[David B]

Hi

Did some adjusting of the compensator's, 34, 31, 1nd 29A & B by ear and had some marginal response on the AM band. The middle, or Police band, seems to be OK, but I have to turn the volume way up to hear the stations. The upper, or SW band, is the one with the worst response. What stations that can be tuned in are garbled as if there is some back ground interference. The voices on this band are distorted and unclear I replaced the two weak 41 tubes and all the capacitors except # 24 which is near impossible to reach it is so buried. I hooked the radio to it's antenna in the case and did my adjusting using it but the SW band as mentioned is still garbled. Any thoughts on why the SW bands reception is so noisy or garbled? Further, I wish I knew how to use he signal generator I have, it's a nice one but I don't know how to hook it up to tune the radio. Any one out there real good at using signal generators, I sure would like to use the one I have.

God bless,

Dave B

[Raleigh]

I don't know anything about your specific signal generator, but if it is an old-fashioned analog generator tuned by a large multi-scale dial, it should be similar to lots of other models. Elements of Radio Servicing has a couple of chapters on signal generator operation and set up. Chapters 5 and 6.

To peak the IF compensators by ear, I would use a strong station to get it close and then a weak station to finish it. Remember that this operation gets all of the IF cans tuned to the same frequency, but not necessarily to the correct frequency. If you can't get fair sensitivity on the broadcast band by this method, either you're way off the 455 KHz frequency or something else is wrong.

To use the signal generator to peak the IF compensators, first short the oscillator section of the ganged tuning capacitor as described on page 422 of Elements.

On your signal generator, find the IF frequency, 455 kilocycles (Kc or KHz), on one of the dial scales. Set the pointer on that frequency. There should be a band selector switch somewhere. Set that to the band with the IF frequency on it. There should be another switch with settings for RF, Modulated RF, External, and maybe Audio. Set it to Modulated RF. A potentiometer somewhere sets the level of the RF. Turn it to about 3/4 of the way up. Another potentiometer sets the audio modulation level. Turn it all the way up.

Connect the black lead (ground) from the signal generator to the radio chassis. Clip the red lead to a .1 uf capacitor, and attach the other capacitor lead to the broadcast antenna terminal (terminal 2, I think.) Do not connect the generator lead directly to the antenna without using a capacitor. Elements suggests connecting the capacitor directly to the mixer grid, but I use the antenna terminal with good results.

If you have a high impedance analog meter, connect the red lead to terminal 1 and black lead to the radio chassis.

Turn the radio on. Turn the signal generator on. Set the radio band switch to broadcast. You should hear a sustained beep in the speaker. If not, turn the RF controls on the generator all the way up. If you still don't hear anything, turn everything off and connect your .01 capacitor to pin 6 of the XXL mixer tube. Not sure which XXL that is in your radio, but I'll make a guess and say the one nearest the IF can #29. Underneath you should see a lead from the mixer tube plate going into that can.

If you get the audio signal (beep) then adjust the 34A, 31A, 29A, and 29B compensators in that order until you get the strongest audio (or the strongest reading on the meter.) Follow the instructions in Elements to lower the modulation level of the signal generator and repeat the adjustments until you can use the lowest modulation.

If you still don't get good sensitivity, there is something else wrong that IF alignment won't help you with. Try adjusting compensators 4 through 4E following the instructions in the John Rider page from Nostalgia Air. Make sure your band switch is clean. It can have a MAJOR effect on sensitivity.

If you don't get the beep, there might be something wrong with your signal generator.

The SW band these days does have a lot of background noise and distorted stations, but there are a few strong stations that you should be able to pick up clearly, especially at night. Radio Beijing is very clear most nights, near 10MHz if I remember right. Use the built-in loop antenna or an external long-wire for best sensitivity on this band.

[David B]

John:

Thank you, you have been more than helpful you have been patient to teach me how these things are done, for that I am very grateful. I will it this week and let you know how I made out. Can the signal generator also be used to tune the SW bands?

God bless,

Dave

[Raleigh]

Dave,

First, I think I misinformed you that compensators 4 through 4E don't effect sensitivity. 4A and 4B definitely do, as they help tune the resonant frequency of the antenna you are using. (I edited my post above.) I would advise to adjust those compensators with the radio connected to the built-in loop, and follow the alignment instructions in whatever service information you have. If you have the Rider pages from Nostalgia Air, use the table and the notes just under the parts list.

Once you correctly adjust the IF compensators 29 through 34, you shouldn't need to touch them again unless you change out a component that changes their resonant frequency.

Steps 5 and 6 of the table in the Rider's alignment instructions show how to use the signal generator for the short wave bands. The alignment chapter in Elements shows how to make a loop of wire to use instead of connecting the signal generator to the antenna lead as you do when adjusting the IF cans. Other than that the only change in the operation of the signal generator is to change the frequency. Once you get a feel for the signal generator, go through these steps in order. If after following these steps sensitivity is an issue, more in-depth troubleshooting is needed.

I can't stress enough how helpful the Philco service packages are that you can get from Chuck Schwark. They are clear and easy to read, and usually more complete than the free ones on Nostalgia Air.