You need to modify the bias supply in order to run the new Tungsols. They run hot and require more negative voltage. This mod cannot be done using just the dual cap can.
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Finished rehab to a stock Fisher 500C
- Thread starter JimWhit
- Start date
Can't do the mod using just the combined can, you need two separate 1000 uf caps.
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I see I miss read that. Is there a solution for my situation without ditching my Hayseed can? Can the resistors on the board be changed to increase the negative voltage?
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If you change any resistors on the IBBA board to get more bias voltage, then you lose adjustment range in the process.
The best thing to do would be to add in one discrete cap of up to 2200 uF to act as the first cap, and then parallel the two caps in the Hayseed can to act as the second cap. Move the dropping resistor into the negative lead then and that will give you 4+ more negative bias volts to tame your hot tubes.
I hope this helps!
Dave
The best thing to do would be to add in one discrete cap of up to 2200 uF to act as the first cap, and then parallel the two caps in the Hayseed can to act as the second cap. Move the dropping resistor into the negative lead then and that will give you 4+ more negative bias volts to tame your hot tubes.
I hope this helps!
Dave
I think I got it, you said move the dropping resistor into the negative lead, is that the 15-ohm 5W resistor in post 21? If so, do I take my feed to the IBBA from the neg post of the 2200uF cap like in the post. Is any 2200 electrolytic cap over 60V DC good? I would like to hook it all up and then post an image before I fire up the machine. Thanks
Yes on both counts. Generally, too high a voltage rating for an electrolytic cap relative to the actual voltage impressed across it won’t allow the cap to hold its nominal capacitance value over its working life. A 50 volt rated cap would be ideal, don’t go over a 63 volt rating.
Dave
Dave
Thanks Dave I have a 63V cap on hand.
I ended up getting the IBBA voltage up to -31 by following Dave's comments and adding the 2200uF cap to the rectifier and moving R142 15-ohm 5-watt resistor between the Hayseed dual section can and the new cap. My heater voltage went up to -29.2 so i dropped a 5-ohm 5-watt resistor between the neg Hayseed lug and the heater wire, it is at -26V now. I can adjust the bias voltage and get three of the tubes to -27V with one at -21V. I flamed one of tubes so I will reorder a pair and dial it in now that I have the board working. Thanks Steve and Dave. Please let me know if adding the 5ohm resistor to drop the heater voltage was a bad thing.
Good job, looks great!
Hi Steve, do you have any EFB boards left?
Messaged you.