Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jukelemon on July 14, 2013, 03:29:36 pm

Title: 5E11 Bright issue
Post by: jukelemon on July 14, 2013, 03:29:36 pm

http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/fenderamps/vibrolux_5e11_schem.pdf (http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/fenderamps/vibrolux_5e11_schem.pdf)

The 500pf cap between the Tone and Volume...

Does that control the brightness of the tone - serve as a low pass filter?

I have one and the amp is way too bright.  Tone set to 1 is like 6 on all my other amps.  Past 5, the Tone knob is not useable.

Thank you.

Title: Re: 5E11 Bright issue
Post by: PRR on July 15, 2013, 12:32:43 am

I wonder if the 0.005u at the other end is kaput.

Title: Re: 5E11 Bright issue
Post by: jukelemon on July 15, 2013, 07:52:39 am

I can check that too.

I subbed in a 1000p for that 500.  Really no change.

Does the .005uf serve as the low pass filter?

Title: Re: 5E11 Bright issue
Post by: PRR on July 15, 2013, 11:49:03 am

When you turn it one way, the 0.005 shunts all the highs to ground, "dull". (Does that happen??)

When turned the other way, the 500 shunts highs around the volume control (so no effect if you play at "10"), "bright".

In the middle should be halfway between dull and bright.

As long as you are subbing stuff-- snip the wire from top of Volume pot to wiper of Tone pot. This "should" be a Flat Amp, balanced bass and treble. That's normally not best for guitar, it's more like playing through a hi-fi or DI to flat studio monitor.

Speaker is always important. Some are just bright. If the voicecoil has got stuck, the bass won't happen but sometimes the shrill gets out fine.

If what you get no-tone-pot is very shrill, and it isn't the speaker, find what's gone wrong in the amp. If it is 50 years old, a 0.05 coupling cap may have faded-away to 0.0005. Or a 470K grid resistor may have drifted to 50K. If a new-build, maybe your helper passed you a wrong-value cap or resistor.

Title: Re: 5E11 Bright issue
Post by: jukelemon on July 15, 2013, 12:32:19 pm

Hi PRR.

No on the 1st Question.  There seems to be no shunting on the .005 side.  At least very little.  I bet that is the culprit.

I need to pull it an make sure the value is right.

There is definitely no dull on this amp.  It is bright to real bright.

It is a homebuilt.

Title: Re: 5E11 Bright issue
Post by: tubeswell on July 15, 2013, 01:02:48 pm

Quote from: jukelemon on July 15, 2013, 12:32:19 pm

There seems to be no shunting on the .005 side.  ...

I need to pull it an make sure the value is right.

What do the markings on the cap say?