OPT and re-installed the old hammond again (correctly). However i still have NO SOUND. something let go? ideas..

there is no burnt parts, or traces, tubes are good & light up. Any suggestion on where to look. maybe my choke is gone.

If tubes light up seems your filament windings good and HV windings gone? Just an observation.

[wawa]

I agree its strange to loose the hv and still have filaments.
I tested the choke and it ok.
I have corrected the HT fuse.


I will keep you posted.

[Trace]

I agree its strange to loose the hv and still have filaments.
I tested the choke and it ok.
I have corrected the HT fuse.


I will keep you posted.

Its not strange to loose high voltage and have the filaments working. This is what happens when the HT fuse is shorted. This fuse will usually short if you blow a power tube.

So you have replaced the HT fuse with a fast acting fuse correct? (not a slo blo). If so, have you taken a high voltage reading to see where the high voltage stops?

Forgive me if I over looked it but did you reinstall the original known-to-be-good OT?

[wawa]

Hi Trace,

Thats correct i installed old O.T. which was good.
The Power trans is ordered 2 weeks away at least.
proper fuses installed.

I will advise when I install new power trans. Thx