ROCKOAL JUKEBOX 1458

[chucksue]

I AM WORKING ON A ROCLOLA JUKEBOX AMP.THE SCHEMATIC WHICH IS HARD TO READ USES A PUSH PULL OUTPUT.THE PLATE RESISTANCE IS 480 VOLTS.THAT IS TO HIGH.I THINK THE RESISTORS IN THE POWER SUPPLY ARE BAD.THEY ARE THE OLD SAND RESISTORS.WHAT CAN I USE TO REPLACE THEM?THEY USE A 12AT7 JUST BEFOR THE 6L6 TUBES.I CAN'T GET ANY SIGNAL THRU THE AMP.ANY HELP WOULD BE APPRECIATED.

[Enzo]

Link us to the schematic

What makes you think 480v is too high?


Did you measure that 480v with the tubes removed? Or were they in their sockets and functioning?

[chucksue]

I LOOKED UP THE TUBE IN MY RCA MANUAL AND THE MAX PLATE VOLTAGE WAS 400 VOLTS.WHEN I TESTED THE VOLTAGE THE TUBES WERE IN THE AMP AND WORKING.IF THE PLATE VOLTAGE IS TO HIGH WHICH IS RIGHT OFF THE RECTIFIER THEN ALL THE OTHER VOLTAGES WILL ALSO BE HIGH.THIS WOULD BE THE GRID ECT.THE TUBE WOULD BE OPERATING IN DISTORATION.THE SOUND FROM THE AMP IS BUBBLIE.THANKS FOR THE REPLY.I STILL NEED HELP.

[flatheadmurre]

Here´s a link to schematic.

http://www.thearcadeboneyard.com/Juk...0SCHEMATIC.pdf

Anode voltage should be 380V.

[Eli Duttman]

Please stop shouting. All uppercase letters is the WWW equivalent of shouting.

The schematic shows a RC self bias network between the 6L6GB cathodes and ground. The plate to cathode potential difference is less than the measured B+ rail voltage. In any event, "old time" equipment makers frequently ignored published spec's.

[aardvarkash10]

Bad resistors? You think? Are you SURE you should be in there doing this on a live circuit???

If you had some idea you would measure the pd across the ceramic resistors. As you haven't figured this out yourself yet, I'm going to play for safety and say get the f#ck out of that thing until you know what you are doing.

I hope I'm blunt enough here. Your questions indicate strongly that you are a danger to yourself and whoever lives with you, and any potential user of the equipment you are "fixing" at the moment.

Stop.

[chucksue]

i have been working on vac.tube radios for years.my father was also a radio repairman before tv was introduced to the public. i know what i am doing.i just wanted an answer to my question.i don't need your help.thank you

[aardvarkash10]

well, you stated the plate resistance was 480 volts, you can't identify how to assess the actual voltage across the tube and you figured the ressistors in the power supply are bad, even though the B+ is taken straight from the rectifier - no resistor.

You may not need my help, but you definitely need help.

Heres a hint - are both output tubes conducting? Do you know how to check this?

[HollowState]

Originally Posted by chucksue

i have been working on vac.tube radios for years..... i know what i am doing.

You have me scratching my head. If you really do know what you're doing, you should be able to fix it. It seems like a simple circuit.

i don't need your help

Then why did you ask for it twice? And you do need help with your grammar. Capitals at the start of a sentense, a space between sentenses and always capitalize a single i.
,