Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Travis8 on April 27, 2021, 09:45:46 am

Title: Help with JCM800 BASS STD 1992
Post by: Travis8 on April 27, 2021, 09:45:46 am
Hi everyone!!!

It makes this sound without any pedal or guitar connected.

Some recommendation?

https://drive.google.com/file/d/1147T6ck39eDy0_sVYTSBnaZ0Q55VFPg5/view?usp=sharing
Title: Re: Help with JCM800 BASS STD 1992
Post by: sluckey on April 27, 2021, 09:49:30 am
Is that the only sound it makes? No music at all?
Title: Re: Help with JCM800 BASS STD 1992
Post by: Travis8 on April 27, 2021, 09:51:27 am
I can play with it, but sometimes Itīs makes that noise in background
Title: Re: Help with JCM800 BASS STD 1992
Post by: Travis8 on April 27, 2021, 09:52:35 am
I try to touch with a pencil all valves but didnīt changue the problem, Iīm sure valves are not the problem (I think)


The noise come and goes randomly
Title: Re: Help with JCM800 BASS STD 1992
Post by: Travis8 on April 27, 2021, 10:04:23 am
The noise also sound with de D.I output of the amp
Title: Re: Help with JCM800 BASS STD 1992
Post by: Travis8 on April 27, 2021, 10:26:33 am
With a pencil I detect maybe the problem is V2 of preamp, I swap witht the other preamps tubes but the problem is always V2
Title: Re: Help with JCM800 BASS STD 1992
Post by: Travis8 on May 04, 2021, 10:45:07 am
I swap preamp tubes and the problem still there.


Some help please?
Title: Re: Help with JCM800 BASS STD 1992
Post by: SILVERGUN on May 04, 2021, 01:07:16 pm
could be RF interference from you phone


the way it starts and stops kinda reminds me of when I have my phone in my pocket and it bleeds through my guitar

Title: Re: Help with JCM800 BASS STD 1992
Post by: sluckey on May 04, 2021, 02:05:48 pm
Pull V1 and V2. Does the noise go away?
Title: Re: Help with JCM800 BASS STD 1992
Post by: Travis8 on May 05, 2021, 03:59:27 am
Quote from: sluckey on May 04, 2021, 02:05:48 pm
Pull V1 and V2. Does the noise go away?

The noise dissapear
Title: Re: Help with JCM800 BASS STD 1992
Post by: Travis8 on May 05, 2021, 04:00:44 am
Quote from: sluckey on May 04, 2021, 02:05:48 pm
Pull V1 and V2. Does the noise go away?

The noise only dissapear without V1 and V2 and without power tubes
Title: Re: Help with JCM800 BASS STD 1992
Post by: Travis8 on May 05, 2021, 04:02:13 am
Quote from: RCZ on May 05, 2021, 04:00:44 am
Quote from: sluckey on May 04, 2021, 02:05:48 pm
Pull V1 and V2. Does the noise go away?

The noise only dissapear without V1 and V2 and without power tubes

The noise dissapear if I remove only V1
Title: Re: Help with JCM800 BASS STD 1992
Post by: pdf64 on May 05, 2021, 05:06:00 am
The noise suggests to me a bad valve / bad anode load resistor / bad connection between valve pin and socket contact / failing solder joint (probably in anode circuit) / coupling cap from anode leaking DC.
Title: Re: Help with JCM800 BASS STD 1992
Post by: Travis8 on May 05, 2021, 05:07:17 am
Quote from: pdf64 on May 05, 2021, 05:06:00 am
The noise suggests to me a bad anode load resistor / bad connection between valve pin and socket contact / failing solder joint in anode circuit / coupling cap from anode leaking DC.

Could be a good idea resolder this?
Title: Re: Help with JCM800 BASS STD 1992
Post by: pdf64 on May 05, 2021, 01:43:37 pm
Quote from: RCZ on May 05, 2021, 05:07:17 am
Quote from: pdf64 on May 05, 2021, 05:06:00 am
The noise suggests to me a bad anode load resistor / bad connection between valve pin and socket contact / failing solder joint in anode circuit / coupling cap from anode leaking DC.

Could be a good idea resolder this?
Got to start somewhere  :icon_biggrin:
Title: Re: Help with JCM800 BASS STD 1992
Post by: Travis8 on May 06, 2021, 04:20:46 am
this is the amp
Title: Re: Help with JCM800 BASS STD 1992
Post by: Travis8 on May 06, 2021, 04:38:42 am
The noise also come out from D.I out