Re: Help - B3 Intermittent loss of highs and intermittent hum

[Marco Montaruli <genpla@flashnet.it>]

At 14:42 02/01/96 -0800, bobs@hopf.dnai.com (Bob Schleicher) wrote:
>>
>>>My B3 intermittently cuts out, best described as a loss of highs, diminished
>>>volume, and sometimes accomp'd by 60Hz hum "
>>
>>
>>  _____________________________________________________________
>>  Marco Montaruli, General Plastics - Rome <genpla@flashnet.it>
>>
>>
>>Check the tone control.  Sometimes spraying cleaner into it and rotating to
>the limits several times will cure, or just replace it (300K linear).
>
>You might want to replace the cathode bypass caps on the 12BH7 and the
>12AX7, which is common to the 6AU6's too.  They may be part of a 4 section
>electrolytic, or tubulars.
>
>Make sure there is no "growth" around the swell cap., and check the shielded
>wire from the swell cap (green in a spring type gizmo) has about 1/8"
>clearance at the end that goes to pin 7 of the 12AX7. I've seen the spring
>move forward and try to ground the grid of the tube.  You might also want to
>check the volume solt switch for "growth".  If all that fails, try C16, .033
>from 12AX7 to the swell comp. network and C23 same value from pin 6 12AX7 to
>the volume soft switch.
>
>Hope thats of some help and good luck.
>
>Bob S.

A very comprehensive check-list, Bob. My deepest compliments and thanks.
I'll do it a.s.a.p. and refer to the list.

Marco

  _____________________________________________________________
  Marco Montaruli, General Plastics - Rome <genpla@flashnet.it>