Rehabing 42-854 AM/SW Portable - Printable Version
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RE: Rehabing 42-854 AM/SW Portable - morzh - 06-01-2016
Now it's just being stubborn.
Terry, tell her you will be feeding her 125V with lots of harmonics to the rest of her life so she barfs every day if she keeps doing that to you.
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 06-02-2016
UPDATE!!!!!!!!!!!!!!!!!
I found the problem with a IF stages it was two fold. I took a dum***s pill before recapping and connected the 1/2 mic cap from the plate of the IF amp to B-. This pretty much shorted all of the IF signal to ground. To confuse thing a bit it looked like there was a jumper ( I think this was a nub from when I removed the old cap) from the plate pin to the next pin which is a NC inside the tube (used as a terminal post) The jumper was a red herring it was where the .5 cap should have been connected. So got that sorted out.
Now the other part of the problem I could get a signal from the grid of the 2nd IF amp but nothing from the 1st IF or Mixer plate. It was suffering from the same problem as my old HRO, the IF transformers where way out of alignment. Set the generator at 455KC and peaked up the three IF cans. The IF on this set is pretty hot when it's all aligned up.
I had some fears that the LO wasn't working as I couldn't hear it in my little transistor set. But once the IF was working I twisted the tuning knob and hear a number of BC stations, this is without a loop connected or ant.
I did use a isolation transformer when servicing to get rid of the AC modulation.
Still need to double check the SW band to see if it is working properly and lube the tuning. It's well on it's way to recovery.
So Mike that 25W resistor still gets pretty hot. Probably about as hot as the 117Z6. 5.5wts would burst into flames!!!
Terry
RE: Rehabing 42-854 AM/SW Portable - sam - 06-02-2016
terry
sure blame the pill
more like a senior moment
by the way don`t do drugs then work on radios silly. you could become a KIRK
RE: Rehabing 42-854 AM/SW Portable - morzh - 06-02-2016
(06-02-2016, 11:19 AM)Radioroslyn Wrote: So Mike that 25W resistor still gets pretty hot. Probably about as hot as the 117Z6. 5.5wts would burst into flames!!!
Terry
I am sure it does. The dissipation rating does not mean if it is rated for what it is dissipating it won't become hot.
Myself I am usually comfortable with factor of 3 if it is constant and factor of 2 if it is intermittent and lasts under a minute or so. Obviously if you have money and space, the bigger the better.
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 06-02-2016
(06-02-2016, 01:19 PM)morzh Wrote:So I presume it gets hotter with DC than AC.(06-02-2016, 11:19 AM)Radioroslyn Wrote: So Mike that 25W resistor still gets pretty hot. Probably about as hot as the 117Z6. 5.5wts would burst into flames!!!
Terry
I am sure it does. The dissipation rating does not mean if it is rated for what it is dissipating it won't become hot.
Myself I am usually comfortable with factor of 3 if it is constant and factor of 2 if it is intermittent and lasts under a minute or so. Obviously if you have money and space, the bigger the better.
Terry
RE: Rehabing 42-854 AM/SW Portable - morzh - 06-02-2016
A DC voltage and the AC onevwith the RMS equal to the DC voltage produce the same amount of heat. In fact this is one of the definitions of the RMS.
Say 120V from the outlet will heat a resistor exactly the same way as 120V DC.
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 06-02-2016
Kewl! I had studied that stuff back in the 80's when I got my ham ticket but couldn't quite remember how it works. So if I wanted to add a zener diode to regulate the 9v 50ma filament string what do I need to do so?? It's running about 10v and if it needs to be a little higher I can get rid of the 117Z6 and replace it with a 1N4007. That will give me instant on and boosts the 9v line up to abt 12v.
I don't know this silicon stuff!!!! except for FET's there like tubes.
Terry
RE: Rehabing 42-854 AM/SW Portable - morzh - 06-02-2016
Zener is a bad way to do that.
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 06-02-2016
I need a jumbo size bottle of good whiskey!!!!!!!!!!!! This thing driving me nutzzzzzz.
Was working fine late night on the BC band and I don't think sw was working at all.
So this morning I snap it on and it's dead!! GRRRRRR! Audio works but I seems like
the IF is dead again. Did some poking around with the generator and wouldn't pass
any 455 signal. My generator has a flaky attenuator which may have been the problem.
Then the IF seem to be working but wouldn't tune in any stations. Hook the generator
to the ant and fed in a signal 455kc above a local station, pick it up fine. GRRRRR!
No LO. Clean the tuning cap, checked the ground connection at the cap. It work
for a few minutes and died. Recleaned the 1LE3 osc socket again. No joy. Started
poking at the tube socket terminals and poking the control grid pin of the oscillator tube
seemed to get it oscillating again. So now all is well with the BC band but how about
the SW? At first it was dead. Then I took a closer listen and it was working but
would die after a minute or so. That turned out to be a bad oscillator tube works
fine on the BC band but not up in the SWs. Tested abt 85% on the tester. So far
it's been working for a hour on SW. Got my fingers crossed and a shot glass!!
Still have to hook up the loop ant and do the RF alignment.
Terry
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 06-02-2016
(06-02-2016, 09:20 PM)morzh Wrote: Zener is a bad way to do that.I know but it's simple and doesn't 5 other xsistors.
RE: Rehabing 42-854 AM/SW Portable - klondike98 - 06-02-2016
Gremlins.....
RE: Rehabing 42-854 AM/SW Portable - morzh - 06-02-2016
(06-02-2016, 09:49 PM)Radioroslyn Wrote:(06-02-2016, 09:20 PM)morzh Wrote: Zener is a bad way to do that.I know but it's simple and doesn't 5 other xsistors.
No it ain't simple and worse than just putting resistors in series.
Zener is justified only where a stable voltage needed with unstable source.
Otherwise you dissipate the same power plus the zener dissipation.
It is the worst way. Like using heavy electric motor as a hammer to drive in nails. Will work but do you think it is a goid use of a motor and is it convenient?
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 06-04-2016
I took it out of the cabinet again the do the RF alignment on it as you can't get to the two trimmers on top of the tuning condenser when it's in the cabinet. And removed the loop too. Got it all set up to do the alignment, All went ok put it back in the cabinet and it DIED. GRRRRRRRRRRRRR.
I think I'm going to replace the oscillator grid leak cap and resistor. That would be #7 and 8 if you are following along. They are connected to the pin that I've been fooling around with to get it running when it dies.
I think I'm going to be an expert on this thing when I get it done! Too bad they didn't make more of them. HA HA.
Overall when it's working it plays well. Pretty loud for a portable and with it's 6" spkr sounds good. I am getting a fair amount noise from the AC line so I'd like to give it a try with batteries. This should be much quieter.
Terry
Sam, How's your set work?????
Joe, I think I'll work on your PT** It will be a cake walk by comparison!!!! Rubber wire and all!
RE: Rehabing 42-854 AM/SW Portable - morzh - 06-04-2016
Terry
When you saying about the noise, are you having it plugged through the isolation transformer?
RE: Rehabing 42-854 AM/SW Portable - Radioroslyn - 06-04-2016
Both, It may be a little less though the transformer. I have to same issue with my modern (1987 Kenwood transceiver) It uses a 35amp 12v transformer power supply. If I leave the set on and turn the p/s off as the filter bleed down there is very little noise. Goes from a S7 or so down about S1. With a S7 noise It's difficult to hear any weak signals. When I unplug my laptop switching charger noise drops to about S5.
Terry