[jerryhawthorne]

Certainly has a few features that mine does not like an external modulation. Nice price so far and I agree, probably not more than $30 or so paricularly if this is the only radio you want to work on. You must remember something most all of us have learned, once you fix one and have it going, more will follow. It's a given.
Jerry

[Pithicus999]

Thanks for advice. Put in bid on eBay, will probably be a week or two before I can get back to you.

I also have a Philco 38-38 that I bought for myself that I'm excited to work on next. Taking good notes on this one, and slowing down a bit. Thanks again for the help!

[codefox1]

Not sure your question was answered, but there are tons of old Heathkit and Eico, etc... signal generators on Ebay, or whatever, that shouldn't cost more than $30 or so delivered. If you get one, you should treat it as an antique radio, change the filter and paper caps and any out of range resistors. Install a 3 prong cord, check your bench supply to make sure all is right, and lose any caps from line cord to chassis on the instrument.

Now get a modern digital frequency monitor, which you should be able to get for $20.00 or so, and you will be all set for AM radio work. Let the signal generator warm up for at least 30 minutes, then use the frequency meter to verify unmodulated signal generator output, disconnect the frequency meter, and restore modulation. Now you have pretty good means to do alignment. I like an analog AC voltmeter or VTVM across the secondary of the Audio transformer (with shunt resistor of say 4 ohms if you don't want to hear the noise.) A digital meter to peak during alignment will drive you crazy(ier.)

Usual warning, absolutely always use isolation transformer on AC/DC sets. Correctness of AC sockets in most places is sadly still not reliable.

[Pithicus999]

codefox1 / Jerry - Funny, it LOOKS you are speaking English, obviously I'm going to have to read up a bit more before going forward so that I understand the terms etc. and how to use the sig-gen etc. thank you for the advice. I will probably need to join the MI club Ron suggested as well. Also, I have an old electronics book from the 50’s that I’ve been using as a reference; it explains all the components that are in the radio which is a great resource as well. I do have an analog meter I can use once my sig-generator comes in.

Steve - I did end up winning that sig-gen on ebay, thanks for the link! Should be here next week.

morzh / TA Forbes – In reference to your Q about the electrolytics on top (#53/#54 the 8 ufd caps) Yes, I did replace those two. They both had the negative coming off a tab that was pinched between the can and the cardboard tube and I replaced them the same way. I’m at work now, but will double check the insulation on the #53 and #54 negatives when I get home to be sure they are properly insulated and not accidentally touching ground, thanks for the tip about the relative charges.

morzh – Your Q about “Have you tried to do the test where you touch the grids with a screwdriver and try to hear the buzz?” Not sure how to do that. Is there a video showing this on youtube?

Morzh / Arran – #40 the triple electrolytics 1uf / 1uF / 2uF I’ll check the wiring and get back to you. Do you think that 450 voltage rating would be enough for these caps? I think that’s what I have.

codefox1 – That sig-gen I bought on ebay looks like it’s from WWII (the seller said it was his grandpa’s and he didn’t know what it was for) plus it’s army green, so just putting 2 and 2 together on this one. Anyway, when I changed the caps/resistors on the radio I used schematics to show me the proper capacitance/volts/ohms etc. hopefully I’ll be able to read the colors of the resistors or the descriptions on the caps in the sig-generator, otherwise you’ll see a whole new ‘thread’ starting on this phourm . I don’t know where I would get a schematic for the sig-generator…?

[jerryhawthorne]

Sorry I confused you. I guess that is our job at some point. My comment on modulation refers to the point that a signal generator of the type we use will add a frequency (audio) that you can hear at the speaker . So if your pumping in an IF frequency to align the IF section, it will carry some tone with it. This is typically 300 or 400 cycles, makes an annoying sound out of the speaker and you can hook you meter to the speaker coil and measure the A/C (low voltage) for peaking. Mine has only one frequency as do most. Yours has another input for putting in an alternate tone or music. Think of putting into that your i-pod and your signal generator becomes a radio transmitter! Dial your sig gen to the frequency of your radio is set your probe near the antenna input of your radio with a small loop of wire and you can become your own transmitter with any frequency adjustable to your radio.
If you didn't have a tone on adjusting the frequency for something like the IF alignment, well, you couldn't hear it or monitor the AVC voltage or speaker, another way to peak. Your new one will work very well.
Just a nice little feature.

