EH Scott Radio Enthusiasts

The Fine Things are Always Hand Made

What schematic best represents the BOL Philharmonic?  The schematics I find seem to be for the pointer dial.  How much difference is there?

Also, my BOL has had roughly half of the capacitor changed using mostly Solar brand.  I presume this was done quite some time ago and was wondering how good these capacitor were/are.  The radio works and is quite sensitive, but there are quite a few problems so I'm thinking of recaping the whole thing.  I wish I had all of the originals so that I could restuff them!

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I think that the filter also helps with any psu noise rejection as well, 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

I think that makes sense

Thanks!!

These Solar Sealdtite capacitors were common on the later Philharmonics.  Solar was out of business by 1948.  It is possible that your capacitors were later replaced with surplus Solar capacitors, but who knows.  They are actually very good for early capacitors.  I have measured a few in the past and they show little or no leakage at 600v on my Sencore LC-75.   It is also very common to find a mix of different capacitor brands in the these sets, including the no-name capacitors.  CD's "Dwarf Tiger" capacitors also show up in this era. 

I have the 9 knob schematic done, but I have not spent the time to compare it closely to an unmolested chassis to confirm the "update" to the 9 knob version.  All the earlier errors have been corrected on it and I was working on doing the chassis layout drawing, but other things have got in the way and it has sat for close to a year. 

Using Mike's method to replace the filter capacitors is best.  I modeled the bass boost circuit a number of years ago here: https://antiqueradios.com/forums/viewtopic.php?f=6&t=278370   (Photobucket ate the photos)  The biggest reason to use Mike's method is because I measured 6 of the chokes I had on hand and they turned out to be very wide tolerance parts. 

You are speaking of the four caps INSIDE the chromed box between the Expander 6L7's and the pair of 6J6 drivers at the rear left corner of the receiver.

Correct, David.  I took the can apart and found that the caps had been changed but with incorrect values.  Using Mike's test method, I found it to resonate at 36Hz.  Not quite right!  Replacing the caps with the correct values didn't get it right on 60 Hz so I did a little tweaking.  It now resonates at 60 Hz as it should.  I haven't tested it in the circuit to see if there are peaks at 70 and 40 as per Scott's instructions.  It didn't help the base any but no judgement can be made until the speaker is in the cabinet. A nude speaker is notoriously inefficient in bass.

I did a lot of investigation into the expander  and got it working as expected as long as I have a strong signal at the volume control (input into the expander driver.)  The problem I have is that the sensitivity varies tremendously using the selectivity control.  Signal level drops decidedly as I move toward the widest bandwidth position (just before it switches to Phono.)  This is where I like to listen as my transmitter goes all the way up past 15K.  The signal level is low so it doesn't activate the expander hardly at all and the volume control has to be way up.  As I move down to mid position, sensitivity is great, I have to turn the volume way down and the expander operates as expected.  Sensitivity again drops as I move to toward the most selective position.  I'm trying to determine if the bias control on the selectivity control is to blame.  Is it normal for dramatic volume changes as you move the selectivity control or do I have a problem?

I made major progress on the expander problem.  When the prior "tech" worked on the radio, he replaced the volume control.  It is, however, a 250K instead of a 500K.  In addition, it does not have the 50K tap. This seems to make the volume control very touchy and a lot of volume with very little movement.  To compensate, I found he had inserted a 3.3K resistor from the input to the control to ground, reducing the signal level dramatically.  This, of course, also reduced the signal to the expander driver.  Without the resistor, the expander works perfectly.  In fact, I can't turn the expander control up to max without annoying results or overloading the audio system.  I'll set up the expander per instructions when I get a new volume control (hopefully I can find one with a tap, even if it's in the wrong place.)  there is a discrepancy between the schematic and the technical description.  The schematic says the tap is at 50k, the technical description says it's at 20k from the ground side.  I'll see what Mark Oppat has.

I checked the sensitivity changes on the selectivity control on the pointer dial.  It too changes dramatically as you turn the selectivity. So, I'm assuming it is normal.  Let me know if it should be relatively constant.  I've checked AVC voltage changes while tuning, and by changing the sensitivity  and selectivity control and they do change quite dramatically, so I assume they are doing what they should.

