Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Antique Radio

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #16  
Old 03-29-2006, 10:04 AM
Blooze's Avatar
Blooze Blooze is offline
AK Member
 
Join Date: Aug 2005
Location: Amarillo, TX
Posts: 7
Jeffhs - which schematic is the one for the K731 on techschematic.org? Is it the 7M07, as I couldn't find one specifically for the K731?

And thanks so much for the info!

I glanced at the tubes in mine yesterday real quick and noticed that the 35C5 has been replaced with a 50C5. Gonna have to change that. I didn't pull the ones with the shielded sockets yet.


Shane

Last edited by Blooze; 03-29-2006 at 02:02 PM.
Reply With Quote
  #17  
Old 03-29-2006, 01:38 PM
Tom Bavis's Avatar
Tom Bavis Tom Bavis is offline
Audiophool
 
Join Date: Jun 2002
Location: Macedon NY
Posts: 371
It should play fine with the 50C5, and the tubes will last longer. I'd leave it.
Reply With Quote
  #18  
Old 03-29-2006, 01:39 PM
Jeffhs's Avatar
Jeffhs Jeffhs is offline
<----Zenith C845
 
Join Date: Feb 2003
Location: Fairport Harbor, Ohio (near Lake Erie)
Posts: 4,035
Quote:
Originally Posted by Blooze
Jeffhs - which schematic is the one for the K731 on techschematic.org? Is it the KM07, as I couldn't find one specifically for the K731?

And thanks so much for the info!

I glanced at the tubes in mine yesterday real quick and noticed that the 35C5 has been replaced with a 50C5. Gonna have to change that. I didn't pull the ones with the shielded sockets yet.


Shane
Shane,

You are more than welcome.

I had the same problem when I was trying to find a schematic for my K731. Try looking under K725, which is practically identical to the K731 as far as the chassis goes; the only difference I can see on my schematic for this set is the chassis number (7K06 for the K725, 7K07 for chassis K731, L, M, R, W, Y) and a different style of cabinet used with the K725 (plastic as opposed to the '731's walnut cabinet). My 731 has chassis 7M07. It could be the later versions of the K731 (the ones that came out in the '60s) used chassis 7K06 and 7K07.

As to that 50C5 in your set rather than a 35C5 I don't know what to tell you, except by all means replace the 50C5 with its 35-volt equivalent. I did some figuring as to total voltage drop across the filament string with a 35C5 and a 50C5 in the output stage; there is a difference of over ten volts between the two (114 with a 35C5, 129 with a 50C5). Look at the tube layout diagram on the bottom of your '731. Is there a 35C5 or a 50C5 shown? If it is a 35C5, and you have a 50C5 in the output tube socket, the set's former owner may have switched tubes, either inadvertently or not knowing any better.

It is always best to use the exact tubes specified in the tube layout chart, especially with a series-string filament circuit; using a 35-volt tube in place of a 50-volt one, or vice-versa, could (likely will) overload other tubes in the string, leading to their premature failure. Series-filament tubes with heater-cathode shorts can also upset voltage drops along the string, causing one or more tubes to fail as well. The total voltage drop across a series filament string must very closely approximate the line voltage. If there is a difference, it is compensated for by a filament dropping resistor.
__________________
Jeff, WB8NHV

Collecting, restoring and enjoying vintage Zenith radios since 2002

Zenith. Gone, but not forgotten.

Last edited by Jeffhs; 03-29-2006 at 01:43 PM.
Reply With Quote
  #19  
Old 03-29-2006, 02:16 PM
Jeffhs's Avatar
Jeffhs Jeffhs is offline
<----Zenith C845
 
Join Date: Feb 2003
Location: Fairport Harbor, Ohio (near Lake Erie)
Posts: 4,035
Fisherdude, OldWolf,

Thanks much for the kind words. That's what we AKers are here for, to help each other out when we run into a sticky problem or need information on a piece of equipment (radio, TV, etc.) we are trying to restore and/or repair. I personally have been interested in electronics and radio since I was eight years old (I will be 50 in July), and an amateur radio operator since the age of 15; I must enjoy this stuff immensely if I've stayed with it this long. I'm always glad to help out wherever I can, although most of my experience has been with tube-powered radios, TVs and ham gear; I'll leave the solid-state stuff to the other folks here who know it better than I.

Fisherdude, I also concur with your last sentence in your post. I love being a member of AK as well. Been here three years and have no intention of leaving any time soon. You guys are the greatest! Without AK, who knows what might have happened to all the antique/vintage radios and TVs we have brought to life, very often (more often than not) after they have been given up for dead on curbs, treelawns, etc.? Don't forget, we are also preserving radio and TV history by restoring these venerable old soldiers. Sets made by the original Magnavox, GE, RCA, Zenith, etc. are treasures, as the old ones (ca. 1920s-'60s for radios and '40s-'70s for electronic television) are becoming scarce. Every set we can restore to past glory is one more we have saved from the landfill.
__________________
Jeff, WB8NHV

Collecting, restoring and enjoying vintage Zenith radios since 2002

Zenith. Gone, but not forgotten.

