Amp Repair HELP

Metlupass2

Well-known member
I just got this Cameron Aldrich JCM 2003x last week and it was fine no issues but today I decided to check and adjust the bias. I was only able to adjust to 32.5 mA even though they needed to be 39. 32.5 was the highest the pot would adjust.

Everything was fine then.

Then I removed the power and preamp tubes to clean the tube sockets with contact cleaner like I always do. I let it sit an hour before firing it back up.

All it did was hum quietly and the plate read 150 and the tube current wasn't even registering with my Eurotubes Pro One. The HT fuse was blown so I replaced it but amp did the same thing, quiet hum no output. I checked the fuse again and it's NOT blown.

I changed the preamp tubes and now it hums REALLY loud.

Look at how hot the one power tube gets right away. I swapped it with another and that other tube got hot in the same socket.

 

panhead

Well-known member
Possibly a grid resistor on that tube socket. Im guessing, Im not an amp repairman but I know enough to be dangerous. Is it gooped is the question LOL
 

Metlupass2

Well-known member
panhead":fo5635fj said:
Possibly a grid resistor on that tube socket. Im guessing, Im not an amp repairman but I know enough to be dangerous. Is it gooped is the question LOL


Yes it's gooped. That's why I'm afraid to take it to the place I normally go.
 

Metlupass2

Well-known member
I attempted to tighten the sockets and the tube does not red plate now and the amp doesn't hum BUT there is no output and its silent.......fuses are not blown.

I wish I had an extra quad of EL34s but I don't.

I could bring it down to Manteo if you know what you're doing..... :LOL: :LOL:
 

LP Freak

Well-known member
Metlupass2":o4nju2ri said:
I attempted to tighten the sockets and the tube does not red plate now and the amp doesn't hum BUT there is no output and its silent.......fuses are not blown.

I wish I had an extra quad of EL34s but I don't.

I could bring it down to Manteo if you know what you're doing..... :LOL: :LOL:
I know enough to be dangerous but that’s about it
 

SpiderWars

Well-known member
Did you look at those power tube socket mounting screws from the inside? The mounting screws are probably grounds for each tube. If one got loosened then all the current flows thru the other paired tube. So that might explain one tube getting hot. When tightened something might spin or break inside.
 

Metlupass2

Well-known member
Current status..... Plate voltage is almost have and EL34 doesn't even register any mA
 

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blackba

Well-known member
Likely a screen or grid resistor is bad on at least 1 power tube socket and probably a bad EL34 took it out. Hum sounds like 60Hz, so that pretty much rules out electrolytic caps where I would expect to hear a 120Hz hum. I think its time for it to see a tech unfortunately. https://mhuss.com/MyJCM/JCM800_2204.gif

If you are willing to bring it to the shop I do repairs for in Mishawaka, I would be happy to get it going, but I am sure you can find someone closer.
 

Wizard of Ozz

Well-known member
I agree on the burned screen resistor or a short somewhere in the power tube socket. Tech time.

That's probably why it was so cheap too.
 

Metlupass2

Well-known member
Wizard of Ozz":j5z4wvre said:
I agree on the burned screen resistor or a short somewhere in the power tube socket. Tech time.

That's probably why it was so cheap too.

Na it was fine before I messed with it. :doh:
 

LP Freak

Well-known member
Metlupass2":3qh69nv5 said:
Wizard of Ozz":3qh69nv5 said:
I agree on the burned screen resistor or a short somewhere in the power tube socket. Tech time.

That's probably why it was so cheap too.

Na it was fine before I messed with it. :doh:
How’d it sound before you messed with it?
 

Wizard of Ozz

Well-known member
Metlupass2":24jtu8vb said:
Wizard of Ozz":24jtu8vb said:
I agree on the burned screen resistor or a short somewhere in the power tube socket. Tech time.

That's probably why it was so cheap too.

Na it was fine before I messed with it. :doh:


Or it wasn't and the movement of the tubes caused a short. Probably a hack repair job. Do you see any burned resistors near the power tubes?

Either way, it should be an easy fix.
 

Metlupass2

Well-known member
LP Freak":3enecbcw said:
Metlupass2":3enecbcw said:
Wizard of Ozz":3enecbcw said:
I agree on the burned screen resistor or a short somewhere in the power tube socket. Tech time.

That's probably why it was so cheap too.

Na it was fine before I messed with it. :doh:
How’d it sound before you messed with it?


I wasn't like "omg omg omg omg" but it sounded good. The bias was only about half what I should be though.
 

LP Freak

Well-known member
Metlupass2":ut7zf2p9 said:
LP Freak":ut7zf2p9 said:
Metlupass2":ut7zf2p9 said:
Wizard of Ozz":ut7zf2p9 said:
I agree on the burned screen resistor or a short somewhere in the power tube socket. Tech time.

That's probably why it was so cheap too.

Na it was fine before I messed with it. :doh:
How’d it sound before you messed with it?


I wasn't like "omg omg omg omg" but it sounded good. The bias was only about half what I should be though.
Should sound something like this :D

 

Metlupass2

Well-known member
FYI I brought the amp in and everything was cleaned, tightened and it's all good.

The ht fuse I put in was new but was not good that's why there was no output.
 

Racerxrated

Well-known member
Metlupass2":5aew1nrr said:
FYI I brought the amp in and everything was cleaned, tightened and it's all good.

The ht fuse I put in was new but was not good that's why there was no output.
Good news!
 

stratjacket

Well-known member
Metlupass2":2x4qi0my said:
FYI I brought the amp in and everything was cleaned, tightened and it's all good.

The ht fuse I put in was new but was not good that's why there was no output.

That’s great news. Was it able to be biased?
 

Metlupass2

Well-known member
stratjacket":2o6s1s1r said:
Metlupass2":2o6s1s1r said:
FYI I brought the amp in and everything was cleaned, tightened and it's all good.

The ht fuse I put in was new but was not good that's why there was no output.

That’s great news. Was it able to be biased?

Yup and the tubes were still good.
 
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