Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Newtonyul on March 12, 2018, 10:27:25 am
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A bit long winded, sorry. So I picked up a use Blues Jr. Series III made roughly 2010-12. After a couple hours playing the tubes got good and warm and the amp started making static noise and some notes would trigger screaming feedback. Microphonic I'm guessing? I've had a Mesa single rec for almost 20 years with no problems and have been running a Peavey Classic 50 212 for a couple also with no issues so I really have had no issues or problems to draw experience from.
I pulled the back panel and started tapping tubes to chase the culprit. Pre-amp tubes no issue, 1st power tube no issue. 2nd power tube when I tapped it, it shorted internally (light up like a light bulb) and fried two traces on the tube PCB. Yay. Problem found. Dead amp unfortunately. Poking around a little i found that a bunch of the solder points on the second pwr tube socket had separated from the PCB.
Long story short I found this forum while searching for replacement parts. I've decided to go with the full meal deal turret board replacement to make this a point to point amp. I'm wondering what helpful hints and tips some of you more experienced builders and tweakers could offer a newbie to the world of amp tinkering. I'm a 15 year AME by trade (A and P Technician for you Americans) so I have pretty good mechanical skills. However I know from experience that there are things with any hobby that experienced people wished they knew when they started. Any thoughts and suggestions would be greatly appreciated.
Thanks in advance.
Cheers
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The tube socket pins soldered to the board on many amps made today, usually always need to be re-soldered to make a good solid connection. Being that tube amp PCB boards are put into a solder bath that barley applies enough solder to the components, it is a common practice to re-solder all tube socket pins to the PCB boards. Input jacks as well.
JMO, I wouldn't put a lot of money into a Blues Jr to repair it. I would repair the (few) scorched solder traces with a thin solid core wire and re-solder all the tube sockets on the PCB board. And only if the board does not have holes burned through the board itself. Use a small wire brush to remove any carbon burn traces on the board first and then clean it with alcohol.
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Thx for your input. I was more thinking that it might be a fun project to end up with a unique amp after all is said and done. You're definitely right it's a bit expensive. At the least I would prefer to replace the tube board with a new board that has proper tube sockets so I don't have to worry about solder points cracking when replacing tubes. Or based on observations, cracking if you look at it funny. Definitely not a robust design.
Cheers
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Actually, that amp would be the perfect amp for you to learn on by rebuilding and using a board. You may have to modify the chassis for bolt on tube sockets.
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That's my thinking on the whole deal. Rotted the amp went down but not like it was a 4 figure amp. I've got a pretty extensive background in aircraft sheet metal work so chassis modification doesn't intimidate me. Looking through the parts list for the rebuild, the tube board appears to be a direct drop in replacement with the bolt in sockets mounted and soldered with the exception of splitting the ribbon connectors from the mains PCB to the tube board. There's always the potential for further requirements with whatever you get into I guess.
Cheers
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A bit long winded, sorry. So I picked up a use Blues Jr. Series III made roughly 2010-12. After a couple hours playing the tubes got good and warm and the amp started making static noise and some notes would trigger screaming feedback. Microphonic I'm guessing? I've had a Mesa single rec for almost 20 years with no problems and have been running a Peavey Classic 50 212 for a couple also with no issues so I really have had no issues or problems to draw experience from.
I pulled the back panel and started tapping tubes to chase the culprit. Pre-amp tubes no issue, 1st power tube no issue. 2nd power tube when I tapped it, it shorted internally (light up like a light bulb) and fried two traces on the tube PCB. Yay. Problem found. Dead amp unfortunately. Poking around a little i found that a bunch of the solder points on the second pwr tube socket had separated from the PCB.
Long story short I found this forum while searching for replacement parts. I've decided to go with the full meal deal turret board replacement to make this a point to point amp. I'm wondering what helpful hints and tips some of you more experienced builders and tweakers could offer a newbie to the world of amp tinkering. I'm a 15 year AME by trade (A and P Technician for you Americans) so I have pretty good mechanical skills. However I know from experience that there are things with any hobby that experienced people wished they knew when they started. Any thoughts and suggestions would be greatly appreciated.
Thanks in advance.
Cheers
That is a great move to get away from the PCB and get into a world where you can actually build fantastic amps from scratch.
I did a very similar thing but designed my own BJ chassis, and then proceeded with the build, which was a great experience but very frustrating. The amp was ok but it wasn't solid.
I came back a short while later and went at it again and re-used the Bjr Chassis and custom cabinet for a 6 v 6 Plexi. I was much more sucessful after studying and discussing grounding with some of the members here.
That style of chassis and cabinet are a little tough to work with, but not prohibitive. You will see after a while what you like and dislike about that vertical chassis style.
Its all a great puzzle! Share photos please