Videokarma.org

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

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #16  
Old 11-05-2012, 08:36 PM
jr_tech's Avatar
jr_tech jr_tech is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 4,510
If you swap the 50EH5s from right to left, do the symptoms change?

jr
Reply With Quote
  #17  
Old 11-05-2012, 10:54 PM
maxhifi's Avatar
maxhifi maxhifi is offline
VideoKarma Member
 
Join Date: Dec 2010
Posts: 1,841
Last night pulled the chassis. Hooked it up through an isolation transformer, connected a pair of Quam replacement speakers and tried some things. New 50EH5s do nothing to remove hum.

Confirmed with scope that hum signal is present at grids of 50EH5s (volume turned all the way down), and shorting each respective grid to ground completely removes all traces of hum from speaker terminals.

Grounded shield on 12AX7 actually increases hum slightly somehow, and disconnecting tone and balance controls, in order to try and remove wiring which picks up hum is also to no effect. Removing 12AX7 entirely (heater is not in series with 50EH5s) cuts hum level to about half, but doesn't totally remove it. If there is a ground loop here, it's not entirely obvious what's going on.

What did work, is hooking up the entire amplifier, heaters and all, to 120V DC. It's extremely tempting to put a little DC power supply inside the cabinet and call it good!

I think the main problem is that the 12AX7 is grid leak biased, with 5M resistors, and is located about an inch from 120V AC power wiring. There's nearly no shielding in the audio section, and the heater wires aren't twisted. The 50EH5 is also a high transconductance tube, and has a huge 1.5M grid resistor.
Reply With Quote
  #18  
Old 11-06-2012, 06:32 PM
jr_tech's Avatar
jr_tech jr_tech is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 4,510
Does the balance control work properly? If the wiper arm was open to ground, hum could be induced, and grounding either 50EH5 grid would likely stop the hum in both channels... just another WAG!

jr

Oops! Never mind, I see that you tried it with the balance control disconnected.

Last edited by jr_tech; 11-06-2012 at 06:40 PM. Reason: added Oops comment
Reply With Quote
  #19  
Old 11-06-2012, 10:15 PM
maxhifi's Avatar
maxhifi maxhifi is offline
VideoKarma Member
 
Join Date: Dec 2010
Posts: 1,841
I substituted a 1M resistor to ground for the balance control, so the 50EH5 wouldn't be floating when I disconnected it. Thanks for your input though, this has got to be something I haven't considered! The stereo sounds good, the hum is inaudible if the furnace is running, i was listening to it for hours last night - recapped the multiplex board and enjoyed some FM stereo.

Last edited by maxhifi; 11-06-2012 at 10:45 PM.
Reply With Quote
  #20  
Old 11-10-2012, 09:09 PM
Beachboy Beachboy is offline
VideoKarma Member
 
Join Date: May 2011
Location: Northeast Kansas
Posts: 115
Very interesting console, but it doesn't look like there's much stereo separation, with the way those speakers are mounted so close together!
Reply With Quote
Audiokarma
  #21  
Old 11-10-2012, 09:47 PM
bgadow's Avatar
bgadow bgadow is offline
VideoKarma Member
 
Join Date: Oct 2003
Location: Federalsburg, MD
Posts: 5,814
Someone on freecycle gave me a Delmonico/Nivico of a similiar style. It looks like they were really trying to engineer something to ship as easy as possible. Take the legs off and the unit isn't too big. I don't plan on ever doing anything with mine, besides trying to find somebody to give it to.
__________________
Bryan
Reply With Quote
  #22  
Old 11-11-2012, 01:20 AM
maxhifi's Avatar
maxhifi maxhifi is offline
VideoKarma Member
 
Join Date: Dec 2010
Posts: 1,841
I guess I like it because it's unusual - I'd have been equally interested in your old JVC

Here in Canada most old consoles are Electrohome, RCA, Fleetwood, maybe a Clairtone, Silvertone etc. There's the occasional Zenith, but this one is something I'd never seen before, so naturally I had to buy it and see what's inside.

I think it's cool how every single component has JAPAN stamped on it, and how they bothered to paint the inside of the cabinet white, but yet didn't budget for a dial lamp. It's neat how they used 50EH5s, and how the stamped metal pieces are different than on a north american made item. I also think it's interesting how they had to outsource a British record player, in a Japanese product! - does Britain make anything at all now? I think it's more interesting as a time capsule of a 60s Japanese expoirt, than as a record player - after all I have a Thorens for that job. That said once the needle shows up I'll still want to use it!

