If you're building up the standard MK-2 version with +/- 37 volt rails than you can leave out the Rb's all together... the original KSA-50's didn't have them. Re should be .68 ohms 5 watts. The .68 ohm value will allow the use of output devices that are not perfectly matched but they should at least be from the same lot code and you should fall within 7 to 10% from device to device. The use of .47 ohm 5 watt is also ok but may require closer output device matching. Its ideal for each device to equally share the load.
Mark
Mark
Mark A. Gulbrandsen said:
Thanks for telling me that when I was busting my butt trying to make this thing! I used .499 10W and the VRE measurements that I made while this was on the bench and before it was put together as I recall turned out to be relatively consistent with a batch of onsemi devices that appear to be from the same lot. Don't know if this is conclusive of a good match or not but now you are making me feel like I did something wrong
This is good stuff to put in the wiki!
If it is a consilation, Mr Green, most PP amplifier designs employ 0.22 to 0.33 Ohms output device emitter/source resistors.
I can even name a couple that have 0.1 Ohms.
Recently i bought a batch of thousands of 5% accurate surplus metalfilm resistors, 100s of one value of the same production run.
Being from the same batch, accuracy between them is far less than 1% for most.
Cost me less than $0.01 per resistor, with better accuracy between them than buying 1% from a mix.
(i measured with a 0.1% accuracy device, not a DMM)
I can even name a couple that have 0.1 Ohms.
Recently i bought a batch of thousands of 5% accurate surplus metalfilm resistors, 100s of one value of the same production run.
Being from the same batch, accuracy between them is far less than 1% for most.
Cost me less than $0.01 per resistor, with better accuracy between them than buying 1% from a mix.
(i measured with a 0.1% accuracy device, not a DMM)
Attachments
Well, you can use just about any value there but the lower you go the tighter matched the outputs will need to be. In my first KSA-50 with the .68 ohm resistirs I had one pitput device that read way different drop than all the others and it WAS from the same batch code. So batch code doesn't necessarily gurantee anything.
Mark
Mark
Mark,
Did you ever try them from the same "tray"?
There can be several trays in a batch and I "hope" the ones on the same tray will match much closer. At least thats what My mesurements show. My Mj21195/96's match to 1% in the same tray. I cannot deduce the correlation will hold generally, but am curious what others have found,
K-
PS: For those hung up on damping factors, a 0.1 ohms design will be 7 times more damped than a 0.68 ohm design. (Not that it will make it sound better or worse or anything).
Did you ever try them from the same "tray"?
There can be several trays in a batch and I "hope" the ones on the same tray will match much closer. At least thats what My mesurements show. My Mj21195/96's match to 1% in the same tray. I cannot deduce the correlation will hold generally, but am curious what others have found,
K-
PS: For those hung up on damping factors, a 0.1 ohms design will be 7 times more damped than a 0.68 ohm design. (Not that it will make it sound better or worse or anything).
Yea, normally thats also what I do with all devices. But with IR mosfets I find that not to be true at all. Over 4 trays that I bought last time they were all easily with in 1% or better and matching to .1% or better between trays was very easy after they were all tested. Only that one time so far did an MJL device chec that far off.
Its still best to at least not assume they will match but to measure the Vd / Re after the amp is biased, stabilized and properly up and running.
Mark
kmj said:
If we do include output transistors it will be TO-3P / TO-247 style since the boards were designed for that. I like On Semi... As for model, what ever is voted... I'm easy. My wife HATES it when I say that... She knows I'm actually quite difficult.
For the driver transistors, then I was leaning towards the On Semi 94/42.
All-
Please review the xls spread sheet attached.. It is curteousy of fellow members and edited to get quantity and part #'s.
We still need part #'s for the caps, either from Mouser or Digi-Key...
jacco vermeulen said:Mr Green will be pleased, he has 3 times higher DF with his quad of 0.499's.
Yes!
Except now I think I should have measured VBE on all 16 xistors. I'm going to have to start making a list of stuff I should have done already. Reading this thread is making me have regrets, but I can't stop, I'm addicted.