You have to ensure the red black wire is connected to the negative (banded) diode lead. This can be a direct connection vs using the circuit board. As you mention it’s surgery to repair or bypass a trace on a pcb. You may not be able to use that connection. So maybe you can solder directly to the diode lead… If you look at the schematic for the board you can see the circuit.
+4
markeby
LeGrace
peterh
Jlskey
8 posters
VTA ST 120 needs surgery!
Rec- Posts : 77
Join date : 2020-03-11
Jlskey- Posts : 18
Join date : 2022-04-07
Rec wrote:You have to ensure the red black wire is connected to the negative (banded) diode lead. This can be a direct connection vs using the circuit board. As you mention it’s surgery to repair or bypass a trace on a pcb. You may not be able to use that connection. So maybe you can solder directly to the diode lead… If you look at the schematic for the board you can see the circuit.
Fantastic! The proximity of that eyelet to the diode made me wonder if maybe, just maybe, that was a possibility. I’ll do that connection when I pull it out this evening.
Bob Latino- Admin
- Posts : 3277
Join date : 2008-11-26
Location : Massachusetts
Jlskey wrote:
Thank you Mr Latino. When performing said voltage check are any of the tubes in?
Second, is it a problem that I seemed to dislodge the metal coating on the eyelet where the red/black wire connects to the pcb board?
You can have the tubes either in or out. I might remove the rectifier tube first though so that you won't have any high voltage running when you do the test. You should have (again) about 55 volts AC where the red/black wire connects to the driver board to chassis ground and about -75 volts DC to ground from the other side of the diode (the non-banded side) to chassis ground.
Bob
Jlskey- Posts : 18
Join date : 2022-04-07
Thanks to everyone who aided me with a variety of great suggestions.
I got amp up and running yesterday and it sounded great. Alas, this morning when I powered it on, the front right channel power tube did not light up. I promptly shut down the unit. Some things to note:
- when setting the bias on the right channel there was slight crackling in the speaker. It almost seemed like it coincided with the movement/initial placement of the red probe of my multimeter. This DID NOT continue while I was listening to some good vinyl;
-After powering off the amp I heard the normal, slight noises that the tubes make as they are powering off. However I additionally Noted that it seemed like I heard one or two about ten to fifteen minutes after the amp was turned off which is unusual based on past performance. Normally ten to fifteen minutes after powering off those little residual noises are done.
-The amp worked for an hour. Only got turned off as it was bed time
- this AM the only issue was the power tube did not illuminate. No red plating, no arching. I didn’t try to play anything because at that point my goal was to avoid a light show if that’s the way it was heading. Is it possible the tube, just that tube would crap out so quickly?
I still need to clean up some solder joints on the 80lug of the quad cap (I’ll save that for another post) but It’s not like I wasn’t going to put the baby back on the work bench right away. I was hoping to get at least a few weeks of listening out of it before an issue arose. Any advice, no matter how obvious to you, is quite appreciated by this relative newbie.
Some things I’m
Thinking of doing from
This point
-opening her back up and checking the solder connections and pin connections for the socket in question;
-maybe even retention the pins;
-look at the connections to the driver board from this socket
-see if I missed any stray pieces of wire snipped that may be creating a short.
Again any help is appreciated, nothing is too simple!
I got amp up and running yesterday and it sounded great. Alas, this morning when I powered it on, the front right channel power tube did not light up. I promptly shut down the unit. Some things to note:
- when setting the bias on the right channel there was slight crackling in the speaker. It almost seemed like it coincided with the movement/initial placement of the red probe of my multimeter. This DID NOT continue while I was listening to some good vinyl;
-After powering off the amp I heard the normal, slight noises that the tubes make as they are powering off. However I additionally Noted that it seemed like I heard one or two about ten to fifteen minutes after the amp was turned off which is unusual based on past performance. Normally ten to fifteen minutes after powering off those little residual noises are done.
-The amp worked for an hour. Only got turned off as it was bed time
- this AM the only issue was the power tube did not illuminate. No red plating, no arching. I didn’t try to play anything because at that point my goal was to avoid a light show if that’s the way it was heading. Is it possible the tube, just that tube would crap out so quickly?
I still need to clean up some solder joints on the 80lug of the quad cap (I’ll save that for another post) but It’s not like I wasn’t going to put the baby back on the work bench right away. I was hoping to get at least a few weeks of listening out of it before an issue arose. Any advice, no matter how obvious to you, is quite appreciated by this relative newbie.
Some things I’m
Thinking of doing from
This point
-opening her back up and checking the solder connections and pin connections for the socket in question;
-maybe even retention the pins;
-look at the connections to the driver board from this socket
-see if I missed any stray pieces of wire snipped that may be creating a short.
Again any help is appreciated, nothing is too simple!
Jlskey- Posts : 18
Join date : 2022-04-07
Got off of work and while I didn’t feel like really working on the old girl, I thought I’d try a minor move. Ended up switching the right channel tubes put the non functioning right front tube in the back and the functioning one in the front. Powered her up and to my surprise: the tube that was in the front that got moved to the back still wouldn’t light! The one that had been in the back and was placed in the front was lighting up! I did note a little popping/static in the right speaker. What do you all think? Bad tube combined w some cold joints causing the static?