[Elijah]

I just received today a BK Signal generator, model 2005B, for the purpose of trying to align several radios I have. The one "under the knife" this evening was the Philco model 49-504. I went by all instructions, set the scale knob of 300-1000kHz, Internal Modulation and attenuator on low and followed instructions per the Sam's schematic. When I got to the last part about setting the generator to 1600kHz, I had made ahead of time a loop of about 5 turns of #20 ga wire and radiated signal into the radio which has an antenna top to bottom and sides of the inside back of the cabinet.

After all this I disconnected everything and put the chassis back in the cabinet and brought it to another area where there wasn't so many electrical wires and connections as on the bench. It's still not tracking properly. I first noticed a strong local station at the low end of the dial, 620KC, was picking up around 650 and it was like that from low to high end. The volume was also low on most all stations. I could touch the antenna around any place just inside the cabinet and volume went way up. Some stations on the high end will go up and down in volume. What have I missed?

[BrendaAnnD]

Probably a stupid question, but is the IF chain properly tuned? I don't see any series capacitance in the LO tank circuit, otherwise I'd say check that. Perhaps there's a high resistance between the tuner rotors and ground? Try cleaning all ground connections with DeOxit.

[Elijah]

What do you mean, "IF chain"? The ground connections are good. What I'm wondering is if I followed the instructions the way I interpreted them. this is what they say about the first step listed....

Use a .1mfd cap on the high side to pin 6 of the 7A8 tube. Low side to B-. Set generator to 455KC and output meter across voice coil.

I did all that except used a .001 cap.

Then, it says to adjust A1, A2, A3, A4.

Remarks column say to turn A3 completely clockwise. Then adjust A1 thru A4 in order given, for maximum output.

I did that except after turning A3 clockwise, I adjusted A1, A2 and then figured A3 followed by A4 to be adjusted for maximum output. I'm wondering now if the meant to leave A3 clockwise and just adjust A1, A2 and A4 for max output. Just an afterthought.

[Ron Ramirez]

Brenda is talking about the IF transformers.

You did OK, except for A3. Philco wanted you to tighten A3 (this is what they meant by completely clockwise), adjust A1 and A2 for maximum output, then adjust A3 for maximum output, and finally adjust A4 for maximum output.

Try it again, it should get better.

One final thought. When you're finished, your 620 kc station may not come in exactly at 620 on the dial no matter how carefully you perform the alignment. Non-linearity in the circuit, especially as these components age, may cause this. Not to mention the fact that Philco did not provide an adjustment for the low end of the band in this set.

[Elijah]

That's what I did, Ron. I adjusted after I tightened A3. I did that first thing. The instructions for the low end was to use a .1mfd cap to the B- side and high side of generator to pin 6 of 7A8 with the generator on 455 and tuning cap fully closed. That was it on the low end. I may go back and try again. I moved the radio to another area and reception/volume was better but the stations are still off by about 50KHz.

[dixierat]

50KHz is a bit much deviation--should get within 10-20KHz except low end. Have you checked sig gen against freq counter or zero beat against local stations?

[Elijah]

I don't have a counter for this one but have yet another generator coming with one...should be here in another few days. I'm not sure what you mean by zero beat against local stations.

[TA Forbes]

Strongly recommend you get a freq counter to verify you are getting what you need to align your set. Always possible that your dial is off.

[dixierat]

Use zero beat to calibrate sig gen if no freq counter available. To zero beat turn on AM radio to station of known freq. Turn on sig gen and set to freq of radio. Place sig gen output near radio antenna to radiate signal to radio. Sound from speaker will probably be altered. Vary sig gen freq to cancel sound from speaker. The sig gen setting when sound is at minium corresponds to the station freq. Make a plot of sig gen indicated freq vs actual freq and you have a calibration curve for your sig gen. Heathkit sig gen manuals describe zero beat in detail. Its easier using freq counter. Other members please elaborate or correct my explanation.

[Ron Ramirez]

Great info, Dixierat; thank you. I can't really elaborate as I use a frequency counter hardwired to my signal generator to avoid such errors.

[BrendaAnnD]

I didn't even consider that the sig gen may be off calibration, since I use PLL sig gens.. that could give a large error in the IF and corresponding mistracking on the dial.

[TA Forbes]

Yep!

[Elijah]

I received the other generator and it does have a frequency counter. I decided to go back through the entire process of alignment per the instructions in the Sam's and it's still off. A local station called Joy 62(620 kHz) still shows as about 675 on the dial. I tried another known spot at 850 and the dial pointer indicates 875. Trying to reset the pointer on this model is tricky as it's sort of a two piece deal. You can't just slide the pointer but it seems most all stations are up the scale from where they should be. Further up the dial at the high end, station 1620 comes in at 1550.

[TA Forbes]

The best you can hope for is doing the high side and low side alignment, repeating as necessary, until both are on.

These old sets are not precision pieces of equipment, you may not have "spot on" dial indication across the entire dial.

[Ron Ramirez]

And don't forget, this one does not have a low side adjustment - just the high side. Manufacturers eliminated the 600 kc adjustment as a cost-cutting measure.