Mellotronists

On Fri, Jun 04, 2004 at 08:50:26AM -0400, Jerry Korb wrote:
> 
> 
> tmoravan wrote:
> 
> > OK - before I replace these worn out tapes, how do I know if I did a
> > thorough job demagnetizing the tape heads?  I know there's
> > magnetometers (gaussmeters) out there, but in fact, has anyone
> > measured the magnetic field strength of a tape head when it's
> > magnetized and/or after being demagged?
> >
> > (Just being paranoid - don't want to wipe the high end out testing my
> > work).
> 
>   ------------------------------------------------------------------------
>  Greetings Tom and everyone,
> 
> Alwayd best to demag the heads and headblock when performing
> any service in that area.   I recently cleaned/polished heads on
> M400/1428 and replaced a suspect tape head.   (Thanks for your
> help, KL !) First order of  business was to demag every head ,
> since my hand tools were  suspect .
> 
> For general Mellotron svc. easiest way to avoid magging the heads
> is to install a 47 K-Ohm resistor across the connector inside the
> M400 preamp.  Reason for this is to dissipate the charge of
> Capacitor  C2 (20uF@6V) each time headblock is removed and
> reconnected. This is an old modification first done by Sound Sales
>  then by DK and now the majority  of us who own/service Mellotrons.
> 

Hmm -- since I apparently have fairly new preamp/amp (it's the single
combined board with the UA741), I'll check it for the 47k resistor.

I hate to keep asking these kind of questions, but has anyone 'gone back'
from the ua741 single board to the older designs for the amp/preamp?

Alternatively, any recommended changes to the ua741 design?