I have worked on really big old Jukebox amps long ago, and thought I would never see
one again, but I have a new friend that has about thirty of them and knows other
collectors, so I am in big juke-amp trouble now
This is a Seeburg stereo tube jukebox amp. The whole thang is on the back door and
to service the amp, you just swing the door out and there it is.
This amp runs 6973 output tubes, which are like a Hi-Fi version of a 6bq5. The amp also has a "AVC" or automatic volume control circuit that keeps one record from being louder
than another record, or one song from being louder than another.
More of this interesting pasta mess of wiring to figure out. There is a high-voltage
supply, a bias and DC turntabe motor supply, two 18 watt power amps, two preamps,
two tone control amps, a and a stereo AVC circuit all in there somewhere
The 6.3 volts AC for the filament comes from another transformer that is in the "Coin
Reciever" unit, so I had to sneak the filament volts off another amp!
The way one of these amps works is this. The whole amp is dead, customer walks up
and puts coins in, the filament volts is turned on and the amp warms up.
Then when the arm starts moving to the first selection, the 115 volts AC to the high voltage transformer is turned on and the 5u4 cranks up the high voltage to the tubes just in time before the needle hits the record. These tricks save the tubes and amp as it in idle, just warm mode until needed, so the jukebox can sit ready all day long.
This is the "Testing method" a stereo turntable and a record of oldies.
I had two of these amps to get running, so we listend to the same oldies while I set the bias on the 6973 tubes, which was a adventure as one tube out of the four was at maxium hot idle and one of the four was at the low idle point. without balancing adjustments, tubes have to be matched for same idle, which means out of ten tubes,
maybe four would really match up
This kind of job is the "Yeah Sure i can do it", then you just have to pile through and use your wits to make it all happen, so the customer can get a good sounding amp back,
and you can get paid, then pay the rent, and go on to another month, more work.
Geja your my Friend. I am technician in Greece and repair jukebox. I would want to me you say that I can acquire a such amplifier. I have for repair a jukebox seeburg ds160 and the amplifier he is destroyed also it does not make choice of disk if you can me help. I thank.
ReplyDeleteHi Niko, you have to have access to your profile made public for me to message to you.
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Hi Shantar,I purchase a day ago ds160.The seller tell me that the machine was working before he move to Florida and something happend by moving.It's not working now.I open rear door and find out that one panel on door is messing,this one with volume control(pic#2).It's possible that the machine works w/o this panel??
ReplyDeleteHello, sure enjoyed the information of how this amp works. My dad runs an amusement company and has for over 50 yrs and now, he is slowing down some and selling off some of all the parts he has accumulated over the years. I have several amps, power supplies, etc. and not sure really how to test them. My dad told me that I could use a microphone and speaker to test it, but I am still unsure because it should be hooked up to the jukebox to test. I must admit that I am mechanically inclined, but don't want to be electrocuted in this process of testing because a whole lot of power goes through that amp. :o
ReplyDeleteThe one I am working on selling right now is huge. It is, I believe, the same one you are working on here. It is a Seeburg Stereophonic High Fidelity Amplifier SHAF5 code A. I do have pics, if you would like to see it.