FM Tuner FET Substitutes

C

cjenrick

Active Member
working on 2270 tuner,

2SK19Y FETS's are stock,

was wondering what you folks use as replacement parts when trouble shooting or repairing,

so far after searching AK we find the 2SK241 mentioned as a possible substitute

NOS 2SK19 G/Y hard to come by

was wondering about modern substitutes also,

thanks!
 
Register to hide this ad
thanks for the suggestions!

in case you never seen what's under the gang cap, not much there, but nice solder flow on the terminals, each section goes from about 5 pf to 30 pf on a cheap tester.

tuner.jpg
 
Last edited:
interesting rev difference on L102,

first two revs have the pri joined to the sec, rev 3 the pri leg is grounded,

l102-3.jpg
 
Oh, I see now that the I(DSS) rank is green so European replacement is BF245B.

The difference of the grounding point of the neutralization winding on L102 either is due to layout considerations or because C107 in some cases can't be adjusted for stable operation.
 
those fets are on evilbay from the UK,

sure would be nice to have a source like digikey

through hole fets in the FM range seem to be a dying breed, and expensive,

maybe it is time to move into the future,

what about this adapter?

it would seem to open up a plethora of new opportunities, or not.

that awaits to be determined in the real world, but what a fun experiment it would be to use surface mount parts in an antique receiver tuner,

yes i have soldered thin leads to surface mount parts for thru hole mounting but it looks kind of weird,

adapter.png
 
yes that was very kind, but i have shipped international and would not wish that upon anyone, filling out custom forms is a drag,

trying to find something on digikey , what do you think of these specs? this is a SOT23 package so it needs to go on an adapter, but should probably be around a while,

http://www.onsemi.com/pub/Collateral/MMBFJ309LT1-D.PDF



https://media.digikey.com/pdf/Data Sheets/ON Semiconductor PDFs/MMBF4416.pdf

now all i need is some piston trim caps and maybe an L102, watch out, those RF coil forms are very brittle,
 
That MMMMMMMMMBF4416 should work because its I(DSS) is 5-15 mA which is the same as the 6-14 mA for the 2SK19GR. That J309 is inconclusive. I don't understand its datasheet.
 
Would work too. Weird that the I(DSS) rank of the two versions differ (2SK19Y vs. GR).
 
did a graph on the 2SK19Y vs 2SK241, the 241 looks great, more linear, a bit more gain,

both transistors had a zero gate voltage current of around 6.5 ma,

the schematic indicates that 6 ma is the bias current for the first fet stage, very close to saturation, so we increased source resistor from 100 to 390 ohms to get the current to around 3.5 ma for the first stage which should mean a more linear operating point.

the second fet stage operates at around 0.4 ma, we had 0.2 ma, so we decreased this resistor from 4.7 K to 1.5 K.

the second stage is probably being operated at a lower Id so as to reduce gain and not distort or overload the FM signal .

so front end sensitivity could be a result of different fet operating points for the fixed resistors used on every unit. but this is just a guess at this point,

these parts look legit and will probably be around a while so we are not going to bother with SMD conversions at this point in time.
https://www.ebay.com/itm/2SK241-Original-Toshiba-FET-Transistor-2-pcs/293456909492?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649

fets.jpg
 
Last edited:
looks like the 2275 uses the same tuner as the 2270,

we pulled one to do A/B testing, found an interesting difference around the first fet, source resistor is 10 ohms instead of 100, could be a mistake, brown and black band easy to mix up, or it could be intentional,

anyway, this 2275 tuner pulls in a lot of stations when spliced into the 2270 we are trying to fix,

0.04 volts on the source instead of 0.6 listed on the schemo, this translates into 4 ma drain current, which seems normal considering the graph we sketched,

so if you need a new front end for a 2270 project, consider the 2275 tuner.

there is a layout difference on this rev 0, the mixer transistor is kludged in under the board with caps and resistors mounted directly to the leads,

2275 FM.png
 
here is the H103 transistor difference, top pic is 2275, bottom 2270, and L106 is being inspcted, there is a dog bone cap inside L106, you can get those at Surplus Sales of Nebraska. They also have piston trimmer caps, (C106 on the tuner board, 5 to 15 pf IIRC)

this L106 had an open secondary which was fixed by a careful reheat. sometimes the enamel insl on the coil wire does not get burned off enuff,

we ran some current thru a 100 ohm resistor at 10 volts to get 10 ma thru the coil, mV readings were taken to get ohms of coil, 0.323 pri, 0.085 sec. this method mimics a Fluke 4 wire ohm meter that will set you back 2 grand.


tuner 2270vs2275.jpg
 
Last edited:
cjenrick said:
those fets are on evilbay from the UK,

sure would be nice to have a source like digikey

through hole fets in the FM range seem to be a dying breed, and expensive,

maybe it is time to move into the future,

what about this adapter?

it would seem to open up a plethora of new opportunities, or not.

that awaits to be determined in the real world, but what a fun experiment it would be to use surface mount parts in an antique receiver tuner,

yes i have soldered thin leads to surface mount parts for thru hole mounting but it looks kind of weird,

View attachment 1779734
Click to expand...
I did that. I think I made my own adapter out of pad per hole board.
 
You must log in or register to reply here.
Back
Top Bottom