Pooched my MP-1! Help! (yes, I'm embarrassed!)

[Kim]

 :o 

Just when you think you've seen it all...

[shredbaron]

REALLY? that why it doesn't work. A transistor is not suited for this and that's why your voltages on G were out of spec.
Now I've seen this before but on the input section, the FET goes down so let's put a transistor in it, that would work fine , euh NOT. You can't believe what some tech's do.

Yeah, I realized this MP-1 had been modded before, there are sockets on some of the ICs that I didn't put in that don't exist on my other MP-1.

No biggie. Got everything finished up today except the replacement of the tubeboard 2SK364 FETs. Military spec 1% metal film resistors in the audio path, replaced all the caps (electrolytic, NP and ceramic) with upgraded versions, did the bass warp pot, mid-scoop pot, replaced the TL072s I had in U11 and U15 with NE5332 op-amps...this things is better than new inside.

Only thing remaining is to get those FETs sorted out and then figure out why the chorus isn't working. I read the other chorus thread, tried a few things, still nothing - so I'm thinking either the trim pot is bad, or the IC has failed. We shall see.

[shredbaron]

REALLY? that why it doesn't work. A transistor is not suited for this and that's why your voltages on G were out of spec.
Now I've seen this before but on the input section, the FET goes down so let's put a transistor in it, that would work fine , euh NOT. You can't believe what some tech's do.

2SK364s arrived today - just installed them - BOOM! everything works great!

just going to replace the volume pot and see if I can sort out the chorus, then it's going back into my rig for some full-volume testing - from what I could tell playing it through my small practice amp, it's a LOT quieter and the EQ is more responsive after replacing all the internals, but I'll know better when I get it going through my tube power amp and 4x12

thanks for the amazing help, it's been very much appreciated

[MarshallJMP]

Aaah great !!!! let me know if I can be of any assistance with the chorus

[shredbaron]

Aaah great !!!! let me know if I can be of any assistance with the chorus

Thanks, I'm thinking it's a bad trimpot. I was able to get some chorusing but it cut in and out with the pot. I'm going to replace it with a new 20K pot (if I read the schematic correctly), hopefully can figure out which one will fit via Mouser.

cheers

george

[MarshallJMP]

531-PTC10V-20K  This one should be the correct one (I hope  ;) )

[shredbaron]

531-PTC10V-20K  This one should be the correct one (I hope  ;) )

Thanks! I was vacillating between a couple of different options last night and thought I'd sleep on it (this was one of them) - really appreciate the heads up!

[MarshallJMP]

No problem!

[Iperfungus]

Another MP-1 came back to life! 

[rnolan]

Another MP-1 came back to life! 

A new take on mouth-to-mouth resuscitation 

[Iperfungus]

Another MP-1 came back to life! 

A new take on mouth-to-mouth resuscitation 

Well, I would prefer a redhead...