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.

[Kent King]

Glad to hear it is working well now. I'm not surprised that the major components were OK, I sell a lot of parts off  chassis, but seldom anything other than controls off the Philharmonic sets. Only notable exception was an antenna coil to a fellow who's set had been hit by lightning. The major components were always over spec, and survive well. Good luck with the remaining work and I'm sure you will get a lot of enjoyment out of that set when finished!

Kent

[Don Jackson]

Quick update, Norman was correct in suggesting that someone had aligned the set with the selectivity / fidelity control in the full clockwise position rather than the maximum selectivity position at full counter clockwise. I aligned the set using the instructions he posted and the selectivity / fidelity control now works properly. A couple of the rotors were loose and one was about 15 degrees out of position, I tightened them before aligning the set. The rf, if and audio diode assemblies were also way off. There is also a note in the alignment instructions about adding a resistor to increase sensitivity. The high end of the C divider measured 31.9 volts, a 1.2k resistor brought it down to to just over 28. The voltage at all the taps is now correct. After adding the resistor the increase in performance was amazing, the set really came alive. Someone replaced the B divider candohm with fixed resistors on a component board, the values they used are a bit off so that might have increased the voltage at the C divider, something else to investigate.

I removed the bass tones assembly, someone had already replaced the caps and all 4 were .022 so I replaced with the closest pairs of .02 and .025 I could find.

This definitely improved the operation of the tone control, it did not seem to do anything before. Now the bass is noticeable at the maximum setting. I also installed a tapped volume control which was an improvement, there is a discussion regarding tapped volume controls on another thread that I will add to. There is still more work to do on this set, but at this point it is working very well. Lots more things to check but the rest should be easy.

Thanks to everyone who responded to my post, I spent a couple of months reading older posts and making notes before starting work on this set which helped prepare me for the task. This is the first Philharmonic I have worked on, fortunately all the major components in the set seem to be good.

[Scott Seickel]

Thank you Don. 

[Don Jackson]

Here is a copy of the 500K pots offered by IRC and a taper chart from the catalog. It appears they did offer some with 25 k and 50 K taps. Any of the tapped audio pots I recall seeing had taps at 100k or more, as you noted. I have a couple of newer IRC 13-133 pots but they are 7/8" diameter but they  don't look hopeful for installing taps.  

[Scott Seickel]

Thanks Don.  Looks like it is easier to do with one of these pots that were designed to accept taps.  I couldn't find a catalog online. 

[Don Jackson]

Scott

The potentiometer is an IRC 13-133. It is listed in an IRC catalog which is available online if you don't have one. In the catalog is is noted as a "left handed logarithmic taper for audio circuit control" with a 3 (C) taper. It was easy to install the lug, there is already a hole there which has to be drilled out a bit larger. I used a 4-40 nut and bolt which fits well. Applying the epoxy was a bit more difficult than I thought, I did 2 and the second one turned out better than the first. The second one has a short shaft so I attached a dial with a 0 - 100 scale and recorded the results. 0=0 ohms, 10=18 ohms, 20=1.4k, 

30=5k, 40=25k, 50=46k. Beyond half scale the resistance goes up quickly to 540 k at the maximum.

I had to trim the epoxy a bit to provide clearance for the wiper but you can shave the epoxy a bit just as it is starting to harden. In the end it measures 21.3 k which is not bad.  The resistance of this pot comes up fairly slowly so it should be better than the pot which is in the set, which comes on really fast and is annoying. Consider this an experiment, if I did another one could do better. The first one ended up at 31k, the resistances changes very fast around the 20k point so it is hard to get the epoxy in the right spot. It is very easy to make a mess with this stuff. I might add that the 40 k point is only about 1/8" past the nut, so the same pot could be modified for a 40k tap. I have lots of various 500k pots, this type seemed like the best prospect, it is 1 1/4" diameter.

[Don Jackson]

Scott

Thanks for clarifying the fidelity caps. I made a copy of the early schematic from the archives and made an enlarged copy and have made note of the values of the resistors and capacitors. There are some fuzzy symbols next to the caps on the schematic which I could not make out. But I see now that C37 is noted at 5000 pf and C32 as 2500 pf. A bit confusing but now it makes sense! And the early schematic shows the switch in the maximum selectivity position. The is a lot going on in the Selectivity/Fidelity circuit so it took a while to figure it out. Also lots of things that could get messed up.

[Don Jackson]

David

Yes, good catch on the capacitors. One could easily assume they are mica capacitors. I checked the C divider and it is fine, but noticed another capacitor that appears to be the same species close to it. I am going to remove the diode assemblies and check them, a bit of a pain but a necessary task.

[Don Jackson]

Mike

Nice boxes! Both of mine are gone, the one for the electrolytics was replaced with an FP capacitor. I made a copy of the dimension and might try making some myself. As for the bass tone assembly, I will probably replace the caps and hope for the best but this is good information to have which I have added to my files for future use.

[mike hadley]

Refering to your bass tone assembly I reworked mine to suit the 50hz mains supply over here in the UK,

there is a mention here

https://ehscott.ning.com/forum/topics/philly-bol-schematic?id=39258...

you can do this

you can run this on the bench as a stand alone filter, using a signal generator through a resistor, someware around 10k will do,

(eliminating the low output impedance of the generator). Place the generator across the whole stack and a scope on one of the taps you can then get the whole thing to resonate. This is wht I did with mine to get 50hz resonance to match the UK supply

Mike