Pointer Dial Philharmonic Selectivity Trimmers

[Don Jackson]

Can someone verify the correct orientation of the selectivity trimmers in an early pointer dial Philharmonic? In my set the trimmer closest to the front of the set is meshed when the selectivity / fidelity control is fully counter clockwise. In this position, from front to back the trimmers are meshed, unmeshed, meshed and unmeshed. Is this correct?

The volume control has been replaced and I wounder if someone removed the fidelity control during the process and messed things up. The set was recapped at some point in the past and plays, but could be better. The set only works when the fidelity control is near the full clockwise position, when you turn the control to the left it dies out. I assume it is way out of alignment but want to check everything before attempting to align. I am planning to replace the volume control with a tapped unit so this would be a good opportunity to check operation of the selectivity / fidelity control or repair.

[David C. Poland]

good that you addressed the step tap caps because they are in a high voltage situation off a tube plate circuit.

And do pay attention that the -C voltage divider is ok.

Replacing the caps inside the 3 diode assemblies is a pain, but do it and check the inside resistors, too.

[Scott Seickel]

"I am going to remove the bass tones assembly and see if the caps have been replaced. I have read other posts here that stress the importance of having pairs of caps as close to .02 and .025 as possible."

I went thru this 10 years ago.  I measured the chokes from 4 sets and found that they varied in inductance by a notable amount.  I modeled the circuit, which is a 6 pole filter,  in LT Spice and didn't get the expected results due to the variation in the chokes.  They are low tolerance parts. 

Best approach is to sweep the assembly out of circuit and adjust the capacitor values for the deepest 60 Hz notch. 

Of course, this is optional.  Most just replace the capacitors and move on.  Only person I know of who did this during their restoration is Mike Hadley who is on this forum.  I don't recall what his final capacitor values were. 

I need to find some of those older IRC potentiometers.  Is there a part number on them? 

[Scott Seickel]

"I attached a photo of the fidelity control, apparently all 5 caps are .01 but 3 of them are mica. From what I have seen most people change them all. I am wondering why the 2 larger caps were used instead of mica. I believe these are paper, both are very leaky but the mica ones are ok."

 

These are the values the capacitors should be.  They are definitely not all .01uF.   I would only replace the larger values as they are paper.  Be careful to not twist the leads of any mica capacitors.

[mike hadley]

If you want to make your own cap boxes I made these a while back,

https://ehscott.ning.com/forum/topics/philly-cap-box?commentId=3925...

Mike

[Don Jackson]

Your suspicions are correct, those caps are awful. They failed the leakage test on my Heathkit IT-28 at 10 volts! As for the volume control, there is another post here with a Youtube video showing how to add a tap using conductive silver epoxy. I made one out of an older 500K IRC pot. There are 2 recesses in the body for taps, one is right at the 20k point. I removed a lug from a similar pot and mounted it using a small nut and bolt and put a dab of conductive epoxy on the edge of the carbon. 20 k seems very low but this pot measures about 46k at the center of the range, so it makes more sense in that context. I took some pictures and can add them to the other post, someone else might want to try making one. 

[David C. Poland]

And -  the 1937 diagram says the volume control was tapped at 20K (rather than at 40K for the later model 1939 diagram). May not make that much difference and tapped controls are hard to locate now. My understanding is the tap's  resistor & cap combo is what we later called a "loudness" control to emphasize bass at low volume.

[David C. Poland]

Suspicious of those 2 rectangular black caps on the step switch pictured. Micromold made a series that looked like that but were really paper, foil and wax, not mica, and so, deteriorate over time. I would replace both. Those caps on the stepped control act as a treble control, cutting high frequency response as the band width decreased when turning the selectivity control counter clockwise. Also effective with phono input. On the Philharmonic 1937 diagram, this 5 step switch is located near one of the two 3rd AF 6J5 drivers, just after the bass tone reactor assemble. (The 1939 diagram revised to a cap and a pot (the R36 Control)).

FYI - The pointer dial Philharmonic power switch was an outboard toggle switch on a 3 foot twisted 2 wire cable emanating from the amp. Toggle switch was mounted on the right side of the console cabinet. (Power switch was not incorporated on the volume control until about the 1940 BOL model Philharmonic with the 2 additional control shafts.)

The switch on the back of the sensitivity control turns ON the phono input at minimum sensitivity.

[Don Jackson]

Someone already beat me to the box with the caps, new caps were soldered in the correct positions and the box is long gone. It looks like someone did a fairly good job recapping this set, but likely quite some time ago and more recently others have been in here. I attached a photo of the fidelity control, apparently all 5 caps are .01 but 3 of them are mica. From what I have seen most people change them all. I am wondering why the 2 larger caps were used instead of mica. I believe these are paper, both are very leaky but the mica ones are ok. I will have to remove them to change the volume control so will be replacing them, just curious why 2 different types of caps were used.. Also, since someone has changed the volume control it appears that if the switch on the back of the fidelity control was removed it might be possible to install with the rotor 180 degrees out when replacing it. The photo was taken with the fidelity control in the full clockwise position. As the control is rotated counterclockwise the wiper meets the contacts for the capacitors as you advance towards maximum selectivity, so no capacitors would be engaged until. At full selectivity it appears that 3 of the capacitors are connected. This seems to be correct, but someone has been tinkering around in here so trying to check everything.

[David C. Poland]

there is also a rectangular soldered box mounted on the inside of a side apron. Contains 7 caps. value documentation is bit un clear - values are are .5 mfd,  not .05. some manage to unsolder, but I cut mine open with my Drummel cutting abrasive wheel.

IMG_1201.JPG

[Don Jackson]

Yes, I am going to remove the bass tones assembly and see if the caps have been replaced. I have read other posts here that stress the importance of having pairs of caps as close to .02 and .025 as possible. I am going to start at the audio section and work my way through the set checking everything so removing the bass tones assembly will be the first thing I will do. And yes, I do have the 4 covers for the air caps.