RE: What's in a Kinder harp mod?

["DL Terry" <so_blue@xxxxxxx>]

> > Anyone tell what circuit changes comprise the Kinder harp mod on a
Bassman or
> > Concert?
> >
> > Jim R

Jim,
Not to "Muddy the Waters", but there's an article Gerald Weber wrote
that details a set of modifications for good Harp Amp Tone on the
JT-30 page that may be of interest to you:
http://www.jt30.com/jt30page/weber/Guitar51.htm. While this is not the
Kinder answer you asked for, it may shed some light....

Here are some quotes from GW's article):

"Low plate voltage on the preamp tubes.  If you have a guitar amp you
are modifying for harp, you could simply increase the value of the
power supply dropping resistor that feeds the plate resistor of the
preamp tubes."

"Larger than normal (.1uF) coupling caps."

"Simple two-stage design. A tweed Champ, tweed Princeton and tweed
Deluxe are examples of amps with simple two-stage design."

"Paraphase style Phase Inverter. There are two types of paraphase
inverters: the fixed and the self-balancing. A good example of the
fixed paraphase inverter would be the 5C3 Fender Deluxe. A good
example of the self-balancing type would be the 5D3 Fender Deluxe. "

"A Cathode-biased, Class "A" push-pull output stage. I used a 250 ohm
10 watt cathode resistor with a 33-uf 100-volt bypass cap."

"High idle plate current in the output stage."

"Tube rectifier."

"How to Stop Feedback and Fatten the Tone:
I told you about the self-balancing paraphase inverter and I told you
I had a happy accident.  When I was designing the harp amp for Paul
Orta, I thought I would use a potentiometer instead of a fixed
resistor so I could dial in the exact value by ear.  To my surprise, I
found that if I deliberately made the waveform non-symmetrical, the
harmonica tone actually fattened up!
Here's the other part of the accident.  I found if I connected the
speaker reverse polarity with respect to which half of the waveform is
bigger, then the threshold of feedback goes up.  This means the amp
can be turn up to ridiculous volume levels before acoustic feedback
occurs! "

Gerald Weber is the Owner of Kendrick Amplifiers which is a great
site, full info on buying, building, repairing and using tube
amplifiers. He writes great articles for Vintage Guitar Magazine
(where this article came from).

So there y'go....

- -Dane