watterson: 527

I recently acquired a Watterson model 527.  It appears to be one of the last models they produced.  I believe they may have been made by the Warwick Co. and branded as Wattersons.  Either way it has a significant "motorboating" problem and I cannot seem to locate a schematic to troubleshoot with.  All the tubes (std AA5 complement) check good with my Hickok 605 and the B+ is about 120 off the electrolytics.  Any help tracking down a schematic as I do not see one under the Watterson schematic link.  Great looking radio, just want to rectify the "motorboating",  Any help would be greatly appreciated.

Charles

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An HT capacitor has dried out.

Try a 16uF (8uF to 32uF) 300V across the B+ / HT  supply rail. 

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    Thanks for the info.  I failed to mention that the electrolytics (multi-section 50/50 @150 volts) and all wax paper non ceramic caps  have been replaced with new ones (rated at 630 volts) and the and the 12AT6 tube shield is in place and well grounded.  Just rechecked the B+ off of the 35W4 cathode pin and it reads a steady 115VDC.  I have not checked the 50C5 tube, could an incorrect plate or grid voltage be causing my "motorboating" symptom.  Thanks again for any help.  Still looking for a schematic also.

Charles

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Only bad connection to a decoupling capacitor or a high resistance decoupling capacitor causes it.

This includes any AGC capacitors to 0V. Though I only saw this once.

A bad 0V buss connection too will cause it.

It will not be caused by wrong voltages or poor inter stage coupling capacitors.

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