Considering Tubelab SSE build

[karl530]

I am considering the Tubelab SSE for use with KT88 output tubes, I currently have a pair of Majestic Transformers OPT's with a a 3.5K primary and 4&8 Ohm secondaries rated for 30W and a Power transformer with 320-0-320 and 390-0-390 secondaries.



Would these be suitable for the SSE? I know i will have to adjust the cathode resistor accordingly but that will not be difficult.


Thanks

 

[boywonder]

If the output transformers are for single ended (SE) operation....sure......


If they are push-pull (PP)....then you will need SE output transformers.


What is the current rating of the power transformers?

 

[karl530]

The output transformers are SE one's.



The power transformer is rated for 300mA on the HV windings.
There is also 5V 4A
6.3V 4A
6.3V 3A


Thanks

 

[boywonder]

You can get an estimate of your rectified DC B+ voltage by multiplying your power transformer AC secondaries by the square root of two.....or 1.41.


So 320VAC X 1.41= 450VDC



and 390 X 1.41=550VDC


In reality the final voltage will be less than these numbers based on the CRC/CLC etc power supply resistance but you can see these voltages at startup before the KT88s start to conduct.


Important note.....finding high voltage electrolytic capacitors rated at 550V can be a challenge, and that that's a lot of HV for a first project...assuming that this is your first tube project.


..most 500V rated electrolytic caps have a surge rating of 550V to take care of the overshoot at startup.


KT88 heaters need 1.6A each so you'll have ample heater current for them..and the driver tubes need a little too.


..and 300ma secondaries is plenty of current as well.....likely more than you'll need for typical KT88 operation so your voltages will likely run high. Your B+ voltage can be tuned a bit by changing the value of the first cap in the power supply.