SissySIT

[Chul]

I see .. the optocoupler needs voltage polarity!

I need to check what THF-51s I have.

 

[Zen Mod]

no , THF51-S are most probably all falling in "adequate" range

what I'm suspicious of are 2SK182

so , re-check them , if you have time , at 22Vdc and 2A

 

[schultzsch]

I am intending to build this amp for some low impedance speakers(3.4ohm the minimum impedance) and for this I want to paralel 2pcs of irfps for a bias up to 3.2amps(for both).
Is this possible?
Any chances that I will get the same thd spectrum as the original amp?

 

[Zen Mod]

match them tightly , and include 0R1 source resistors for each mosfet

THD spectra will stay practically the same , but amount of THD will change , no doubt

 

[schultzsch]

Will do, thanks.

 

[EUVL]

2SK2145BL is rated at 6~14mA per FET, max. dissipation 300mW for 2 FETs.
Assuming 10mA average, running them at 15V Vds means you are right on the absolute maximum rating (at 25°C).

Brave man !!


Cheers,
Patrick

 

[Zen Mod]

7mA per case , 12V6 , less than 90mW

 

[Chul]

@ Zen Mod
I checked two 2SK182 @ 22V 2A and they showed Vds around -1.1V.
I used a battery for Vgs. There was something funny when using linear power for previous tests.
From left in the picutres, Vgs Vds and Iq (analogue meter) are shown.

 

[Chul]

and the other one I tried in the circuit was Vgs -1.8V Vds 14V 1.25A

 

[Zen Mod]

if that's the case , 2SK182 , at least some of them ..... are applicable in SissySIT circuit

though , still best to have them , test them , then everything is crystal clear

regarding final result - THD spectra and all ........ it must be sort of similar to THF 51-S ... but how much similar , I can't tell without actually having them

 

[Michael Rothacher]

Most of the big Tokins I've tried in the past exhibit 100uA or greater gate leakage current at the Drain currents mentioned, so the internal resistance of the Vgs source becomes a factor.

 

[Chul]

Yes, That was what troubled me and I thought ZM's SissySIT circuit was using it to set the bias voltage.

 

[Chul]

Is this the excuse to use the grid chokes?

 

[Michael Rothacher]

I mention it only because it's good to know when measuring your SITs, since they need to fall within a certain range of Vgs.

 

[chromenuts]

I ordered two pair of the THF51S from the recommended eBay source this past week along with a Sissy board package from ZM.

I’m educating myself by re-reading the related development threads that I just sort of checked in on previously to see what progress was being made.

I know at one point there was testing being done on the THF51S, albeit by members with high tech labs.

Is there a process that can be outlined for the less fortunate simple folk like myself that can help confirm basic operational integrity and parameter viability of these SITs using voltmeters and the like?

 

[Zen Mod]

voltage source of some 20-25Vdc , capable of delivering at least 3A (you can borrow positive rail of your existing Papamp, if you have one ) ...... goal Iq is 2A

what the heck , you can use 19V power brick ,either from your ACA or your laptop

plain 9V battery for gate voltage (sonnested to gnd of above , to be negative)

10K pot or trimpot for setting that gate voltage

1K gate resistor

some kind of heatsink , best to have 8-12cm fan cooling it all the time of test ...... just to prevent temp. build up ..... you can use main rail for it , just reg it down to fan voltage .....or use 24V fan

ampermeter (one DMM)

gate voltage meter (second DMM)

have all that ?

if yes, I'll draw schm

 

[noelectrix]

would highly appreciate that little schematic too

btw, are normal FW heatsinks sufficient for sissysit?

best,
stefan

 

[Russellc]

Until the smoke clears (for me) I am hesitant to order these SITs, as I don't know what measurement I need, or what is being supplied.

Are these still being manufactured? There seems to be several sellers on eBay...don't want to miss out.

Russellc

 

[Russellc]

voltage source of some 20-25Vdc , capable of delivering at least 3A (you can borrow positive rail of your existing Papamp, if you have one ) ...... goal Iq is 2A

what the heck , you can use 19V power brick ,either from your ACA or your laptop

plain 9V battery for gate voltage (sonnested to gnd of above , to be negative)

10K pot or trimpot for setting that gate voltage

1K gate resistor

some kind of heatsink , best to have 8-12cm fan cooling it all the time of test ...... just to prevent temp. build up ..... you can use main rail for it , just reg it down to fan voltage .....or use 24V fan

ampermeter (one DMM)

gate voltage meter (second DMM)

have all that ?

if yes, I'll draw schm

This schematic may be helpful for me as well

Russellc

 

[noelectrix]

1pc THF-51S TOKIN V-FET(SIT) (similar 2SK77,2SK180) NOS Original, Japan Made | eBay

This Japanese seller still has 80 of them.