Learning the Ropes

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Learning the Ropes

Post by Zeek on Thu Jul 04, 2013 1:40 am

Greetings from Virginia. Just received my, "new" Zenith K725 today. Set up my FM transmitter, hooked it to my iPad and played some old time horror radio for the kids.

I'm looking to restore her to as new condition as possible and hope some folks can point me in the right direction.

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Re: Learning the Ropes

Post by Tony V on Thu Jul 04, 2013 2:05 am

Welcome to TRF! We have several members from VA including me.
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Re: Learning the Ropes

Post by Zeek on Thu Jul 04, 2013 2:42 am

Thanks Tony...I know where Waynesboro is; I used to head through that area at least once a year on my annual motorcycle trip down to Pigeon Forge. I live up in congestion...er northern VA area.

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Re: Learning the Ropes

Post by 75X11 on Thu Jul 04, 2013 11:36 am

Be careful to avoid using it too much before replacing the electrolytic and paper capacitors. You will see that warning a lot on the site. They can fail and short abruptly and without warning and cause damage to the radio. That is a good radio but may be a little complex for a first restoration. You may want to try a simpler unit to get the "feel" of the process.
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Re: Learning the Ropes

Post by Guest on Thu Jul 04, 2013 11:50 am

Welcome to TRF Zeek. Where in Virginia are you located?

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Re: Learning the Ropes

Post by Bill Cahill on Thu Jul 04, 2013 2:27 pm

Welcome to TRF Zeek.
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Re: Learning the Ropes

Post by Wildcat445 on Thu Jul 04, 2013 7:16 pm

Welcome, Zeek. Your K725 may be new enough that it has ceramic caps instead of paper. They are usually pretty reliable. You should test the selenium rectifier for output. Those babies get weak and cause all kinds of strange problems. I have several Zenith radios of that vintage still running the original selenium, but that is a fairly rare occurance, and I realize I am running on borrowed time. My general rule of thumb is to not mess with something that is not broke. Also check the 12DT8 if there is one, or whatever RF amp is used for AM and FM. It is usually found near the tuner and has a shield around it. I have NEVER gotten a Zenith radio with one of those tubes in it that the tube was good. One half of it is weak and that kills one band or the other. Zenith AM-FM radios also suffer from notoriously dirty band switches.

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Re: Learning the Ropes

Post by Zeek on Fri Jul 05, 2013 3:26 pm

75X11, thanks for the advice. I figured I was safe after I read the forum post on what radios not to start with (dipped circuit boards etc.). I'd like to start with something easier however, I really do like this radio for some reason. I think I'll move forward and hope I don't screw anything up. I found the wiring diagram schematics online, so hopefully I'll be in better shape.

I'm a complete novice when it comes to these radios, I did serve in the military in satellite communication and do have experience tuning oscillators and such, but most of what we did was hook up a signal generator here, measure the signal there and pluck and chuck the component that didn't seem to be working. The only tube pieces we worked with were the actual transmitters and they just had one giant tube. In addition to this, I haven't worked on electronics in over 20 years, so I'll have to refresh my memory quite a bit.

Mezlaw, I'm in northern VA near Quantico. I'm originally from Colorado, but the military took my dreamsheet on places I wanted to visit and places I never wanted to visit and reversed them. I put Washington D.C. on the list of where I never wanted to go along with the middle east and Korea...needless to say, I was in the middle east, then Korea and left the military at Ft. Belvoir. Still not quite sure who I pissed off lol.

Thanks Bill, appreciate it. Read up on a few boards before joining this one...seems the folks here are pretty helpful without a lot of the drama associated with a lot of the boards.

Wildcat, really appreciate the information. I ran it for a couple of hours just enjoying listening to it, but shut it down because I didn't know potentially any damage I may be doing to it. Your explanation on the tuner, seen a number of ebay listings that fit your explanation. I'm like you, if it's not broken, I generally won't fix it, but being a novice in this area I really am unsure as to what to expect.

Thanks again all!

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Re: Learning the Ropes

Post by 75X11 on Fri Jul 05, 2013 5:53 pm

Take it a step at at a time and use care and you will find things coming back to you. My last MOS was 26V20 And I maintained microwave equipment that could've been used in a museum.
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Re: Learning the Ropes

Post by Art Hoch on Mon Jul 08, 2013 12:15 pm

Welcome and good luck with the Z, probably my favorite brand of tube radios.
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Re: Learning the Ropes

Post by Bill Cahill on Mon Jul 08, 2013 1:45 pm

Zeek, How's the radio doinbg?? Fairly straightforward set, now that I've seen it.

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Re: Learning the Ropes

Post by Zeek on Sat Jul 13, 2013 1:47 pm

Thanks for the follow up all; it's not going too badly. I've only pulled the chassis out of the case and studied the schematics against the physical chassis...then the work week called, so I'm back on it this weekend.

It's extremely clean inside and I contacted the previous owner to see if he'd done any work on it. The owner said that he hadn't however, the radio was rarely used.

Right now, I'm still exploring it and I also purchased a Zenith 510Z-1, black with red dials (AM only), that I've also pulled apart.

The one thing that I've seen is that a crack across the top of the older radios seems pretty common; is this due to the heat causing the cases to expand and contract constantly?

75X11, thanks for the advice, that's exactly what I'm doing. I got over my initial reaction to play with the radios and not rushing anything.

Appreciate the welcome Art!

Thanks for following up Bill, I'm really enjoying these radios, I know a lot of guitarist still use tube amplifiers for their electric guitars due to the sound and I've found I like the sound of tube radios over solid state as well...sometimes electronic progress isn't all it's cracked up to be.

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Re: Learning the Ropes

Post by 75X11 on Sat Jul 13, 2013 2:36 pm

Many times a stress fracture across the top toward the middle is caused by something heavy laid on the top, or someone pressing down heavily on it. Heat damage on other plastics than bakelite is usually accompanied by distortion of the plastic. Heat on bakelite will slowly cause the surface to pit microscopically and produce a flat appearance. Bakelite is a hard material and will fracture with a sharp blow. Styrene plastics can be affected by the elastomers in rubber cords, etc. and they can leave discolored impressions in the case.
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Re: Learning the Ropes

Post by Zeek on Sat Jul 13, 2013 2:40 pm

Thanks much 75X11!

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