Jerry

[morzh]

Pith

yes 450V rating is enouhg for all those caps.

As for the test, you just touch the grid cap with a wire (I touch it with my finger but if you are not at the point where you are copmfy doing that, just use a wire or a scredriver, or a meter's lead). Just touch them - you will hear a 60Hz buizz. If your audio works.

[Pithicus999]

My mistake, they are not 450, they are only 250 voltage rating, will that be cutting it close?

After I finish with these 3 caps, I’ll check the voltages and report back. I’m still waiting on my signal generator to be delivered, so I’ll hopefully be ready to use it next week (providing that it works!)
Thanks for the help, and everyone have a good weekend!

p.s. Ron, thanks for the help.

[TA Forbes]

250 not enough. As a rule I use 450V electrolytics.

Exceptions: 1. When the set calls for electrolytics rated higher than 450V. You often find this in the high wattage output sets; 2. When working on AC/DC sets where physical size of the cap limits what you use. In these cases I use 160V electrolytics.

[morzh]

Agree, 250V is not universal. Can be used in some places but not against the B+.

If you want to not to think about the rating, use 450V and you can use them across the whole thing.

[Electrothaumaturgist]

I always try to use at least 630v across the board. Normally, the higher the v rating, the better. (Better safe than sorry).

[TA Forbes]

When you go above 450V electrolytics they get pretty expensive. As a rule I always keep a few 600V 10mFd and 20 mFd caps on hand, but most of my electrolytic stock is 450V. I do keep a small number of 16V, 50V, and 160V electrolytics for the occasional (ick) AC/DC set I work on.

630V poly caps are what I (mostly) use for all cap values below 1mFd. The poly caps are physically too big when they exceed 1mFd. I do keep a small number of .0033mFd, .033mFd, and 0.1mFd that are rated over 1000V for some applications.

Oh yes, I also use ceramic caps for values from 10pF to 4700pF. (Yes, I overlap the poly .001, .0022, and .0047 caps.)

[Pithicus999]

Thanks guys, I'll have to go back and get some more 450's the only place I can find them is online. Is that what you find as well? Or is there a physical place you go to get them? Radio shack doesn't really have a whole lot.

I still need to check my voltages, didn't do that yet but I will. In the meantime, I have some tuning questions:

I need some help tuning this radio. This is a Philco model 18 (code 121) and the schematics show how to use the signal generator to tune this radio but they don’t tell you where to put the (+) & (-) leads from the multi-meter, so I need some help with that. Basically I would like to know where to put the leads from the multi-meter and signal generator and get some confirmation on a few things.

From what I can see, it looks like there are three stages to tuning the radio. I have these three stages broken out below and I have some questions for each stage.

STAGE 1: I.F. Intermediate Frequency –3 adjustments

QUESTION 1: Where do you put the leads for your multi-meter? Instructions say connect to ‘primary output transformer’ but I do not know where that is?
QUESTION 2: (Please confirm) With the multi-meter hooked up properly, I just tighten/loosen the hex bolt and look for the highest voltage rating on the multi-meter, correct?

Making the 1st, 2nd & 3rd adjustments:
(1) QUESTION 3: (Please confirm) Signal Generator at 260 kc and connected to the cap on the 6A7 tube (with 6A7 grid cap wire unplugged).
(2) 1st adjustment - adjust the 1st I.F. Primary (which is # 24 on the 121 schematic) hex bolt tighten/loosen
(3) 2nd adjustment - adjust the 1st I.F. Secondary (which is # 25 on the 121 schematic) hex bolt tighten/loosen
(4) 3rd adjustment - adjust the 2nd I.F. Primary (which is # 28 on the 121 schematic) hex bolt tighten/loosen


STAGE 2: ANT. H.F. Detector and the OSC. H.F. Condensers –3 adjustments

I had to go to the schematics for the code 124 on this one. The schematics I had for the 121 were incomplete. I had to use the 124 instructions and tie back the correct part number to match my code 121 schematics. The schematics state that these 3 adjustments ‘are located on top of the Tuning Condenser and are adjusted from above’.

