Raoul Duke wrote: ↑Wed Feb 07, 2024 10:59 pm
Thanks Dan,
I see the yellow and green wires to pin 5 now. Funny how you lose sight of the obvious when you stare at something long enough, lol.
Yes, I’m omitting the courtesy outlet. The leads aren’t very long, so I’m thinking the terminal strip probably is the neatest way to organize the run to the AC in vs having “2 into 1” splices flying above the PT, but I’m still pondering that…
Interesting side note regarding the relay board: I was looking at some 2nd gen ODS pics and see that HAD sometimes fed the indicator light from that board vs the heaters. I see a lot of the same type of light as mine - but some are shorter.
My question about power tube pins 4 was also because I can’t really tell what’s going on with those terminal strips. It looks to me like the 470R goes from pin 4 to a terminal, and the red wire goes to the same terminal - then that’s repeated on the other socket, then backs up to the B+2 eyelet on the PS board. Am I close?
I appreciate the feedback
Yes, that is correct. You will see in HAD's later designs he used pin 6 to tie B+2 into the screen resistors and pin 1 to tie the grid resistors into pin 5. But the 2nd gens are little different mechanically, but not electrically. He was just using unused pins on the socket as a terminal point. Maybe it depended on if he was using a 6v or 12v pilot light?
Raoul Duke wrote: ↑Wed Feb 07, 2024 10:59 pmMy question about power tube pins 4 was also because I can’t really tell what’s going on with those terminal strips.
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Upon closer inspection, the F-313X leads reach the back of the chassis with about an inch to spare, but the switches are still a good 3” away towards the center of the chassis. Still debating which route to take, terminal strip or 2 into 1 splices. How would you guys do it?
Also thinking about adding the “ power amp in” to the circuit. I know it’s not 2nd Gen, but having it might be useful? I imagine I could probably copy the hook up from a later generation layout?
Opinions?
Thanks!
Last edited by Raoul Duke on Thu Feb 08, 2024 5:27 pm, edited 1 time in total.
Also thinking about adding the “ power amp in” to the circuit. I know it’s not 2nd Gen, but having it might be useful? I imagine I could probably copy the hook up from a later generation layout?
Opinions?
Thanks!
Using the fx loop wiring from #124 is a useful thing. In #124 the master pot is pre fx loop, not overloading the fx for that matter. (In the 2nd gen pics I've seen the the master pot is post fx loop.) Of course you have to adapt the relay wiring but that's not a big thing.
I see you've added caps across the rectifiers. Why not across all six? Waiting on parts?
On the FET board, be sure that the case of the 100u electrolytic won't touch the eyelet on the positive end (the case is probably electrically connected to the negative lead), and recall that you will have to adjust the source resistor to bias that particular FET.
Actually, I added the caps across the rectifiers based on advice you gave on another 2nd Gen build thread. I wasn’t sure how many to use and I had 4 on hand. I’ll order two more if that’s the best way to do it.
When making the FET board, I tried to stretch those eyelets out a little more. Probably could have gone wider still, but I did make sure the entire cap is slightly elevated and clear of the eyelets. Thinking of a dab of RTV for support, but the leads are pretty stout and the cap seems very stable. I’ll probably do it anyway (belt and suspenders).
I plan on biasing the FET today. I used 2nd Gen values, but have a decent selection of resistors on hand if I need them.
This is definitely going easier than the first time thanks to the great education I’ve gotten on this board! Today is supposed to reach 50 degrees so I may start the cab later. I have to time the outdoor work IAW the weather. I ain’t as tough as I used to be, lol.
Raoul Duke wrote: ↑Fri Feb 09, 2024 1:30 pm
Actually, I added the caps across the rectifiers based on advice you gave on another 2nd Gen build thread. I wasn’t sure how many to use and I had 4 on hand. I’ll order two more if that’s the best way to do it.
The caps help balance the voltage on the diodes, but you need one on each. This is similar to placing resistors across stacked filter caps. Actually 3x 1N4007 on each leg is probably overkill, two would provide 2kV max inverse voltage, which is about twice what is required. Fender used three when they switched from vacuum to solid state rectifiers, and that was probably a good idea for the rectifiers that were available back then.
So I’m biasing the FET and got a little arc as I was adjusting the pot. Couldn’t really tell where it came from, but I’m testing the individual components to try and see what fizzled. I can definitely smell it…
Upon further testing - all resistors are fine, using my cheap Newcason cap tester- 100p cap is fine, one 4k7 tests 4.6, the other 2.9, and the 100uf cap tests 150. The arc seemed to come from the + side of the 100uf, but I see no obvious signs of damage anywhere.
Not sure how to test the FET, but it looks fine from the outside.
Raoul Duke wrote: ↑Fri Feb 09, 2024 5:32 pm100p cap is fine, one 4k7 tests 4.6, the other 2.9, and the 100uf cap tests 150. The arc seemed to come from the + side of the 100uf, but I see no obvious signs of damage anywhere.
Not sure how to test the FET, but it looks fine from the outside.
I'd replace the 4u7 that reads 2u9, the 100u is ok at 150. If the FET biases as expected that's a good indication that it's ok. They aren't the kind of thing that goes up in smoke. When you run signal through and listen to it you will know for sure.
Ok, replaced that.
Could I be causing the problem because I’m using 2nd Gen values for this? I.e. the resistor across the top of the 10k and 150k is 8.2k and not 18k, and the stock Rs is 1.6k. Everything else is the same.
The FET supply voltage Vdd on the 2nd Gen is low due to the 150k-8k2 divider. The FET bias doc shows that configuration at about 11V Vdd. 2x 9V batteries is too high for presetting that. If you are going with a 12V regulator for your relays, you could power that up and use it to bias the FET.
You still have the option to center bias the FET (Vd = half of Vdd) or going with lower Vd for some FET distortion by adjusting the source resistor Rs. Doesn't matter what value Rs is. If you can't get Vd in the expected range, the FET may be bad.
I used the two 9v and came up with 2.7k for Rs (vs 1.6) after changing to a new test pot because the original was going open at about 2/3 of the CW sweep. I verified the new pot before using it as well to be sure.
Based on your previous post, does this mean my 2k7 is wrong then?
Tested everything on the board (except the FET) after getting the 2k7 and everything is within tolerance.
