NAD problems. Blankenship 1959 Clone

Discussion in 'The Workbench' started by lonewolfsx, Sep 25, 2020.

  1. lonewolfsx

    lonewolfsx Active Member

    Joined:
    Dec 4, 2010
    Messages:
    245
    Likes Received:
    149
    Location:
    Florida
    Hello. Just picked up this pretty amp, I didn't know what to expect as far as sound considering I've never had a NMV (modded or otherwise) and this one has been modded obviously so who knows what's going on.

    However, I'm positive it isn't supposed to sound like this. It literally sounds like a wet fart. I don't mean it sounds bad, I mean it sounds broken. Almost like a broken speaker or blown subwoofer. Especially when playing on the lower strings(tuned to E std), the notes have no definition or punch and especially if you hit another note at the same time - there's like a sag, dive, super compression that kicks in for a moment almost as if voltage is dropping or something.

    Just to rule it out, I did cycle in a full set of known working power and preamp tubes but that solved nothing.

    So I'm thinking it has bad caps or something along those lines. Hopefully not a blown transformer since this thing has Mercury's and the cost of replacing one of those I'll just return the amp (I can return no questions ask for 45 days). I couldn't find a picture on the web like I wanted that shows what a bulging cap of this size looks like so I wonder if someone here could tell me from this picture if what I'm seeing on the caps appears to be related to the issue I'm describing or if there are some other quick things I could check - I'm acceptable at amp repair and I'm comfortable safely working inside an amp, but I've only done a few PCB mods, small cap changes etc - nothing this big before and I don't own the parts to do it right now anyway.

    Cheers for any help

    The amp:
    [​IMG]

    The caps:
    [​IMG]
    They sure look weird to me...
     
    NewReligion likes this.
  2. NewReligion

    NewReligion Well-Known Member Double Platinum Supporting Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    11,380
    Likes Received:
    8,507
    Location:
    Paradise
    You said Blankenship but there is a Kruse logo??

    Upon closer inspection there is a potentiometer labeled Kruse Variac. That gets my attention immediately as voltage can and will do stiff to fatty things to an amp especially in conjunction with who knows what else.

    The front panel clearly states Master where the Presence normally would be. Being blind I am inclined to think it is a type of PPIMV as that would remove all NFB/ Presence from the circuit and leave the TMB (Treble, Middle & Bass) very limited in function. So much that KennGischer of Train Wreck Amplification (RIP) would not even use Presence.

    Really hard to say with limited data.

    1.) That delamination does not appear to be the source of your issue as many caps may simply have that plastic start to delaminate as a couple of my amps have.

    Look at the bottom side of the dual caps to see if electrolytic paste is escaping from the bottom. I am guessing not.

    2.) What value are the dual caps?

    3.) Can you provide gut shots of the circuit and board?

    4.) Last but certainly not least I have had a couple of the Kruse amps come through with exactly what you are defining. I was a little surprised to see some of the odd ball components.

    It is what it is.

    I would not go too far as to void your ability for a refund.

    David
     
    Last edited: Sep 25, 2020
  3. lonewolfsx

    lonewolfsx Active Member

    Joined:
    Dec 4, 2010
    Messages:
    245
    Likes Received:
    149
    Location:
    Florida
    David, thanks so much for the reply. The bubbling on the caps does just press in/out like stretched plastic and they are clean on the bottom. That was a iffy guess on my part.

    So this is a weird amp, it’s a Blankenship hardwired 1959 copy, has a Blankenship plate and SN on the inside of the chassis, but whoever owned it before me stuck that Marshall logo on. The amp I guess was sent in to Kruse for modifications. I’ve been to Kruse’s website but I don’t think this is one of the “named mods,” since you can just send it in and ask for one or two things and looking inside it looks like the only three changes are:
    1- presence replaced with MV
    2- weird variac/volume control on rotary dial
    3- effects loop added

    I do have pictures of the circuit. Give me just a moment to upload and I’ll post them here. I agree I’m not going to dive in so deep as to void my repair but considering it’s basically unusable at the moment I can probably go pretty far and still be able to return without much hassle, so I’m willing to try a few things.

    It does sound less flubbed out when at the 100w setting on the rotary, but only barely so. It’s definitely the worst at 3w (lowest). That control is also coated in some funky epoxy probably to make it harder to copy the circuit...

