Crate G40C schem?

[The Link Wray Way]

Hello all, I'm new here to the forum. I have an older Crate G40C and I'm trying to track down a few bugs in it. Wondered if anyone had a schematic for it. I've got some intermittent audio and intermittent channel switching as well as a few other minor issues I'd like to sort out. I'm also interested in what the tone stack looks like and what values they use for that.

Thanks.

[bobsamps]

Originally Posted by The Link Wray Way

Hello all, I'm new here to the forum. I have an older Crate G40C and I'm trying to track down a few bugs in it. Wondered if anyone had a schematic for it. I've got some intermittent audio and intermittent channel switching as well as a few other minor issues I'd like to sort out. I'm also interested in what the tone stack looks like and what values they use for that.

Thanks.

I got one that has a hum and been huntin' for bad part off and on with spare time. But I havn't seen a schem for the old version either.....sorry.

[The Link Wray Way]

Yeah, I've done some looking/searching and schematics for the G40C just don't seem to be very widespread.

Maybe someone has a copy?

[Suusi M]

Originally Posted by The Link Wray Way

Hello all, I'm new here to the forum. I have an older Crate G40C and I'm trying to track down a few bugs in it. Wondered if anyone had a schematic for it. I've got some intermittent audio and intermittent channel switching as well as a few other minor issues I'd like to sort out. I'm also interested in what the tone stack looks like and what values they use for that.

Thanks.

try phoneing crate and asking for a schematic, you will need the serial number

the sent me my blue voodo's schematics afetr about a week

[bobsamps]

Originally Posted by Suusi M

try phoneing crate and asking for a schematic, you will need the serial number

the sent me my blue voodo's schematics afetr about a week

So just curious...where did you get your schematic? I was directed to get info/parts from Loud Technologies( last time I tried to get one) , and they are located out west. And when I went looking for this older (first version-i.e. 'C" ) model, there was no information out there for it.

[Suusi M]

I phoned Loud technologies in the UK and spoke to their spare parts person.

you have prolly seen this page but

crate support


or you could try emailing

General Contact Infomation
For general questions please email:

misupport@loudtechinc.com

[JustRob]

What is the number on the pcb? Should be a number starting with 07- or 07A

[Enzo]

I was directed to get info/parts from Loud Technologies( last time I tried to get one) , and they are located out west. And when I went looking for this older (first version-i.e. 'C" ) model, there was no information out there for it.

CONTACT them. Just looking on their web site doesn't access everything they have.

[Enzo]

I have the G40CXL and the GX40C, but no G40C.

Intermittent audio and random channel changes just screams out jack problems. Measure the resistance of the cutout contacts on the footswitch jack and the FX return jacks and/or power amp in jacks. Those contacts when touching should show less than half an ohm. 1 ohm may seem like a nice low resistance, but it is too high and is a clue that the contacts are not clean. 1 ohm itself won;t get in the way, but if it shows that high, the contacts are not pristine.

[bobsamps]

Originally Posted by Enzo

CONTACT them. Just looking on their web site doesn't access everything they have.

I had talked to them on the phone. Uh it's been a while but I'll try them again. I seem to remember that they didn't have that older model info. Dunno if the U.K. address may have something in their files?

[bobsamps]

Originally Posted by Enzo

I have the G40CXL and the GX40C, but no G40C.

Intermittent audio and random channel changes just screams out jack problems. Measure the resistance of the cutout contacts on the footswitch jack and the FX return jacks and/or power amp in jacks. Those contacts when touching should show less than half an ohm. 1 ohm may seem like a nice low resistance, but it is too high and is a clue that the contacts are not clean. 1 ohm itself won;t get in the way, but if it shows that high, the contacts are not pristine.

HUM ! Mine appears to have a shorted part. Have tried several substitutions (i.e. filter cap,+ others). I just gotta keep searching for it I guess....time ya know. Too many projects, I gots to to get to. I just keep going back to it in my rotation of things.

[bobsamps]

These older Crates seem to develop that loud "Thunk" when turned on too, apparently indicating a shorted part. I've noticed that it seems to get worse as part(s) begin to fail. Old Peavey amps seem to act that way too. Talking solid state stuff..

[Enzo]

Turn on thump is not usually a failed anything, it is just what the amp does.

[JustRob]

Is this what you're looking for? Not the best quality, but beats the snot out of nothing!

[Enzo]

Cool.

[bobsamps]

Originally Posted by JustRob

Is this what you're looking for? Not the best quality, but beats the snot out of nothing!

Thanks! Cool old sheets. I'll have to take a new look at it now.

[mhd720]

I have the G40CXL and the two x '50Ω 10W' resistors (see pics) are almost too hot to touch when clean volume is > half.

I measured voltage across them and it was only about 7.8V each. Assuming they're still 50Ω, then that means about 0.16 mA through each one, which should not be enough to make them > 60 degrees C, right?

Will replacing the resistors be enough? and should I replace with ones with higher power rating?

[Dano]

In regards to the turn-on thump, after going through a Crate G40, trying to find the cause, (we are talking weeks of hours, sometimes I get too obsessed with things) I finally called SLM which used to be the old Crate Factory.

The tech said the thump is normal and there is no turn-on muting circuitry.

Got to know this amp pretty well.

[mhd720]

I have replaced the 50ohm resistors, but they still get warm. Now I'm wondering if maybe I need to replace the large 3300uF caps next to the transformer. my multimeter has a CAP function but it definitely isn't going up into the hundreds or thousands of microFarads...

[Enzo]

They are dissip[ating over a watt. That is enough to make them hot. it is normal for dropping resistors to get hot.

[dobrota]

Originally Posted by mhd720

I have the G40CXL and the two x '50Ω 10W' resistors (see pics) are almost too hot to touch when clean volume is > half.

I measured voltage across them and it was only about 7.8V each. Assuming they're still 50Ω, then that means about 0.16 mA through each one, which should not be enough to make them > 60 degrees C, right?

Will replacing the resistors be enough? and should I replace with ones with higher power rating?

No, 7.8V/50Ω is 0.156A !! current through each one and about 1.2W heat on each one, so they're too hot to touch.
It's normal, "hot" resistors before zener diode for decrease high voltage for power amp to get lower voltage for preamp section. It seems from 35V to 20V in (worst quality) schematics and so about 4.5W heat on each one - 10W rating is for longer resistors life time

[mhd720]

What output should I expect from the transformer? I get 28v AC on each side so I assume it is center-tapped, hence the two red wires and one green wire....

[dobrota]

Originally Posted by mhd720

What output should I expect from the transformer? I get 28v AC on each side so I assume it is center-tapped, hence the two red wires and one green wire....

There's 35V DC after bridge rectifier in the schematics, so about 28V AC is OK.
But only two wires - pin J21, J22 on secondary wiring, no center tap.