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

[Kent King]

I strongly recommend using the FM Philly schematic and ignore the FM components. They based the diagram on the 9-knob Deluxe Philly and it is the closest diagram available.

[Stephen Scheel]

thank you!!

[Stephen Scheel]

Do you all think these are original?  There are 3 of the ones on the bottom and one of the one on the top.    Not going to be used but i would like to keep them on the amp if they are original, (they look later than 30s to me).  If they are not original i'll start looking for some 30s caps to fill the holes instead of these. 

[David C. Poland]

Yours look like replacements. What I have seen has the specs pressed into the metal, not printed in ink.

The one with big hex mount may be close, but only if your BOL example is really late production. My late 1941 Scott Laureate has like construction.    IMG_0026.JPG

But most likely the photo of this 1940 Philly BOL with logging scale has the amp having a set of taller original filter caps.-  a bit taller than the 6L6's , with breathing holes on the slightly domed tops. 

Philharmonic%20AM%20red%20band%20pointer%20dial%20w%20amp.jpg

Be a bit hard to find old originals after all these years.

May be best to find  matching style set, not being to concerned with exact match to a photo. After all, Scott butlt the Philharmonic for several years and may have sourced what was available over time.

[Scott Seickel]

I am late to this party as usual....

The 4/4/39 dated schematic IS the one to use.  There is a scratch suppressor switch on both AM variations.  There are errors in all the schematics.  

Here are the changes from the 7 knob set to the 9 knob set: 

• 1st and 2nd IF tubes had 400 ohm cathode resistors introduced with associated 0.05 uF bypass capacitors.
• IF AGC tube had 600 ohm cathode resistor introduced with associated 0.05 uF bypass capacitor.
• RF AGC line was split, adding AGC action to second RF amplifier tube, instead of just the first RF amp.
• The Ultra SW band has it's signal now passed thru both of the RF amp stages instead of being introduced directly to the converter tube.
• The audio diode assembly has the 2 associated 25 pF capacitors changed to 50 pF.
• Volume control is now tapped at 40K and the associated low volume compensation inductor has been removed. The tap resistor and capacitor remain, but the values changed.
• Scratch suppressor control is fed from a potentiometer to provide adjustment voltage range from -6v to -4.5v, instead of steady -6v with no adjustment. This new pot is mounted on the C divider.
• Scratch suppressor on/off switch is no longer a pull out switch, but rather a rotary switch added to right side of front to provide symmetry with new treble control.
• Scratch suppressor, 6B8G, has capacitor change from 360 pF to 500 pF.
• Treble control is added, consisting of a single capacitor and potentiometer. This circuit is installed in place of 5 audio tone capacitors that were ganged via a switch to the selectivity control and intended to cut the audio response at the same approximate frequency that the bandwidth was set.
• Sensitivity diode circuitry has 2 resistor values change and an 800 ohm resistor added to the -28v supply.
• Tuning eye adjustment is no longer by a 300 ohm cathode pot, but rather by a new potentiometer controlling grid voltage.
• VR150 tube was relocated from rear to the front of chassis for all sets. 

Stephen Scheel said:

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

[Stephen Scheel]

Thank you David,

I'm going to keep an eye out to see if i can find a set that match the amp in the Philharmonic picture..  If not these may just get polished up and go back on the chassis until i can find some.  

Scott,

THanks so much for the detailed reply!!  

I'm contemplating one of these:

https://www.paleophonies.com/FM-DW/FM-DW.htm

Somehow use the Ultra-shortwave band switch position to enable it.

Steve

[Stephen Scheel]

Once i got all the old main electrolytic caps out .. it would appear they have been taken apart, re-stuffed and then epoxied back together.    Seems C73 was replaced sometime on or after 2004 as it had a Nichicon cap in the circuit with that date code.    I am assuming these Cornell-Dubilier caps were stuffed during the same repair session.

Yet another question.   Do you folks leave this Phono Jack in the circuit?  If you do, do you use it?  Its wiring seems a bit convoluted and looks like an unnecessary possible failure point or source of noise if left in. 

I'm guessing this is going to be a long road to restoration.  I hope you guys have patience with all the questions.  LOL

Thanks,

Steve

[Alex R. Whitaker]

I've only electronically restored one Philharmonic, a very early pointer dial set. That was 25 years ago.  But, I still remember I replaced 75 paper and electrolytic capacitors.  It's quite labor intensive, but the end result is way worth it!

[Stephen Scheel]

75!.. holy smokes.. Two wishes from the Antique radio gods.... 

1.  Whomever recapped the powersupply/amp also recapped the Reciever.

2.  They did a better job than they did on the on the PS/Amp (not likely) :)

Steve

[David C. Poland]

it is helpful for benefit of future owner to use a Sharpie or some other way to indicate on an inside surface the extent of restoration and a date. A folder of set history is too easily separated from the radio, so is insufficient.

Restuffing the original wax caps with modern film caps is a really labor intensive long term upgrade. Shame to inadvertently discard such work with unnecessary replacements.

The factory ear phone jack on the amp have two positions: earphone jack partially inserted, the speaker continues to sound. Totally inserted, silences the speaker by interrupting the audio paths to the output tubes. Pretty complicated jack because the driver tubes are push-pull parallel too.

[Kent King]

I've never had any noise introduced by the jack on the amp, I also never use them. For originality, I would leave it in circuit, it hurts nothing.

Kent

[Stephen Scheel]

David,

Good Idea.. I'm thinking a index card under the chassis when installed.      I'll definetely check to see if the papers have been restuffed.  The reciever is still setting in the cabinet for now. 

Kent,

Good to know.   I'll just deox it and leave it alone then.    Along the lines of "if it aint broke don't fix it"..

Steve