Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: gawlersteve on September 28, 2018, 06:54:33 am

Title: carvin vl100 problem.
Post by: gawlersteve on September 28, 2018, 06:54:33 am

Hi Have a carvin vl100 distorting through return jack. have tried multiple tubes( el34 and 12ax7 ) , leads, checked voltages v1 v2 v3 v4 v5  replaced grid resistors tried dfferent capacitors c39. c59 .c69 etc etc. anybody have ideas. done the phase inverter debug with no joy. dont have an oscilliscope Any help would be appreciated. sounds like ripped carboard and yes tried other speakers. bias resistor seems ok but not sure if nfb is correct

Title: Re: carvin vl100 problem.
Post by: cboysen on October 04, 2018, 04:49:57 am

Hi Gawlersteve

I don't have much experience with this amp, but I wouldn't leave you unnoticed.

Do you have a schematic for this amp?
When you say "distorting through return jack" I assume you mean, that you hear a distorted signal through the speaker, when plugging straight into the power amp section?
Does it distort when sending the the signal of the send jack into another amp / load box etc?
Is it a combo? - and if so, does it does it distort with the amp plugged into an external speaker?

Kind regards
Christian

Title: Re: carvin vl100 problem.
Post by: gawlersteve on October 15, 2018, 04:49:54 am

legacy is 100w head. has separate speakers . dont have another amp to try it through. think there is a problem in the phase inverter but have replaced nearly all the parts including power caps. still no chnange.  it worked properly for 5mins when i replaced c69 but when redoing the solder joint it has gone awry again. have re soldered numerous parts to check for continuity etc and nothing changes. is there a possible fault in the tran. although the test seem to indicate these are alright also. a schematic is readily available  but updates unknown

Title: Re: carvin vl100 problem.
Post by: Willabe on October 15, 2018, 09:33:18 pm

Quote from: gawlersteve on September 28, 2018, 06:54:33 am

Hi Have a carvin vl100 distorting through return jack.

Return jack?

Title: Re: carvin vl100 problem.
Post by: gawlersteve on October 16, 2018, 01:33:43 am

No the send and return jacks are fine. the pots become quite 'live' when connecting to chassis. volume pot on clean is connected to grid earth but then hits and misses when connecting to the chassis, like the chassis earth is overiding something. Bit hard to explain. Have checked pot connections and everything tests out continuity wise. wondering if signal bleed somewhere is going thru chassis somehow

Title: Re: carvin vl100 problem.
Post by: Willabe on October 16, 2018, 02:50:28 am

No, what do you mean by "return jack"?

You said it's distorting through the "return jack".

I'm trying to figure out what your referring to as the "return jack".   :dontknow:

Title: Re: carvin vl100 problem.
Post by: Willabe on October 16, 2018, 03:04:16 am

Ok, I see your from Oz. Maybe it's a language thing?

Quote from: gawlersteve on October 16, 2018, 01:33:43 am

volume pot on clean is connected to grid earth

Are you saying that with no guitar cable plugged into the input jack, the clean channels 1st preamp tubes grid is grounded?

Quote from: gawlersteve on October 16, 2018, 01:33:43 am

but then hits and misses when connecting to the chassis, like the chassis earth is overiding something.

Do you mean, when you plug a guitar cable into the input jack the guitars signal is intermittent?