F6 Illustrated Build Guide

Will need to measure them. They were the b grade matched pair from the store.

5.1V zener is giving me max 70mV bias (cold), will pop the 6.2V in with the 3.3K resistors.

Best to know what Idss you have it could happen again.
I'd keep them under 9mA. Nelson recommends 8mA.
Zen Mod suggested putting a clip on heatsink which is worthwhile.
Either way you want to keep them under 55 degrees in my opinion.
How hot do they feel to the touch?
 
I'll have a feel tomorrow when I get the amp back up and running. The 6.2v zener with 3.3K resistor biases beautifully, very nice and stable. I almost destroyed the amp PCB when pulling out the 5.1v zener, the copper strip lifted off the surface of the PCB by about 1mm. Got lucky that it all stayed in tact. Not sure I'd be able to get away with pulling out the zener a 3rd time...
 
I'll have a feel tomorrow when I get the amp back up and running. The 6.2v zener with 3.3K resistor biases beautifully, very nice and stable.

Hi,

Since you have both experienced the 9.1V and 6.2V, How would you compare the bias stability between the two zener?

I have build my F6 using the 6.2V zener though Im using 5K. Bias
is quite stable too.

Cheers.
 
are the VISHAY IRFP 240 ok for this amp or do you recommend any other brand?
IR would be the other brand i´m able to buy.

I plan to buy a tiny batch of 25 pieces and try to get the best matched out of it.
Never did matching before so I´ve no experience how much to buy.

stefan
 
25 is plenty although matching is not really that critical for F6.
Try and get them from the same manufacturing batch packaged in a tube, you will get better matching that way.

that´s what i do and 25pcs is the smallest batch i can order. i just hope its not just 25 pieces, randomly packed out of a mixed huge bucket, but rather 25 nicely packed straight from production. I´ll see :)

thanks for ur opinion,
st.
 
that´s what i do and 25pcs is the smallest batch i can order. i just hope its not just 25 pieces, randomly packed out of a mixed huge bucket, but rather 25 nicely packed straight from production. I´ll see :)

thanks for ur opinion,
st.

Looks like standard package in a tube is 25 from digikey.
They should be from the same batch (touch wood) as that is how the manufacturer packages them
 
Hi,

Since you have both experienced the 9.1V and 6.2V, How would you compare the bias stability between the two zener?

I have build my F6 using the 6.2V zener though Im using 5K. Bias
is quite stable too.

Cheers.

Measuring off the 0.47 ohm resistor - I have it centered at 600mV (=1.28A). With the 9.1V zener with 10Kohm resistor it climbs up and down by about 3% each way. So it will climb up to 620mV and down to 580mV. With the 5.6V zener and 3.3Kohm resistor it climbs up and down by max 1mV (0.2%).

The 5.1V zener/10Kohm R did not allow me to raise the bias past 70mV (0.150A)!!
 
Measuring off the 0.47 ohm resistor - I have it centered at 600mV (=1.28A). With the 9.1V zener with 10Kohm resistor it climbs up and down by about 3% each way. So it will climb up to 620mV and down to 580mV. With the 5.6V zener and 3.3Kohm resistor it climbs up and down by max 1mV (0.2%).

The 5.1V zener/10Kohm R did not allow me to raise the bias past 70mV (0.150A)!!

Hi Buddy,

This is great. We have same result. Not to mention the DC offset stays at +/-0.5mv for so many hours .

Cheers.
 
Finally Built F6 with Crees

Finally finished the F6 with the Crees biased up nicely approx 975mA. 0V offset running slightly higher voltage do not want to cook them yet.
Burning in as we speak! The sound stage is fantastic thank you Nelson! IMG_20151009_195404_hdr (1024x1024).jpg IMG_20151010_082957_hdr (1024x1024).jpg
 
Thank you FR.

No reason for the transformer just happened to have one available and I'm not using correctly but it gives the desired result.
It is 600Vac in and 120 Vac out so just sticking 110 Vac up the front end and get 24 Vac out but very little voltage droop so even pulling a couple of amps it is around 27 Vac with oodles to spare. Less 3mV ripple after the CRC the amp is so quiet the only way I know it is on is if I have to look inside at the LED's.
It eventually will have a couple of Dekatrons on the front panel to indicate BIAS ala PassLabs voltmeters.
The only issue is the weight of this beast well over 100lbs!