[jerryhawthorne]

LC, nothing wrong with pulling the output tube but it is much like pulling the speaker! Should kill the hum. Be happy, you have a good speaker with related parts.
Jerry

[loosecannon]

thanks guys,

yes, after seeing some pics of other peoples' speakers i felt quite lucky to see a complete intact cone when i removed mine.

as per Ron's suggestion, i am going to brush some mineral spirits on the cone to give it a little bit of resiliency.

if anyone thinks this is a bad idea, please speak up and let me know why.

LC

[jerryhawthorne]

LC Ron will not steer you wrong. Don't worry about the speaker and stay focused on the problem getting the radio working.
How is the hum going? If you can hear it, your speaker is working fine right now. Your becoming a loose cannon!!!!
Best, Jerry

[loosecannon]

LOL!
loosecannon is my old CB handle, and boy is it fitting!

i usually restore old CB radios from the 70's. thats why this stuff can get a bit confusing at times. im used to pc boards and transistors.

i am at work and wont have a chance to do any testing until late tonight.

i will post back tomorrow afternoon.

[jerryhawthorne]

Matt, your doing fine. Repairing these beasts requires a bit of a structured approach. First "iron" the fact you have hum indicates the major iron is just fine, speaker/output transformer and power transformer. Great.
This type of radio is "relatively" simple, a bit like a guitar amp. Volume on the front end (antenna) amplification of the RF signal for several stages to perk up the signal then on to a detector tube to strip the audio off of the RF signal. Just a diode like in a crystal set.
Once that is done you have audio (AF) which the output stage will amplify for the speaker. You need to address the hum. It could be coming from almost anywhere, hence pulling tubes on at a time.
The audio amp runs flat out as the volume control is not on it but on the antenna. Just an FYI. Volume is controlled in the antenna section, far before the signal is turned into audio.
I'm not familiar with the regen type radios but seems they get additional gain out of the RF section by feeding back the signal for another pass through for more gain on the cheap. Hence perhaps alignment might be more critical to assure they are passed back for amplification properly. Not proper, squealing as the signals are not in sync properly. No doubt wrong about that part but my simple take on it.
Have some fun. I'm learning as well as you.
Best, Jerry
PS: do check all coils in circuit. Should be very low resistance.

[loosecannon]

thanks again Jerry.

yes, as far as i understand it, these "regen" type radios take full advantage of the "flywheel effect".

the volume control had me completely stumped before i figured out that it was actually an RF gain control.
Gary from PTOTP clued me in by telling me that the volume pot was a linear taper when i was sure it would be audio taper.

Ok, first the good news. I am pulling in stations!!!!!!!

they actually sound pretty good even if they are on top of the hum.

i am embarrassed to say that i think the reason i didnt notice them before is that i didnt let the set warm up enough before i tuned around the dial. (typical solid state guy)

now, on to the hum issue. i will take you guys through the steps i did and let you tell me what you think.

first, i pulled the 2nd oscillator tube. the hum disappeared!

then i put the 2nd oscillator tube back in and removed the detector oscillator tube.
the hum was still there.

next i put the tube that was in the detector oscillator location, into the 2nd detector location.
hum was still there.

this says to me that the hum is coming from the 2nd oscillator section, and its not the tube itself.

i had read that the 1 meg ohm resistor in this section should be mounted as far from the #14 coil as possible, so i added some wire to one end and moved it away a bit.
no change. hum still there. (not sure if this had anything to do with the hum, but it was worth a shot!)

next i began poking around with my trusty chopstick that i use for all high voltage situations, and couldnt make any change in the hum

finally, i grabbed the wire going to the control grid (top) of the 2nd oscillator tube, and the hum got much louder.
i had previously removed this coil in order to change the 50pF cap and to do Ron's 4meg to 2meg mod. i also replaced the wire going to the grid cap.

this makes me wonder if i somehow changed some parameter of the 2nd oscillator circuit by doing this change. obviously the size of the new components is not exactly the same as the old ones.

