Crate GX1200 devices?

[drewl]

Hello, I have a Crate GX1200 h (head) with bad output transistors.
It's got Tip142 and TIP147's (2 ea) in it that have been changed before.
Does anyone know if these are the correct devices?
Thanks.

[Gtr_tech]

Sounds right...I see those pairs alot in Crate stuff.

[Enzo]

I'd bet my lunch money on them being right.

[drewl]

Thanks, just wanted to make sure.
Anyone know if any Crate solid state schematics are around?

[Enzo]

Around? They're all over.

I am assuming you want this one?

[drewl]

pardon my ignorance your highness, I have as yet needed the schems to fix any Crates
And thanks again.

[chosenfool]

Around? They're all over.

I am assuming you want this one?

thanks for the schematic post! this is the only page that has the schematics as of this writing, and deep in the search results too. search engines are getting harder to use with useless page rankings...

i appreciate this, Enzo! much obliged!

- Marc

[drewl]

Hey this was my post!
anyway I fixed another one of these last week and have another on the bench, so thanks again for the schem!
The one I have now looks like an older model just called a GX 212. The board is cheaper but the layout looks to be the same.
Someone was in here before and they had a 1k resistor across the base and emiiter of one TIP 142 and one TIP 147.
They're blown of course, and this one keeps pulling current trying to blow the output devices again.
It has a TL072 driver instead of the 5532 that looks like it was replaced.

[Enzo]

5532 is a low noise op amp, but the TL072 should work too.

The 212 and the 1200 are the same amp. Combo versus head. I bet the panel is upside down on one compared to the other.

Don't try to sort out bad ones, just replace all the outputs. CCheck the cement ballast resistors - .47 ohm 5w. And real important, check the bias transistor Q8, the little MPSA06.

The outputs connect directly to it, no driver stages between, so if they burn, it might too. It cost 15 cents, just replace it. But if it is damaged, then check all those resistors around it.

And make sure R65 is not burnt open. it is the resistor in your little stabilty network right at the output.

When you get it stable, set bias colder than you might, and accept a little crossover distortion.

I do not use this reading to set bias, but you should have about 2mv across any one of the .47 ohm 5W resistors - 5mv MAX.

[gyrofloyd]

crate 1200H

This 1200H has had outputs replaced. It still draws current. You mentioned replacing Q8. On this one, R65 was burnt. There is no Q8. I am guessing that it is Q10 on this one? The schematic I have does not match this unit. Help anyone?

[Enzo]

That was in reference to the 212


Is your amp a GX1200H? There are other 1200H amps from Crate as well. ALways use the complete model name.

Does the schematic in post #5 match your unit? The R65 on that schematic seems very unlikely to burn up.

[isoarcars]

Yep - those will do. Probably blew them - overdriving input with another preamp or even another amp.