Model 66 - help post recap - Printable Version
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+--- Thread: Model 66 - help post recap (/showthread.php?tid=17204)
Model 66 - help post recap - gcerio - 08-29-2017
Hello forum, I just got finished re-capping a nice but filthy Model 66 tombstone. I purchased the radio in somewhat working condition - prior owner had replaced the electrolytics - and left the rest untouched - on a variac I got garbled audio across the dial and one or two stations. I replaced all of the remaining wax capacitors, cleaned up a bunch of mud dauber wasp nest under the chassis and now it has excellent sensitivity and clear audio -except for an annoying hum that does not change with volume. Audio is now clear with plenty of volume and set gets both bands fine but the hum doesn't go away. I've re checked solder points and grounds but found all okay. I have no idea of the age of the replacement capacitors installed by the previous owner. They look modern like what you'd buy today from Mouser or DigiKey but then who knows. The hum is a slightly higher octave (?) than a 60 Hz bad cap hum. I've gone as far as shutting off all breakers in the house except my shop feed to see if I could isolate it IF it was interference.
The questions I have are: What is the correct voltage for the e-caps in this set? The schematic shows a 6 and two 8 mfd - - the radio has three 10's installed - two that are 450V and one that is 400V. I understand you can be flexible with the capacitance but not sure on the voltage since the schematic does not list a value. I am thinking of replacing the one's I didn't do since I'm not sure what else would be causing the hum. One last thing: The speaker is a Jensen brand - looks old, but not as old as the radio - Any thoughts would be appreciated - thanks!
RE: Model 66 - help post recap - Radioroslyn - 08-29-2017
450v is pretty much standard fair these days which is fine.
The Jensen spkr isn't original to the set. Is it a pm or electrodynamic spkr?
If it's a pm job you'll need more filtering in the p/s to remove the hum.
Inductance is a much better filter than resistance.
RE: Model 66 - help post recap - gcerio - 08-29-2017
RE: Model 66 - help post recap - Radioroslyn - 08-29-2017
The deal is this measure the DC voltage from one leg of the 80 filament to the center tap of the power transformer. When you first turn it on the DC volt will spike up as the 80 is directly heated and all the other tubes have cathodes. The 80 will start to deliver high voltage before all the others cathodes are hot causing the tubes to draw plate current.
Essentially the power supply has no load for the 20-30 seconds.
If the voltage spikes above 400v at startup go w/the 450v.