Crate Stealth 50 combo - self inflicted issue

[olddawg]

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.

You have no output when you drive the power amp via the effects return. Something is also affecting the power amp. Make sure the power supplies are there on those ICs.

[Billshire]

power is getting to all ICs. Replaced IC1 and 2; I seem to be getting even less signal through to the reverb send and nothing afterwards still. This is all completely frustrating at this point in time and I may just sit on it or leave it as a project, or build some other smaller amp out of the parts... That or take it to some tech to fix... I don't know.

Any votes on what to do?

[52 Bill]

Any votes on what to do?

This amp is full of things that can cause the symptoms that you have. Making things even harder is the fact that there are both tube and solid state elements in the signal path. Besides the ICs, if any of the opto isolators or the fets is bad, it will also kill the signal.

I suggested to start at the power amp and work forward because at least from the speaker to the input of the power amp the circuit is all tube. Once the basic tube power supply is working then you can move on to the solid state elements.

Have you tested the tube power supply including all of the different nodes?

[olddawg]

power is getting to all ICs. Replaced IC1 and 2; I seem to be getting even less signal through to the reverb send and nothing afterwards still. This is all completely frustrating at this point in time and I may just sit on it or leave it as a project, or build some other smaller amp out of the parts... That or take it to some tech to fix... I don't know.

Any votes on what to do?

I would exercise some patience. Maybe put it aside for a day and look at it with fresh eyes. Are you sure you have +16vdc on pin 8 and -16vdc on pin 4 of the IC? Do you have signal on pin V1A coming from the volume pot with a signal source on the input? Does it vary with the volume pot? If it does go to the next stage. If it doesn't find out why. Randomly replacing parts will just cause more problems. Don't guess.

[Steve Conner]

By switching the red and orange wires, you may well have put 400V onto the power rails of the solid-state circuitry. This could have blown just about every IC in the unit.

If you're lucky it will simply have blown the filter caps or the dropping resistors in the Zener regulator section.

In any case, I'd be tracing the low voltage supply rails, not the signal.

[Billshire]

Thanks all for the advice. I slept on it, waited and thought. I'm going to continue screwing around with this till it works. I was able to replace IC1 and 2 with another opamp which does not sound so good it appears; BUT I was able to get distortion signal all the way to my effects loop send. Perhaps I have blown a transistor or the clean signal is just failing somewhere else that I have to diagnose, but when I am running through the distortion channel, I get signal all the way to the power tubes. I am then not getting anything out of my output transformer. I think that I have shorted/fried my output transformer and I will need a new one. I am in the process of testing it, but I will be ordering a replacement soon I guess.

I want to say thank you again for everyone's help as this has been an expensive lesson learned. Not as expensive as college, but expensive. With any luck I will be able to replace a few ICs and an output transformer, maybe a transistor or ten and have a working amp.

I'll probably have a reply back with what the output transformer is looking like soon...

In the meantime a very good friend has loaned me an amplifier so that I am not without while I get mine fixed.

[g1]

Before even thinking about the OT, what kind of DC voltages do you have on pins 3 and 4 of the power tubes? Pins 1 and 6 of the phase splitter (V3)? The signal going to the power tubes needs to be fairly big. I would suggest sticking with the power amp for now and applying signal at the FX return jack. You will need to verify U4 is ok.

[Billshire]

so on the distortion channel, I get signal from the main input through to the power tubes. Pins 3 and 4 on the power tubes have about 400v at them. pins 1 and 6 of V3 have about 400V and 600V respectively.

Doing a signal trace around the power tubes, I get lots of signal through pin 5; no signal through anything else really. There is extremely faint signal that can be heard on pins 6, 7 and 8, but that may just be stray electrons in the tubes or due to my poorly shielded signal trace probe. There is absolutely no signal through at pins 1, 2, 3 and 4. I guess that is bad... There should be loads of signal at pin 3 on the power tubes.

Basic continuity tests of the output transformer seem to check out. I do not have a spare 6.3v filament transformer for more advanced testing.

Have I fried my power tubes? They do not seem to be visibly bad, but they are the original old Hot Rod tubes that came with it and are mostly blacked out.

[52 Bill]

pins 1 and 6 of V3 have about 400V and 600V respectively.

These readings must be wrong, recheck when you have a chance. There is no 600 volt supply, and the 400 volts should be lower if the tube was actually drawing current.

[Billshire]

Sorry; it must have been late and I was tired.

Pin 1 has 192v and pin 6 has 222v

Possibly my multimeter was not on the right setting, sorry for the erroneous info...

[Jazz P Bass]

That looks better
What I like to do is remove the output tubes & then inject a signal into the front end of the amp (input jack)
Then I'll go straight to the grid pin of the output tubes. (pin 5 in this case)
At this point, while monitoring the Vac on pin 5, turn up the volume on the preamp.
You should get a nice healthy signal on the grids.
(Roughly 30-40 Vac for 2 6L6, double for 4)
If you do not have that the output tubes will not work.
If you do have the Vac then you can install load & the tubes.
If you still have nothing on the output, the tubes or the OT is suspect.
For testing the tubes, you can try one tube at a time (some amps this is not so, notably certain Peavey's where the heaters are in series).
Even one tube should put some signal on a good OT.
Still nothing, you have known good tubes, the OT is bad.

[Billshire]

I have checked pin 5 for signal with the tubes installed and there is a very healthy signal there.

While I have signal on pin 5 with the tubes installed, there is absolutely no signal on pin 3 of any power tube.

From what I understand of pentodes, the voltage must be higher at the anode than at the screen grid; which I can check on when I get home. I suppose if something happened and shorted some resistor, there could be more voltage on the screen grid and preventing signal from flowing to the anode, but there is no signal at pin 4 either.

I can try the output tubes in pairs, but not individually.

A bad OT wouldn't have nixed the signal at pin 3 would it? Since I was going to get some anyway, I ordered new output tubes, they should be here by Saturday.

The OT passed all the basic continuity tests. I'll continue to troubleshoot as possible.

Sounds like bad power tubes?

[Jazz P Bass]

Do you even have a high voltage at the screen pins?
Does Pin 8 (cathode) deffinitely connect to ground?
As Steve Connor so politely pointed out to me,() if the screen resistor is open the tube will not conduct a signal.
Also, if the cathode is not grounded, the tube will not conduct at all.
On to the OT.
With the output tubes removed & the power supply drained, what resistance do you read on the OT primary.
(Red to Blue/ Red to Brown/ Blue to Brown.)
A continuity check is not enough.
The secondary is going to read less than an ohm.
Keep in mind it is a transformer.
Resistance readings tell you one thing.
You will need a low voltage ac source to check it further.

[Billshire]

I know pin 4 has voltage but I am going to check it to see if it has higher voltage than the anode... I'll get on your suggestion as soon as I can.

Thanks.

[g1]

Sorry to ask, but you do have heaters lit up at the power tubes? You said the filaments were lit, but I wanted to double check on the power tubes specifically.