Project Planning (Steps/Order)

Rosinante · 13th December 2010, 02:03 PM

Alright.....I've got this Pilot 602 that appears to be in pretty good, unmolested condition and I am likely to restore it. You know....new caps and such. It works, and sounds fairly good already, but it does have a few problems. This thread is for the purpose of gathering advice regarding what steps to take first, second, etc. I wonder if I should investigate and fix the known problems first, then recap this thing, or vice versa.

FM works.....AM does not work.

There is a low hum in both speakers, continuously, as long as the volume is turned on. The hum does not seem to increase as the volume is increased, but it goes away once the volume is turned all the way down.

Occasional crackling sound in the right speaker. Static-y sounding.

The "phono" circuit is not working properly. It plays okay, but only at "idle" volume. Anything more than idle volume and there is a scary, low, bass-ey rumbling. If I were to turn it up much, I'd guess it would damage speakers. There is no sharpness to it, the kind that really damages speakers quickly, but it is a powerful-sounding, flabby rumble.

I will start this project probably in January, and just wonder if I should replace all the caps and then re-evaluate........or should I attempt to investigate and troubleshoot and address these individual problems first, then do the overhaul.

6L6 · 13th December 2010, 02:12 PM

By what you are describing it seems that you have an incredibly out-of-spec powersupply. it has to be up to scuff before you can tackle any other problems.

My suggestion for an order of operations -

Clean the unit as best you can.

Replace selenium bridge, and power supply electrolytic capacitors.

Add dropping resistor to compensate for modern diodes.

Test tubes.

Bias and adjust as best you can.

- At this point hopefully the amp will be working better... And without a PSU that is producing a clean, noise-free voltage you will not be able to continue... But certain things in the circuit (caps and resistors) will be still be out of whack. Then the arduous process of testing and replacing will truly begin!

DF96 · 13th December 2010, 06:29 PM

Investigate and troubleshoot, including known troublespots such as power supply electrolytics and leaky coupling caps upsetting grid bias.

Simply changing every cap in sight is as likely to create faults as fix them.

13th December 2010, 02:03 PM	#1
Rosinante diyAudio Member Join Date: Nov 2010	Project Planning (Steps/Order) Alright.....I've got this Pilot 602 that appears to be in pretty good, unmolested condition and I am likely to restore it. You know....new caps and such. It works, and sounds fairly good already, but it does have a few problems. This thread is for the purpose of gathering advice regarding what steps to take first, second, etc. I wonder if I should investigate and fix the known problems first, then recap this thing, or vice versa. FM works.....AM does not work. There is a low hum in both speakers, continuously, as long as the volume is turned on. The hum does not seem to increase as the volume is increased, but it goes away once the volume is turned all the way down. Occasional crackling sound in the right speaker. Static-y sounding. The "phono" circuit is not working properly. It plays okay, but only at "idle" volume. Anything more than idle volume and there is a scary, low, bass-ey rumbling. If I were to turn it up much, I'd guess it would damage speakers. There is no sharpness to it, the kind that really damages speakers quickly, but it is a powerful-sounding, flabby rumble. I will start this project probably in January, and just wonder if I should replace all the caps and then re-evaluate........or should I attempt to investigate and troubleshoot and address these individual problems first, then do the overhaul.

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13th December 2010, 02:12 PM	#2
6L6 diyAudio Member Join Date: Oct 2010 Location: Denver, Colorado	By what you are describing it seems that you have an incredibly out-of-spec powersupply. it has to be up to scuff before you can tackle any other problems. My suggestion for an order of operations - Clean the unit as best you can. Replace selenium bridge, and power supply electrolytic capacitors. Add dropping resistor to compensate for modern diodes. Test tubes. Bias and adjust as best you can. - At this point hopefully the amp will be working better... And without a PSU that is producing a clean, noise-free voltage you will not be able to continue... But certain things in the circuit (caps and resistors) will be still be out of whack. Then the arduous process of testing and replacing will truly begin!

13th December 2010, 06:29 PM	#3
DF96 diyAudio Member Join Date: May 2007	Investigate and troubleshoot, including known troublespots such as power supply electrolytics and leaky coupling caps upsetting grid bias. Simply changing every cap in sight is as likely to create faults as fix them.

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