Yes, Another JTM45 Build!

Discussion in 'Building the Classics' started by Chris-in-LA, Jul 31, 2020.

  1. Chris-in-LA

    Chris-in-LA Well-Known Member

    Joined:
    Jul 19, 2018
    Messages:
    1,921
    Likes Received:
    1,646
    Location:
    Los Angeles
    Uhh, no, they don’t seem to show it in the Valvestorm manual either. Do you have pictures of one?
     
  2. neikeel

    neikeel Well-Known Member

    Joined:
    Feb 12, 2014
    Messages:
    5,164
    Likes Received:
    3,640
  3. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

    Joined:
    Jan 30, 2019
    Messages:
    1,106
    Likes Received:
    2,364
    Location:
    WA state hinterlands
    I don't think you need it Chris the PT is located so close to the edges of the chassis I think strength wise you are good there. You could use some thicker washers if you want, that's going to be as good or better than that ring.
     
  4. Chris-in-LA

    Chris-in-LA Well-Known Member

    Joined:
    Jul 19, 2018
    Messages:
    1,921
    Likes Received:
    1,646
    Location:
    Los Angeles
    Are we thinking that an aluminum chassis is not as rigid as a steel one and needs a little extra added protection from abuse?
     
    tce63 likes this.
  5. neikeel

    neikeel Well-Known Member

    Joined:
    Feb 12, 2014
    Messages:
    5,164
    Likes Received:
    3,640
    I use them as they finish off the cutout around the pt.
    -certainly not necessary on steel chassis.
    - just part of my ocd!
     
    tce63 and william vogel like this.
  6. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

    Joined:
    Jan 30, 2019
    Messages:
    1,106
    Likes Received:
    2,364
    Location:
    WA state hinterlands
    Machinist hat on...first that supposed stiffening ring is pathetic. If one really felt the need to stiffen the chassis I'd use some thick spec fender washers and would in any case. You are using a laydown transformer with a huge footprint. The only direction of force you really need to worry about is if you turned the amp upside down and dropped it several feet onto the floor. In that scenario the PT would pull up and away from the chassis with the footprint of the nuts and washers the only thing holding it from the underside.

    As for steel I have seen many steel chassis damaged from being dropped during shipping where the weight of the transformer bends/deforms the chassis. More typical of stand up transformers though, laydowns are anchored pretty good. So steel isn't a guarantee vs Aluminum.

    I'm having steel chassis manufactured as I type this for am amp. Mostly because it's quite a bit deeper than a typical Marshall chassis, 22x9x2.5 inch. I'm also using a laydown PT for this reason and stiffening brackets on the stand up OT.
     
  7. william vogel

    william vogel Well-Known Member

    Joined:
    Dec 18, 2016
    Messages:
    493
    Likes Received:
    463
    tce63 and neikeel like this.
  8. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

    Joined:
    Jan 30, 2019
    Messages:
    1,106
    Likes Received:
    2,364
    Location:
    WA state hinterlands
  9. william vogel

    william vogel Well-Known Member

    Joined:
    Dec 18, 2016
    Messages:
    493
    Likes Received:
    463
    Which one, the Erie or the ARS?
     
  10. Amadeus91

    Amadeus91 Well-Known Member

    Joined:
    Apr 9, 2019
    Messages:
    178
    Likes Received:
    252
    I think he's referring to the ERIE
    Very nice build, Mr. Vogel.
    [​IMG]
     
  11. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

    Joined:
    Jan 30, 2019
    Messages:
    1,106
    Likes Received:
    2,364
    Location:
    WA state hinterlands
    That water heater bolted to the end of the chassis.
     
  12. william vogel

    william vogel Well-Known Member

    Joined:
    Dec 18, 2016
    Messages:
    493
    Likes Received:
    463
    It’s just a 32 + 32 500 volt ARS. They are big.
     
  13. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

    Joined:
    Jan 30, 2019
    Messages:
    1,106
    Likes Received:
    2,364
    Location:
    WA state hinterlands
    I like the bravado of that cap.
     
