Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Darkpr0 on March 20, 2020, 07:15:57 pm

Title: 1964 Vibroverb AA763 Reverb noise
Post by: Darkpr0 on March 20, 2020, 07:15:57 pm

Hey everyone!

I am working on my beloved Vibroverb. It is an original 1964 Vibroverb and plays great. One issue I have noticed is the reverb is quite noisy. Turning up passed 3-4 adds a good amount of noise into the channel. Looking for suggestions on what to troubleshoot. I am fairly handy with amp repair, just need a place to start. Couple of notes:

- Amount of noise scales with turning the reverb knob. Almost no noise when at 0.
- Noise occurs with or without reverb tank connected
- Noise does not occur if footswitch is disabled
- V3 tube is an 12AU7 instead of 12AT7

Please let me know if you have any advice. Amp photos were too big to add here, so I made an Imgur Album: https://imgur.com/a/aA7wh41

Title: Re: 1964 Vibroverb AA763 Reverb noise
Post by: Johnny_Riff on March 20, 2020, 11:26:11 pm

howdy. my first post here too.. have you tried new/different tUbes?

Title: Re: 1964 Vibroverb AA763 Reverb noise
Post by: nandrewjackson on March 21, 2020, 12:40:37 am

Nice looking vintage amp !




So would this be correct?


Reverb tank not connected, reverb pot half way up, the reverb footswitch can turn the noise on/off?

Title: Re: 1964 Vibroverb AA763 Reverb noise
Post by: Darkpr0 on March 21, 2020, 12:40:39 pm

More info to clarfiy:

- Tubes are brand new. I tested swapping out the V3 12AU7 with some others, and a 12AY7. No change.

- With reverb tank not connected, and the reverb disabled via footswitch, the hum noise does not appear. There is still static when reverb knob at 5 (I would describe it as vintage amp white nosie0
- With reverb tank not connected and the reverb ENABLED via footswitch, there is a noticeable hum on top of the ambient static. It might be 60 cycle hum, I am not an expert so I couldnt say definitely. Amount of hum increase / decreases with the position of reverb pot.

Let me know if there are voltage reading that would be of assistance.

Andrew

Title: Re: 1964 Vibroverb AA763 Reverb noise
Post by: shooter on March 21, 2020, 12:48:20 pm

Quote

reverb tank not connected, and the reverb disabled via footswitch, the hum noise does not appear.

so you isolated it to about 5 parts and some solder connections, $5 and 1/2hour walla  :icon_biggrin:

Title: Re: 1964 Vibroverb AA763 Reverb noise
Post by: Darkpr0 on March 21, 2020, 03:33:55 pm

In a completely accidental discovery, i have found that the noise occurs despite having the V3 Reverb Send tube installed

Title: Re: 1964 Vibroverb AA763 Reverb noise
Post by: PRR on March 21, 2020, 03:46:38 pm

> reverb tank not connected and the reverb ENABLED via footswitch, there is a noticeable hum

So if the tank is not connected, don't turn up the reverb!

If you plug a cord to your amp, but not your guitar, and turn up, you get hum, right? So don't do that. Why would you turn-up on a disconnected input?

Or connect to the reverb tank and see if hum goes down.

Title: Re: 1964 Vibroverb AA763 Reverb noise
Post by: Darkpr0 on March 23, 2020, 11:41:26 am

Bit of an update:

The noise persistent with and without reverb tank connected. I ended up reflowing all solder connections on V3 and V3, as well as reflowing all the grounds. After cleaning the RCA jacks and ground connections as well, much of the noise is gone. Its not 100%, but its a lot better