Rehabing 42-854 AM/SW Portable - Printable Version
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+--- Thread: Rehabing 42-854 AM/SW Portable (/showthread.php?tid=14647)
Rehabing 42-854 AM/SW Portable - Radioroslyn - 05-22-2016
So after rebuilding the 5 section filter cap I started in on the paper caps I could get to. Most were in the power supply and audio sections. After doing that I thought I'd give her a try and see what happens. So power up and nothing. 117Z6 was doing fine and making HV but no audio at all. Checked the filament voltage and had 0. On these portable set the filament voltage is derived from the HV though a resistor divider network. Well guess what #56 was open, that's half of the divider the other half is #48. Went into the deep dark basement and found a couple of resistor that could may up to open one ( it's a power resistor about 5w or so). Clipped those in and the filament sprang to life. So now I've got audio but haven't fed any signals into the IF of mixer to hear what else is working. Started moving some coils out of the way so I can get at the last few caps and check resistors. The second pic is of #56 it's open.
http://www.nostalgiaair.org/pagesbymodel/562/M0013562.pdf
Terry
RE: Rehabing 42-854 - morzh - 05-22-2016
Oh compared to my fence just falling on the ground, the whole thing being rotted out, its nothing
(ka-ching sounds in my mind).I love the filament string there.
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 05-23-2016
After manipulating the rf coils I was able to get the rest of the paper caps replaced. Gave it a try and now I have no output from the 1LH5. Plate voltage is high and filament is at about .5 volts. Methinks some pin cleaning is in order.
Terry
RE: Rehabing 42-854 AM/SW Portable - sam - 05-23-2016
terry
looking good so far
I`ll restore mine 41-844 when your done
been 2 weeks and I already lost bag of philco knobs and grill plate that I got off kirk
looked at na no schematic for it ?
sam
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 05-23-2016
Well you could try Chuck or use the 1942 diagram, it dated April '41. I can't imagine much of a difference. Obtw I found the missing pushbutton broken in the living room floor.
Terry
RE: Rehabing 42-854 AM/SW Portable - morzh - 05-23-2016
I am sure it was Mr. Cat who stepped on it and crushed it.
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 05-25-2016
So after tearing my hair out trying to figure this filament string out I found the problem. I only had .5v across the 1LH5 tube and the two IF amp tubes where low too. Now the confusing thing is that these three tubes are in the middle of the string. The three tubes (osc and mixer at one end/ 1LB4 at the other) all show about 1.5v as they should. Also to confuse things a little since the filament act as the cathode there is resistors and caps in the filament circuit which can seem like it's the problem but it's a red herring.
The actual problem ended up being a bad connection at the 117Z6 supplying the hv to the dropping resistor (56). As for #56 there is a service bulletin stating that the original part is prone to fail (dropping in resistance then going open) and damaging the tubes filament. Philco did recommenced a replacement with a larger wattage resistor. Found a 25w unit that should do nicely.
Sam if your resistor looks like the one in my second pic you may replace yours. The philco replacement is a long candohm that is mounted upright on the top of the chassis behind the second IF transformer.
http://www.ebay.com/itm/LOT-OF-1800-OHM-5-25W-DALE-RESISTORS
Onward to injecting some signals to hear what is working.
Terry
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 05-25-2016
Seem as though I misspoke. Filament where working ok then it went back to having .5v on the IF amp and the 1st audio tubes. And the voltage on the other 4 tubes is a little high from 1.75 to 2.0v. GRRRRRR I think I hate loctal toobs!!!
Have cleaned the pins and sockets, replaced 56 and 48 (voltage divider resistors) jumper out the filament choke in the mixer circuit, cleaned the ac/battery switch. Can't find my 0-30vdc p/s, thought I would put it in the dc mode and power the filament though the p/s and battery cables to see if the voltage even out across string. This thing is mighty annoying!!!!
1st pic is a simplified diagram of the filament wiring and what the voltages should be.
Pic 2 is what I've got. Should have 1.5v across each one.
Terry
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 05-26-2016
Think I'm going to set this one aside till the 1800 ohm 25w resistor shows up. Then I can grind out the old one and start fresh. The old candohm may be leaking some voltage back to the chassis screwing up things.
The Admiral is playing nicely and I can't wait to dig into the 41-300 but that portable GRRRRRRRRR!!!!!!
Terry
RE: Rehabing 42-854 AM/SW Portable - sam - 05-26-2016
Some mentor you are.
little radio kicks your butt
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 05-26-2016
Not done yet just a few more possibilities to check out. I suppose if worst comes to worst I could rewire the filament circuit. But I don't wantah!
Terry
RE: Rehabing 42-854 AM/SW Portable - morzh - 05-26-2016
Terry
25W 1800 Ohm? Are you sure? Why so many Ohms at so much wattage?
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 05-26-2016
It's dropping 120vdc down to 9v @50ma. Have a 10w and it runs pretty hot. Found a 25w unit on epay. Original is mounted to the chassis to help dissipate heat (candohm) #56
Terry
RE: Rehabing 42-854 AM/SW Portable - morzh - 05-26-2016
Could you use a cap? That would be a small one. Plus no heat. Unless you want true AC-DC or there's something else?
And your dissip is 5.5W, so 10W is adequate.
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 05-26-2016
Could you use a cap?
http://www.nostalgiaair.org/pagesbymodel/562/M0013562.pdf
Don't think so it's dc not ac as these are 1.5vdc directly heated tubes. Resistor is #56.
And your dissip is 5.5W, so 10W is adequate.
Might be adequate but would melt solder.
I can smell it after a minute or two.
Terry