#16
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If you swap the 50EH5s from right to left, do the symptoms change?
jr |
#17
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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. |
#18
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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 |
#19
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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. |
#20
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Very interesting console, but it doesn't look like there's much stereo separation, with the way those speakers are mounted so close together!
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Audiokarma |
#21
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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.
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Bryan |
#22
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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. |
#23
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Quote:
IIRC, it's simular to the Sanyo mentioned. |
#24
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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.
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Bryan |
#25
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Quote:
The oil port had two plastic tubes, that went to the motor bearings. |
Audiokarma |
#26
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Quote:
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. |
#27
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i love it and i am a fan of older built sanyo stuff. great score steve
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#28
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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 |
#29
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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 |
#30
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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 |
Audiokarma |
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