Here are my questions:
QUESTION 4: (Please confirm) I see 3 screws on top of the Tuning condenser (one of them is connected to the 6A7 tube) I believe that these three screws need to be adjusted for the ANT. H.F. Detector and the OSC. H.F. Condensers correct?
QUESTION 5: Where do you put the two leads from the multi-meter? And is it the same place for all three of these adjustments?

Making the 4th, 5th, & 6th adjustments:
(1) Replace the 6A7 grid cap wire and hook up the sig generator antenna lead to the antenna post.
QUESTION 6: Does ‘antenna post’ mean connect the sig generator lead to the antenna wire/clip on the chassis at the back of the radio?
(2) 4th adjustment - QUESTION 7: First, adjust the “OSC; H.F” (#15 on the 121 schematic. This is the screw that is NOT near front of radio AND NOT connected to the 6A7 grid cap wire—Please confirm) – Set Sig-Gen to 1500 kc
(3) 5th adjustment - QUESTION 8: Second, adjust the “Detector: (#11 on the 121 schematic. This is the screw connected to the 6A7 grid cap wire—Please confirm) – Set Sig Gen to 1400 kc
(4) 6th adjustment - QUESTION 9: Third, adjust the The “ANT; H.F.” (#8 on the 121 schematic. This is the screw closest to the front of the radio—Please confirm) – Sig Gen at 1400 kc


STAGE 3: “OSC.; L.F.” Condenser –1 adjustments

QUESTION 10: Where do I connect the lead from the sig generator?
QUESTION 11: Where do you put the two leads from the multi-meter?

Making the 7th adjustment:
(1) Set station sig generator and station to 600 kc
(2) 7th adjustment - (#18 on the 121 schematic the “OSC.; L.F.” condenser) adjust from the rear of chassis the hex bolt (tighten/loosen) until you see highest voltage rating.
(3) Tuning condenser should be rocked while adjustment is made.

QUESTION 12: I saw a guy on You Tube tuning his radio but he had to solder in a 0.5 ufd capacitor to one of the ends of a tube pin…do I need to do anything strange like that here?

Please let me know if anything listed above looks incorrect, I’ve never done this before.
Thanks for your help!

[jerryhawthorne]

Pith, sounds like your moving along. Let's start at the back end of the radio. For your multimeter (I hope it is analog and not digital) I prefer to hook up the leads to the wires going to the voice coil due to low voltages and easy to get to. Sometimes. Set your meter for a very low range A/C, perhaps 3V. With your new generator and the proper frequency set on it your ready to rock! As indicated your gen to ground and the signal side to the top of the tube indicated with the cap off.
Radio volume at full blast and signal generator as low as possible to hear the modulated tone (make certain you turn that tone on). This is where it nice to watch a analog meter with the nice needle instead of a jumping digital. As you move along adjusting the IFs in the proper order you will notice hopefully that that tone is getting louder as indicated by ear and meter. After each peak, turn the output level on the signal generator down to just a comfy hum out of the speaker. Once you have those IF adjustments peaked, your ready for phase two!
Let us know how it goes.
Jerry

[TA Forbes]

Definitely agree, an analog meter is much better to use.

[Pithicus999]

Ok, first things first I guess. I was able to do the first three alignments provided that my 100 yr old sig generator still works and that I was using it correctly...

I turned up the volume full blast, started with the 1st tuner, adjusted it slowly till I saw the voltage (analog) going up then back down, and I went back to the voltage peak for the first three adjustments and the speaker got louder with each adjustment so I feel good about that.

But, it went downhill after that. Once I unhooked the signal generator lead from the 6A7 and replaced the grid cap, I hooked the sig gen lead up to the antenna clip on the back of the radio. That's where (I think) the instructions say to hook it up. There was no voltage shift when I adjusted the OSC; H.F” (#15) or the other two the Detector: (#11) and the ANT; H.F.” (#8 ) the three screws on top of the tuner.

Nothing happened.

Maybe I have the signal generator on the wrong settings? There are some dials on the bottom, not sure what the one on the far left or far right should be set at?

Also, and maybe more importantly it says to turn the dial to the same channel (1400, 1500, 600 etc.) as the signal generator, but my dial only goes up to 150...is the dial's 150 really 1500?

Here is a short video of my radio dial and the WWII signal generator I'm using.
http://www.youtube.com/watch?v=u6P8NFx_gK8