9 knob BOL Restoration

[Stephen Scheel]

Hello All,

I’m finally getting around to starting the resto/repair process on my 9-knob, AM-only BOL Philharmonic. I’ve done this many times on ordinary radios, but for this particular set is there a tried-and-true process to power up and check things as I go? Looks like the amp/PS has had some work done to it at some point in the past already.

Thanks, Steve

[Norman S Braithwaite]

Make sure to tighten the rotors on the variable selectivity trimmers.  The rotors are fastened to the shaft using set screws through pot metal collars.  Over time the pot metal collars expand causing the set screw to become loose and allow corrosion and resistance between the set screw and the shaft.  In the worst cases, the rotors can become completely loose allowing the rotor to spin freely on the shaft.  Also, be aware that there are four wax-paper capacitor inside the base choke shield and two inside the tuning capacitor shield that will need to be replaced.  

Norman

[Stephen Scheel]

Thanks Norman.   i'll remedy that stuff after i give the PS a once over. 

[David C. Poland]

The "bass choke shield"assembly is the topside chrome plated box (left rear) between the pair of 3rd audio 6J5's and the pair of Volume Expander 6L7's. Unsolder the 4 wires (making careful notes). Failure to replyace the caps inside risks damage to the bass control potentiometer. Allows better access to clean that chrome area, and access to replace the shock mount grommets for those 6L7s.

Also, expect to find a soldered box with seven .5 MFD (not .05) caps (approximately below the Expander tubes). This is part 1321 on page 14-60 in Riders (aka C51 on the diagram). I dismount that box to open it up, after cutting the 7 wires near the box. I re-stuff that box with modern 630 volt caps and connect to the 7 cut wires (with heat shrink spaghetti), rather than trying to trace and unsolder those long leads. The box is ground for the these caps.

Those underside diode assembles in metal boxes also have a protruding cap to replace. Tedious but important. 

By the time you are done, you will be well acquainted with the Philharmonic. Do read through the owners manual too. Have Fun.

[Stephen Scheel]

Excellent!  Thank You David.

[David C. Poland]

Bass choke assembly consists of two chokes and 4 caps, it is a resonator to increase bass response.

IMG_1345.JPG

[Stephen Scheel]

oh wow.. i had no idea.  this is going to be fun.   

David C. Poland said:

Bass choke assembly consists of two chokes and 4 caps, it is a resonator to increase bass response.

IMG_1345.JPG

[Stephen Scheel]

Hi,, 

Which version of the reciever chassis is in Riders Volume XIV?  Seems there are 7 shafts sticking out of the chassis photo.

7 knob?

Oh.. and if its the 7 which if the schematic that fits mine?  

Steve

[Scott Seickel]

I believe that Riders has the 1939 diagram which is proper for the 9 knob (non-FM) sets.  There are a bunch of errors in the published schematics, so be careful to follow how the set was originally wired.  

Stephen Scheel said:

Hi,, 

Which version of the reciever chassis is in Riders Volume XIV?  Seems there are 7 shafts sticking out of the chassis photo.

7 knob?

Steve

[Kent King]

There are materials available in the Scott Info Archive here on the site...check it out as well!

Kent

[Stephen Scheel]

Thanks Kent.  I downloaded all of that :).   If the schematic has a Scratch switch present i am assuming thats the 7 knob?  There is a scratch switch in the Riders Volume XIV schematic.

[Kent King]

Yes, that is the push-pull switch located under the tuning knob on the 7-knob sets. The scratch suppressor was changed significantly in the 9-knob sets.

 

[Stephen Scheel]

Thanks Again Kent,

I looked at all the schematics in the library here.  All of the AM only schematics show that switch.  Does a 9 Knob AM online schematic exist?

Steve