Replacing of electrolytes in T-500

[Joakim Bergstrom]

I just aquired my first ever Hammond, a T-524 in need of some TLC. As soon as it is in good working order I intend to do several of the mods discussed in this forum. Now in the course of replacing the large can electrolytes in the power chassis I see that C615 (1500/25V) has its single terminal connected to the ground while the outer shell is connected to the circuit. I.e. reversed compared to the other electrolytes. I am a novice regarding electronics and thus extremely thankful for all information you others kindly have provided through this forum. I have read about the importance of connecting electrolytes the right way - correct polarity but since this cap - as well as the neighboring caps seems to be all original ones I become become very confused and wonder how I shall connect the new capacitor. Also I intend to replace these large caps with the same capacitance rating as in the diagram but with slightly higher voltage rating, like 50 VDC for better margin/longer life. I hope this is the correct way of thinking.

[enor]

I don't have the schematic handy, but from what you describe it seems that C615 is filtering a negative voltage. The (+) end of the cap should be connected to the highest potential, which might very well be the chassis i(f the other end is negative).

[Joakim Bergstrom]

Of course - It never ocurred to me but as you say, the voltage in the circuit is a negative 25 volts and connects to the power &reverb. Thanks for the info and also for the replacement key which came with the mail today.

[Drawbar Dave]

I don't have the schematic handy, but from what you describe it seems that C615 is filtering a negative voltage. The (+) end of the cap should be connected to the highest potential, which might very well be the chassis i(f the other end is negative).

Yes I'm working on two of these at the moment and I noticed it too. The R100 I've been restoring does the same thing with a slightly higher voltage.

[Joakim Bergstrom]

Seems like restoring a Hammond organ is the most fun way to learn about electronics for us novices and the most creative hobby for those with experience. Trying to get my purchase list together for recapping as well as modifications I got stuck with following problem: According to Carsten M's step 2 mod. the two transistors on the percussion board shall be replaced with PNP type transistors, suggestedly BC557. Problem is that there are about eight versions of this transistor in our online shop named ELFA and I do not know which parameters are crucial and which ones are not important. Further, would anyone possibly know what would be the preferred voltage value of the two 1uF bipolar caps to be added on the recovery amp as described by Kon Zissis in order to remove bass roll of effect in the circuit? I understand that voltage on an electrolyte need not be exact as long as there is a margin, preferably higher value but with the lack of experience I do not like to take any chances..

[Papus]

Before you do ANYTHING - replace the motor run capacitor - it is filled with carcinogenic PCB oil and is prone to explosion at this point in its lifespan.
In 50Hz-land, it is difficult or impossible to obtain the correct value for this obsolete capacitor, but you can use a series pair of commonly available modern capacitors to obtain the correct value.
Ceiling fan motor run caps are a good option.
I used a pair of 2.5 micro farad 475V caps on my 240V 50Hz T202, for a total capacitance of 1.25 micro farads.
You should check your cap and motor first though, you never know - it could be an oddball Hammond

[Joakim Bergstrom]

I appreciate the advice. Waiting for the capacitors including these two 2.5 run motor caps to arrive.