L'Amp: A simple SIT Amp

[generg]

yes I understand your intention Mike....

my deviations are more due to the lack of the bulbs but ....

I ordered already three 3,3 Ohm (50W) and three 1 Ohm resistors (50W) so I will build up a chain and "dial in" for the sweet point....

I also ordered the halogen sticks ZM recommended....

So in some days I will have the published version .......and will take it as basis.

[Tea-Bag]

I could also port over some Grey Market Bulbs for you, if it's legal.
But I think the resistors might well be a great solution to put in a 'normal' chassis.

[generg]

hi tea-bag,

that is really very nice and if the resitors do not work or do not have the magic (what do you think Mike) I will return to your offer ....

[stefanobilliani]

Hello all !

I am reporting some values from my amps build :

I am pushing right now at 2 amps of current , which is obtainable - in my set up - with a 1500 halogen bulb ( 220 volt ) .

So at 16volt of Vds ( without degeneration example ) the halogen sticks offer about 13 ohm of load @ 42 volt of Vdd .

My couple of 2ks82 KD33 I have are a different match : -5,16 Vgs and -6,5 Vgs . I have ordered one more couple and hope to have a better match , even if I do not feel audible differences between the channels .

Now , at 2 amps the heat sinks run pretty hot ( with grease applied ) , so I will not take them that way for a long time , unless I find some bigger hardware in the next days .

Interesting is , that like in the DeLite amp - with my "6 ohm" speakers I "tend " to prefer a load around 15 or 16 ohm , which in that case of the Dmosfet the result of the bottom end of the music was a little more boomy but in a good way . Interesting -just , that the boomy effect is gone comletely listening to the Sits , so I think I will try the same configuration with a 16 ohm load ( around 1300 watt halogen bulbs ) and raise the current trough an higher VDD . We'll see .... and listen .

Soon back to 20 ohm and less dissipation .

[stefanobilliani]

By the way they sound very good @ 2 amps . Wonderful amp .

[Michael Rothacher]

Originally Posted by stefanobilliani

By the way they sound very good @ 2 amps . Wonderful amp .

Sweeeet!

Originally Posted by generg

(what do you think Mike)

Resistors are fine (probably ever so slightly better). They're just not as glowy.

[generg]

oh, I found some information about the meaning of KD-33 I think in an old manual of the Sony TA-N88

the marking seems to be the pinch off voltage (?) and the fluctuation of one Vp rank is acceptable, could been KD-33 and KE-33 is in a comparable range.

also interesting to know when I first measured the S-D resistance I was shocked by the low resistance and thought I had shot one, but look at the text, S-D is normally 1-3 Ohm and S_G and D-G should be diode characteristic........

[generg]

and for this .... for me and other people that do not know....


a similar problem was discussed here..

Sony TA-N7B VFET Help!!

The problem with these parts, apart form the price, was the very fact they were depletion mode, with Vp of about 25V for the J18/K60, and a whopping 55V on the J28/K82.

Hi-Voltage JFET's

[Franz Gysi]

with a 1500 halogen bulb ( 220 volt )

Don't you worry this is not a long time solution?

Because the halogen bulb will not reach the needed operating temperature (>240 degree celsius on the bulb) to recycle the vaporized tungsten back to the filament. Resulting possibly in a black bulb and shorter lifetime than expected.

Franz

[Michael Rothacher]

Looking at Stefano's numbers and Gerd's Vp info. It looks like the grades may represent a fairly wide range of Vp, which relates to Vgs.

This isn't a big deal for Figure 10. And your devices needn't be Vgs matched precisely from channel to channel.

But, if you build Figure 11, and your KD-33's Id is more than 2.4-2.7A, you'll probably want to start building a separate bias supply and move on to Figure 10.

I got a couple of KE-33 and they biased-up at around -8V in Figure 10.