Mods to Phillys

[Joe Miller]

Were Philly's modified in later production runs without updating the schematic?

I found the IF AGC tube's cathode grounded rather than connected to ground through a 600 ohm resistor with a bypass cap as shown on the Rider's schematic.

Was this a factory change or the result of some one before me making changes?

Thanks,

Joe

[David C. Poland]

Interesting thread. Last few times I ran my pointer Philly a problem of fluctuating volume seemed to relate to that 6H6 as though the sensitivity was unstable. Been 50 years since I recapped the audio side (left side) of the receiver. Likely time to do it again as part of going over the set plus rep;lacing the 7 caps in that metal box under the expander tubes i learned of recently. Likely this Winter project and I am so much better equipped to go over my Philly now.

[Bill Liers]

The circuit is similar to what's used on the FM version, although a separate tube is used. I also think their must be an error on the FM schematic as it leaves out any cathode reference. Likely their is a connection to the 170k shown below the text. In either case, this would be a simple clamp for positive going impulse and would only be effective at very low detected voltage. Any significant signal level would drive the detected output negative and reverse bias the diode. The 2 meg resistor would also give the circuit approximately a 100 ms time constant so I wonder how effective it can be. Guess I'll run some tests when the set is complete.

[Norman S Braithwaite]

Impulse noise was not likely to be a problem on strong signals.  Is it possible that this circuit was designed for reception of weak distant signals?  Or, maybe the circuit was included to boost revenues.  There are plenty of errors in Scott schematics!

Norman

[Bill Liers]

I have to use my imagination here Norman. I could see where, in a radio with so much gain and listening to a distant weak station, the gain and volume are up. The Mrs. turns on the vacuum in the next room and blows you out of your chair. I'll try to bypass the sensitivity side and run an indoor antenna with my DC drill running nearby. Pulling the tube should give us an answer.

I can almost understand errors in "published" schematics, but In the dozen Scotts I've worked on, nearly every one has a wiring or manufacturing error where the radio plays albeit poorly. Is your experience the same?

[Norman S Braithwaite]

I have found more errors or disparities in Scott published schematics than actual factory wiring errors (later service wiring and component errors, especially improper lead dress not counted).  The most notable Scott wiring error is in the Philharmonic power amplifiers and has no significant consequence in performance.  Most of the Scott receivers that I rebuild have poor performance upon initial tests but this can almost always be explained by misalignment and sometimes lousy prior service work.  I will not even try checking performance before rebuilding but changed component characteristics and bad ground returns will top the list of problems prior to rebuilding.

I look forward to hearing about your test results.  I am beginning to suspect that the Dickert noise suppressor was more of a marketing feature than a practical option.  If so, it would not be the only impractical option.  The volume range expander, if working properly, is only of benefit to orchestral and operatic performances.

Norman

[Joe Miller]

Hi guys,

Just found time to get back to this.  Bill, thanks for the schematic, mine is wired the same.  I don't think the circuit does anything?  Diode pins 3 and 4 either conduct or they don't.  If they don't, then there is no impact on the eye tube or the signal to the VC.  If they do conduct, then the 2 meg shunts R23 (no real impact) and the .05 mf shunts R24 and essentially "squelches" the signal.  But I don't see how the diode would ever conduct (thoughts?)  Am I looking at this right?

Also, since the three of us are all restoring the same radio, let's try to collect and catalog all the schematic errors we find so that others might benefit.  Maybe Scott would incorporate them into his CAD version once we finish?

Joe

[David C. Poland]

Have you folks considered that some of what you observe are merely running changes in production (thinking of the AW-15 saga of evolution) during the 4 year run of the 30 tube Philly? Your serial numbers, dial type and control configurations may suggest the relative production dates of your several receivers.

[Norman S Braithwaite]

Yes.  Although I have been annotating a single Philharmonic schematic with both corrections and production changes, there is no question that there are some errors.  However, in all fairness I cannot blame Scott for the errors in the only published schematic for the Scott Special Communications Receiver.

Norman

[Joe Miller]

The only discrepancy I have found so far in my restore is the one noted previously on the power amp which I have corrected and the "Dickert Noise Suppressor" on the tuner.  In the later case, my as-found wiring matches Bill's as-found wiring so I will just mark up my schematic to reflect it.

BTW my serial # is KK-54.

Joe
 
Norman S Braithwaite said:

Yes.  Although I have been annotating a single Philharmonic schematic with both corrections and production changes, there is no question that there are some errors.  However, in all fairness I cannot blame Scott for the errors in the only published schematic for the Scott Special Communications Receiver.

Norman

[Norman S Braithwaite]

The plate filter capacitor on the Philharmonic record scratch control tube (6J7G) tube is marked C35.  It is C55 which is a 35-pf mica capacitor (C35 is .01-mfd, 200-v paper capacitor).  The resistor in the 4th IF diode network marked R1 is really R17 (10k vs 125-ohms).  The cathode filter of the record scratch diode (6B8G) is not marked.  It is 1/7 of C51.  Every AW-23 I have ever worked on has a 0.5m resistor paralleling one winding of the last IF which is not marked on any schematic.

Norman

Oh, and C42 is identified as "4 mf 300 v" in the Philharmonic parts list but it is really 4 X 4 mf 300v.

[David C. Poland]

Joe - My pointer Philharmonic is KK-237. Has 5Z3 rectifiers. I seem to recall a date stamp inside receiver chassis near year end 1937.

[Joe Miller]

I'm getting ready to replace caps under the chrome rectangular can.  I removed the fasteners and thought the can would just pop off, but it seems to be hung up by the leads going through the chassis.  Does it need a little persuasion or are the caps underneath captive to the can?  I was hoping I could just remove the cover, replace the caps and be done with it.

Joe