A request from a non member

[richard296]

will do Thank you sparky.

[pwdrive]

If I'm reading Refugee's post ( #138 above) correctly, 20 watt resistor should be more than adequate. Remove the 150 ohm and replace with the 100 ohm 20W. This should dissipate no more than 10 watts, since the voltage drop across it will be (55-25) = 30, and the current (I = E divided by R) should be 3 Amps.

Maybe 300 ma ?

Lawrence.

[Refugee]

Yes It is the wattage and the difference between the working voltages of the capacitors.
The blown 35 volt working capacitor is normal if the power supply it plugged in with no load.
There is a mistake with the decimal point in message 140 It should be 0.3 amps.
I am getting the feeling that the sound generator board has constant currant driven parts in it and that too higher resistor value will always get hot due to the way the circuit works on the main boards.
Does the sound generator produce any notes yet?

[Old Sparky]

Whoops! Mistake now corrected in post #140, but I don't see how to correct it as Lawrence quoted it in post # 142.

[richard296]

I did know from previous threads from yourselves that it's drawing around 300 ml amps.
Fitted the 20 watt resistor. Amp sounds good putting the cd player through a mixer first. Volume levels are correct now. As refugee says even with the larger resistor both physical size and higher wattage it is still getting hot to touch. Amp was on a good 30 min and the resistor is Not as hot as the 15 watt after 15 min i couldn't even touch that at all. The hot resistor is enclosed in the inverted aluminium housing which i think traps the heat. My question now is. Will it get hotter the longer it's switched on. Can i either use a heatsink on the hot ceramic resistor. Or use an alloy housed resistor with a heatsink. Or can i fit a 2" computor heatsink fan to draw the warm air away. Bear in mind the heat seems to be the initial problem. Please advise I don't want the resistor to blow and be back to square one. Thank you richie

[richard296]

Refugee I forgot to mention yes the sound generator is working also with the accordion plugged in most functions of the accordion are working. Again it's well used so needs a little attention ( knowledge from yourselves required) I thought i would start my own thread for that Yes ? Thank you richie

[pwdrive]

The 20 watt resistor is rated at just that ie: 20 watts max dissipation without any heatsink, with the unit all up and running and hunky dory measure the voltage either side of the 20 watt resistor, from that you can determine how many watts it's dissipating with the unit functioning normally, post the voltages measured either side of that resistor on the forum.
The two voltage readings should not change over time, if the output voltage from the resistor changes over time then you need to investigate.

Lawrence.

[Refugee]

It is good to hear that the accordion is running.
The way to kill the heat that has not yet been said is to buy an aluminum resistor and just drill the power supply cover and bolt it on with a dab of computer processor paste. The heat will then be on the outside in open air.
If you do both resistors it will stay nice and cool inside the power supply.
If you are intending to restore more instruments like this it would be worth getting a metered bench power supply for this sort of work and add further to the tool kit with a frequency counter and audio signal generator for tuning up.

[richard296]

pw checked resistor. exact same voltage to the nearest tenth of a volt. after two minutes of playing then 90 min later. And still sounds the same. think iv'e cracked it. Refugee I will do what you say regards resistor. I know now that the resistor will get hot. But it seems stupid in the box. It's like an oven the resistor has got to get hotter. (Heat rises) The original ventilation was at the bottom just 2 @ 4" x 1/4" slits then the base plate was dented which made the slots even smaller. As for the other resistor it isn't even warm don't think that's a problem. As for tools. I now have a double 30v @ 1 amp dc power supply cap tester and the little gizmo from china to check esr and all resistor values etc. The signal generator etc are in hand. Many thanks richie. ps I need a couple of things sorted on the accordion generator side. I will open a new forum and hope you's will be good enough to assist

[pwdrive]

It would be good to post the voltages on here for reference in case anyone else comes across one of these amplifiers.

Lawrence.