Crate BV120H , 500 plate volts, no current ?

[gtrplayr1976]

Geez. I forgot all about this. I did get this running after I replaced the slow-blo fuse. I biased it ,and it was sounding good. The fuse was causing the no sound condition. I will be getting this one back again . He says it has no sound on one channel ,and weak on the other. Back to work.

[Jazz P Bass]

The Sidac (thyrister) is being used to divert the B+ if it gets into the heater circuit. (tube failure)

[gtrplayr1976]

The Sidac (thyrister) is being used to divert the B+ if it gets into the heater circuit. (tube failure)

Wonder why it has been suggested to remove it. I know they had said it was a source of noise,and no one seemed to know exactly what it was for until now. I guess it should be replaced ?

[Steve Conner]

The SIDAC is an attempt to stop the 470 ohm hum balance resistors (and maybe the preamp tubes too) from getting smoked if one of the power tubes shorts out and puts B+ onto the heater circuit. Seems to have been a partial success.

If it shorts, as far as I can see, it'll be the same as turning a hum balance pot all the way to one side: more hum from the heaters. It shouldn't blow the heater fuse unless the other heater line was also shorted to ground somewhere.

[Jazz P Bass]

Without knowing the full part number there is no way to tell how much current the device can withstand.
If it does do it's job during a power tube failure (into the heater circuit), does it get damaged & then cause noise?
Possibly.
I do not see the device causing noise when the device is operating properly.
I guess it's value would be in protecting the power transformer.

[gtrplayr1976]

Without knowing the full part number there is no way to tell how much current the device can withstand.
If it does do it's job during a power tube failure (into the heater circuit), does it get damaged & then cause noise?
Possibly.
I do not see the device causing noise when the device is operating properly.
I guess it's value would be in protecting the power transformer.

Sounds like I need to get that back in the circuit hoping it hasn't caused any damage. The part is labeled on the schematic TR1. Part # 73-401-01 SIDAC 120volt

[Jazz P Bass]

That part number does not provide any meaningful info.
There will be no damage to anything if your tubes are good.

[gtrplayr1976]

That part number does not provide any meaningful info.
There will be no damage to anything if your tubes are good.

Yeah, that's the PV # I guess. I'll have to see if I can get the number off the part. If I recall , it looked like a rectifier without the white band.

[g1]

It is not clear to me whether the SIDAC is good, bad, or removed. As Steve mentioned, if it shorts you will get more hum.
I haven't seen any other manufacturer using this arrangement and I don't know if Crate still uses it.
It is an added safety feature but is not necessary.
I'm pretty sure it has nothing to do with the problem the amp has right now. ("no sound on one channel ,and weak on the other")

[gtrplayr1976]

It is not clear to me whether the SIDAC is good, bad, or removed. As Steve mentioned, if it shorts you will get more hum.
I haven't seen any other manufacturer using this arrangement and I don't know if Crate still uses it.
It is an added safety feature but is not necessary.
I'm pretty sure it has nothing to do with the problem the amp has right now. ("no sound on one channel ,and weak on the other")

I removed it the last time I had it ,or clipped on end. January 2012 I think. I'll be getting it back in the near future I'm sure