Last edited by Jeffhs; 03-29-2006 at 02:21 PM.
Reply With Quote
  #20  
Old 03-29-2006, 05:30 PM
Chad Hauris's Avatar
Chad Hauris Chad Hauris is offline
VideoKarma Member
 
Join Date: May 2003
Location: West Texas
Posts: 2,085
50C5 in place of 35C5 is fine. I have tried this substituion when I didn't have a 35C5 with no trouble. It is only the other way around that there would be an overload to the tubes.
__________________
Chad Hauris
http://www.youtube.com/user/retrochad
Reply With Quote
Audiokarma
  #21  
Old 03-30-2006, 08:22 AM
Blooze's Avatar
Blooze Blooze is offline
AK Member
 
Join Date: Aug 2005
Location: Amarillo, TX
Posts: 7
Quote:
Originally Posted by Chad Hauris
50C5 in place of 35C5 is fine. I have tried this substituion when I didn't have a 35C5 with no trouble. It is only the other way around that there would be an overload to the tubes.

This is what I was thinking. Just running the tube at 70% or so on the filament, correct?
Reply With Quote
  #22  
Old 03-30-2006, 09:43 AM
Nolan Woodbury's Avatar
Nolan Woodbury Nolan Woodbury is offline
Shaken, not stirred
 
Join Date: Apr 2005
Location: Central Arizona
Posts: 194
Blooze,

When I first looked at the chassis photo of your K731 and saw the enormous amount of splooge around the electrostatic tweeter, I laughed out loud and thought; "What idiot squeezed all that in there?" then it dawned on me. I've been having a devil of a time getting harmonic buzz out of my C730, so last night I pulled the tweeter out (it's held in with two fragile little clips that attach to the corners) and fashioned a neat little silicon 'bed' then re-attached the tweeter. Magic! The buzz is gone, and my favorite radio can once again be cranked and enjoyed as intended.

See, it pays to look at the pictures!

Last edited by Nolan Woodbury; 03-30-2006 at 09:47 AM.
Reply With Quote
  #23  
Old 03-30-2006, 01:00 PM
Jeffhs's Avatar
Jeffhs Jeffhs is offline
<----Zenith C845
 
Join Date: Feb 2003
Location: Fairport Harbor, Ohio (near Lake Erie)
Posts: 4,035
Quote:
Originally Posted by Chad Hauris
50C5 in place of 35C5 is fine. I have tried this substituion when I didn't have a 35C5 with no trouble. It is only the other way around that there would be an overload to the tubes.
Chad -

Thanks for that little bit of info, though it was in response to another post. I couldn't remember which substitution could overload the string; now I know. I'll file this with the rest of my Zenith radio info, of which I have quite a bit.
__________________
Jeff, WB8NHV

Collecting, restoring and enjoying vintage Zenith radios since 2002

Zenith. Gone, but not forgotten.
Reply With Quote
  #24  
Old 03-30-2006, 01:23 PM
Jeffhs's Avatar
Jeffhs Jeffhs is offline
<----Zenith C845
 
Join Date: Feb 2003
Location: Fairport Harbor, Ohio (near Lake Erie)
Posts: 4,035
Quote:
Originally Posted by Nolan Woodbury
Blooze,

When I first looked at the chassis photo of your K731 and saw the enormous amount of splooge around the electrostatic tweeter, I laughed out loud and thought; "What idiot squeezed all that in there?" then it dawned on me. I've been having a devil of a time getting harmonic buzz out of my C730, so last night I pulled the tweeter out (it's held in with two fragile little clips that attach to the corners) and fashioned a neat little silicon 'bed' then re-attached the tweeter. Magic! The buzz is gone, and my favorite radio can once again be cranked and enjoyed as intended.

See, it pays to look at the pictures!
Hi Nolan:

I saw that picture of the "innards" of Shane's K-731 and also noticed all that gunk around the electrostat. I wondered myself what it was. I couldn't imagine Zenith would have used such a cheap method of securing the tweeter to the cabinet in a radio like this (or any of their other vintage receivers, for that matter); the original Zenith Radio Corp. had too much class for that, IMHO. Then I read the rest of your answer and saw your comments about the four clips that hold the tweeter in place in the cabinet; that made a lot more sense.

I haven't had the back off my own K-731 in months, so don't know whether the tweeter has the same stuff around it that Shane's has. It probably does, though.

Now you have me wondering. What on earth was the purpose of all that junk around the electrostat tweeter? If it was not to mount the thing in the cabinet, then I'm baffled.

BTW, I will send you a PM addressing another matter after I write this.
__________________
Jeff, WB8NHV

Collecting, restoring and enjoying vintage Zenith radios since 2002

Zenith. Gone, but not forgotten.
Reply With Quote
  #25  
Old 03-30-2006, 02:38 PM
Nolan Woodbury's Avatar
Nolan Woodbury Nolan Woodbury is offline
Shaken, not stirred
 
Join Date: Apr 2005
Location: Central Arizona
Posts: 194
Quote:
Jeff asked: "Now you have me wondering. What on earth was the purpose of all that junk around the electrostat tweeter? If it was not to mount the thing in the cabinet, then I'm baffled."
I seriously doubt it Jeff, unless a previous owner encountered the problem of broken mounting clips. In my case the silicon was used to dampen the unit from speaker vibration. The material used to make the tweeter is very thin, almost a clamshell design. I squeezed just a bit in the joint and (neatly, I might add) ran a bead behind where it mounts. The main speaker mounts right next to it, on small board of (either) blackish pressboard or very thin plywood. The grill cloth attaches to the other side.

