[HAM] TG capacitors Was High voltage ceramic caps on the 6550 valves in the 122

[Kon Zissis]

Hi Pete
Thank you for your reply and for the links that you sent me.
When I recapped  the TG of my 1962 C3 a few years ago ,  I used the
readily and cheaply available  ( less than $20 Australian dollars for
the full set of caps  ) 100 volt rated small yellow square shaped MKT
polyester caps. As I am an amateur experimenter with a curious mind ,
late last year or earlier this year  I replaced the recapped capacitors
tray of my C3  with the red mylar capped capacitors tray from a 1970
T-300 and vise versa . I measured the mfd values of all the red mylar
caps with my capacitance  meter  and they were all  very well within
their  proper tolerance  therefore they have not drifted up in mfd value
with age. Because of this I wanted to see if there would be a noticeable
difference in the output levels of the TG notes 49 to 91  with the
original recapped capacitors and transformers tray  and the red mylar
capacitors and transformers tray . 
Some people have written that when a TG is recapped with new capacitors
that are tested and  selected to   produce the peak output levels,  then
the output levels of the TG notes 49 to 91 become louder than what they
originally were when the then new wax capacitors were installed and the
TG then calibrated at the factory, thus resulting  in  the  recapped TG
now  producing an excessively loud upper midrange. With this in mind I
expected that the levels of TG notes 49 to 91 of my C3   would become a
little  weaker after I  installed the red mylar caps tray from the 1970
T-300 , however after I measured the TG note 49 to 91 output levels ,
the TG notes 49 to 91 had become very noticeably stronger.  This
indicates to me that the transformer coils with the bright red enamelled
wire used with the red mylar capped organs of the late 60's  either had
a  slightly different winding  or perhaps the diameter of the red
enamelled wires was slightly different  with the result that the
transformers with the bright red  enamelled wire produced a higher Q or
resonance factor  than the older transformer coils with the dark  brown
enamelled  wire like those that were originally in my 1962 C3.
I needed  to recalibrate the  TG in order to restore a more normal sound
and I decided to try out a louder than normal stock  TG output curve in
order to produce an improved signal to noise ratio and this has worked
well.  Although I have increased the output levels  by around 10
millivolts peak to peak , the tone wheel sine waves are still pure
sounding. However there is a limit to  closer you can set the TG pickups
to the tone wheels because  if  the pickups are set  too close  then the
tone wheel sine waves will become less pure  and more warbly thus
spoiling the organ sound and if you try to set the pickups too close,
you will end up hitting the tone wheels and possibly  destroy them. 
 
With the new  louder TG output curve  with the improved signal to noise
ratio  I no longer  have a problem  with the hum pickup that would be
audible when playing  chords on the upper octaves of the manuals  when I
boosted the bass control from the 12AX7 based EQ / overdrive unit that I
built into my C3  . I have built this same EQ / overdrive unit in my
friend Ray Vanderby's ( leader and Hammond organist of  the band Cosmic
Nomads )   recapped  1959 C3  which has the stock TG output curve and
when I boost the bass control on Ray's C3  , I can hear  the hum when
playing chords on the upper octaves of the manuals . 
 
This is an interesting  thread and I am interested to read about other
people's  experiences and views  about TG capacitors and amplifier
capacitors.
All the best.
Kon
 
 
Pete Mazich wrote :
Kon, I've also experimented w/ different cap types on the TG filters, 
sprague 715p's, 716's, solen polyprops, xicon polyprops, mallory 
150's (metallized polyester). conclusion: they all basically sounded 
the same in this particular application, tho' the lower voltage ones 
seemed to work a little more efficiently ( That is they sounded a bit 
louder-keep in mind, I took voltages randomly and basically went by 
ear). The ones I ended up using were 100 V polyprops (xicons). the 
organ sounded great and it didn't cost alot for the recap.  I believe 
that in the case of the filters the only possible issue w/ cap types 
be ESR rating  because the caps are being used to filter audio- not 
their original intended purpose. (I don't know how ceramics hold up 
in that respect-I didn't try them).