JCM200 TSL low output

[pontiacpete]

This amp is putting out less than a 1/3 of the volume than expected. All the controls work, channel switching etc.
I pulled the rear board out with the effects loop and speaker jacks and found a lot of bad solder joints and replaced one of the send jacks and one of the return jacks, they had damaged threads. Tried jumping between the send and return jacks.
This amp was previously modding with the 5.6k grid resistor on the power tubes.
One of the J174s were removed. ??
I removed the main board and checked for bad solder connections.
The voltages on the EL34s are
465v plates
453 screens
-37v grid voltage
I biased them to 75mAs per side.
I'm not sure where to go from here, does anyone have any suggestions.
Thanks

[g1]

Can you try to narrow it down to the pre-amp or power amp section by using the FX loop jacks? Maybe use this amps send into a different amps return, or a different amps send into this amps return.
Which J174 is removed? They are often used for muting. Is it possible someone removed it to try to solve this problem (but was unsuccessful)?
Or was the amp working fine before and this problem just occurred?

[Jazz P Bass]

What is the maximum signal that you can get on any of the EL34 grid pins?
What is the output voltage (max clean on the scope)?
Into what load & which OT tap?

[pontiacpete]

g-one , TR4 was the FET removed. Not sure why. I can send the pre to another amp and it works well. But the reverse not so well, the volume is very low.

JP --With 250mVac signal in the input on an 8 ohm dummy load I measure 2.3vac, not much, .6watts. Sounds a lot louder than that a half watt, why is that? There's not much of a clean signal. The wave i"m getting is irregular, the peaks aren't symmetrical.
I'm using the 8 ohm tap. I've used all taps, though with the same issue.
When running this signal in the plates start to get red at full volume, but have not run away on me.

I'm contemplating getting one of those power boards they sell at CE for like $150.
Think that might be the way to go?

[g1]

If you are red plating at full volume, yet low power output, to me it implies a shorted load. Any chance you have a bad load or speaker cable?
Otherwise maybe output jack wiring, or (I hate to say) possibly the output transformer.

[pontiacpete]

I'll swap in an OT next and see what happens. I have a twin output transformer that I can clip in.

I don't think it's the cord, it works with other amps. And i'm having the same results in all 3 speaker jacks.

[pontiacpete]

The twin output transformer works way better. Good call g-one.
I didn't suspect the OT, because the sound it was putting out was clear and even, if that makes any sense.

[AMPREPAIR]

I have not worked on a JCM200, but the JCM2000 has a horrible design flaw that "smacks" of your concern. In the JCM2000, the 16 ohm speaker jack does not provide a good ground through the "sleeve" spring contact when no speaker is plugged into the 16 ohm jack. A sure sign the 16 ohm jack is not providing a good ground is when the metal of the spring "sleeve" contact looks "dull" or over-heated as compared to the other jacks.