Hello!!
I have seen many posts saying its OK to use IRF240 instead of IRF244 MOSFETs to pair with the IRF9240 and same thing goes for the IRFP versions but for the specific use in the ADCOM GFA-5800 would it be OK, does anybody know?
Thanks in Advance,
Alex
I have seen many posts saying its OK to use IRF240 instead of IRF244 MOSFETs to pair with the IRF9240 and same thing goes for the IRFP versions but for the specific use in the ADCOM GFA-5800 would it be OK, does anybody know?
Thanks in Advance,
Alex
It is likely IRF244 has a closer matching transconductance curve to irf9240.
However IRF240 will certainly work with IRF9240, and is quite commonly done.
However IRF240 will certainly work with IRF9240, and is quite commonly done.
you only need to Vgs match if using multiple pairs.
However source resistors are often used to get some balance.
If you buy mosfets from same batch they should be close anyway.
However source resistors are often used to get some balance.
If you buy mosfets from same batch they should be close anyway.
Well yes, the GFA-5800 has Multiple pairs by channel and yes I agree that MOSFETs from the same batch should be close enough but both the IRF244 and the IRF240 are obsolete by now so it’s not easy to order them in bulk from the same source, they’ll most likely be found as surplus here and there, unless someone knows something I don’t?
If so, please share that info with me...
Thanks!!!
logic is that all in same channel and on same rail are connected in parallel , and they must be of exact same type and they must be matched to , say, 50mV of Ugs at same current, preferably at Iq used in exact circuit
but!, taking in account that source resistors are sorta highish ( 1R) , you can use mosfets matched in 100mV Ugs bracket
find Iq info in attached SM, divide by number of vertical pairs and you'll know what's Iq per device
regarding T03 mosfets availability , can't help with that ......... rummaging on net is only hope and even then , don't forget to buy them in quantity
who knows, maybe Good Guys and Girls at PL are having some quantity to sell, saved on side for purpose of old PL products servicing
but!, taking in account that source resistors are sorta highish ( 1R) , you can use mosfets matched in 100mV Ugs bracket
find Iq info in attached SM, divide by number of vertical pairs and you'll know what's Iq per device
regarding T03 mosfets availability , can't help with that ......... rummaging on net is only hope and even then , don't forget to buy them in quantity
who knows, maybe Good Guys and Girls at PL are having some quantity to sell, saved on side for purpose of old PL products servicing
I recall the 244 had normal sized pins. The 240 had extra fat pins.
Thanks Mr. Pass!!
Fortunately there was no need to replace any MOSFETs, after testing and re-matching they all ended up good, had to replace a few of the smaller MOSFETs, capacitors and a few resistors, I really thought the power MOSFETs would be bad since this and another GFA-5800 were damaged by lightning that hit my house last year!!
Thanks and Everyone!!
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