i stopped there since it was very late and i hadnt actually made the radio worse.
(always a good place to stop!)

so thats my progress so far.
ill hold off on removing the #14 coil until i hear back from the group.

thanks again for the help,
LC

[jerryhawthorne]

Just a sanity check, my sanity, please review caps 34, 35 and 37. The first two have the negative going to the center tap with the + to HV connections. Cap 37 is a little different in that it has its negative going to the center tap but the positive to ground if I'm not mistaken. Quite common to mess this one up.
Jerry

[loosecannon]

looking at my self drawn wiring diagram and the schematic right now.

making sure we are on the same page.

34 is the 8uF

35 is the 4uF

37 shows on the schematic to be a .015uF cap. i did not notice on the schematic that it was polarized. i am using a .01uF non polarized polyester film cap here.
should i be using a polarized cap here?
LC

[jerryhawthorne]

Sorry LC if I added a little confusion. I was looking at the schematic for the 80 that was posted earlier. It seems to indicate that item 37 is a 10mfd. I couldn't find a parts list on the posting. Take a peak at this link under the 80.
Jerry
http://www.nostalgiaair.org/PagesByModel...013843.pdf

[Pillo69]

In this scheme there is also a capacitor #38 of .01, no other existing schemes.

[morzh]

Jerry
What you refer to as #37 is not a lytic, it is a backelite paper cap across the wirewound resistor.

[loosecannon]

in looking at the nostalgair papers, there is a note about a change in the production runs of the model 80.

cap 37 was indeed a 10uF cap, and in a newer production run it was changed to a .015uF non polarized cap.

cap 32 was also eliminated in this run.

i believe i have the version with the .015uF cap because there was a big metal box mounted to the front panel that had three leads (two caps and a common ground im assuming) one lead is part 25 and one is 37 if i am thinking correctly.

i am thinking about adding part #32 back in, as it cant hurt and im guessing was eliminated as a cost saving measure.

just so we are all on the same page, my philco 80 is at this point correct with this schematic:
http://www.philcoradio.com/tech/images/80.jpg

please, if any of you see anything in this schematic that i should change, let me know!

i didnt get a chance to mess with the radio last night, but i will be working on it later tonight so im open to any suggestions or things to try.

i still havent measured the resistance from the center tap to chassis ground (should be about 330 ohms in my case) and im wondering if this was shorted, would that cause this hum?

thanks for all the help so far.
LC

[morzh]

LC

Stick to your production run, do not add anything or try to improve anything, get it working first.

Then if you want to exeriment, do what you will. At early stages of restoring all these "let me improve upon..." are distractions and only add to confusion.

[loosecannon]

the radio is working, it just has an AC hum in the audio.

when the 2nd detector tube is removed the hum is gone.

when the det-osc tube is removed, the hum is still there.

i tried switching the type 36 tubes and it made no difference.

when i touch the wire going to the control grid (top) of the 2nd detector tube, the hum gets quite a bit louder.

this leads me to believe that the problem is in the 2nd detector section.

if someone could either confirm or refute my suspicion, it would be very helpful.

logic tells me that the problem is in the rectifier/ power supply section, but i dont have the experience with these sets to be sure.

i really appreciate all the help so far.
without you guys i would be lost.
LC

[jerryhawthorne]

Your not lost Matt, just trying to follow all of our ideas. I'm glad someone recognized that cap as a 10mfd on the N/A schematic. I guess there is a little of my mind still working. You do have the radio working. That is important. I agree with Mortzh in that don't mess around with changes unless it is working. I would try a 10mfd cap with a clip in just to see what happens. Nothing is going to blow up, put the positive to ground and the negative to the other two. A low voltage any where from 50 to 160 should be fine. Sorry I was looking at the N/A schematic and perhaps not the proper version of that radio. Not knowing anything, it appears that cap is to filter some small negative voltage generated as the center tap from the transformer is "floating" a bit above chassis ground by the resistor to ground. What do I know? NADA!
Jerry