sds cap board st 70 mod

by Dave Sun Jun 06, 2010 10:19 pm

Dave: Guest

Post n°1

sds cap board st 70 mod

by Dave Sun Jun 06, 2010 10:19 pm

I have an st 70 that has been modified output trannys hammond 1650n, VTA board, 6l6 ouyput tubes, and SDS cap board. I use the VTA to its max, no mixing bias or anything from the SDS board. The SDS board is set up using
1st section 100/100 to rectifier
2nd section 390/390 to trannys
3thrd section 100/100 to B+
4th section 100/100 to no where

the first thing I would like to do is swap out section 3 to section 4 for B+. In turn make section 3 as an added capacitance for the output trannys. I just am unclear if I can just tie this section to section 2 with a jumper wire or is a resistor needed? What would the max capacitance be acceptable for this section if more can be added .....how much?

The second thing I would like to do is add esl caps , im not sure how do figure this one

thanks for any input
Dave

by **Bob Latino** Mon Jun 07, 2010 6:19 am

Bob Latino

Bob Latino: Admin; Posts : 3277
Join date : 2008-11-26
Location : Massachusetts

Post n°2

Re: sds cap board st 70 mod

by Bob Latino Mon Jun 07, 2010 6:19 am

Dave wrote:I have an st 70 that has been modified output trannys hammond 1650n, VTA board, 6l6 ouyput tubes, and SDS cap board. I use the VTA to its max, no mixing bias or anything from the SDS board. The SDS board is set up using
1st section 100/100 to rectifier
2nd section 390/390 to trannys
3thrd section 100/100 to B+
4th section 100/100 to no where

the first thing I would like to do is swap out section 3 to section 4 for B+. In turn make section 3 as an added capacitance for the output trannys. I just am unclear if I can just tie this section to section 2 with a jumper wire or is a resistor needed? What would the max capacitance be acceptable for this section if more can be added .....how much?

The second thing I would like to do is add esl caps , im not sure how do figure this one

thanks for any input
Dave

Hi Dave,

To add section 3 to section 2 just run a jumper wire between section 2 and 3. You can use almost any amount of capacitance after the choke. Keep in mind though that the amp will only use just so much capacitance and then anything over that will be useless. With the VTA driver board you then run a 2200 ohm (1 or 2 watt) resistor between the 3rd and 4th sections. The purpose of the resistor is to drop the B+ about 20 to 30 volts to the main B+ input eyelet on the driver board.

ESL capacitors are bypass capacitors that are used to break up resonances in a large capacitor bank. Just using the SDS board as you have IMHO you don't need ESL capacitors.

One other thing. The SDS board is set up with each pair of capacitors in series. When you use capacitors in series the effective capacitance is cut in half while the power handling is doubled. The 100/100 section in series gives you an effective capacitance of 50 uF, the 390/390 section gives you 195 uF etc.

Bob

by Dave Tue Jun 08, 2010 9:23 pm

Dave

Dave: Guest

Post n°3