Hello to everyone, I have a problem with my SA-606 (SA-6700 version for Europe): There is an hiss similar to white noise through the headphone output.
In the past I did some maintenance:
1) Recapping - used Nichicon "audio grade" KA series (light blue sleeve) for everything but main filters (replaced with 2 8200uF Cornell Dubilier CDE 63v 105°C).
For bipolars, capacities under 2,2uF and 2 CSZA tantalum I used WIMA MKS2 film caps.
2) Cleaned everything, in particular the old thermal paste between power transistors - mica - heatsink was replaced with Arctic MX-4 thermal grease.
3) Replaced original burnt lamps with some from ebay (incandescent, not LED) rated for the same specs of the original ones.
Recently I noted this problem and proceded to replace 45 year old transistors with onsemi ones from Mouser:
Board: GWK-111 AF Assembly
Q3 - Q4: 2x 2SC1312 -- 2x KSC1845FTA
Q5 - Q6: 2x 2SA798 -- 4x KSA992FBU matched Hfe pair and thermally coupled
Q7 - Q8: 2x 2SC1885 -- 2x KSC2383YTA
Q9 - Q10: 2x 2SA912 -- 2x KSA1013YBU
Q15: 1x 2SB507 -- 1x KSA1010YTU
Q16: 1x 2SA720 -- 1x KSA1013YBU
Q17: 1x 2SC1318 -- 1x KSC2383YTA
Q18: 1x 2SC945A -- KSC2383YTA
Q19: 1x 2SA904A -- KSA992FBU
Q20: 1x 2SC1914A -- KSC1845FTA
Q11 - Q12 - Q13 - Q14 driver and power transistors were left untouched
Board: AWX-136 Tone and Indicator Assembly
Q1 - Q2: 2x 2SA720 -- 2x KSA1013YBU
Q3: 1x 2SA850 -- 1x KSA1013YBU
I also replaced on GWK-111:
R100 - R101 - R123 (62ohm - 2W) -- 3x 594-5083NW62R00J metal film (62ohm - 2W)
R110 - R111 (0.5ohm - 2W) -- 2x 71-RW80UR500F wirewound (0.5ohm - 2W)
R71 - R72 - R73 - R74 (0.5ohm - 5W) -- 4x 71-RS005R5000FE73 wirewound (0.5ohm - 5W)
R67 - R68 - R69 - R70 (4.7ohm - 0.5W) -- 4x 594-NFR25H0004708JA5 metal film (4.7ohm - 0.5W)
Everything else is original.
Bias is within range (10mV to 70mV range, mine hovers at 50mV) and I have 12mV DC voltage on speaker output.
After this the hiss was less audible but is still there, even when volume is at 0. Strangely it increases up to 4, then decreases up to 6 the increases again till 10.
I also discovered that if I set treble pot to max (5) the hiss increases considerably.
My headphones are: Sony MDR.7506 (32ohm) and Sony WH-1000XM4 (47ohm when wired).
Can somebody shed a light on this?
In the past I did some maintenance:
1) Recapping - used Nichicon "audio grade" KA series (light blue sleeve) for everything but main filters (replaced with 2 8200uF Cornell Dubilier CDE 63v 105°C).
For bipolars, capacities under 2,2uF and 2 CSZA tantalum I used WIMA MKS2 film caps.
2) Cleaned everything, in particular the old thermal paste between power transistors - mica - heatsink was replaced with Arctic MX-4 thermal grease.
3) Replaced original burnt lamps with some from ebay (incandescent, not LED) rated for the same specs of the original ones.
Recently I noted this problem and proceded to replace 45 year old transistors with onsemi ones from Mouser:
Board: GWK-111 AF Assembly
Q3 - Q4: 2x 2SC1312 -- 2x KSC1845FTA
Q5 - Q6: 2x 2SA798 -- 4x KSA992FBU matched Hfe pair and thermally coupled
Q7 - Q8: 2x 2SC1885 -- 2x KSC2383YTA
Q9 - Q10: 2x 2SA912 -- 2x KSA1013YBU
Q15: 1x 2SB507 -- 1x KSA1010YTU
Q16: 1x 2SA720 -- 1x KSA1013YBU
Q17: 1x 2SC1318 -- 1x KSC2383YTA
Q18: 1x 2SC945A -- KSC2383YTA
Q19: 1x 2SA904A -- KSA992FBU
Q20: 1x 2SC1914A -- KSC1845FTA
Q11 - Q12 - Q13 - Q14 driver and power transistors were left untouched
Board: AWX-136 Tone and Indicator Assembly
Q1 - Q2: 2x 2SA720 -- 2x KSA1013YBU
Q3: 1x 2SA850 -- 1x KSA1013YBU
I also replaced on GWK-111:
R100 - R101 - R123 (62ohm - 2W) -- 3x 594-5083NW62R00J metal film (62ohm - 2W)
R110 - R111 (0.5ohm - 2W) -- 2x 71-RW80UR500F wirewound (0.5ohm - 2W)
R71 - R72 - R73 - R74 (0.5ohm - 5W) -- 4x 71-RS005R5000FE73 wirewound (0.5ohm - 5W)
R67 - R68 - R69 - R70 (4.7ohm - 0.5W) -- 4x 594-NFR25H0004708JA5 metal film (4.7ohm - 0.5W)
Everything else is original.
Bias is within range (10mV to 70mV range, mine hovers at 50mV) and I have 12mV DC voltage on speaker output.
After this the hiss was less audible but is still there, even when volume is at 0. Strangely it increases up to 4, then decreases up to 6 the increases again till 10.
I also discovered that if I set treble pot to max (5) the hiss increases considerably.
My headphones are: Sony MDR.7506 (32ohm) and Sony WH-1000XM4 (47ohm when wired).
Can somebody shed a light on this?