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Heath-Zenith (Heathkit) Frequency Counter Model SM-2420
#11

Very often, you'll find that Heath equipment suffers from poor/missing solder connections.  Sometimes, all I have to do is go back and heat up the connections and add a little solder to cure "problems".  Remember too, that this thing is probably 50 years old or older, and even good solder joints will deteriorate over time due to poor, or substandard, solder.  Use a different radio to determine the generators operation, before you use it to troubleshoot another non working radio.  If you don't do that, your test gear can lead you down a rabbit hole.  You can be trying to "fix" an issue that doesn't exist and creating more issues in the process. 

On your Philco 116, before you condemn tubes, check your voltages in the set.  Have you re-capped the radio COMPLETELY??  Check the resistors values.  It's a pain on a set that large, but you save a lot of time troubleshooting.  If the set was working and suddenly stopped, it's unlikely that it's a tube.  Many times, even when tubes are weak, the set will play, but the performance will suffer.  But it still works.  If you need tubes, I can probably help with that.  I have LOTS of them.  It's far more common for things like the Candohm resistor to open on a section, which takes out the plate or screen voltages, and the set quits.  The Zenith 9S262 I currently have on the bench had four of the five sections in it open.  They are made from Ni-chrome wire, and they open up from over-current (leaking bypass caps) or corrosion.  Even some of the resistors that Philco used in their older radios are not immune to this.  It's also possible that a Candohm will SHORT out to ground.  I've seen that create lots of problems on higher tube count sets.  I make it a practice to NEVER re-use a Candohm resistor.  They get replaced with a new network from individual resistors on terminal strips.  Its also possible that one of the IF transformers has opened up on a winding, or one of the antenna coils has done the same.  Corrosion or a poor solder joint will be the cause.  Your ohmmeter is your friend here.  After 50 years of doing this stuff, I check all the resistors as I recap a radio, AND I check all the transformers for continuity as I go.  Saves time down the road.  The solder back in the '30's wasn't good.  That was 80 years ago.

Kim Herron W8ZV
w8zv at goldenradioservice.com
1-616-677-3706


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RE: Heath-Zenith (Heathkit) Frequency Counter Model SM-2420 - by W8ZV - 05-07-2020, 07:00 AM



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