F5 Turbo Builders Thread

Hitting it with 40V doesnt make sense. If he has the resisotrs in the proper place, why would the base of the bjt see anything other than the proper voltage. I assume the greatest possiblity is that he fried the bjt with too much bas current, but I dont know. It doesnt make sense that he is dropping 16V across the larger of the two resistors in the divider network.

Thats also a possibility. Just to make sure, the pot should be dialed so that TP1 >TP2 and TP3 > TP4 should be at the lowest resistance correct?
 
Ok I made a mistake. I must have written the wrong numbers in a drunken stupor.

So I took out the BJT's. Powered the FE board.
voltage across R27/R28 (4.75K) = 16.28V
voltage across R25/R26 (12K) = 41.8V

So looks good no?
the sk170 has a drain voltage of -40V and the J74 has a drain voltage of 25V so I don't think it would have blown either one..... I hope. unless of course I installed them wrong. which I don't think i did.

Base to collector on Q7 (BJT) is 40V same as Q8. (nothing connected just the holes)
With the two BJT's out I shouldn't be able to get any readings on the Q1 and Q2 (jfets) but I do get some fluctuating voltage between drain an ground in the order of 10mV or so (again just at the board holes, no jfets in )


edit :
Just tested the two BJT's I have an hfe tester on one of my DMM's they seem ok against a couple brand new ones I have. (similar numbers)
 
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Do resistors R5, R11 and R6, R12 affect the gain

Since I am using Toshiba 2sk1530/2SJ201 in my V3 build, 45 V loaded supply rails, was not sure whether changing the resistor values in NP's schematic for R5, R6 from 1K to 475R and R11, R12 from 2.24 to 1.21R will affect the overall gain of the amp.
I am aware of the formula posted by Jacco for calculating gain based on R3 and R7, R8 but I seem to vaguely recall Buzzforb mentioning that changing R5, R11 and R6, R12 wiil "change the gain structure".
Could someone please explain this and if the gain is affected will it be higher or lower?
Thanks.
Nash
 
This is odd.
So when just the BJT's are in I get predictable voltages as per my last post.
"15.87V from Drain to Ground at both Q1 and Q2."

I just put the jfets back in and I now measure the voltage from drain to ground and drain to gate at the extra holes where one would normally parallel jfets and again I get 0.7V at Q1 (n-side) and 0.5V at Q2 (p-side)
Is this correct?
I don't have the secondary boards installed here, and nor do I have a signal input.
 
ok I just put in new jfets.
I took the ones that I had on the other channel FE board which I previously populated but never powered.
Guess what...
Same thing! with the Same voltages as above!

two pairs of dead jfets in a row?!?!?

I don't think I've passed 40V to them, as I said before I tested the holes with only the BJT's in an nowhere did I ever get 40V , only 15.86V from drain to ground AND drain to gate.
now what ?! this is getting frustrating.
 
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