I recently blew the fuse and 5Y3 rectifier tube on my LSS 4x10 combo, a problem described in other threads and related to running in 15w and 5w modes. Here's a PDF of Mesa's "5Y3 Mod" which "Reduces likelihood of premature or frequent 5Y3 rectifier tube failure, and subsequent loss of operation in 5 & 15-watt power modes." https://www.dropbox.com/s/szkgy7ggwm5jpa9/Lone Star Special - 5Y3 Mod.pdf?dl=0
Lone Star Special - 5Y3 Mod
- Thread starter Moxie
- Start date
Help Support The Boogie Board:
Howdy - I live "in the middle of nowhere" Wyoming - no close by Mesa authorized techs, etc. However - I've built a few Marshall and Fender clones. This looks fairly straight forward. Did you do your own 5Y3 mod? If so, is there anything to watch out for (other than properly draining filter caps and the usual safety precautions)? Mine is way out of warranty by now - I think I can do this without any problems. Thanks much.
- Joined
- Oct 8, 2018
- Messages
- 670
- Reaction score
- 336
Yea there's a number of posts WRT issue. When I picked up my LSS there were fried resistors in the rect circuit and I chose to replace them with NOS higher wattage ones. Have not had an issue since. The root cause was the a change in the Rect tubes specs that came on the market after they had begun production. IIRC there was a mod they did to the circuit in order to reduce the circuit current and allow a wider range of rect tubes.
It's not a difficult component swap.
It's not a difficult component swap.
- Joined
- Oct 8, 2018
- Messages
- 670
- Reaction score
- 336
I dug up the notes on this. Found 3 cracked resistors when the chassis was removed for inspection. Also was experiencing intermittent cracking sounds and the sound was cutting out. These are found in the power amp section.
Two of the 100ohm R100 & R102, and R104 68ohms were cracked. The 470ohm, R101 & R103 were visually ok |
replaced R104 with a 68ohm 2W Allen Bradley NOS carbon resistor |
replaced R100, R102 with 100ohm 2 W, R101, R103 with 470ohm 2W |
tbonesullivan
Well-known member
I better look into this. I have a 36** Lone Star Special, so chances are it's still in the OG configuration. I think it probably still has the original Tubes in it though, so maybe as long as I don't change out the 5Y3?
I mean, right now I can get some NOS JAN 5Y3s for not much more than the cost of a new one from Mesa...
I mean, right now I can get some NOS JAN 5Y3s for not much more than the cost of a new one from Mesa...
Last edited:
I spoke to Mesa yesterday. This is probably old news to some, but it was new to me. The 5Y3 is for 15 and 5 watt settings. As for 30, I believe it's diode rectified and will work without the tube. I told him this explains why mine wouldn't work on 15 or 5, but worked fine on 30. He mentioned the mod to save rectifier tubes thats covered in this thread. It's a free update - just have to get it to an authorized tech, etc. But - you may/may not need the mod. He said that the problem was based in part on tubes they were installing at the time - that they couldn't handle whatever this amp was doing. He said that later manufactured rectifier tubes did not have this issue and he said JJ tubes, for example, could handle the extra load. So, I told him I'd run the JJ 5Y3 and see how it holds up for now. He said not all amps needed it, etc. Well, I suppose if he's correct on the tubes being factor, then that makes sense. As for original tubes for you - it just depends I suppose. Mine must have had one of the suspect 5Y3's - "Mesa" branded. I selected 5 watts for practice volume and it wouldn't work. As long as you are running good - you're probably OK. It's a personal choice perhaps on the mod. If I were gigging and running it for a few hours, I'd go ahead and get the mod which reduces stress on the rectifier tube. Since I don't live anywhere near a Mesa tech and I can't justify the cost of shipping, if I go with the mod I'll do it myself. I have a background in electronics and feel more than comfortable doing this. Hopefully this helps. Maybe give them a call. I spoke to Chris - great guy. he didnt try to rush the call or anything - he took time to answer my questions and explain how it all worked. Good luck.
- Joined
- Oct 8, 2018
- Messages
- 670
- Reaction score
- 336
Yea mine is in the 18xx range... I'd suspect you should be able to tell if those resistors were getting warm with a nice brown tinted outline on the PCB.
tbonesullivan
Well-known member
Next time I have it out I definitely will be pulling the chassis to check. Though getting some NOS 5Y3s is definitely a good idea when they are cheap like this. JAN tubes are as close to bulletproof as they get, and shouldn't have any issues.Yea mine is in the 18xx range... I'd suspect you should be able to tell if those resistors were getting warm with a nice brown tinted outline on the PCB.
I picked up a bunch of NOS 5U4GBs for $25 a pop pre-pandemic, so my other amps with rectifiers are set for a while.
