EH Scott Radio Enthusiasts

The Fine Things are Always Hand Made

I've recapped my dial pointer Philly and it plays good on all bands, but I have a few nagging issues that I would like to take care of before I start the alignment.  I want to make sure these are real problems and not "operator error". 

1.  When I rotate the sensitivity control I get increasing gain as expected, but there is a very narrow spot just off the CCW position that increases gain to the  max.  I've shot the pot with cleaner but no change.  I assume this is not normal, correct?

2.  When I turn the expander control on, the expander eye tube opens up indicating maximum expansion but I can't hear any difference.  Once I turn the expander on, the eye tube remains open no matter what other actions I take (tune off station, rotate the expander pot, rotate the selectivity control, etc.)  I've rechecked the expander wiring and all looks fine.  How is this feature supposed to work and is there a good way to test it?

3.  Every once in a while, the set seems to almost want to go into an oscillation, but it doesn't.  Not sure what this means.

Tomorrow I am going to recheck all supply and tube voltages.  Any other ideas on problems 1-3 above?

Thanks,
Joe

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This thing is kicking my rear.  All done, alignment complete, sounds good except for this darn low frequency feedback.  See video and audio at

http://youtu.be/s7Rnah5xq_4

The feedback comes and goes but is normally aggravated by turning up the bass.  (BTW the bass control doesn't give me any bass).  I've been into the bass choke can twice and everything looks good.  Here is what I am thinking:

1.  Does polarity matter on the choke windings?  Could I have mutual inductance occurring between the 2 coils?

2.  I am using a modified organ speaker that sounds good but could it be causing the feedback?

3.  Scott, on both of your redrawn schematics you show a 1 Meg resistor (R94 on the most recent schematic) from the plate of the expander amp to the bass choke assembly. I have 15K resistors from the plates of the expander amps to the bass chokes.  Does anyone have the 1 Meg resistor there or does  everyone have 15 K on both legs?

Please listen to the link.  Would appreciate your thoughts on this?

Thanks,

Joe

15k is correct for both legs as you have. 

You could try to switch the choke legs, but I doubt that will work.  You may want to check the cap wiring in the choke can- maybe an error occured. 

I would take a scope and work my way from the 2nd audio out until you found exactly where it is happening, then you can concentrate on what may be wrong. It is possible that the feedback issue is not happening on the tuner chassis.  

So it is fine with the bass control all the way down, but you get the feedback gradually as you turn the bass control up? 

Joe,

Sorry about your rear. Patience is a virtue. No, polarity doesn't matter. Mutual inductance effects should not be an issue.

The 15K values are correct, the schematic needs correction

There is possibly a mis-wire somewhere. Maybe an audio de-coupling cap missing? Maybe from the 7-0.5 can or similar?

Another good possibility is acoustic feedback. The speaker is very close to the chassis. Can you move it away (as far as possible) to see if anything changes? Tap all of the tubes with a pencil to check for micro-phonics. You will hear something but shouldn't hear any ringing. My last Phil had a howl which turned out to be just a crummy tube.

Also does it happen in phono mode with the input shorted? Did you check the expander voltages against the setup procedure in the technical doc?

good luck

This is re your youtube video.

I have seen many sets with microphonic 6J5G's and or other tubes that handle audio. If the speaker is located away from the chassis you may find the oscillation disappears. Tapping tubes will usually locate the tube or tubes. I've had to go to 6j5GT's to get rid of the feedback / oscillation.

Good luck

Jeff

Fixed.

It was one of the 6J5s located in the 1AF position.  The tube tests very good but it sure caused a growl.  Sounds great now with high volume and bass full on.

I must say I don't get much bass out of it though.  Kind of like the 800Bs without Norman's bass mod installed. 

This is a powerful set.

Thanks everyone for all your help.  All I have left to do now is to install my new dial glass that I got at Radiodaze and put it back in the cabinet.

Joe

Joe,

The bass should improve in the cabinet. Also, measure the difference in the output voltage comparing 100Hz and 1kHz. At nominal settings they should be the same (ie: 1 volt) then turn up the bass and see how much gain (delta) you get at 100 Hz vs 1 kHz

Should be at least 6:1 or more

good luck

Yes, a cabinet makes all the difference. Need some distance between the front and back of the speaker. The Philharmonic owners manual says to have a baffle board ... and to avoid a flimsy cabinet. Also, before advancing the bass control very far that the fidelity control be at least half way on to avoid overloading the speaker.

The manual also says the 6L7's in the expander circuit can be a source of hum. Also to position the amp so the power transformer is away from the left side (audio side) of the receiver.

Thanks for the tips guys. I think I have some bass control now. It is going in a solid Warrington cabinet. I think I have located a better speaker too.

Well, I found one more glitch.  The set plays great now.  I installed the new dial glass, no problem.  I went to install the pointers and have several questions:

1.  The red "second hand" slips.  Looks like the large gear and the gear on the pointer shaft are not quite meshing.  I don't see any adjustment for that and before I take everything apart wanted to get some advice.   Has anyone had this problem before?

2.  My white pointer does not cover the full face of the dial, so on AM the needle stops short of the indication on the dial.  I can live with this, but now I wonder if I have the wrong pointer? Is there a longer one out there? (I can send picture if that is needed)

3.  The green dot that lights up to identify which band is playing is about 3/8 inch off from the actual station.  I assume the dot is not intended to also act as "pointer".  Am I correct on that and is mine displaying as it should (being off about 3/8 inches)?

Thanks,

Joe

On number 2: I have seen this. I think the long end goes to the top scales.

On number 3: Check each end of the dial. It should stop at the extreme end of each direction.

Maybe your tuning shaft slipped "setscrew" or the dial scale need to be aligned per the book. The pointer should be over the green dot.

Jeff

Jeff,
Thanks for your suggestions.
1. I think I can make this work by pushing down on the large gear. I think it may have come out of alignment when I pushed hard to put the red second hand on.
2. My white pointer is symmetrical around its center, short in both directions. I think the green dot (once aligned) will help visually.
3. I'll loosen the set screws and fix the green dot alignment in the morning.

The dial pointer that you have is for a stationized dial.  The short leg of the pointer should cover the upper half of the dial.  If you have the stationized dial, regional stations are identified on the top scale above the end of the pointer..  An illuminated dot should appear at the station when each regional station is tuned in.  The dial scale light should be directly behind the pointer.  If the pointer is correctly adjusted for the ends of the bands and the traveling illuminated dot is not directly behind the pointer, the lamp mask is not correctly aligned.

Norman

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