[GaryK]

philco-m-38-40-sc1433.pdf Size: 2.7 MB  Downloads: 146

i received a 38-40 radio with the range 2 antenna coil missing. I'm trying to run the radio without it beceause, if i'm right, it is the Shortwave coil. I tried to just bypass it. I changed all paper caps and electrolytics and NOS tubes. The radio plays but is very quiet. I tried to align but the tone is also barley audible. Would not having the range 2 coil be a problem or do i not need it. I don't care about receiving SW anyway. I would like to elimanate this from my troubleshooting process. Thanks GaryK

[rfeenstra]

Hi GaryK and welcome!

Never worked on one of these. It looks like the range 2 coil is always in the circuit. When you say "bypass", do you mean you shorted across connections from pins 1 and 2, and across 3 and 4? Or, is the coil completely out of the circuit with no such connection? There would be some inductance in that circuit, but whether it is enough to detune the input to the 1st detector sufficiently to prevent a broadcast band signal from getting through is a question for the EE's among us!

[GaryK]

The range 2 coil, #1 on the schematic, is out of the circuit. I connected range 1 coil as follows, connection 1 to "antenna in" lug on back of chassis, connection 2 to ground, connection 3 to grid of 6A8, connection 4 to the line to plate of 6J5.  That was my main concern that the radio would work in the AM band without that antenna coil. All of the A1, A2, A3, A4, A5, A6, A7, connections are not in the radio either. The band selector, #60, is badly broken. It looks like someone before me tried to make permanent connections for the AM band, bypassing this broken selector that is out of the circuit.

[radio1]

Check number 5 coil to ground, point 2
.

[rfeenstra]

"connection 4 to the line to plate of 6J5"

??? Through the 1 meg resistor 17?

It appears that A2 and A3 are normally closed contacts in BC band. Is that connection there?

[GaryK]

The coil #5 looks to be grounded through coil #6 at two points, through the 120K resistor #8 and through trimmer #7A and cap #9. My band selector is out of circuit so A2 and A3 are not there. I have a parts chassis from a 38-14 comming, i will try to use the band selector from that and try to get this thing connected properly. Thanks.

[GaryK]

Yes, point 4 of my antenna coil is going through a 1meg resistor #17 to the plate of 6J5. I measure about -1.5 volt to -2.5 at the plate of 6J5. The connection A2 and A3 are not there beceause the band selector is out of circuit. So could i use a jumper wire to close that connection? I have a parts chassis comming from E-bay, a 38-14 and it looks like it may have a band selector i could use and maybe the range 2 antenna coil as well. Thanks.

[rfeenstra]

It would appear that A3 should be grounded for the BC band to work. Maybe someone who has experience with this or similar radios can confirm. Bur, I would try grounding it and see what happens.

[462ron]

Gary, if I’m understanding this right, your terminal 2 of coil #1 is going to ground according to what you did. Doing that effectively by passes the primary of coil #2. Then terminal 3 of coil #1 is going to the grid of the 6A8G but terminal 4 you say is going to R17, effectively bypassing the secondary of coil #2. In doing that, you have no way of getting a signal from the Ant. terminal to the 6A8G. Coil #1 isn’t there and coil #2 is bypassed so no signal being induced in coil #2. Hopefully if you get a good band selector switch and a coil #1, things will work!

Ron

[GaryK]

Thanks, i had a feeling something wasn't wired correctly since the band selector wasn't in circuit. I was trying to follow what was done to this radio before i got it. Thanks for your diognosis, i'm not profeceint enough in the circuits of these radios to know what to do. I started this hobby about a year ago, so i'm pretty new at it.

[radio1]

Might also want to check the Battery/AC selections, are they in right?

[GaryK]

I assumed that the AC/Battery selector was in the AC mode since the radio is working on AC power, although very quiet. I didn't do any work on the battery power circuit of this radio. I wasn't intending to run it on battery power. On the antenna coil being grounded on the primary side, i did lift this ground connection and put a loose coil of wire on that point and the radio did work better, a little louder. I tried to align and the tone was more audible, so improvment on that.

[GaryK]

So i removed the range 2 antenna coil that i had tacked in. The radio seems to be working great with just range 1. The volumn was a little low and after many hours of snooping around, i found a 500ohm resistor that should have been 500K ohm. It went to the screen of the output, 6G6. That was my mistake. Thanks.