Crate Stealth 50 combo - self inflicted issue

[Billshire]

Hey all; first post and I hope someone can point me in the right direction.

I know there is a stigma about Crate amps but the Stealth 50 has treated me pretty well. I really like it and it was the only good amp I had until I screwed around with it.

Long story short; I was hoping to replace some non-polar electrolytic caps for polyester film ones for some clearer sound. When I wired the transformer back up; I mis-wired an orange and red wire back to the board. Turn the amp on; very audible hissing noise; pop; power off. Opened everything back up and realized my mistake; put the cables back where they should have been and tried to turn it on. No go. Checked the main fuse and it was blown. Replaced the fuse and turned it on. I get the power LED; tubes filaments turn on; no sound out of any channel. No sound out of the line out. When I plugged the effects loop send into the input of a friends amp, I get some hissing instead of silence but no signal.

One of the red transformer wires that should wire up to J21 or J22 were wired to J23 or J24 where the orange wires should connect; and the orange wire was wired onto the jumper where the red wire should have been. As it was late and I was worried that I just destroyed my amp I did not make not of which wires had crossed; and for that too I am a fool.

There is nothing visibly wrong on the board; no scorch marks; no blown caps... I replaced the polyester film caps I got with the ones that were originally on the board and that didn't change anything.

Since I am not even getting sound out of the line out; I do not think that I fried the output transformer; but I am wondering what I have broken... Have I fried an IC or a transistor; even all of them?

If anyone can point me in the right direction for testing stuff; I would be forever grateful. I am not in a good financial situation where I can buy a new amp.

I have attached the schematic for the stealth 50 in case anyone is curious.
GT-50H,_50_Schematics.pdf

I guess if nothing else I am wondering if I have irreversibly killed this amp and I should start saving for a new one, or if anyone on the forum thinks it is salvageable.

Thanks for your help,
Will

[Jazz P Bass]

The first thing to do is see if the power transformer is good.
Disconnect the Red/Green/Red wires. (label them) This is the 400 volt winding.
Disconnect the Orange/Orange winding. This is the 40 volt winding.
I would try to get a Volt ac reading off of each winding.
Red(1) to Green. Red(2) to Green. And Red to Red.
Any Red to Green will be half the voltage of Red to Red.
If that checks out, move on to the Orange/ Orange winding.(35-40 Vac)
If that checks out, leave them disconnected & do the test points on the Blue (16 volt) winding.
If all of that checks then we find where it got toasted.

[Billshire]

Red 1/green: 153
Red 2/green: 153
Red 1/Red 2: 310
Orange/Orange: 88
Blue 1/Blue-White: 15
Blue 2/Blue-White: 15
Blue 1/Blue 2: 30

Seems a little off to me?

Thanks

[olddawg]

Not to be condescending... But have you checked F2? You just said you checked the main fuse. Transformers usually work or they don't. I would guess you have a power supply problem. I would be checking the dc out of those bridge rectifiers after reconnecting the PT. Then check the output of those regulators.

[Billshire]

Thanks for the input olddawg; I should have mentioned everything I checked. F2 is good; voltage coming out of the diode/rectifier circuits seems to be spot on when checked with a voltmeter. To be certain; I just replaced F2 and there was no change; so I put the original back in. I have also attempted to trace back into the circuit a ways with my multimeter; everything seems to be good on the orange/bias circuit back to the power tubes I am thinking that some component or something in the signal path has failed.... Maybe one of the FETs?

[olddawg]

Have you plugged something into the main amp in or effects return? An iPod will do, or a headphone output from anything. That will tell you if the output stage is working or not. You have already determined that the preamp has no output. If the power amp has no output as well it is something common to both. If it works the problem is related to the preamp.

[Billshire]

Just plugged my guitar into a high gain pedal and into the effects loop return. No sound out of the amp on any channel; even with all the knobs all the way up. Not even that ominous hiss of an amp turned up all the way while it is amplifying silence...

[olddawg]

Still sounds like power supply. Check your high voltage B+. Be careful. Tube amps can kill you. If you do not know how to do it safely, take it to a tech. Also check your +\- 16v rail voltages, 5v supply, etc.

[Billshire]

Thanks for the advice; I know tube amps can kill me; wiring breakers can kill me; just about anything can kill you if you aren't careful. 16v seems to be good across the IC1 2 and 3, B+ is good at 420 across all power tubes. Where in the circuit is there 5V, maybe I am missing it...

After looking at the schematic again; the line out is past my output transformer... Possibly it is blown? If I recall the only way to check would be to swap in another transformer...

[olddawg]

Thanks for the advice; I know tube amps can kill me; wiring breakers can kill me; just about anything can kill you if you aren't careful. 16v seems to be good across the IC1 2 and 3, B+ is good at 420 across all power tubes. Where in the circuit is there 5V, maybe I am missing it...

After looking at the schematic again; the line out is past my output transformer... Possibly it is blown? If I recall the only way to check would be to swap in another transformer...

Many line outs are speaker output run through a voltage divider. This is so when you DI it you get the character of the whole amp. The effects send should be a pre-out. If you look at the power supply section of your schematic on the right you have all of your high voltage nodes. On your left you have all of your regulated low voyage supplies. After the bridge rectifier there are a bunch of 3 pin regulators. Make sure that both the + and - 16v rails are there. The 5v supply is labeled and just above that. If all of the supplies are good you need to put a signal source on the input (Ipod or something) and start signal tracing. A scope helps. If you don't have a scope you can make a signal tracer out if a small amplifier and a probe with a coupling cap.

[Billshire]

Thanks much for the thought and I will do that in the morning but for now it is 2AM where I am and I am going to sleep. I'll update this tomorrow with the results.

[52 Bill]

Maybe I'm missing something here or looking at the wrong schematic, but I don't see any low voltage regulators or a 5 volt supply. The low voltage supplies are Zener regulated.

This amp is mainly tube, but there are a lot of solid state elements in the signal path, so both power supplies are are important. As Olddawg suggested, check all of the supplies and make sure that they are all working. Once that is done, start with the power amp and speaker and then work your way forward to the inputs.

Is the speaker okay? Is it plugged into the correct jack? Is the impedance switch set correctly? Can you hear anything from the speaker, hiss, noise? Have you tested the output transformer for basic continuity of primaries and secondaries?

[Billshire]

Speaker/Impedance/Correct Jack is all fine. Just did some basic resistance testing on the output transformer and it seems healthy... I hear nothing from the speaker; no hiss, no noise, nothing. Absolutely silent. I will get something together to test signal through the circuit; but for now I have to run errands. I'll be back later and get another update on here. Thanks again for the guidance.

[Billshire]

So I put together a signal trace and I'm using it to step through the system/ On the clean channel; I am able to trace the signal up to the reverb send J12. I then get nothing out of j13, 14 or 15 and nothing of the clean signal farther down the system. Tracing the distortion channel, I get it going into IC1 but nothing after anywhere.

Might be some blown ICs that I have to replace?

Also; should I be getting any signal past the reverb tank? the other half of IC3 is there and I am not getting any signal past that....

[52 Bill]

So I put together a signal trace and I'm using it to step through the system/ On the clean channel; I am able to trace the signal up to the reverb send J12. I then get nothing...

If the signal is getting to the reverb driver chip it should also be getting to the input of IC2B. If it stops there, then start by replacing IC2.