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

[Norman S Braithwaite]

Joe:  That is a darn good question!  After inspecting the three Philharmonic tuner chassis I presently have upended, one remote early version being restored, one standard early version for parts, and one remote late version for reference, it appears that the bypassed 600-ohm resistor was a factory modification added at some time during the long run of chassis.  The bypassed resistor is only present in the late version having an inspection date stamp of October 19, 1939.

Norman

[Joe Miller]

Thanks Norm,

I installed a 680 ohm resistor and the bypass cap to make the set match the schematic.  The RF AGC circuit has a similar design, but I haven't got to it yet to see if the cathode is grounded or if the resistor scheme is installed.  Looks like a bear to get to that one.

Joe

[Norman S Braithwaite]

The bypassed 600-ohm resistor was not used in the RF AGC circuit.  Don't change everything to match the schematic.  The schematic contains numerous errors and does not show the Dickert impulse noise suppressor.  The noise suppressor was supposedly optional for additional cost but I have yet to find a Philharmonic without it.  There is a good chance that it was included on all chassis but only those ordering the option paid for it.

Norman

[Joe Miller]

Okay,

If I run across any other deviations, I will point them out on this thread so everyone can see what I am finding.

BTW, where should I look to find the Dickert noise suppressor since it isn't on the schematic?

Thanks,

Joe

[Norman S Braithwaite]

Three resistors and a capacitor on one half of the 6H6 labeled sensitivity diode.  The schematic shows both halves of the 6H6 wired in parallel.  It will be real obvious if this is not the case.  Two of the sets have 50k, 120k, 2m and what I believe is the earliest has 100k, 75k, 2m.

Norman

[Joe Miller]

Making progress on the restore.  Yes, I have the additional components connected to the sensitivity diode rather than them being wired in parallel as shown on the schematic.

What does the "Dickert noise suppressor" do and how does it do it in simple terms?" I wonder how Scott described this feature in its marketing materials?

[Norman S Braithwaite]

I am not certain but I think that the Dickert noise suppressor operated like an FM limiter suppressing strong RF impulses caused by sources such as unsuppressed spark plug ignition, lightning, and high voltage switching. It was a well marketed feature in the late 1930s but is little recognized today. The original patent can be found at the link below.
http://www.google.com/patents/US2171625

Norman

[Bill Liers]

Norman, Joe,

You guys have me looking at the chassis I'm presently working on in noise suppressor search mode. My sens. diode is separated. However, the only additional components (from gen. p/l) seem to be a 2M resistor going to the diode plate from the junction of R23 & 31 along with a 0.05uf from Plate to ground. The cathode of the diode ties to R24. Although the plate would shunt a positive impulse to ground to a small degree, I find it hard to imagine that this actually meant to be functional with the values present. I'm scratching my head here. Do you both have the same hookup? Regards...

[Joe Miller]

Hi Bill,

On pin 3, I have a .05 mf (connected to ground) and a 2 Meg resistor (I didn't check to see where the 2 Meg connects, but  I will later)

On pin 4, I have a .01 mf and an 80 K connected to terminal strips (didn't bother to chase these down either) and a 40K to ground.

I've not tried to figure out how the diode (pins 3 and 4) works (since I didn't bother to chase down where the .01 mf, 80K and the 2 Meg resistors connect.

RU working Bruce's Philly now?  I'm working mine now as well so let's compare notes along the way if we find anything remarkable, okay?

Joe

[Norman S Braithwaite]

Sounds like there are four of us working on Philharmonic chassis at this time (one has yet to identify themselves if they so choose).  I will sketch a schematic of the two versions (same circuit, different component values) in the upended chassis here shortly.

Norman

[Bill Liers]

From my notebook. The starred components are the ones not shown on the schematic.

[Norman S Braithwaite]

Bill:

Thanks.  One of my late chassis plus one earlier chassis that had been updated around 1940 have 50k resistors at R24 and 120k resistors at R23 on your schematic.

Norman