JCM 800 4010 Noise when plugged in to high input

[66fora69er]

As the topic says, when im plugged into the high input there is a crackling sound. It stops when you pull the cord out of the jack. No noise when plugged into low input. The amp works great otherwise and sounds awesome. I just want the noise to stop. I took a video but cant figure out how to post it. Thanks

 

[Gunner64]

A noisy/ microphonic V1? Try a different 12ax7 in that postion.

 

[66fora69er]

Would it need to re-biased if I change the tube? If that ones bad should I just change them all? It's a 1987 amp and I have no history. I love the way it sounds though! Thanks for the reply

 

[Gunner64]

No biasing of pre amp tubes. If it was mine I would just change v1 with a known good tube, and clean the socket and jacks.

 

[66fora69er]

No biasing of pre amp tubes. If it was mine I would just change v1 with a known good tube, and clean the socket and jacks.

Thanks

 

[Russ Selzer]

Replace the cathode cap (C1) on V1a. And the plate cap (C3) as well on V1a. Just went thru this exact issue on my 800. Fixed it.

 

[Gutch220]

Replace the cathode cap (C1) on V1a. And the plate cap (C3) as well on V1a. Just went thru this exact issue on my 800. Fixed it. View attachment 154037

For C1 and C3, do you know the capacitor voltage ratings?
C1: 0.68 uF
C3: 0.022 uF

 

[Russ Selzer]

I would say the standard 600v rating. Get a good poly film cap.

 

[Russ Selzer]

For C1 and C3, do you know the capacitor voltage ratings?
C1: 0.68 uF
C3: 0.022 uF

I would say the standard 600v rating. Get a good poly film cap

 

[Russ Selzer]

Did ya get er fixed?

 

[DirtySteve]

Couldn't it just be a dirty jack?

 

[66fora69er]

Did ya get er fixed?

The replacement of the tube did not get it fixed. I don't think I'm skilled enough to replace a cap. Thank you for all the replys

 

[66fora69er]

I tried cleaning the jack with no success. Thanks

 

[66fora69er]

I would say the standard 600v rating. Get a good poly film cap

Whats a good source for caps? Thanks

 

[66fora69er]

Sorry for the delayed reply I did not have notifications turned on.

 

[66fora69er]

Did ya get er fixed?

Taking to a tech on Wednesday to get caps replaced. Fingers crossed

 

[Joesatch]

most likely this is dirty jacks. the low input shunts the first and second gain stages together when nothing is plugged in there. Make sure all jacks are cleaned with deoxit

 

[maico996]

most likely this is dirty jacks. the low input shunts the first and second gain stages together when nothing is plugged in there. Make sure all jacks are cleaned with deoxit

This is what fixed the same issue I was having with my 4010. Deoxit on a big pipe cleaner shoved in both jacks. I did the speaker jacks too, just 'cause. Solved my noise issue. Not a bad idea to have the caps replaced if they're the originals.

 

[66fora69er]

This is what fixed the same issue I was having with my 4010. Deoxit on a big pipe cleaner shoved in both jacks. I did the speaker jacks too, just 'cause. Solved my noise issue. Not a bad idea to have the caps replaced if they're the originals.

Thanks for all the help. It’s an ‘84 so not sure what’s been replaced. I’ll give cleaning a go again.

 

[66fora69er]

The tech said someone has been in here before. There was this poorly replaced capacitor. He is going to replace the caps while hes in there