Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Philco 118 alignment issue
#31

If I may...

Tube Radio, with all due respect, you are missing the point of a proper alignment in a Philco receiver.

These sets were not intended to give razor-accurate tuning across the AM band.

For the purposes of my argument, allow me to focus on the AM band only.

The proper way to align the AM band in a Philco set is to first peak the trimmers (oscillator, RF if used, and antenna) at the high end (usually 1500 kc). This is done to set the upper end at 150 on the dial, yes.

However...

The purtpose of the low end padder is not to set the dial exactly at 60 (or 580 kc as is sometimes used), but to make the oscillator properly track with the set's IF.

This is where "rocking" the tuning gang comes into play.

Once the high end has been aligned, you set your signal generator for low frequency alignment and tune the radio to wherever the 600 kc signal is coming in. It may be as much as 50 kc off (more if the radio is badly out of alignment).

Now...

You want to adjust the low frequency padder slightly in one direction or the other, then retune the radio to keep in tune with the signal from the signal generator. You need to watch your output meter or oscilloscope while doing this.

If the amplitude of the signal increases, do this again (turn the padder very slightly, in the same direction as before, then retune the radio to keep the signal in tune).

If the amplitude decreases, you want to turn the padder slightly in the opposite direction and then retune the radio to keep the signal in tune. This is the "rocking" procedure.

You continue to slightly turn the padder, and retuning the radio each time, until you reach a point where the signal does not get any stronger and in fact begins to fall off.

When that happens, you need to turn the padder slightly in the opposite direction to re-establish that peak.

Then...

Go back and realign at 1500 kc (or wherever the Philco instructions tell you to for the high end).

Then repeat at 600 kc.

Usually going through this twice on each end is sufficient, but if you're really picky and have a lot of time to spend, you can repeat this as many times as you wish.

When you are finished, your radio will be accurate at 1500 kc but will probably not be accurate at 600 kc. However, by doing your alignment in this manner, you will have set it up so it has the best possible sensitivity across the band and the oscilator will properly track with the set's intermediate frequency.

Do you now see why your set's sensitivity is lower at 600 kc? It is because you aligned for the 600 kc signal to come in exactly at 60 on the dial.

Repeat the set's alignment using the method I have outlined, and you will find that the sensitivity will be higher on the low end even if the tracking is not 100% accurate.

These radios were consumer appliances, not laboratory standards, and a high degree of accuracy simply isn't possible with these old Philcos.

--
Ron Ramirez
Ferdinand IN
#32

I do agree, but if I cannot get a peak at 1500KHz at all even with the high end AM band oscillator trimmer nut as far out as it will go what should I then do?

If I adjust the low end trimmer cap I can get 1500KHz to come in properly, but then 600KHz is way off and getting it close makes it to where 1500KHz is off by more than the trimmer can compensate for.

Thing is I remember it being quite accurate initially after the first alignment using the 1K resistor in place of the shadow meter coil and the AM band high side oscillator trimmer cap nut was in a different position. Then once the shadow meter coil was installed I did the initial alignment and all seemed good. Shortly thereafter I noticed the dial was off at 1000KHz and before removing and reinstalling the oscillator coil in order to get a peak at 1500KHz I then had to have the trimmer nut almost fully backed off.

Now that I removed and reinstalled the oscillator coil exactly how I removed it including lead dress I cannot get a peak at 1500KHz at all and with the trimmer cap nut all the way backed off as stated previous the best can do is 1492KHz.

I know something must have changed to cause that.

Ron, it would have been nice if the Philco alignment instructions had said what you did about the alignment. It would have saved many people a big headache.

That said if someone takes a properly working Philco 118 and checks the dial, couldn't they determine where the dial is off and have one of the dial makers make a dial that is correct or is it that one 118 will be off slightly differently than another 118?
#33

It would still be different slightly with every radio. Or even every 6A7 tube.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#34

Figured it would be slightly different.

Wonder what made the sudden change in mine?
#35

Mike is right - not every 118 is going to be the same, nor every 6A7 tube, nor has every 118 oscillator coil aged quite the same...

Now as to the alignment. If you can't peak the high end at 1500 kc then it's time to get radical. Turn the low frequency padder enough to make the 1500 kc signal come in above 1520 kc on the dial. Then start the alignment procedure as I outlined in post #10 above. It should prove helpful unless you have a serious problem in there somewhere. Before suspecting such, though, I strongly suggest trying the radical readjustment followed by a proper alignment.

--
Ron Ramirez
Ferdinand IN
#36

I just realized that we had two threads going on the same subject (118 alignment), both started by the same author, which is not permitted per Phorum Rules...so I merged both into one.