    Oh, and to answer question #2: The two bigger caps look like they are doubles, so 100m + 100m rated at 500v. The smaller ones to the right are 350m 385v.

    Pictures of the circuit:
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    Those are from my cell phone so if you need something more clearly I can get it too.

    Thanks again for your advice.
     
  4. lonewolfsx

    lonewolfsx Active Member

    Joined:
    Dec 4, 2010
    Messages:
    245
    Likes Received:
    149
    Location:
    Florida
    I think it's a little odd that the Kruse mod just cuts out the standby switch entirely too.. very strange.
     
  5. Chris-in-LA

    Chris-in-LA Well-Known Member

    Joined:
    Jul 19, 2018
    Messages:
    1,666
    Likes Received:
    1,373
    Location:
    Los Angeles
    It looks like it has a master volume of some sort and maybe power scaling. Maybe you can try turning the master up to 10 and the power scaling up to 100v and see if the amp sounds more like a real 1959.
     
  6. neikeel

    neikeel Well-Known Member

    Joined:
    Feb 12, 2014
    Messages:
    4,715
    Likes Received:
    3,121
    The amp looks like a kit built (metroamp or similar?) 100w based on a '70/71 JMP100 (100k NFB and no V2a bypass cap) added cap on the normal channel.

    The MV mod has been badly done (wires on the PI couplers cut and simply soldered (possibly shrink wrapped) to the hook up wire - recipe for things coming adrift.
    The effects loop was also a basic installation looking at the soldering and other aspects.
    Things to try would be bypassing the loop with a jumper or even bypassing internally.
    I would remove the master and reinstall the presence. At the moment I cannot see what has been done to the purple presence wire from the NFB resistor. The modder has wrapped tape around the NFB resistor to stabilise the floppy wire from the coupler - not a good move for noise.

    Probably just needs a good going over from front to back to check the connections, tidy up the lead dress, add some grid stoppers to the output tubes and, personally speaking I would ditch the variac and PPIMV and use an attenuator as required. If you do want a PPIMV I would install it on the back but use shielded wire and grid stoppers. The MV they have used (aka Rich mod) does not sound bad vs other versions - LarMar take on the Fischer type) but it should be done properly.

    Yes some more pics with better lighting would be helpful.
     
  7. lonewolfsx

    lonewolfsx Active Member

    Joined:
    Dec 4, 2010
    Messages:
    245
    Likes Received:
    149
    Location:
    Florida
    There's no way I'd be able to do that haha, but I did do them separtely - at the lowest wattage setting and master maxed, it's still weird sounding, and with the master low and the highest wattage it's the same story. I know that's not a perfect test but I can't possibly turn this thing up that loud in my house.


    I did try bypassing the loop with a jumper but that didn't make any difference either. I definitely was suspicious of the loop to start as well.

    It's not a kit exactly, it is a "production" model Blankenship amp. Looks like he doesn't have a 100w model listed any more but here: https://www.blankenshipamprepair.com/price-list.html
    It looks nicely made and has some high quality components but the mods are definitely on the low end of worksmanship.

    Anyway I appreciate the advice but honestly when I called about this amp they told me it sounded incredible and it was like $1600 so I'm just going to return it. It's ridiculous to spend hours troubleshooting a bunch of internal crap that should've been sorted before they sold it to me, and for that price I can buy a plexi in perfect working condition.

    Cheers...
     
    Chris-in-LA and neikeel like this.
  8. CROWEMAG

    CROWEMAG Active Member

    Joined:
    May 22, 2018
    Messages:
    417
    Likes Received:
    234
    Take it back and bail.
     
  9. lonewolfsx

    lonewolfsx Active Member

    Joined:
    Dec 4, 2010
    Messages:
    245
    Likes Received:
    149
    Location:
    Florida
    Bailed and bought a JCM800 instead, which is what I really wanted anyway. Just lucked out that it worked out that way, the GC I went to return to had the JCM800 I've been looking for anyway and it was cheaper so wins all around.

    Thanks again for trying to help me out everyone.
     
  10. CROWEMAG

    CROWEMAG Active Member

    Joined:
    May 22, 2018
    Messages:
    417
    Likes Received:
    234
    What model and year 800? Congrats!
     
  11. lonewolfsx

    lonewolfsx Active Member

    Joined:
    Dec 4, 2010
    Messages:
    245
    Likes Received:
    149
    Location:
    Florida

Share This Page