RIVERA KR7 troubleshooting

[gpente_gr]

Hi guys!I have a Rivera KR7 and suddenly has no sound output.You can hardly hear something from the speakers if you crank up the 2nd or 3rd channel.I have swap all the tubes and I have also check the signal path in the preamp section and it seems to be ok.I have some experience on building some hardwired amps but the pcb in this amp drives me a little bit crazy instead of point to point wiring!!!It would be very helpful if I could find a schematic,but no luck!Any ideas/help would be appreciated!

[dgrainger]

I've gotten a schematic from rivera by asking them. May depend on the support guy you get...

[gpente_gr]

Thanks mate!I'll give it a try!

[Stevem]

Turn all 3 effects related pots up to 5 and then jump the effects send and return jacks with a cable, does the amp then play ?

[gpente_gr]

Turn all 3 effects related pots up to 5 and then jump the effects send and return jacks with a cable, does the amp then play ?

Thanks for your answer Stevem!

I try your way but with no luck.I am tracing the signal with an oscilloscope,and I see that theres no signal on V5 grids (Pin2,7) thats the phase inverter.The problem is that this amp is too much complicated and is hard for me to proceed without a schematic.Does anyone know if the KR7 is based on some other Rivera's schematic thats already on the internet?I found some schematics of knucklehead and although the KR7 head says "MODEL KNUCKLEHEAD" I see there are some differences on the schematic and that complicates the situation more!

[Stevem]

If you have a audio generator pump in zero DB into the effects return jack , if you get a little better audio volume out of the speaker then I would say that the amps PI section and output section are ok.

Better yet if you have a mixing board take that output and drive the return jack with + 4 DB.

If you have cathode voltage of like 1.2 volts and plate voltage of at least 120 volts on the plates of all the preamp tubes then my guess is that one of whatever Rivera uses to switch channels ( relay, optocoupler or whatever ) has gone bad.

[gpente_gr]

If you have a audio generator pump in zero DB into the effects return jack , if you get a little better audio volume out of the speaker then I would say that the amps PI section and output section are ok.

Better yet if you have a mixing board take that output and drive the return jack with + 4 DB.

If you have cathode voltage of like 1.2 volts and plate voltage of at least 120 volts on the plates of all the preamp tubes then my guess is that one of whatever Rivera uses to switch channels ( relay, optocoupler or whatever ) has gone bad.

Stevem,my thought also is about the optocouplers for channel switching.How could I test them without desoldering,Is it possible?I am about to feed a signal straight on the PI grid

[sluckey]

I am about to feed a signal straight on the PI grid

Best to use a coupling cap between your signal source and the PI grid to prevent mucking with the PI bias.

[Stevem]

Your can check signal flow without a scope of you like.
Use your voltmeter set for AC volts .
As long as you on the out bound side of a coupling cap you will read signal.

Once you get passed the first gain stage if your inputting like .150 mv to the input you should after the first gain stage never have less then 2 volts of signal within the amp if the master is wide open .