Scryer ... or how F8 met Mighty SissySIT

[Zen Mod]

-heatsinks on BD - mount them in opposite way (rotate that most of length is going up), still enough meat for back of transistor(s)

that way no touching of resistors, even if BD are sunk all the way

-you have clear note on schematic that you don't need isolation for pair of BD - collectors are connected, just use thermal paste

- who drew these pcbs? they're Gorgeous

 

[von Ah]

Thanks! The PCBs are choice.

Noted on BD sinks.

I know all the little sinks just needed goop, but I don’t have any. 😆 Plenty of Keratherm.

Reattached everything and crossing fingers for better result than before…

 

[von Ah]

No dice. This is going to take a little while to figure out. I think next step will be swapping out that SIT for another one (I still have two more unused K2087Cs just for this contingency).

 

[Zen Mod]

what's voltage between lower and upper mosfet gates?
that's M101 and M102

and then, voltage across R134

all that ref to schm in #7

feel free to compare them to same on functional pcb

 

[von Ah]

Apologies for drek question, but do you mean one meter lead on M101 gate and other lead on M102 gate?

 

[Zen Mod]

xctly

 

[von Ah]

M101G to M102G
Bad channel 8.48V
Good channel 9.60V slowly falling

R134
Bad 3.6V slowly falling
Good 3.6V slowly falling

 

[Zen Mod]

hold your horses, do not pull anything yet

question - did you test your 2SK2087 for Ugs?

first step:go back with Iq trimpot, then replace R116 with 680R

ref to attached schm, taken from #44

 

[von Ah]

I will need to acquire 680R resistor. 1/4 or 1/2 W?

Attached are the results from my simple transistor tester measurements of my 2SK2087Cs. The one on this troublesome board is either #2 or #5. Can’t see my label on it now. So I did not do a more thorough assessment of my little batch of 10 (of which I now have 2, 5, 1, 7 available).

#3 and #9 are in my TDV amp doing very well.

Thank you for the troubleshooting help.

 

[Zen Mod]

well, power of 680R is really irrelevant in this case

as it is, 620R to 750R will do

you can solder 1K5 on top of 1K, even if temporary

 

[von Ah]

Swapped in the 680R for R116. Full range of Iq pot: 3.4mV to 3.5 mV.
Go lower for R116, or look elsewhere?

 

[Zen Mod]

can you measure voltage between mosfet gates, for max and min trimpot positions?

by measurement across R122, we confirmed that CCS side of current mirror is functional

now, observing voltage between gates, we'll know does other side of current mirror is working or not

all of that , presuming that there is no wrong resistor value somewhere ......

 

[von Ah]

M101G to M102G 8.42V to 8.52V full range of pot from most R to least R.
I hope I don’t have two resistors in the wrong places…

 

[Zen Mod]

gate to gate voltage is not high enough nor is having enough span

3 things:

-check all resistors (values, position); that includes trimpot values

-take cotton swab, clean top of all 6 SMD bjts (those in current mirror), find good lens/loupe and check their markings; 3 same ones in positive rail, 3 different same ones in negative rail; that in case some bloody greenhorn behind Iron Curtain did solder wrong SMD part ......... if needed compare with good channel

-check position and value of all SMD resistors; those at rails are 470R, base resistors are 100R, in between mosfet gates are 6K8

nomenclature as per schm in #188

if nothing else, while you're staring at small ones and if you can't find my error, you'll find your own

 

[von Ah]

Thank you for the logic process. Let the staring begin!

 

[Zen Mod]

I did look at your pics and I can see all resistors (smd) are in place

now, loupe for bjts

though, that's the thing I'm OCD-illy checking trice while soldering and after

but, Murphy (as mentioning him is relieving me of responsibility) .......

 

[codyt]

@Samuel Jayaraj Scryer vs Sissy42 (42 essentially same as R3). Both having same OS, so differences in FE. Scryer has active FE w/ feedback; Sissy iron FE and no feedback. They're cousins for sure. Scryer is more transparent and a bit more quiet, which gives it a sense of having better dynamics. Sissy has more of the richness and virtue that comes with a passive FE and no feedback. I love them both immensely. If I want more resolving and transparent, I go Scryer; if I want more richness I go Sissy. Both have the SIT magic. Right now my favorite is Scryer....next month it could be Sissy, or Old Soul, or Singing Bush, or .....

 

[flocchini]

Cody
They are all so good it really is hard to decide !!! 😊
We are very lucky greedy boys.
I do need to add ( I know I keep saying it ) - the Iron Pumpkin IMHO adds the next level of enjoyment
Be safe

 

[codyt]

Any luck yet @von Ah ?

 

[von Ah]

Thanks for asking, codyt. I haven’t had the opportunity to dive into the examination, yet. I was planning on looking over the errant board today.