Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Travis8 on March 27, 2023, 10:54:12 am

Title: AC15 weird electric noise
Post by: Travis8 on March 27, 2023, 10:54:12 am
Hi,

My vox ac15 make a weird noise without tubes and If i insert the tubes the noise come bigger.

Also the signal of the guitar doesnt sound and I check the basic, all look fine... some ideas?

Thanks you all

https://drive.google.com/file/d/1Z34eSeIxhBKVUNcRixGKHs7o5MULbwET/view?usp=sharing
Title: Re: AC15 weird electric noise
Post by: PRR on March 27, 2023, 12:45:51 pm
It is a solid 100Hz buzz. I assume you are not in North America?

If this is self-built, it looks like an oversight in wiring the power supply.
Title: Re: AC15 weird electric noise
Post by: Travis8 on March 27, 2023, 01:21:43 pm
Quote from: PRR on March 27, 2023, 12:45:51 pm
It is a solid 100Hz buzz. I assume you are not in North America?

If this is self-built, it looks like an oversight in wiring the power supply.

Itīs a AC15C1 Iīm in europe.
Title: Re: AC15 weird electric noise
Post by: Travis8 on March 28, 2023, 01:50:35 am
I will check 5W resistors today, yesterday I check with tubes and without it, and the noise still there.

Itīs weird..

Title: Re: AC15 weird electric noise
Post by: Travis8 on April 11, 2023, 05:00:06 am
I try to replace 5W resistor and the noise still there.

When I pull out tubes the noise come down but when I put the power tubes the noise comes up very high.

Some ideas?

Thanks
Title: Re: AC15 weird electric noise
Post by: Travis8 on April 11, 2023, 05:12:39 am
How can I check if power supply caps are ok?

thanks
Title: Re: AC15 weird electric noise
Post by: tubeswell on April 11, 2023, 08:32:27 am
Filter cap(s)
Title: Re: AC15 weird electric noise
Post by: Travis8 on April 11, 2023, 09:00:32 am
Quote from: tubeswell on April 11, 2023, 08:32:27 am
Filter cap(s)
Yes I will try to changue it, some way to test it before?

Thanks..
Title: Re: AC15 weird electric noise
Post by: tubeswell on April 11, 2023, 02:03:49 pm
Quote from: Travis8 on April 11, 2023, 09:00:32 am
Quote from: tubeswell on April 11, 2023, 08:32:27 am
Filter cap(s)
Yes I will try to changue it, some way to test it before?

Thanks..


If you solder-tack a suitably rated electrolytic cap in parallel with the suspect cap (observing the same polarity) and the noise goes away, there it will be.
Title: Re: AC15 weird electric noise
Post by: Travis8 on May 03, 2023, 05:51:50 am
Quote from: tubeswell on April 11, 2023, 08:32:27 am
Filter cap(s)

C53 was bad