02-08-2013, 09:32 PM
Pithicus
We don't do hazings here....(should we?)
As for "all electrocytics go to heaven" (all minuses to GND), this should be "most" i/o "all".
The rule is:
ALL ELECTROLYTICS' MINUSES GO TO THE POINT THAT IS NEGATIVE RELATIVE TO WHERE THE PLUSSES GO.
So, if the Chassis is positive towards something else, the plus wil'l go to it.
In the 18, as in many Philcos and other radios, the most negative point of ANYTHING EVER (well, let's not go to complicated cases of non-radio related stuff and AC-coupled circuitry; let's talk power) inside a radio is its recifier's section winding's centertap (in case of the full-wave with centertap rectifier, such as based on 80 tube). It does not get any more negative than that in the power grid inside a radio.
But, to create some biases that are more negative than the chassis, the rectifier's negative is connected to the chassis via a low-ohm (few hundred ohm down to 30-70 Ohm) resistor, often a milty-tap. The voltage drop across it is decoupled with this very cap you are talking about (in code 124 it is the cap #59 and the resistor is #52). The #59 will have its plus to the Chassis, and its minus to the centertap.
As for the sound, yes check the speaker, but as there is no feedback from the secondary this is not Positive feedback at play.
As someone suggested, nay be bad decoupling capacitor.
Speaking of which, your electrolytics on top look untouched, but you said you replaced all caps, so that means you replaced the lytics also, correct?
Very similar sound was produced by my 80jr when the regenerative was out of whack: upon the warm up the same thing happened, only it took 2 seconds, and then the radio would play.
Could be some feedback.
Have you tried to do the test where you touch the grids with a screwdriver and try to hear the buzz? This would check the Audio section and detector.
IMPORTANT: Trial and error when wiring the speaker can result in smoke or damaging your transformer, your speaker and/or your 42 tubes.
We don't do hazings here....(should we?)
As for "all electrocytics go to heaven" (all minuses to GND), this should be "most" i/o "all".
The rule is:
ALL ELECTROLYTICS' MINUSES GO TO THE POINT THAT IS NEGATIVE RELATIVE TO WHERE THE PLUSSES GO.
So, if the Chassis is positive towards something else, the plus wil'l go to it.
In the 18, as in many Philcos and other radios, the most negative point of ANYTHING EVER (well, let's not go to complicated cases of non-radio related stuff and AC-coupled circuitry; let's talk power) inside a radio is its recifier's section winding's centertap (in case of the full-wave with centertap rectifier, such as based on 80 tube). It does not get any more negative than that in the power grid inside a radio.
But, to create some biases that are more negative than the chassis, the rectifier's negative is connected to the chassis via a low-ohm (few hundred ohm down to 30-70 Ohm) resistor, often a milty-tap. The voltage drop across it is decoupled with this very cap you are talking about (in code 124 it is the cap #59 and the resistor is #52). The #59 will have its plus to the Chassis, and its minus to the centertap.
As for the sound, yes check the speaker, but as there is no feedback from the secondary this is not Positive feedback at play.
As someone suggested, nay be bad decoupling capacitor.
Speaking of which, your electrolytics on top look untouched, but you said you replaced all caps, so that means you replaced the lytics also, correct?
Very similar sound was produced by my 80jr when the regenerative was out of whack: upon the warm up the same thing happened, only it took 2 seconds, and then the radio would play.
Could be some feedback.
Have you tried to do the test where you touch the grids with a screwdriver and try to hear the buzz? This would check the Audio section and detector.
IMPORTANT: Trial and error when wiring the speaker can result in smoke or damaging your transformer, your speaker and/or your 42 tubes.