In a way it reminds me of that Bel-Aire TV/Radio/Clock that someone posted about earlier this year, that would be another cool item to tear into and repair.

It's just an oversized table radio with a built in record player on skinny legs. And something causing it to hum a bit too much, but I haven't dealt with that yet. One man's trash, another's treasure, I suppose.

Last edited by maxhifi; 11-11-2012 at 01:30 AM.
Reply With Quote
  #23  
Old 11-11-2012, 10:11 AM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 7,562
Quote:
Originally Posted by bgadow View Post
Someone on freecycle gave me a Delmonico/Nivico of a similiar style. It looks like they were really trying to engineer something to ship as easy as possible. Take the legs off and the unit isn't too big. I don't plan on ever doing anything with mine, besides trying to find somebody to give it to.
Is that the one with the Japanese changer, that has the oiling tubes?
IIRC, it's simular to the Sanyo mentioned.
Reply With Quote
  #24  
Old 11-11-2012, 09:27 PM
bgadow's Avatar
bgadow bgadow is offline
VideoKarma Member
 
Join Date: Oct 2003
Location: Federalsburg, MD
Posts: 5,814
I've never looked at mine that close, but that sounds interesting-guess I'll have to take a look as soon as I get the chance.
__________________
Bryan
Reply With Quote
  #25  
Old 11-12-2012, 01:33 PM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 7,562
Quote:
Originally Posted by bgadow View Post
I've never looked at mine that close, but that sounds interesting-guess I'll have to take a look as soon as I get the chance.
I thought it was novel, when I first saw one.
The oil port had two plastic tubes, that went to the motor bearings.
Reply With Quote
Audiokarma
  #26  
Old 11-12-2012, 03:27 PM
zenithfan1's Avatar
zenithfan1 zenithfan1 is offline
Mark
 
Join Date: Jan 2008
Location: Kenosha, Wisconsin
Posts: 4,211
Quote:
Originally Posted by bgadow View Post
Someone on freecycle gave me a Delmonico/Nivico of a similiar style. It looks like they were really trying to engineer something to ship as easy as possible. Take the legs off and the unit isn't too big. I don't plan on ever doing anything with mine, besides trying to find somebody to give it to.
The reason for Japanese stuff like this being so small is the space in most of their apartments is at a premium. They don't like big bulky consoles unless they're well off and have space for them. Shipping is another reason like you stated too. That is why they also designed their own color sets, ours were too big. They only made a very few roundies, Sharp made one in the early '60s and borrowed some of RCA's designs to do it (it had a 21FBP22 and a somewhat cloned CTC 10 chassis). Then they made their own stuff for the most part.
I wonder what the little JVC you have would cost to ship? I'd love to take it off your hands.
__________________
My TV page and YouTube channel
Kyocera R-661, Yamaha RX-V2200
National Panasonic SA-5800
Sansui 1000a, 1000, SAX-200, 5050, 9090DB, 881, SR-636, SC-3000, AT-20
Pioneer SX-939, ER-420, SM-B201
Motorola SK77W-2Z tube console
McIntosh MC2205, C26

Last edited by zenithfan1; 11-12-2012 at 03:31 PM.
Reply With Quote
  #27  
Old 11-21-2012, 09:35 PM
rcaman's Avatar
rcaman rcaman is offline
VideoKarma Member
 
Join Date: Nov 2002
Location: mississippi
Posts: 745
i love it and i am a fan of older built sanyo stuff. great score steve
Reply With Quote
  #28  
Old 11-22-2012, 01:32 PM
maxhifi's Avatar
maxhifi maxhifi is offline
VideoKarma Member
 
Join Date: Dec 2010
Posts: 1,841
thanks!
It's currently waiting for the needle to arrive from VM so I can try out the record player. I've also built a little DC power supply to get rid of all hum
Reply With Quote
  #29  
Old 11-22-2012, 02:24 PM
maxhifi's Avatar
maxhifi maxhifi is offline
VideoKarma Member
 
Join Date: Dec 2010
Posts: 1,841
thanks!
It's currently waiting for the needle to arrive from VM so I can try out the record player. I've also built a little DC power supply to get rid of all hum
Reply With Quote
  #30  
Old 11-22-2012, 03:57 PM
maxhifi's Avatar
maxhifi maxhifi is offline
VideoKarma Member
 
Join Date: Dec 2010
Posts: 1,841
thanks!
It's currently waiting for the needle to arrive from VM so I can try out the record player. I've also built a little DC power supply to get rid of all hum
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 08:03 PM.



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