Filter cap change photo blog

Discussion in 'The Workbench' started by PaoloJM, Dec 3, 2009.

  1. PaoloJM

    PaoloJM Well-Known Member

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    Thought some of you might be interested in this.
    Been busy with other work but got some time yesterday to do some long needed work on my own amp.
    This is '71 JMP 50 (see serial number below) that I bought about 3 years for a very good price.

    [​IMG] [​IMG]

    I got the price because the power transformer had been changed at some point. It was replaced with a good quality replacement that had been fitted very well so it didn't bother me in the slightest, plus it sounded great. :dude:

    It still had the original caps in there and lately (for the last 18 months!!!) I'd been noticing I was pushing it harder to get the same punch plus t was getting a bit noisy.
    Got the time yesterday so it was time, eventually, to get in there and do something about it.

    Following a closer inspection the history of the amp became a bit clearer. The bias circuit had been modified and the IEC power connector and earth lug were definitely new. See photo below.
    My theory now is that this was an American model with 6550s that someone brought over to the UK, where I bought it. The guy who brought to the UK, my guess, plugged it straight in damaging the PT, power switch and fuse holder. The tech seems to have replaced the PT with a 240Vac model, installed a grounded IEC plug and modded the bias circuit for EL34s.

    [​IMG]

    Here's the preamp section as I bought it.

    [​IMG]

    Anyways, I decided that I wanted to replace the electrolytic capacitors, internally jumper the input channels and install a post phase inverter master volume, but do it all in careful manner that I could easily reverse at a later date.
    I plan on keeping this amp for the foreseeable future so I went with the best quality replacement capacitors that were available from my usual suppliers. I went with TADs.

    My first step was to remove the old capacitors. Notice the red jumper cable in this photo.

    [​IMG]

    This jumper is discharging the capacitors using the V1 plate to ground method. I first verified that the discharge path from the main cap was complete and this is very important when using this method.
    If there is an open somewhere along the line this method will not work. I like to leave it in place a long as is practically possible especially when working on vintage amps.

    Here's where the preamp filter is located. Beside it a shot of all the caps removed.

    [​IMG][​IMG]

    Here's a shot of what, hopefully, is a nice solid solder joint.

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    Notice that it looks nice a shiny, even with lead free solder, with not too much solder blobbed on.

    Here the preamp and poweramp after the cap change and mods.

    [​IMG][​IMG]

    Hopefully it looks nice a neat!! :)

    Here's the rear of the amp after work showing the new caps and master volume.

    [​IMG]

    How does it sound?
    It sounds f*ckin' awesome!! :dude:
    I'd have clips made only I plugged in and started playing and only stopped when the neighbours called!
    The MV works great but I still like to push it too 5/6 to get the feel and that's still too loud for a three bed semi apparently!!
    Won't get chance to record properly 'till the weekend. :(
     
  2. jcmjmp

    jcmjmp Well-Known Member

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    I wonder why people only change the main power supply filter caps but rarely do people talk about the bias filter caps and the signal path electrolytics.

    What kind of caps did you put in there? They look too tall to be JJs.
     
  3. PaoloJM

    PaoloJM Well-Known Member

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    The main filter and bias filters are both changed to TAD.
    Didn't change the signal cap as I didn't have a suitable replacement on hand.
    I would prefer to replace exact like for like there and will someday soon.
     
  4. MajorNut1967

    MajorNut1967 New Member

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    Good post Mate. How are those TAD caps, I have never used them?
     
  5. PaoloJM

    PaoloJM Well-Known Member

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    I've recapped 6 Marshalls so far with them, both 50 Watters and 100 Watters, so I've bought nearly 50 of them so far and not one single one has failed, that I've been made aware of anyway.
    I'm inclined to rate filter caps purely in their ability to perform their task and their reliability and I'd score TAD caps highly on both counts.
    I'm not convinced that there any tonal difference with different brands though I can hear tonal differences with different capacitance values.
     
  6. jcmjmp

    jcmjmp Well-Known Member

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    definitely.
     
  7. MajorNut1967

    MajorNut1967 New Member

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    Ya the plain fact is that the filter caps at the same stock value won't change a bloody thing tone wise, i don't even believe it is a point of discussion!
     
  8. Rev-al

    Rev-al Member

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    Very nice job mate - I've just taken my '73 jmp 50 to my tech for this same work. Where did you buy the TAD caps? I'd like to get some for the SL 100 which goes in next.
     
