Marshall Mosfet model 3210

[Billy R aka DynaFreak]

Quick question. I am fixing a Marshall Model 3210 that came with the 2SJ49/2SK134 outputs, which are blown, along with their emitter resistors. Bridge rectifier was also blown, and has been replaced. Is there any reason not to go ahead and carefully power up the amp with the blown Mosfets removed from the circuit so I can check the power supply and preamp functioning before ordering a suitable replacement for the obsolete mosfets? I have variac, current meter, all that stuff, I just don't do much mosfet amp repair and am concerned about possible damage to parts associated with mosfets and drivers during power-up.

PS: looks to me like the ECF10N16 ECF10P16 EXICON SET is the best currently available replacement. Are these truly drop-in replacements?



thanks,

DynaFreak

[Jazz P Bass]

Seeing that the mosfet gate is voltage driven, I would not think there would be any harm in firing it up to check the rest of the amp.

[olddawg]

I realize it is totally subjective, but before you put money and time into this amp. I might suggest that you do a little looking on EBay. Working examples sell for around $125 and they are considered problematic. I watch for them dead locally to reuse the cabinets.

[J M Fahey]

Yes, the Exicons are great.
There even is a double-die version (2 transistors inside the same case) which is incredibly robust. (Check their site).
Wouldn't hurt to spend a few bucks extra and improve reliability big time.

[Billy R aka DynaFreak]

thanks, guys. I was able to power it up with the outputs removed and trace signal through the amp, find a bad transistor in the PA front end, and generally confirm that the rest of the amp is OK. Based on that, I ordered the ECF10N16 ECF10P16 EXICON SET.

I agree the amp is not worth much even repaired. But I am in the business of repairing amps and when the customer asks me to repair an amp I tend to say OK. This one has the light brown grill cloth which is probably my favorite Marshall "look" from that era.

[olddawg]

thanks, guys. I was able to power it up with the outputs removed and trace signal through the amp, find a bad transistor in the PA front end, and generally confirm that the rest of the amp is OK. Based on that, I ordered the ECF10N16 ECF10P16 EXICON SET.

I agree the amp is not worth much even repaired. But I am in the business of repairing amps and when the customer asks me to repair an amp I tend to say OK. This one has the light brown grill cloth which is probably my favorite Marshall "look" from that era.

Yeah...if someone wants to pay to get it fixed, you do it. The problem is it staying fixed. The schematic says it will take a 4 ohm (even a 2 if I remember correctly), but they were originally sold with one or two 16 ohm cabinets. If the customer cranks it with a 4 ohm load it will be back blown again. Marshall expected a lot out of 2 transistors on that heat sink for that model. Make sure you cook for a while it on a load bank before you send it out and check his cabinets and cables. They also have weird controls that work differently if you have the foot switch. The customer may be confused as to how it works if he got it non-working. I know because I have one. The chassis is on a shelf in a cardboard box now. I built an 18 watt clone in the head box. People always ask me what year my red Plexi is, lol. Looks good with the matching 1965A cab. I paid $100 for both working.

[Enzo]

Will it stay fixed? Amen to that.

For that reason we quit taking in Marshall Mode4 amps a long time ago. I could fix one, but I refuse to put my name on the repair. If it blows up a week later, they'd be bringing it back to me and complaining. Not worth the hassle.

[jamesmafyew]

I certainly feel the same way as Enzo about the Mode4. But the 3210 I toured with for years. I blew the outputs and the rectifier early on, just like everyone else. I replaced the rectifier with a huge 8A bridge, bolted to the chassis for heat dissipation, and the outputs with Magnatec BUZ-series which were significantly overrated for the job. It was a reasonably cheap repair. It drove a 4-ohm 4x12 at enormous volumes for several years on the road, before I sold it. I know the guy who has it now and it's still doing fine.

Anyway, I really do think that it can work reliably cranked with a 4-ohm load, IF the outputs and rectifier are replaced. Get those Hitachi MOSFETs out of there and sell them on Ebay, and you might even come out ahead.

[Just Mike]

Reviving an old thread...I picked up one of these from an old retired repair tech who had a stroke and was retired. He said the output devices were bad and he had checked voltages and was "pretty sure" the rest of the circuitry was OK. So I replaced the outputs with the above mentioned Exicon set and it fires up, but I hear a "motorboating" sound even with all knobs turned down. Any ideas?

[drewl]

Check for a bad filter cap connection or some other bad pc board connection or cracked solder joint.

[Jazz P Bass]

When you check the voltages on the capacitors, flip your meter to read Volts ac.
In most instances, a high ripple (which is Vac) will tell you that a capacitor is bad.

[moozikaldood]

I know this is an old thread, but I have this amplifier and would love to do the the same mods that you're explaining here. I just have a question reguarding where to find the parts used that you mentioned. I can find 8A bridge rectifiers, but nothing bigger than what is already in the amplifer, and cetainly nothing big enough to bolt to the chassis. Also, Magnatec BUZ-series mosfets, if you could list the parts used, (including any resistors or caps you may have upgraded) it would be most appreciated. Thanks!

I certainly feel the same way as Enzo about the Mode4. But the 3210 I toured with for years. I blew the outputs and the rectifier early on, just like everyone else. I replaced the rectifier with a huge 8A bridge, bolted to the chassis for heat dissipation, and the outputs with Magnatec BUZ-series which were significantly overrated for the job. It was a reasonably cheap repair. It drove a 4-ohm 4x12 at enormous volumes for several years on the road, before I sold it. I know the guy who has it now and it's still doing fine.

Anyway, I really do think that it can work reliably cranked with a 4-ohm load, IF the outputs and rectifier are replaced. Get those Hitachi MOSFETs out of there and sell them on Ebay, and you might even come out ahead.

[J M Fahey]

Not sure about the Magnatecs, but the Exicon are available.
And there's a "double die" version, 2 transistor chips inside a single case, which is even stronger.
The rest of the circuit values should be the original ones, the Exicons are compatible with the original ones.
Anyway start the amp plugged into a series lamp limiter for safety until you are happy that everything is fine.
As of the chassis mount rectifier, you can go higher than 8A capability if you wish, it won't hurt.
Post a couple pictures of the heatsink area, maybe we can suggest some bolt-on add on , a fan, a window, anything to improve cooling.
Good luck.

[moozikaldood]

Thank you! Question though, It seems that everyone here who has replaced the mosfets after they've blown, end up having to replace the rectifier and the emitter resistors. That has not happened yet for my amp, but am cuirous as to how well the double die Exicons will work with the original rectifier. I'm hoping the mosfets are all I need. I honestly don't need to be pushing a 4 ohm load at enormous volumes, 8 ohms will do just nicely, and I'll be lucky to crack that volume past 4-5, 100 watts in british terms is quite loud indeed.
Thanks again.

[J M Fahey]

Double die Mosfets does not mean they will *pull* more current than before, but that they will be stronger and harder to kill.
Current depends only on the load applied, i.e. 4 ohms vs 8 ohms. (given that the power supply is always thge same, which is the case).

As of a larger bridge rectifier, browse the (huge) catalog at Mouser.