  14. Chris-in-LA

    Chris-in-LA Well-Known Member

    Joined:
    Jul 19, 2018
    Messages:
    1,921
    Likes Received:
    1,646
    Location:
    Los Angeles
    Did some more work. The manual has me add 2 ground wires to the output jacks, the common to the OT and a second wire grounded to the chassis. Is that just redundancy?

    upload_2020-9-19_16-34-11.jpeg

    upload_2020-9-19_16-35-8.jpeg
     
  15. william vogel

    william vogel Well-Known Member

    Joined:
    Dec 18, 2016
    Messages:
    493
    Likes Received:
    463
    You have to attach the output jack to the chassis specifically because the circuit (Jtm45) has negative feedback. It’s always a good idea to ground the secondary of the output transformer to the chassis even without negative feedback.
     
  16. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

    Joined:
    Jan 30, 2019
    Messages:
    1,106
    Likes Received:
    2,364
    Location:
    WA state hinterlands
    Chris I have a couple suggestions for you, or I could just keep my mouth shut, let me know.
     
  17. Chris-in-LA

    Chris-in-LA Well-Known Member

    Joined:
    Jul 19, 2018
    Messages:
    1,921
    Likes Received:
    1,646
    Location:
    Los Angeles
    Suggestions are fine but I probably won’t be able to comprehend anything that is drastically different from the Metropoulos directions.
     
  18. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

    Joined:
    Jan 30, 2019
    Messages:
    1,106
    Likes Received:
    2,364
    Location:
    WA state hinterlands
    Nothing like that, for your next build really...

    1. For your filament (heater) wiring consider arching the wire up, over, then down to the socket pin vs straight through flat with the socket to keep the AC wiring away from everything else and AC hum to a minimum.

    2. A trick for straightening bus wire you may already know, cut a length about 12-16 inches. Grab each end with a pair of pliers or clamp one end to a workbench. Now pull on the wire, put your back into it, when you feel it give slightly presto perfectly straight bus wire.

    3. Try PTFE plated interconnect wire next time vs the PVC insulated stuff. For a given gauge it's much smaller in diameter and just makes wiring so much easier vs the bulky PVC insulated wire. The PTFE insulation also has a much higher melting temp.

    4. My local hardware store sells 1/4 inch thick rubber sheet. It comes in a 4 foot wide roll by the foot. A 2x4 foot piece protects both the amp and the workbench plus after you can give it a good scrubbing with soap and water to remove any gunk.

    5. You know what makes great component lead cleaner, the StewMac fret erasers. Seems like more often than not I get new components in and the leads are a bit grungy.
     
    Chris-in-LA likes this.
  19. neikeel

    neikeel Well-Known Member

    Joined:
    Feb 12, 2014
    Messages:
    5,164
    Likes Received:
    3,640
    The heater technique is a good one, just that the wires need to be tighter together.
    Good point on bus wire.
    I quite like the Valvestorm pre-tinned wire. You should not really be getting the wire hot enough to melt the insulation on that (it is quite resistant, not so much as PTFE) if that is happening it is back to soldering school for the user!
    I need to get a similar rubber sheet when winter comes and the work comes inside!
     
  20. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

    Joined:
    Jan 30, 2019
    Messages:
    1,106
    Likes Received:
    2,364
    Location:
    WA state hinterlands
    Here's a late breaking one. For years I have not been able to find a shielded coax wire I like, it's been the search for the holy grail trying to find something. Had a thought recently, build my own. Turns out you can purchase the outer shielding (tinned copper strand). Turns out you can purchase PTFE shrink tubing, didn't even know that was an option. So out on my workbench for an experiment today I have some 24 gauge, 7 strand PTFE interconnect wire, this stranded shielding .0625 ID, and a length of this PTFE heat shrink tubing. If this works out I'll be able to use PTFE plated interconnect wire for the core, the OD should be well under .1 inch, I can shape it and it will retain it's shape and position and I'll be able to solder a 24 gauge ground wire to the outer shielding vs trying to twist a bunch of the shielding strands into a wire.
     

Share This Page