Marshall Class 5 woes

Ok, here's the story. I picked up a sweet cream colored class 5 a few months ago on ebay and fell in love with the awesome warmth and grit of this little sweetheart, but the other day it snap crackle and popped a bit and then went quiet.

Hmm, power tube blew right?

Replaced the el84 and ... nothing.

I popped the top and saw that the one fuse was blown a T125mA L250V fuse to be exact. I replaced it with a series of 4 T125 250v fuses that blew on startup. I put a T315 250v in there and it powered up, but with some popping.

I checked the rectifier diodes and they all seem to be fine.

So, fuse problem or something else?

Take the valves out and power it up. If the fuse still blows you have a problem. If not then it's one of the valves.

I'll give that a shot today. I just replaced all of the tubes before this started because the power tube actually had gone bad and I wanted different preamp tubes in there. I tried it with 2 separate new power tubes and the fuse blew either way.

Alright, no tubes and the fuse still blew.

Before I dig in too hard let me ask a question. There was an "L" in the original fuse code that was not in the replacements I bought. Could that make a difference?

I moved recently and I'm hoping that the trip didn't cause a cold solder joint to crack or something like that. Well, actually that would be an easy fix but a PITA to track down.

If this gets messy I'm thinking about gutting it and building either a point to point class 5 an 18 watt lite or an ax84 P1

If this gets messy I'm thinking about gutting it and building either a point to point class 5 an 18 watt lite or an ax84 P1

I like this idea!!!!!!! That's a pretty snazzy cabinet :).

If this gets messy I'm thinking about gutting it and building either a point to point class 5 an 18 watt lite or an ax84 P1

+1

I blew away a Marshall Class5 with an ampmaker SE-5a....not much room in there for an 18 watter. But anything you build will be an improvement on that SS/tube hybrid :wink:

Mine is actually the second version with the transformers mounted outside of the chassis and the tubes mounted down from the chassis, so there's plenty of room in there.

I really liked the tone of the class 5 and I would prefer to resurrect it in some way close to the original design, but an 18 watt lite would be a close second.

I saw someone rebuild a class 5 point to point with the original schematic and that seems like a viable solution

Alright, no tubes and the fuse still blew.

Before I dig in too hard let me ask a question. There was an "L" in the original fuse code that was not in the replacements I bought. Could that make a difference?

I moved recently and I'm hoping that the trip didn't cause a cold solder joint to crack or something like that. Well, actually that would be an easy fix but a PITA to track down.

If this gets messy I'm thinking about gutting it and building either a point to point class 5 an 18 watt lite or an ax84 P1

I believe the "L" code is for long delay, as in a Slo-Blow fuse, I think, and yes, there is a difference.

I thought that's what the "T" was for

Wait... You're Mike Argento? Like York Daily Record Mike Argento?

If so, I grew up in York and I used to read your column all the time.

Wait... You're Mike Argento? Like York Daily Record Mike Argento?

If so, I grew up in York and I used to read your column all the time.

Yep, that's me. I'm still writing the column and have published a novel. Small world.

And I may be wrong about that fuse code.

I'll check into it, and I'll have to check out that novel as well!

I recently flipped a Blackheart 5 into a Class 5-ish build. That chassis has enough room, although I had to make a separate board for power filter diodes for the HT supply and a DC supply for the 12AX7s and mount it on the side.

http://i1117.photobucket.com/albums/k597/Craigars/CraigarAmps/5amp01.jpg

If the BH-5 and Marshall have about the same size pan, you should be OK space-wise to do either Class 5 or 18wLiteII.

FWIW, if you're trying to fix the Class 5 and not gut and rebuild, have you tried checking the PT and OT for shorts?

Craig that looks really nice! Do u have a link to the class 5 schem? I didn't see one.

That's a nice tight build there!

Update on my class 5

I was tire of poking around making guesses so I pulled the chassis today and pulled all of the boards out looking for problems. The solder joints all looked pretty sound visually, but being that we just moved (bouncing around in the back of the truck) and I just switched tubes I re-flowed all of the solder joints on the tube sockets to be sure. I also fixed some dodgy looking solder joints on the rectifier diodes. Which seems to have done the trick.

When I tested the diodes from the top of the board for continuity they all tested fine, but I think it must have been a bad joint on the bottom causing problems with the rectifier. I was probably running too much voltage for the old el84 which died, and popping fuses like a champ. (not the 5f1 kind!)

Temporarily I have a 315mA fuse in there to test it while I source some more 125mA fuses which seem to be next to impossible to lay my hands on locally.

Anyway, sounds great again. I'm really waiting for new fuses before I put it through the paces in any serious way.


I still may look into building an 18watt or ax84 amp for kicks. Who makes a good 18lite kit?

Craig that looks really nice! Do u have a link to the class 5 schem? I didn't see one.

THanks, I'll have to see if I can find that link. Hopefully it hasn't been taken down!

That's a nice tight build there!

Update on my class 5

I was tire of poking around making guesses so I pulled the chassis today and pulled all of the boards out looking for problems. The solder joints all looked pretty sound visually, but being that we just moved (bouncing around in the back of the truck) and I just switched tubes I re-flowed all of the solder joints on the tube sockets to be sure. I also fixed some dodgy looking solder joints on the rectifier diodes. Which seems to have done the trick.

When I tested the diodes from the top of the board for continuity they all tested fine, but I think it must have been a bad joint on the bottom causing problems with the rectifier. I was probably running too much voltage for the old el84 which died, and popping fuses like a champ. (not the 5f1 kind!)

Temporarily I have a 315mA fuse in there to test it while I source some more 125mA fuses which seem to be next to impossible to lay my hands on locally.

Anyway, sounds great again. I'm really waiting for new fuses before I put it through the paces in any serious way.


I still may look into building an 18watt or ax84 amp for kicks. Who makes a good 18lite kit?

Awesome! Glad you got it going again. I'm not sure about the Lite versions, but replica 18w kits are all over the internet. I like to do my builds from scratch, so I'm not up on who's got the best bang for the buck. Offhand, I don't know if Boothill offers an 18w, but the 5F1 and 5E3 kits look damn nice!