Pioneer SX-20A - UK Vintage Radio Repair and Restoration Discussion Forum

g0hze snowy · 15th Oct 2025, 7:38 pm

I have recently acquired the above amp, D.O.A as sold.
initial visual inspection revealed R317L (100ohm) cooked, its in the collector feed to 2sd2390y, shorted, so its pnp partner 2sb1560 also changed as o/c collector to emitter.
Found O/C on one side of R510L, these are twin 0.27ohm 5watt in single package, can i substitute 2 of the correct value, just commoning up the legs as i dont seem to be able to find the replacements.
Then looked at C310l (100mf @ 80vw) way out of spec. I was going to change the 3.8v zener, nearest value i can get is 3.9v, would be ok?
As always your advice valued, TIA.

Diabolical Artificer · 16th Oct 2025, 12:54 pm

Quote:

can i substitute 2 of the correct value, just commoning up the legs

Yes, better if you use two cement packages thermally joined. I have two 0.22r double resistors if any use.

Quote:

I was going to change the 3.8v zener, nearest value i can get is 3.9v, would be ok?

Should be ok zeners are never bang on as the current & temperature they operate at changes the voltage.

Andy.

g0hze snowy · 16th Oct 2025, 1:32 pm

Andy
Thanks for your offering, i am unable to find the OEM twin resistor (0.27ohm 5watt) as fitted anywhere on any of the usual sites.
Ok on the zeners, i didn't think that they would be a problem, i would change both left and right channels, they test out as diodes ok but i was doing a belt and braces job on the equipment, whilst it was apart.
watch this space as they say.

John_BS · 19th Oct 2025, 1:16 pm

1. Individual 0R27 resistors fine
2. Zeners are there to act as back-stop current limiters for the ouput darlingtons. I'd sugguest using 3V6 as that's what the schematic device coding suggests ?
3. C310 value is non-critical and anything from 10 to 100uF @ >10V fine.
John

g0hze snowy · 19th Oct 2025, 6:51 pm

Ok John, the resistors arrived yesterday, so tomorrow i will fit them.
Ok on the zeners i was foolish! enough to buy a box with many values in, 3.6v are in there.
Thanks for your input.
I can always rely on sound, pun intended, from the members on this site.

15th Oct 2025, 7:38 pm	#1
g0hze snowy Hexode Join Date: Oct 2013 Location: Peterborough, Cambridgeshire, UK. Posts: 396	Pioneer SX-20A I have recently acquired the above amp, D.O.A as sold. initial visual inspection revealed R317L (100ohm) cooked, its in the collector feed to 2sd2390y, shorted, so its pnp partner 2sb1560 also changed as o/c collector to emitter. Found O/C on one side of R510L, these are twin 0.27ohm 5watt in single package, can i substitute 2 of the correct value, just commoning up the legs as i dont seem to be able to find the replacements. Then looked at C310l (100mf @ 80vw) way out of spec. I was going to change the 3.8v zener, nearest value i can get is 3.9v, would be ok? As always your advice valued, TIA.

16th Oct 2025, 1:32 pm	#3
g0hze snowy Hexode Join Date: Oct 2013 Location: Peterborough, Cambridgeshire, UK. Posts: 396	Re: pioneer sx-20a Andy Thanks for your offering, i am unable to find the OEM twin resistor (0.27ohm 5watt) as fitted anywhere on any of the usual sites. Ok on the zeners, i didn't think that they would be a problem, i would change both left and right channels, they test out as diodes ok but i was doing a belt and braces job on the equipment, whilst it was apart. watch this space as they say.

19th Oct 2025, 1:16 pm	#4
John_BS Octode Join Date: Dec 2008 Location: Wincanton, Somerset, UK. Posts: 1,932	Re: Pioneer SX-20A 1. Individual 0R27 resistors fine 2. Zeners are there to act as back-stop current limiters for the ouput darlingtons. I'd sugguest using 3V6 as that's what the schematic device coding suggests ? 3. C310 value is non-critical and anything from 10 to 100uF @ >10V fine. John __________________ When you don't know what you are doing, do it neatly.

19th Oct 2025, 6:51 pm	#5
g0hze snowy Hexode Join Date: Oct 2013 Location: Peterborough, Cambridgeshire, UK. Posts: 396	Re: Pioneer SX-20A Ok John, the resistors arrived yesterday, so tomorrow i will fit them. Ok on the zeners i was foolish! enough to buy a box with many values in, 3.6v are in there. Thanks for your input. I can always rely on sound, pun intended, from the members on this site.