  9. PaoloJM

    PaoloJM Well-Known Member

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    I buy the TAD stuff directly from the Tube Amp Doctor web-site.
    I've found that the 2 x 50uF @ 500Vdc does the job just nicely for most Marshall's I've seen, including Super Leads.
     
  10. PaoloJM

    PaoloJM Well-Known Member

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    Started work on my 800 today and thought you might like a look.

    Here's the existing caps

    [​IMG] [​IMG]



    Most amp porn you see is pretty much like Playboy, it's kinda nice and decent and you wouldn't mind too much if your mom found your stash.
    For those of you with a weak stomach then look away.
    Here's some of the nastiest, legs around the ears, filthy, skanky amp porn you're gonna see on the web. This kinda stuff you really don't want your mum to find...

    [​IMG]

    That's the first preamp filter fitted and soldered up.



    Can you guess which four solder joints I've made here? Please humour me and say you can't even if you have to lie!!

    [​IMG]

    Actually just spotted that I took this pick before the last joint was done. Dammit!!



    Nearly there but my new build gear arrived and then I cracked open a six pack and am currently getting sloshed, so I'm only half done. Never drink and solder folks!!

    [​IMG] [​IMG]

    I'm using TADs again for this amp.
     
  11. PaoloJM

    PaoloJM Well-Known Member

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    uTube Vids

    Lads,

    As promised here the uTube vids.


    First up is the JMP 50.
    It's recorded with a SM57 => MBox Mini 2 => MacBookPro => ProTools with no post processing.
    It was my first time using iMovie so there's no editing at all.
    The quiet bit in the middle is just the guitar volume being rolled back.
    The PPMIV is set to about 4 here, both channels are internally jumpered and both volumes are set around 7/8.

    [ame="http://www.youtube.com/watch?v=wdfvC7xEm6s"]http://www.youtube.com/watch?v=wdfvC7xEm6s[/ame]


    Here's the JCM800.
    I bootstrapped the master volume and it set to 3 in this vid.
    Bootstrapping means you don't loose any low end even set to 1, whereas you would with the standard 800 master volume. Gain is reduced a bit still though.
    Gain is set to 7/8 and the resonance control is at about 6.

    [ame]http://www.youtube.com/watch?v=gXKe_1K05uI[/ame]

    Lemme know whatcha think!! ;)
     
  12. Rocko

    Rocko New Member

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    The JMP 50 is absolutely beautiful! I love it.
     
  13. Mullard Man

    Mullard Man New Member

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    Another great post from PaoloJM. I just love these type of threads.

    I'm going to look at TAD caps, as I'm used to using F&T.
     
  14. PaoloJM

    PaoloJM Well-Known Member

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    Thanks guys, appreciate your comments.

    I noticed yesterday evening that the link wasn't working properly.
    iMovie uploaded the vid as being private, and uTube was looking for you to be my friend before you watched the clip.
    Not that I don't want you to be my friend or anything :)laugh2:) but I've changed the settings now so that you can watch directly from the thread, hopefully.......
     
  15. Rev-al

    Rev-al Member

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    Nice one Paulo
    Your JMP 50 is almost identical to mine - which is a '73 too. Wonder what your Tag board signatures say ?- probably similar - I love those small details.
    I ordered the TAD caps today - ( I spoke to Watford Valves -re caps - and also faulty valves I bought, and they were actually quite rude to me and I certainly will not be spending my money there in future)
     
  16. Iron Mang

    Iron Mang New Member

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    Great post, very informative.
     
  17. Max Riffage

    Max Riffage New Member

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    Hey Paolo, you've been so helpful already, so it's abit cheeky, but...... Is there any chance you could post some really sharp pics of the under-chassis of your JMP50? I noticed on your youtube background the pics look perfect.

    It's much closer to how my amp looks than anything I've seen on amp archive or anywhere else. All your wires are exactly the same colours, some of the caps look more like mine than other layouts, even down to the yellow board they only seemed to use for about a year or two!

    Plus, you've done the mods I want, I think. Just the PPIMV and big-can caps, right?

    That's the only mod I'm going to do while rebuilding - I'm gonna leave the FX loop idea until I've got it working and tried it with some pedals in the front.
     
    Last edited: Jan 7, 2010

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