Seeking advice on driver tube for SE 300B

Strange to use EL37 as a driver tube. It will " poluted " the sound of 300B as a triode SE. ECC32 is good to drive 300B but expensive.

Hi,  I am in overseas and cannot response to your email. I have complete the construction of a 300BSE amp recently using Sunaudio 6sn7 driver tube but change the Main B+ to 420V for 300B, I recommend this circuit as I have compared this one to various 300B amp like audionote conquere and found that it sound better. I am also using premium parts like Jensen copper tube cap , RMG resisitor, Blackgate cap and Tango XE20S output. Cost me about 10,000 but it is worth as I have compared it to various amp like MC240, MC275, Marantz 8 . I found my taste is still prefer this 300B SE amp. My friend like it very much and take it in this home and work with JBL. I am now planning to work it as a mono-block. Hope this will help.

If you look at all those diagrams, they are effective the same principle thought the grip resistance are difference which 6Sn7 working on different working condition. The third diagram using a 880ohms cathod resistor so the 300B is working at a different condition then the other diagram. I had not tried this low cathod resistor as not all 300B suitable for such voltage. ( i was told that Full Music 300B should work at 1.1K instead) . Any way, i have attached my diagram that i have build but I have modified the B+ to 420V and using 1K cathod resistor for 300B to gain more power. Power Supply had also modified by using 2 Black Gate 100U x2.

This is my early version of 300B and now rest in my friend's home. He is quite happy at the moment.

I had also duplicate the circuit for EAR 734p and using it a phono amp at home.

Dear Cheaplow,
Sorry for being late in answering you question. Since my first machine is no longer with me, I cannot measure the voltage. However, I have already built another machine using negative bias on the Grid, i found that 300B needs about -83V on China one in order to get a current of 70ma. For Full music , the negative bias needs to be much lower, so in order to achieve a 70ma working condition, I finally decide to add another transformer and give a negative voltage to the Grip, the Cathay resistor has been reduce to only 100ohms just for the sake of measuring the current flow. I am qiote sute that this will maximise the performance of each type of 300B.

please send pm to me. I will send you the details.

Dear Steve 138

Replied

Hi Cheaplow,

Yes, I own a WE 300B and will put in it once run it. The current for the plate is 70ma as I am providing a negative voltage of -83V to the grid, that is why the cathod resistor value does not matter. I think it is more easy to control the plate current than using a fixed value of cathod resistor. Hope you have a nice trip..