Re: combo preamp / 122

[Ted Thompson <tthompsn@mail.bcpl.lib.md.us>]

Dallas Selman wrote:
> 
> ----------
> > From: Ted Thompson
> > To: hammond@zk3.dec.com
> > Subject: Re: combo preamp / 122
> > Date: Saturday, June 29, 1996 10:30 PM
> >
> > Hickybyrd@aol.com wrote:
> > >
> > > Hi,
> > > I sold a small 6 pin preamp to a guy out of state with a leslie 122.
> That was
> > > my first mistake. He called back and left several messages about
> arcing,
> > > popping, and generally unpleasant things happening. I haven`t called
> him back
> > > yet. My father is in critical condition in the  hospital so my brain
> has not
> > > been working very good. Why I sent him this preamp without checking
> what
> > > model leslie he had first is a mystery. I`ve checked the hammond faq
> and
> > > other resourses for anything that might help and here I am. My
> questions are:
> > > 1) Can I modify the preamp in anyway to work with balanced lines and
> dc motor
> > > control? and 2) What kind of damage was done to the 122 amp if any?
> > > I`m a MITA member and an organ tech since 1978 so be as technical as
> you
> > > need. I have no problem with taking the preamp back but I`m ticked
> that my
> > > stupidity may have wrecked a probably good leslie amp! and my
> reputation as
> > > an excellent tech. Good thing thid guy is out of state! Thanks for any
> help
> > > you send my way.
> > >
> > > Don Hicks
> >
> >
> > Well, the cobo amp could be converted for the control and signal using
> > the standard switching circuit, if you can get a transformer for it and
> > figure out where to put it.  I doubt the space is there.  As to the amp,
> 
> > wellll...  110 vac woul;d have been applied to the ground and B+ out of
> > the 122.  Hard to what that would do, lets see.... it would have been I
> > guess about 20 mils of ac current across the B+ of the power supply
> > (Through the 10K resistor).....  If you like I can supply a device which
> 
> > will allow an unbalanced input and a 1/4 jack for switching speed as
> well
> > as a power cord for this 122, then he could use a standard preamp (Blue
> > tube perhapes) to get his system going.  Assuming the amp is undamaged.
> 
> > If I were you I'd make a quicky plug with a power cord on pins 3&4 and
> > two leads conected to pins 6&1 for audio, so this guy can see what
> damage
> > was done.  add a droping resistor and a Neon bulb and it can check for
> > the presence of B+ too......
> >
> >
> > --
> > ****************************
> > *  Maryland Organ Service  *
> > *      Ted  Thompson       *
> > *      (410)666-2264       *
> > ****************************
> >
> > Ted, an odd question maybe, what is the function of the B+ ?. Does it
> figure into a 147's
> operation also...?
> 
> Thanks,
> Dallas...

No, on a 147 pins 2 and 5 are used for a 110vac circuit, which operates 
the speed switching relay.  There is no B+ output on a 147 amp.

On a 122 pins 2 and 5 are ground and B+.  THe B+ serves two purposes one 
to supply the DC nessasary for speed switching (Which is piggybacked on 
th audio line) and if the hammond is an A,AB,C,D,G,E,BV,CV,BC,B2,C2,RT, 
or RT2 it supplies the nessasary DC for the preamp to work.  Latter 
madels like your A100 (B3) had a full power supply built in, but early 
console preamps had only the filament supply (6.3 vac) built in and were 
intended to recieve the high voltage B+ from the tone cabinet (Hammond or 
Leslie) (BTW: B+ is around 400vdc or so)

I think Hammond figured at first, why build it twice?  The tone cabinet 
has got to be there so...  Why not run one more conductor in the cable 
and steal it from the power amp?


-- 
****************************
*  Maryland Organ Service  *
*      Ted  Thompson       *
*      (410)666-2264       *
****************************