Marshall JTM 60 filter cap and Bridge rectifier advice

[Smitty02]

Hi guys ....I have a JTM60 310 version with typical JTM60 issues blown rec dry joints and crappy caps... I made a bridge rec from some 1n4007's that got my preamp tubes up again, amp plays but has heat damage and I want to do a cap job while I got it apart as one filter cap is all dented up and the heat they take from the tubes yes someone has been in here before but I just see several touched up joints. The power tubes show flux I assume from the heat these generate plus he changed the tubes and didnt rebias.... all the pretube joints look dry dull and week. I want to remove all the old solder and redo them as one needs to be replaced, the PI socket has heat damage, possibly from the meltdown when it gave out and blew the filament fuse?? either way I am going to replace as i got some crackle and popping nothing major though but noticeable.. So the million dollar questions are, and yes Ive read alot of post about this but would like fresh opinions..the 47uf 550v 85 degree filter caps.. I found some 56uf 500v 105 degree that I want to use as they will fit perfect actually a little shorter than the 550v's. They are Nichcon's from Digikey will this be a ok move, or is bumping them up to 56uf going to be a bad move?? I see many posts of guys using 500v's sucessfully but no post saying they crapped out I did find the right part # for the original Marshall replacements but was told it would be a 4-8 week wait by AES, the guy needs it asap....So do you think using 56uf 500v filter caps is a bad idea .... and should I go to a oem rated replacement bridge rec and pull my homemade BR. I have seen opinions that the oem bridge rec is to small.. Thanks guys

[g1]

As far as the filter caps, what kind of voltage are they seeing? If it's anything close to 500V then you should stick with the 550V ones. If it's only 450V or so, then the 500V should be fine. 47 to 56uf is close enough that it shouldn't make a difference.
For the bridge, why not go with a higher rated one? And if there is heat damage from the bridge, try to mount it a bit further off the board.

[Smitty02]

I am getting 485v at c112 and 480 at c111 That is just running at idle, why is Marshall is using 550v caps here ? I planned on mounting the kbl04 4a 400v bridge rec higher off the board but do you think going to a kbl06 4a 600v would be ok? I dont want to smoke anything on this pup.. I am not a fan of Marshalls I am much more use to Fenders

[g1]

How is your line voltage? If you are hot, like 123V or more, then the 500V will probably be ok. If you are lower, like 120, and the amp gets used somewhere with 125VAC line voltage, how high will that 485V get to? Marshall probably used those caps because they had them, or could also use them somewhere else that needed a bit more voltage.
If you can fit the bigger bridge, might as well upgrade.

[Enzo]

We have 120v mains, which can get up to 125 in places. Marshall also has to deal with the 220/240v side of things, and there are apparently a wider range of potential voltages to contend with, Maybe having more voltage headroom is a result of that.

[Steve Conner]

Is that bridge rectifier for the preamp tube heaters? If so it doesn't matter whether you use a 400V or a 600V one, they'll perform the same. 1N4007s are a bit underrated at only 1A. For extra geek points you might like to try a bridge of MBR340 Schottky diodes.

The caps are rated 550V to allow for a technician powering the amp up with the power tubes removed for test purposes, or the user turning the power on with the standby switch already in the play position. Either of these unloads the power supply and allows the voltage to rise even higher than idle.

European voltages can vary widely. There used to be two voltages, 220 nominal in continental Europe and 240 nominal in the UK. It is all nominally 230 now, but the EU bureaucrats simply made the tolerance band wide enough to accommodate all the old voltages. So, a "230V" product has to handle 216-253V.

My home workshop measures between 240 and 245V, but I have done gigs at a theatre in the same city that had 217V. The head electrician said that the place had its own substation and he set it to 217 to make the bulbs in the stage lighting last longer, but my homebuilt gear didn't appreciate it. I also once had the reverse problem, a SMPS module from a Spanish company that was designed for 220V and couldn't handle the voltage at my house. Magic smoke everywhere.

[Smitty02]

I didnt know they had such a voltage curve in Europe. Yes the 4007 BR diodes I used are 1amp 1000v rating are for the heaters OEM BR is rated at 4a 400v. I think I understand why now they used these 550v caps thanks guys. I did just order the 500v caps and the stock rated BR hopefully the cap tolerance will do its job should it have to.. I hate magic smoke, sorry to hear that. I believe the issues he had with this amp was caused by the caps from the tons of posts on these amps, not Marshalls best work, all seem to have same problems. This guy is just a hobbist player not a gigging musician but it is his main amp. I think it will do fine for the use it will see. I am amazed at all the shoddy joints on this board, while probing it I can make it snap crackle and pop without even messing with the tube sockets and these traces are crappy too. I cant believe Marshall would slap there name on it and i thought the DSL's were crappy...well they are crappier than this one anyways imo. They couldnt even get the hot melt glue on the caps right they are pretty much all loose. Not all that bad sounding though lol but Im not a big Marshall fan. I do like the 18 watt clones though Thanks for your input guys I was looking for any red flags or deal breakers for what I am using to repair but think it will do ok Ill post a update when I get done.. Thanks again hopefully I wont run into any magic smoke Steve. GREAT site, great people I know Im not the sharpest tool in the shed but have and am learning alot Thanks again guys

[Smitty02]

Up date... I finished this cap job and mounted the stock replacement BR off the board on the chassis and then mounted a small 12vdc fan tied to the heater supply worked well fan does run slower but is enough to pull the hot air out of the chassis and is quiet, stripped all the old solder off the power supply board while I had it out re-soldered the whole board as the old solder looked poor, dull flat questionable, so I had at it. Fired it up reset bias.. let it run for a good long time small bias adjustment. Then cranked it, played it for 45 minutes or so. Nice stable sounded great for all the work paid off, re-soldering the board really helped stabilize all the bad connections this amp had. one of the ps filter caps was shot the nichicons were a tad smaller and dont stick out over the tubes. All went well, owner very pleased. I am confident it will hold up for him. Though Marshall could have done a much better job with this amp I did not do no mods other than mounting BR to chassis and a fan. I think the amp sounds fine the way it is for what it is.