tubelab SE 300b power transformer

[adwsail]

Tubelab, been lovin the SE for a couple of years now, popped one of the 2SK2700. Any off the top recommendations for replacements given they aren't readily available any longer?

 

[Tubelab_com]

The 2SK2700 mosfet has gone extinct due to ROHS laws. Toshiba decided to discontinue the part rather than make an unleaded version. I have found two suitable substitutes, the Fairchild FQP1N50 and the Supertex DN2540N5. I have been using the Fairchild part in my amplifiers. The Supertex part is only rated for 400 volts. The mosfet gets the B+ voltage on one end and the grid bias voltage (negative 50 volts or so) so it may me marginal in some amplifiers. Several users report good results with it though.

 

[adwsail]

Outstanding. I really appreciate the help.

 

[Evenharmonics]

I have found two suitable substitutes, the Fairchild FQP1N50 and the Supertex DN2540N5.

Do the Mylar insulators come with the parts? If not, where can they be bought?

 

[Tubelab_com]

The mylar insulator is not needed on the mosfet. This will cause a high voltage to appear on the heat sink, but that voltage is already on the heat sink of the CCS chip. Mylar insulators can be used on those parts if you want though.

The insulator is needed on the filament regulator chip though. The insulators do not typically come with the parts. I use BER114-ND from DigiKey.

 

[Boris_The_Blade]

I use kapton (polyimide) insulators and shoulder washers from digikey with great success. They don't use messy silicone paste which is really nice.

 

[Evenharmonics]

What about the fuse?

Will the power fuse be dependent on PT? And what value should one use for Tubelab SE?

 

[Tubelab_com]

I have been using 2 amp fuses in 120 volt powered amps and 1 amp fuses for 240 volts.