--
Ron Ramirez
Ferdinand IN
#37

Will do

Far as the alignment goes following Ron's method I get 9Vdc AGC voltage at 1500KHz and with the dial set around 593KHz I get 5.5Vdc AGC voltage and I can get it no better than that.

I still believe that the high side LO trimmer adjustment nut is farther out than where it was when I had near perfect dial tracking.

Oddly enough I was able to get a peak at 1500KHz today without adjusting the low frequency LO trimmer.
#38

Ok I'm back to working on the Philco 118.

I replaced two 16K resistors (in series to make 32K) which were marginally rated far as the wattage goes given the discoloration of those resistors.

I also replaced the 800pF cap with two caps that make 800pF when put in parallel this time reading the numbers right to be sure I had the proper value of caps.

So far here's what I get.

At 595KHz on the dial with a received frequency of 600KHz the best I can get is -5.1Vdc AGC voltage.

At 1500KHz on the dial for a received frequency of 1500KHz I get -8.2Vdc AGC voltage.

Is it normal for an early-mid 30's Philco to have lower sensitivity on the lower BC band?

Think I may use my scope and do a frequency sweep of the RF stage to see if the RF level changes any as I go from 600-1500KHz

Then again I don't know if my RF generator is putting out the same RF level at 600KHz and 1500KHz.

If it is putting out a lower RF level at 600KHz that could partly explain the lower sensitivity.

I really need to get me a good quality modern RF generator versus the old service grade RF generators I have.

I'm thinking that something like this http://www.pongrance.com/DDS2016.html would work good for the time being.

EDIT:

And it looks like I have found one issue.

This is the output of my EICO 315 RF generator.

600KHz

[Image: http://i863.photobucket.com/albums/ab196...161425.jpg]

1500KHz

[Image: http://i863.photobucket.com/albums/ab196...161426.jpg]

Maybe that is part of the issue I am having with the alignment. The signal could be causing the frequency display to show the wrong frequency which would mean I am using the wrong frequency for the alignment.
#39

I have an update.

Was reading the September finds and losses topic on the Antique Radios forum and saw where a member had gotten a Philco 118 that either was already restored or he restored it.

Anyways I asked him to check the dial tracking and his dial was pretty much spot on except for being off high by 10KHz starting at 1540. he did say that he thinks it may be a Radio Daze dial, but I don't know if that has anything to do with it.

That means I do indeed have a problem unless there was that much of a variance between the Philco 118 radios where some would be right and others off by varying degrees.

Another thing that makes me think I have a problem is as I said previously the alignment was nearly perfect on AM and off on SW when using the resistor for the shadowmeter, but was initially the same right after re-installing the shadowmeter then right after the alignment it went to the AM band being off and the SW band being pretty much spot on.

I am thinking of getting a N3ZI VFO and using that for an RF generator then trying the alignment procedure again.
#40

To be honest, the oscillator output does not look great. I know many of them clip the signal (mine does) due to a cathode follower at the output stage but not as bad.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.




Users browsing this thread: 3 Guest(s)
[-]
Recent Posts
Jackson 715 not working
Now that you posted the schematic, I don't know why that Sprague electrolytic cap is across the meter, as it is not indi...MrFixr55 — 05:51 PM
HiFi (Chifi) tube amp build - but my own design.
What may be lacking in the PP Tube amps may be the 2nd harmonics, which some, especially RCA back in the day called &quo...MrFixr55 — 05:32 PM
Jackson 715 not working
Usually in an emission tester, the tube under test is measured as if it were a diode. So, some testers connect all the g...RodB — 04:17 PM
Restoring Philco 37-604C
Yep. F5 is green, D5 is Red. Red is Bad. Green is Clean.morzh — 01:30 PM
Jackson 715 not working
I did start to do that but I stalled out because I could not figure out how the grid and plate get voltage. In this diag...daveone23 — 11:52 AM
Restoring Philco 37-604C
(Insert Homer Simpson "DOPF" Here.) When all fails, look at the can. Took the Ron Ramirez advice, red Caig D...MrFixr55 — 09:23 AM
Philco 91 Speaker Replacement
From your text I am not sure if you intend to use the existing speaker with a resistor instead of the field coil. It wo...morzh — 08:44 AM
Philco 91 Speaker Replacement
My field coil is bad. I am still hoping to find an original, but if I can't I will go with a fitting Philco speaker, 125...dconant — 08:34 AM
Philco 91 Speaker Replacement
As Rod said, it is OK to use a fitting speaker, and then look for an original one. If you buy a Hammond 125 output tr...morzh — 08:15 AM
Philco 91 Speaker Replacement
Yes, I often have to substitute, then keep an eye out for an original. In the meantime, the radio is working and being e...RodB — 08:02 AM

[-]
Who's Online
There are currently no members online.

>