EH Scott Radio Enthusiasts

The Fine Things are Always Hand Made

I am trying to help a friend who is working on a Philharmonic AM FM model. There are two bleeder resistors shown on the schematic of the tuner chassis. One has +250V on one end and multiple taps. The other has 17V on one end and multiple taps. Both have one end grounded. One of them may be the R1 listed as being a 125 ohm 10W resistor. The other one does not appear to be listed anywhere. Have any of you measured the resistances of the sections of both resistors and their total end-to-end values?

In the set being worked on, the defective resistor is in the circuitry where one end is connected to +250VDC. This resistor has no continuity to any of its connections end-to-end or either end to any of the taps. My friend says that he is afraid to dig into the insulation of the resistor as it is so tough and brittle he is afraid that he will shatter it if he forces scraping or probing into the tap area. The way he described the part, it sounds as if the connections are depressed or sunken into the surface of the ceramic body in such a way as to defy attempts to expose wire, scrape clean and resolder (if it is indeed a wire-wound type as we suspect). He said that just looking at the part it appears it could be a 20Watt resistor.

Joe

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Jeff;

Thanks for this update. The resistor with the ? was so blurry that I could not tell if it was an 8 or a 9. Since it is a 1K ohm resistor it has to be an R9. Having two pins identified as pin 4 makes no sense at all. However I tend to agree with you that is how they numbered it. I put an X through the lead coming through the envelope in the diagram as there is no such internal to external connection. I added dashed lines inside to show the actual internal connection from the suppressor grid to the cathode.  In the parts list C28 is a .05uF@200V so it may actually represent a filtering or bypass capacitor at pin 4.

Joe

Jeff;

I found another area of the schematic that I am not certain about. To the left of the Local Oscillator in the front end, there is an arrowhead pointing to the left toward the L-A coil assembly. This arrowhead comes from the lower of two coils that have the caption "SEC. BOOSTER". I think it indicates that lead is connected to the top of the C14 capacitor although it does not have a dot showing a connection. It looks like the capacitor was either added in a revision or left off of the schematic originally and drawn in later very small so it would fit in the space on the drawing.

It appears that the Philharmonic has coil assemblies that cover the RF front end essential tuning parts (other than the multi-section ganged capacitor and a few other parts) which rotate into position over some stationary contacts on the chassis. This appears to be similar to the AW-15 and AW16 models that preceded this model.

Am I correct about the arrowhead indicating a connection?

Joe

Followup: It appears from a few examples of the underside of the Philharmonic model that conventional rotary wafer switches are used in the front end, with each being confined to a shielded chamber and one long inter-connecting shaft, so there are no moving coils, just rotary contacts to each coil set. However I still want to be sure about the exact connection to the nearby coils/capacitors.

Joe

This is the AM oscillator section.   Forget the capacitor numbers and the terminal numbers below, they are my addition to clarify the mess. 

If you right click the image above, then click "view image" it will expand it to be readable.

Scott;

Thanks for this well thought out view of the RF Oscillator circuit!

Did you redraw the entire schematic? That is pretty much what I am doing at present. Maybe I am wasting time if this has already been done.

Joe

I have the 7 knob version completely redrawn with chassis layout, parts list, coil diagrams, you name it.  All laid out for easy reading.  I verified this drawing against 3 early sets and they all matched up 100%.  All errors in original drawing were corrected.  I spent probably 150 to 200 hours drawing and verifying against 3 unmolested chassis.   I offer these to people who are restoring their sets at a reasonable price as I have to print them on 18"x24" pages and it takes some time to print, mail etc.  Certainly not a money making proposition- barely beer money,  but I enjoyed doing it.  I have not put it in the public domain because there have been plenty of people who have stolen other peoples work and sell it on E-bay. You have little recourse other than to pay a lawyer to threaten to sue them and hope they stop.   Plus, I do a first run print directly from Autocad which produces a superior print compared to generating an image file or PDF.  So anyway, it is offered to people who need it as a set of prints only.  

I also have drawn the AM/FM, but I have not spent the time to verify that against my 2 AM/FM chassis. 

The 9 knob AM only set has eluded me as the only one I have been able to acquire was molested badly.  I pretty much know all the circuit differences and have drawn it out also, but I need a 9 knob AM set to verify. 

Here is a chassis layout of the oscillator area. Again, right click the image below, then click "view image" it will expand it to be readable.

Scott;

I need to check with my friend and see just what version he is working on. The schematic I downloaded from the archive here is supposed to be an AM-FM version, but so far I have not seen a discriminator in the diagram. In any case, if the unit he is working on is an AM & SW model, your diagrams should be excellent to work from. I have been taking schematics that I improved to FedEx and having them printed out on B, C or D size paper to make reading them easy. I download the *.pdf or *.jpg file to a memory stick and let them import the image file to print. I have a copy of AutoCad 13 Mechanical Desktop on my other computer that I used to use in order to do some work at home. I used to export EPS files to network printers at work. Our mechanical engineers used different software on Sun Unix based computers but we were able to share files through the IGES conversion process.

Your drawings show excellent attention to detail including the physical layout illustrations. Once I learn which version he is working on I will arrange to order copies from you. I have some work I am doing on a Fisher RK-20 remote control system for a friend in California. I recently repaired mine and will be working on the companion MF-300 tuner next. I need to get back to those projects.

Joe

I have another question on the Philharmonic LW/AM/SW version, what is the value of the Sensitivity Control? It is not specifically identified in the parts list. There are two resistors in parallel with it, R35 (600 ohms) and R7 (500 ohms). It would make sense for the control not to be a high value since it is in the cathode circuit of the 6H6 Sensitivity Diode.

R33 is shown just to the right and below the Sensitivity Control and appears to have the labels "FID" and "SEL" associated with it. What do those abbreviations represent? "SEL" may mean selectivity, but what does "FID" mean? And what is the function of R33?

Joe

"FID" = fidelity as in high fidelity.  Really, it is broad bandwidth as opposed to narrow bandwidth or selective.

Norman

Norman;

Thanks for that input. I suspected that was the purpose of the control, but was uncertain.

Do you know the value of the Sensitivity control? The ends are marked "Lo" and "Hi", but there is no "R" number shown with this control and I do not see it listed in the parts list.

Joe

On both the 7 knob and the 9 knob AM sets the the 600 ohm is 500k, and the 500 ohm is 50k. They were close on the schematic, weren't they...LOL.

The Sensitivity control is 1k. 

I thought you were working on an AM/FM set?

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