I'm sure yours is tidy, but my C730 has seen some wars before coming into my life. Still, I've been working on it for about 8-months now and not only does it have SOLID gain and excellent reception, it has developed a nice glow from all the attention and polishing. A VERY sweet radio and a Zenith classic!
Attached Images
File Type: jpg office 2.jpg (70.9 KB, 20 views)
Reply With Quote
Audiokarma
  #26  
Old 03-30-2006, 02:56 PM
Sandy G's Avatar
Sandy G Sandy G is offline
Spiteful Old Cuss
 
Join Date: May 2003
Location: Rogersville, Tennessee
Posts: 9,571
Nolan, I've got the blonde version of yr set...Really needs to go see Terry & get "tuned up". It was my granmother's & she kept it on a station in Black Mountain, NC, that played classical all the time. She had an antenna for it-I hooked it up to a portable TV/AM/FM once, & I swear, I was picking up stations from Atlanta...The entire FM band was just one big station.
__________________
Benevolent Despot
Reply With Quote
  #27  
Old 03-30-2006, 03:22 PM
OldWolf
Guest
 
Posts: n/a
Aren't these models called "Long Range" receivers or some similar? I thought I read that somewhere.
Reply With Quote
  #28  
Old 03-30-2006, 04:24 PM
Sandy G's Avatar
Sandy G Sandy G is offline
Spiteful Old Cuss
 
Join Date: May 2003
Location: Rogersville, Tennessee
Posts: 9,571
The earlier-late '40s ones were, I think...
__________________
Benevolent Despot
Reply With Quote
  #29  
Old 03-30-2006, 04:24 PM
Jeffhs's Avatar
Jeffhs Jeffhs is offline
<----Zenith C845
 
Join Date: Feb 2003
Location: Fairport Harbor, Ohio (near Lake Erie)
Posts: 4,035
Quote:
Originally Posted by OldWolf
Aren't these models called "Long Range" receivers or some similar? I thought I read that somewhere.
Yes. The phrase Zenith used was "Long Distance." Most older Zenith radios had this printed on the back covers, underneath the "Zenith." The company dropped the designation, however (I think), when they started making radios in Taiwan. Neither my Zenith R-70 portable nor my H480 Zenith clock radio, both made in 1980, have this anywhere on their cabinets (for that matter, neither does my 1958 TransOceanic transistor portable), but the other sets in my collection do show it prominently on the back. These radios lived up to the claims made in the slogan, though--all my Zeniths will pick up all sorts of distant stations on AM at night. My C845 is a real distance champion, though, as it will receive stations like crazy at night when the band opens up, not to mention getting Cleveland stations during the day my other radios do not hear at all, or so poorly as to be unlistenable. It does a fantastic job with weak FM signals as well. I can often hear stations 50 to 100 miles from here with signals good enough to listen to; this using only the radio's internal FM antenna--think of the stations you'd hear with a good outdoor FM antenna or even just a cheap set of TV rabbit ears! These sets must have sold like hotcakes in rural areas, miles away from the nearest station. With their high-performance signal circuits, not to mention high-fidelity sound, I wouldn't be surprised if they did. I sometimes plug in my C845 and just listen around the AM radio dial at night. There's a whole world of AM stations out there, and Zenith radios do one whale of a job picking them up at night. All you hear on AM during the day as a rule are your hometown stations and a few semi-locals, but at night the rest of the country is heard from...and your Zenith can hear it all or at least much of it, depending where in the US you live; here in northeastern Ohio, I can hear AM stations up and down the East Coast and Eastern Seaboard, west to Indiana and a bit beyond, as well as much of southwestern Ontario, Canada. My favorite Canadian station is CHWO AM 740 in Toronto, big bands and standards, as well as two stations about 90 miles from here with the same format, not to mention a 5-kW oldies station 35 miles east of here (and most of the local stations from Cleveland, of course). My C845 gets them all, and well. Zenith did not refer to its 1920s-'70s radios as "Long Distance" for nothing.
__________________
Jeff, WB8NHV

Collecting, restoring and enjoying vintage Zenith radios since 2002

Zenith. Gone, but not forgotten.
Reply With Quote
  #30  
Old 03-30-2006, 08:34 PM
wa2ise's Avatar
wa2ise wa2ise is offline
VideoKarma Member
 
Join Date: Dec 2002
Location: USA
Posts: 3,147
Lightbulb

As powerline voltage is usually on the high side, close to 125V, the 50C5 in placce of the 35C5 would work fine.
Reply With Quote
Audiokarma
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 06:04 AM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.