P-P bassman mod

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Andy Le Blanc
Posts: 2582
Joined: Sat Dec 22, 2007 1:16 am
Location: central Maine

P-P bassman mod

Post by Andy Le Blanc »

Fender Bassman modded to Marshall JCM lead master volume.
Point to point on tag strip. It works well much to my surprise.
Some bit still to finish. The amp came to me half cooked and
Half modded... Bias wacky with cooked tubes and screen grid resistors.
lazymaryamps
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M Fowler
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Joined: Wed Jan 16, 2008 2:19 am
Location: Walcott ND

Re: P-P bassman mod

Post by M Fowler »

Looks good Andy and great use of space.

Mark
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xtian
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Re: P-P bassman mod

Post by xtian »

Ha ha, you said "P-P".
I build and repair tube amps. http://amps.monkeymatic.com
Andy Le Blanc
Posts: 2582
Joined: Sat Dec 22, 2007 1:16 am
Location: central Maine

Re: P-P bassman mod

Post by Andy Le Blanc »

Ohh jeeez.

Still surprised its not a cockup and works and sounds nice
despite how rough the appearance.

The problem has become how to get the two channels to play
nicely together.

I found examples resistance mixing in very early fenders.
The volume pot. is turned around with input on the control wiper.

So imagine a typical fender channel before inverter.
The coupling cap and 220k... And instead of the verb/trem mix
the top of the master vol. ... which is a 1M to ground.
vrs. the 220k/50k trem pot to ground..

Still have noodle with it and see if its practical.
Be able to put up a schematic in couple days
lazymaryamps
Andy Le Blanc
Posts: 2582
Joined: Sat Dec 22, 2007 1:16 am
Location: central Maine

Re: P-P bassman mod

Post by Andy Le Blanc »

Reversing the function of the master vol. appears to be the right
idea for this application. It becomes an old school mixer.
I've played with some doggy master vol. rigs and the first impression
was a surprise. I can live with it..

Tone is good even at low and moderate volumes.
Get the clean tone vol. to where the rig likes it
And bring up the drive to match...

This approach is usually for verb or trem mixing but you can find
It in old fender.. Les Paul... Kay... Rickenbauker as mixer/vol. for two
circuit inputs.

See about a schematic soon.
lazymaryamps
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