Hi all,
I'm hoping someone could help me identify some of the mods/repair/band-aid on my newly acquired st-70.
Little history. I got the amp from Goodwill, sold as "has power but does not function" and as far as I can tell it's only missing the output tubes (I have not powered the amp in the current condition). It came with all the original paperwork including several printed emails and restoration documents that I was able to use to identify some of the mods, but with my limited knowledge and experience, I'm not able to tell if the mods were installed correctly and if I should keep them.
I'm trying to find out if the mods were installed correctly (good or bad) and if I should keep the modifications (keep or remove).
List of mods (could be more that I'm not seeing):
-Photo 1) Selenium rectifier replaced with silicon diode
-Photo 2) Speaker terminal modded
-Photo 3, 4) RCA input modded: Photo 3 - According to the included email, it's a 10,000 ohm resistor and .02 mf capacitor installed to both left and right channels. Photo 4 - According to the included email, it's a 1000 pf cap in parallel with each of the two 470,000 ohm resistors on the input switch. Note: The email also calls out to remove the four .1 mf caps from the board and replace with four 1mf caps which was not done. Should I complete this mod and replace the .1 mf with 1mf caps?
-Photo 5) Parallel capacitors on PC board - looks like the original .05 mf 400 v caps were replaced with .056 mf 200 v and later added a 1000 mf 400 v (not sure if I'm reading this right).
-Photo 6) Added 1.0 mf 1000 v capacitor on quad filter capacitor lug 1 to ground
-Photo 7) Added .056 mf 200 v capacitor on 7 lug terminal strip from lug 1 to 3 and replaced 50 mf bias caps with 100 mf 100 v caps
-Photo 8) Added .1 mf 600 v capacitor on back of PC board from eyelet 8 to 20
-Photo 9) Added .11 mf 600 v capacitor on back of PC board from eyelet 10 to 19
-Photo 10) Added .04? mf 600 v capacitor from quad filter cap lug 1 to main ground lug
-Photo 11) Front biaset socket modded, resisters and wire to eyelets 3 and 18 removed, Mono/Stereo switch is disconnected
Sorry for the long list and thank you in advance for any help identify any of mods.
I'm hoping someone could help me identify some of the mods/repair/band-aid on my newly acquired st-70.
Little history. I got the amp from Goodwill, sold as "has power but does not function" and as far as I can tell it's only missing the output tubes (I have not powered the amp in the current condition). It came with all the original paperwork including several printed emails and restoration documents that I was able to use to identify some of the mods, but with my limited knowledge and experience, I'm not able to tell if the mods were installed correctly and if I should keep them.
I'm trying to find out if the mods were installed correctly (good or bad) and if I should keep the modifications (keep or remove).
List of mods (could be more that I'm not seeing):
-Photo 1) Selenium rectifier replaced with silicon diode
-Photo 2) Speaker terminal modded
-Photo 3, 4) RCA input modded: Photo 3 - According to the included email, it's a 10,000 ohm resistor and .02 mf capacitor installed to both left and right channels. Photo 4 - According to the included email, it's a 1000 pf cap in parallel with each of the two 470,000 ohm resistors on the input switch. Note: The email also calls out to remove the four .1 mf caps from the board and replace with four 1mf caps which was not done. Should I complete this mod and replace the .1 mf with 1mf caps?
-Photo 5) Parallel capacitors on PC board - looks like the original .05 mf 400 v caps were replaced with .056 mf 200 v and later added a 1000 mf 400 v (not sure if I'm reading this right).
-Photo 6) Added 1.0 mf 1000 v capacitor on quad filter capacitor lug 1 to ground
-Photo 7) Added .056 mf 200 v capacitor on 7 lug terminal strip from lug 1 to 3 and replaced 50 mf bias caps with 100 mf 100 v caps
-Photo 8) Added .1 mf 600 v capacitor on back of PC board from eyelet 8 to 20
-Photo 9) Added .11 mf 600 v capacitor on back of PC board from eyelet 10 to 19
-Photo 10) Added .04? mf 600 v capacitor from quad filter cap lug 1 to main ground lug
-Photo 11) Front biaset socket modded, resisters and wire to eyelets 3 and 18 removed, Mono/Stereo switch is disconnected
Sorry for the long list and thank you in advance for any help identify any of mods.
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