Mellotronists

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).

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 .

Not sure what field strength of magged vs. demagged heads might be.
VERY tiny, I'd  guesstimate. Zero Gauss for demagged-heads, obviously.

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.

Cheers,  Jerry Korb (c/o North Country Restorations)

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?

At 11:22 AM 6/4/2004 +0000, tmoravan wrote:
>OK - before I replace these worn out tapes, how do I know if I did a
>thorough job demagnetizing the tape heads?

Hmmm...First of all, is there any high end to wipe out on one of these 
things?  ;-)

For years I have used a Teac demagger I got at Guitar Center, but I have 
also taken care not to magnetize the heads by plugging the heads into the 
preamp without shorting the preamp first (#805 needs the 47K resistor 
treatment).  Most of the time I'll demag anyway just because.  So far, so 
good.  I guess I "just do it" without worrying whether it's "done" or 
not.  If the thing is buzzing, it must be doing something, right?  :-)

Yeah, screwing up a set of tapes would suck...

Note that "screeching cable rot" 
(http://www.kleonard.com/gear/tronecdo.htm) could certainly cause problems 
in this regard.  If it has not been done, replace the cable going from the 
preamp to the head block with new cable---the wire turns to dust after a 
while and begins to fail intermittently...shudder...

...kl...
M400 #805 - needs to get buzzed
M400 #1037 - has the 47k treatment courtesy of 50y.o.jk


* Block Lists:  If your e-mail address is on a block list
*   such as SpamCop, I will no longer receive your e-mail.
** Ken Leonard - Web Table of Contents:  http://www.kleonard.com
** Get Outdoors New England:  http://www.GONewEngland.org

On Fri, Jun 04, 2004 at 11:00:01AM -0400, Ken Leonard wrote:
> At 11:22 AM 6/4/2004 +0000, tmoravan wrote:
> >OK - before I replace these worn out tapes, how do I know if I did a
> >thorough job demagnetizing the tape heads?
> 
> Hmmm...First of all, is there any high end to wipe out on one of these 
> things?  ;-)
> 
On the current set of tapes, virtually none.  Although, some of the
less-played notes still have that original bite and grit to them.  

> Note that "screeching cable rot" 
> (http://www.kleonard.com/gear/tronecdo.htm) could certainly cause problems 
> in this regard.  If it has not been done, replace the cable going from the 
> preamp to the head block with new cable---the wire turns to dust after a 
> while and begins to fail intermittently...shudder...
> 

When I was taking out the headblock I noticed that the visible
shielding looked corroded, almost like that ash that forms on
aluminum (or aluminium if you prefer).  Replacing the cable is now
on the task list (since I'm pulling the amp block anyway).


Has someone prepared an "essential maintenance" list for anyone that
picks up a Mellotron?  I've pieced together some stuff to do and to
look for based on scanning message archives, websites, newsgroups, etc
but it wasn't all in one place.