The radio is really starting to perform!  There are still a bunch of original caps in the IF and RF section.  They are on the low voltage side of coils.  Wherever there is plate voltage, the former tech replace them with Solars and a couple of Sprague black caps.  Before I do a complete alignment, I may change all of the caps.  I would like to make them look original, though.  Although, I've replaced several resistors and they don't look original! 

I had a very similar scenario, the volume control was 500k but linear, this made the volume loud or very loud,

the if bandwith gearbox was assembled wrong, the caps in the tin boxes had not been changed, also there were some oddly placed screened leads around the audio circuitry. The ht bias resistor had been removed and a very nasty array of odd power resistors fitted, in order to compensate for the heat generated by the undersized resistors he used ptfe wire, quite a mess,

maybe we had the same 'tech' work on the radio,

I think that you are going to have to check everything, who knows what you may find?

well worth the effort though.

Mike

The tin box (symbol 74 on the parts list) with seven caps are .5 MFD - not .05. I just use 630 volt caps.

I chose to clip the leads close to the tin box. Cut open the box with a Dremmel tool.  Then maintaining color code wire on the new caps and use shrink spaghetti over the solder connections.

There are valuable Philharmonic threads on this site. Use the search box at top right of this site. for example a couple long ones:

- From Dec 2015 - Philharmonic Spring 1939 Production Changes. started by Scott Seickel 

       https://ehscott.ning.com/forum/topics/philharmonic-spring-1939-prod...

-also Dec 2014. -    Mods to phillys 

https://ehscott.ning.com/forum/topics/mods-to-phillys?id=3925821%3A...

For what it's worth here is the drawings I made for the boxes in my Philly, one box was missing, the other had already been messed with, they are made from 0.2mm tinplate this is used in metal cans that holds auto oil and similar, mine was isopropyl tins.

Folded up inside out they are easy to solder.

I did an alignment today.  I wondered why I had no signal when the selectivity control was turned to the most selective position.  IF alignment was way off with different stages off in different directions! Signal getting through the first IF was getting blocked by subsequent stages.  IF and RF AGC diodes were way off so AGC was not working to full capacity.  Now I get excellent sensitivity at the most selective position.  Sensitivity still goes down considerably as I approach the broadest selectivity extreme.  I have to compensate with the sensitivity control and the volume control.  Much better than it was, though.

Waiting for a new volume control from Mark Oppat.  He will make one that has the tap in the proper position and with the long shaft.  then I'll be ready to put it back in the cabinet.  The cabinet has a few loose joints so I'll repair all of that first.

This is the first Philly I've worked on and am fairly impressed so far.  Great sensitivity and can separate close shortwave stations with the selectivity control.  In the HiFi position, music sounds very good even with the speaker out of the cabinet and without tweeters.  Should be a great radio!

Thanks Mike.  The box that held the 4 - 4mfd caps had been replaced with a 4 section can electrolytic.  so, I may make one to replace that!

mike hadley said:

For what it's worth here is the drawings I made for the boxes in my Philly, one box was missing, the other had already been messed with, they are made from 0.2mm tinplate this is used in metal cans that holds auto oil and similar, mine was isopropyl tins.

Folded up inside out they are easy to solder.

Thank you, David.  I will read those threads!!

David C. Poland said:

The tin box (symbol 74 on the parts list) with seven caps are .5 MFD - not .05. I just use 630 volt caps.

I chose to clip the leads close to the tin box. Cut open the box with a Dremmel tool.  Then maintaining color code wire on the new caps and use shrink spaghetti over the solder connections.

There are valuable Philharmonic threads on this site. Use the search box at top right of this site. for example a couple long ones:

- From Dec 2015 - Philharmonic Spring 1939 Production Changes. started by Scott Seickel 

       https://ehscott.ning.com/forum/topics/philharmonic-spring-1939-prod...

-also Dec 2014. -    Mods to phillys 

https://ehscott.ning.com/forum/topics/mods-to-phillys?id=3925821%3A...

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