Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: silverface on March 05, 2011, 06:08:45 pm

Title: 1973 Fender Silverface Vibro Champ low volume problem
Post by: silverface on March 05, 2011, 06:08:45 pm

Hi everyone i'm a newbie here and was wondering if anyone ever had a problem with a fender silverface vibro champ with a low volume problem. What mine is doing is there's no volume from 1 to 3 on knob and starts to get loud at 4 and up but not as loud  as another champ i have. I already swaped the volume pot with a new one and tried swaping  tubes from another champ with no change. Has anyone ran into this before? Thanks!

Title: Re: 1973 Fender Silverface Vibro Champ low volume problem
Post by: rafe on March 05, 2011, 09:12:05 pm

the speaker needs to be a 4 ohm has someone changed it?

Title: Re: 1973 Fender Silverface Vibro Champ low volume problem
Post by: silverface on March 05, 2011, 10:59:30 pm

The speaker is a weber 8sigA-s4 and that should be ok its a 4 ohm

Title: Re: 1973 Fender Silverface Vibro Champ low volume problem
Post by: rafe on March 06, 2011, 12:25:31 am

I just noticed that this is posted in "Introduce yourself" You need to re-post it to "Tube amp building-tweeks-repairs" you will get feedback that way. edit: moved to correct forum by a moderator

Do you know how to take voltage readings? Safely?
Anyway it could be a number of things, There were a few threads on champs you could try to find, plus there is a great library here. I had a resistor that was never attached in my 74 VC but it still functioned albeit poorly.

Title: Re: 1973 Fender Silverface Vibro Champ low volume problem
Post by: jojokeo on March 06, 2011, 11:53:48 am

Quote from: rafe on March 06, 2011, 12:25:31 am

I had a resistor that was never attached in my 74 VC but it still functioned albeit poorly.

What's that? The removal of nfb? It wouldn't have an affect on poor performance though unless it was wired differently from original. Now if it was a grid leak, this could be a different story.

The vol issue seems like the vol pot's divider network has gone awry somewhere?

Title: Re: 1973 Fender Silverface Vibro Champ low volume problem
Post by: rafe on March 06, 2011, 12:27:11 pm

I'm just saying that the problem with mine was the 220K grid resistor not being attached properly
(No solder).
Post some voltages?

Title: Re: 1973 Fender Silverface Vibro Champ low volume problem
Post by: jjasilli on March 06, 2011, 03:18:43 pm

Post some voltages? Ditto, actually post all voltages.

Also try the tube amp debug section at www.geofex.com

Title: Re: 1973 Fender Silverface Vibro Champ low volume problem
Post by: silverface on March 06, 2011, 05:59:19 pm

 Yea i'll have to do some research and check voltages and get back. Thanks!