I forgot to turn it off, it was working fine, left the room, when I returned 3 days later I found the 3 preamp tubes out with the power tubes at full glow. I have ask many times, are the tubes on a circuit that if the first in line goes will it cut the power to the others? I haven't received a straight answer yet. But now I'm presenting my problem to the SMART forum. Can I get your thoughts as to the possibility's. I have suspected the tube or tubes just finished their duty and quit but I really don't know and haven't dug into it except to pull the tubes to get them checked. (this is the embarrassing part) that was 5yr's ago.
And also is it possible to do some tube checking with a multi meter maybe just comparing the 3 to see if one is different than the others.
Thank you so very much in advance, Less Opinion
And also is it possible to do some tube checking with a multi meter maybe just comparing the 3 to see if one is different than the others.
Thank you so very much in advance, Less Opinion
V1 and V2 have DC heaters supplied through BR1 and from the same AC supply as the rest of the valves. Take a look at the service information.
I had a nice reply typed up last night, then this site went down for maintenance just as I was about to post it.
Your 6vAC powers the power tube heaters, so you know it is OK, the preamp tubes are heated by DC made from that 6vAC in BR1. So the first suspect is the bridge BR1 itself, or the solder to it. In my experience, the solder often did not wet the leads of the bridge when the amp was made. By removing the old solder, scrubbing the bridge leads, then resoldering it, I usually get voltage restored. At worst, a new bridge.
Your 6vAC powers the power tube heaters, so you know it is OK, the preamp tubes are heated by DC made from that 6vAC in BR1. So the first suspect is the bridge BR1 itself, or the solder to it. In my experience, the solder often did not wet the leads of the bridge when the amp was made. By removing the old solder, scrubbing the bridge leads, then resoldering it, I usually get voltage restored. At worst, a new bridge.
Enzo, JonSnellElectronic, thanks for the the help. I will ID the BR1 and check in to it. I should have 6v dc down stream of the BR1 to the tubes, if not it is most likely the connections or the BR1 it's self. I have heard that this amp has solder issues so that could very well be the issue. That's a place to start.
Again Thanks, Less opinion
Again Thanks, Less opinion
I have that amp, and it sounds like it could be the classic problem with BR1, which powers V1 to V3, but not V4 or the power tubes.
The board traces get very hot from the tubes, combined with not very good ventilation. then the BR1 adds its own local heat and melts its solder joints. Other traces may also be an issue and when you have it opened up, its a good idea to reflow all the joints. getting to the underside is a bit of a PITA though.
When you replace the BR, its best to set it up on longer legs about 1cm, and bolt a heatsink to the top,
its a good amp though, I've had mine for 9 years and really enjoy it. While you are in there, you might like to consider a few small mods to improve the loop, reverb and OD tones. Here what I did, including the BR1 fix:
DSL401 - loop, tone and heat mods - MarshallForum.com
The board traces get very hot from the tubes, combined with not very good ventilation. then the BR1 adds its own local heat and melts its solder joints. Other traces may also be an issue and when you have it opened up, its a good idea to reflow all the joints. getting to the underside is a bit of a PITA though.
When you replace the BR, its best to set it up on longer legs about 1cm, and bolt a heatsink to the top,
its a good amp though, I've had mine for 9 years and really enjoy it. While you are in there, you might like to consider a few small mods to improve the loop, reverb and OD tones. Here what I did, including the BR1 fix:
DSL401 - loop, tone and heat mods - MarshallForum.com
Remove the pcb from the chassis. That way you can work at the board without doing any damage.
Use a permanent marker to write the connector ID on the connector.
It saves you from inserting the wrong connector.
And as in post #5, use longer legs when you replace the diode bridge (who probably is dead) and a heatsink is no luxury..
To be sure no other problems lie between the bridge and the heaters,
Remove the bridge and connect a psu with about 6V to the heaters of the preamp tubes.
If all is well then they should glow.
Replace the new bridge and of you go (remove the 6v first...)
Use a permanent marker to write the connector ID on the connector.
It saves you from inserting the wrong connector.
And as in post #5, use longer legs when you replace the diode bridge (who probably is dead) and a heatsink is no luxury..
To be sure no other problems lie between the bridge and the heaters,
Remove the bridge and connect a psu with about 6V to the heaters of the preamp tubes.
If all is well then they should glow.
Replace the new bridge and of you go (remove the 6v first...)
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