Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on June 04, 2018, 03:20:30 pm

Title: Crossline MV - Is it necessary to add two further coupling caps ???
Post by: kagliostro on June 04, 2018, 03:20:30 pm

A friend today asked me how to add a crossline MV to an amp that has fixed bias and the firtst thing that come to my mind was to put two

additional coupling caps between the pot and the 220k resistors, but later I've think again to this thing and ....

is it really necessary to add those caps ? (on the red square)

(https://i.imgur.com/fAB6K85.jpg)

Thanks

Franco


p.s.: The schematic is only an example

Title: Re: Crossline MV - Is it necessary to add two further coupling caps ???
Post by: sluckey on June 04, 2018, 04:50:23 pm

no

Title: Re: Crossline MV - Is it necessary to add two further coupling caps ???
Post by: kagliostro on June 04, 2018, 04:51:20 pm

Thanks Steve

Franco

Title: Re: Crossline MV - Is it necessary to add two further coupling caps ???
Post by: leroy on June 06, 2018, 09:10:44 pm

Aren't the second caps there to stop the bias being shorted to ground?

Leroy

Title: Re: Crossline MV - Is it necessary to add two further coupling caps ???
Post by: sluckey on June 06, 2018, 09:47:27 pm

Quote from: leroy on June 06, 2018, 09:10:44 pm

Aren't the second caps there to stop the bias being shorted to ground?

Nothing about that crossline MV is connected to ground.

Title: Re: Crossline MV - Is it necessary to add two further coupling caps ???
Post by: OrganicEffects on June 09, 2018, 10:24:46 am

I believe those caps are present in the MV that AllenAmps mods Fender amps with?

Title: Re: Crossline MV - Is it necessary to add two further coupling caps ???
Post by: sluckey on June 09, 2018, 10:41:21 am

Quote from: OrganicEffects on June 09, 2018, 10:24:46 am

I believe those caps are present in the MV that AllenAmps mods Fender amps with?

The caps are on some of the Allen amps, but not all. Regardless, Allen uses a completely different dual pot MV, not a crossline MV like being discussed in this thread. So, not applicable.

Title: Re: Crossline MV - Is it necessary to add two further coupling caps ???
Post by: OrganicEffects on June 12, 2018, 07:00:06 pm

Quote from: sluckey on June 09, 2018, 10:41:21 am

Quote from: OrganicEffects on June 09, 2018, 10:24:46 am

I believe those caps are present in the MV that AllenAmps mods Fender amps with?

The caps are on some of the Allen amps, but not all. Regardless, Allen uses a completely different dual pot MV, not a crossline MV like being discussed in this thread. So, not applicable.

Ah I see where we got confused. The crossline MV uses out of phase signals to cancel each other out and reduce the volume?

Looks like the version I was thinking of using a dual pot with either end to ground.