chuck
New Member
Posts: 8
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Post by chuck on Mar 20, 2019 20:21:14 GMT
I am working on this jukebox. The amp is model MRA3-L6. I have replaced all the capacitors and electrolytic. Checked the tubes on my Hickok 800. They are all good. I have a modern turn table hooked to it. I jumpered the play control relay to get power to the 5u4. It plays but the volume is very low. All I have are the schematics from the internet. Not much information on them. Any ideas. Does the mute plug have anything to do with it not having volume?
If you need more information let me know.
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Post by Ron Rich on Mar 20, 2019 20:39:33 GMT
Chuck,
Please read the FAQ's as to where to purchase the Service Manual Package, for your phonograph.
What type cartridge is in your "turntable" ? Which cart. is in your jukebox ? Yes--you need to jump the 3rd pin on the mute plug to ground, to set the squelch.
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chuck
New Member
Posts: 8
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Post by chuck on Mar 20, 2019 21:23:57 GMT
The turn table is a Technics and the cartridge has signet written on it. All I have is the amp and power supply chassis. I will have to ask the owner to get me the turn table cartridge info.
I looked in the faq section and saw a manual for a 100 c.
Hope I am posting correctly
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Post by Ron Rich on Mar 20, 2019 22:28:38 GMT
Hi Chuck,
You need to know what type cart. is in that TT--not the brand name--it must match the amp !
If you read "Hi Newbies" you would hopefully order a "manual Package".
As for posting--please read the stickies in "User Introduction" section here.
Ron Rich
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chuck
New Member
Posts: 8
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Post by chuck on Mar 21, 2019 0:03:05 GMT
This turn table is a modern unit that I have. Probably not compatible with the jukebox amp. Cartridge has mr5.0 written on it.
Didn’t understand adjusting squelch.
I tested all the voltages listed on the schematic and all are real close.
unit should work but no amplification.
I have no loud numb out of the speaker. Nice and quiet.
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Post by Ron Rich on Mar 21, 2019 2:41:35 GMT
Chuck,
Probably will work--try it in phonograph !
Ron Rich
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Post by robnyc on Mar 21, 2019 5:50:50 GMT
Check, that cart is a typical "audiophile" with low output, probably on the order of 3-5 mv. The original cart for that machine was 30+mv on a "loud" record.
Also, the AGC will go into squelch mode if pin 3 on the mute/squelch plug is not grounded. Or you can just remove the 6SK7 tube.
There are other things that can cause low output including a bad output transformer.
The schematic alone is fully adequate to service these amps, provided you understand the circuit.
If you are going to do any number of these old phono-only amps, an RIAA to Line adapter is easy to build and handy for tests>
If using a device that offers "inverse RIAA" as some computer players do, you can use that but be careful about the level. A simple voltage divider (two resistors) or a pot of anywhere from 10K-ohm -up will allow level matching. Source device to high side of pot. pot arm to amp input. Low side to amp ground.
RobNYC
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chuck
New Member
Posts: 8
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Post by chuck on Mar 21, 2019 12:09:18 GMT
Thank you so much. I will look at it again today.
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Post by robnyc on Mar 21, 2019 12:40:11 GMT
Chuck, re-read my above post. I meant to say 3-5 mv from your cart. That is much lower than the juke's cart and will account somewhat lower output. Again, there are other factors that may cause lower level too.
RobNYC
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chuck
New Member
Posts: 8
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Post by chuck on Mar 21, 2019 13:20:45 GMT
I just checked my cartridge and it is 3.5. That is a start into solving the problem. I will have to use another input and a pot. Thanks
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chuck
New Member
Posts: 8
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Post by chuck on Mar 21, 2019 19:52:26 GMT
I took the amp over to the owner. I had never seen the jukebox cabinet. I told him after seeing it that all the cabinet and the mechanics would have to be cleaned. That is out of my expertise.
Thanks to everyone for their support.
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