[philconerd]

This is the console version with the 6 tube chassis that I purchased at an auction.

While working on the recapping etc.  and getting the radio to working condition, I noticed a couple of issues and wondered if anyone else has experienced these?

* The chassis was very sensitive to any tapping with an insulated tool  to any part of it.  Sounded like it would go into oscillation and loudness varied with the volume control.   So one by one I pulled a tube starting at the front end and working towards the 42 output tube.  When I pulled the 75 first audio tube the problem stopped.  I replaced the 75 tube with an NOS and the problem is fixed!  Are these old 75 tubes known to cause this oscillation problem?


*  Next question is normally does the glass 6A7 Oscillator tube need a shield?  My chassis does not have a shield or bracket on the tube socket for one.  Should I be using a metal tube here?  The chassis drawing seems to show a shield.

Thanks 
G.

[morzh]

Typically 6A7 is not shielded, unless for some reason the mfr puts the shield around. If you do not have a bracket for it, you do not need it. In any case, if the shield were essential, you'd probably noticed some oddities in performance.

As for the microphonics of the 75, you probably got a particular tube with some loose element inside. As long as the new tube fixed it, you're OK. Often times the 75 if near the 42 is shielded and the grid cap should be INSIDE the shield. It being outside could cause oscillations. Are you sure you did not have it outside before changing?

[philconerd]

Okay, thanks for the reply.

Yes, the 75 tube does have a tall shield around it that covers the grid cap.

So far I don't notice anything strange with the oscillator tube but I will keep an eye on it.  I had to replace the 3 rubber grommets under the tuning cap and while replacing them I had to move wires around to reach the fasteners under the chassis.  So I am watching for any possible changes in performance caused by any moved wires.

G.

[morzh]

Sorry: by "grid cap" I meant - the cap AND the wire. The wire should be inside too. Is it?

[philconerd]

Okay,

I think I took the easy way out with the shields.  I left the grid cap wires outside on all 3 tubes.  So I will go now and install the grid cap wires correctly.

G.

[morzh]

Only the grid caps coming from under the chassis (typically come through a corner of the shield or inside the base ring for the round ones) have to be inside. Those coming out from above (from the tuning caps or from IF/RF cans) or those coming from under the chassis but outside the shield perimeter (it is pretty intuitive: they cannot be easily put inside the can) should stay outside.

I have not seen more than one wire inside in the radios like 630 - I recently finished 620, which is similar; I think there's just one and it is the 75.

[philconerd]

Yes, you are correct, only the 75 tube.

After I posted here I looked at the chassis again and only that tube would have the grid cap wire inside the shield.

Next I will be checking the wire dress after I moved them around to have room to install the tuning cap grommets.  I noticed I have a nasty humming oscillation on band 3, somewhere around the 15 or 16 mhz frequency.  Tomorrow I'll have time to work on it.

G.

[philconerd]

Okay, now for another question.

I am going to start the alignment procedure and I want to look at the AVC line to monitor the signal level.
I am trouble locating the AVC on the schematic.  Can someone help and tell me where to connect my VOM?

G.
http://www.nostalgiaair.org/Resources/811/M0013811.htm    Page 6-31

[Mondial]

Connect your meter to the ungrounded end of the 330K resistor marked 73 on the diagram. That's the output of the detector where the AVC voltage is generated.

[philconerd]

Okay,  I just couldn't make any sense of the AVC on the schematic .

I located resistor #73 and found the AVC voltage.  My VOM reads about -1.5 volts for a broadcast station before doing any alignment.

Now this will make the adjustments easier to see and I can keep the volume turned down.  Thanks for your help.

G.

[philconerd]

Hello Forum-

This is an update for the 630 radio.  It is now aligned and working on all three bands.  I am measuring about -3 volts on the AVC for strong broadcast stations located 100 miles away in the daytime.

But, I have been following the thread above titled Philco Model 610 by Radio Hound.  I am experiencing the exact same voltage measurement issues as he is, such as Tube 80 pin 1 reads 389 volts.  and most plate voltages are about 50 volts higher than those listed in the table on the schematic.

Like I said the radio works and sounds good but I am at a loss for the cause of the higher voltages.  Could it be the 121vac line voltage at my bench?  Could it be my Radioshack DVM ?  So I will be watching the thread mentioned for more information.

Also, I found this chassis is a real pain to match up to either schematic or parts list.  Closest to page 7-97.
http://www.nostalgiaair.org/pagesbymodel...013811.pdf


Thanks
G.

[Mondial]

Your high line voltage may be part of the reason for the higher DC voltages. I have found that the schematic voltage readings pretty much agree with measurements at a line voltage of 112 to 115 VAC or so.

If your 42 is weak, it will load the power supply less and the DC voltages will be higher.

What voltages do you measure at the 42 screen grid and plate, and what is your measured voltage across the wirewound resistor marked 70 on the schematic?

[philconerd]

Okay, for the 42 plate = 327 vdc.  Screen = 341 vdc.

For the WW R70 =  -21 vdc.

So it seems like our higher line voltages are part of the reason for measuring higher than voltages posted in the chart.
I have been reading many threads about voltage readings high in the various 610, 620, 630 and 650 Philcos'.

I guess since this radio seems to be working well, I'm not too concerned about the voltages.

G.

[Ron Ramirez]

It isn't just higher line voltages (although they are a contributing factor).

Bear in mind that the original measurements as made by Philco technicians and printed in their Service Bulletins not only assumed a line voltage of 110 or 115 volts, but they also used voltmeters with an input impedance of 1000 ohms per volt. These old meters tended to load the circuit under test, making the readings appear lower than they actually were. But it was all that they had at the time, so that is what they used.

Today's digital multimeters have an input impedance typically in the megohms per volt, which does not place as much of a load upon the circuit under test. As a results, voltage measurements will be higher than they will be with an old meter with an input impedance of 1000 ohms/volt.

[philconerd]

Ron, thanks for the example about those old voltmeters.  It is easy to forget that our modern meters have such high impedance compared to the old ones.

Now I can enjoy listening to the Philco without too much concern about un-diagnosed problems.

G.