How would you salvage a Peavey Delta Blues

Discussion in 'Shock Brother's DIY Amps' started by wtk0315, Apr 21, 2019.

  1. wtk0315

    wtk0315 Tele-Holic

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    I see. I should have read the fine print. .11" is less than 1/8". Put two together in a piece of heat shrink and I'd have a 1/4" OD two conductor that looks nice and neat.

    So what is the preferred method of attaching the shield to ground? My plan is isolated input jacks and a solder tab bolted to chassis near the jacks. Can I solder a jumper wire to the shield, or do I have to strip back enough shield to reach this point? It shouldn't be a big deal on the normal jacks, but it would be about an 1 1/4" stretch from the bright jacks.

    Sorry for confusion. Will post pics when I get back on the build.
     
  2. wtk0315

    wtk0315 Tele-Holic

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    Thank you. I'm not going to try it if it likely won't work.
     
  3. Nickfl

    Nickfl Tele-Afflicted

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    I bet your problem was design not lead dress. PTP wiring can look bad, but is almost always quieter than circuit board layouts because of shorter wiring runs. It's hard to say since you haven't posted a schematic of your design, but if you have just cut and pasted circuit blocks from different amps without doing the math to see if they work together it can go off the rails pretty easily.
     
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  4. wtk0315

    wtk0315 Tele-Holic

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    Well it wasn't really PTP or turret strip. I had a board, two actually. (I'll post a pic of my board just sitting in the chassis). Basically I covered the tube sockets so I couldn't diagnose anything. (That and the meter gave out.)

    The Delta Blues power supply isn't drastically different from the Plexi. There's one more filter cap. The actual values are fairly similar. Folks have built 36 watt TMB, although all that I've seen use cathode bias and mostly tube rectifiers.

    My money is still on either biasing the tubes into cutoff or something off with negative feedback/plate leads. Nobody had an idea of why it would sound good after I cut the power, but if the bias supply drained first, the tubes would hit the appropriate bias for a second or two as the caps drained.
     
  5. wtk0315

    wtk0315 Tele-Holic

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    IMG_20190817_130719427_PORTRAIT.jpg
     
  6. wtk0315

    wtk0315 Tele-Holic

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    IMG_20190925_155054022~2.jpg
     
  7. wtk0315

    wtk0315 Tele-Holic

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    She's rebuilt! Mostly good. I've got a high pitched feedback on the bright channel only. After perusing a few Marshall forums I found info that factory JMPs often came with a 7pf 1000V cap soldered between the grids and plates of V1A and V1B, directly to the tube sockets.

    I did not use RG174. It's extremely flimsy. I have not yet wired my 6.3V transformer CT to my 75V DC standoff. I also would like to shield the cab. Peavey only had one small piece of shielding over the inputs. It's about 3"x5" I guess.

    I realize my power rail looks messy on the schematic. I forgot about the choke! When I first hooked it up the preamp voltages were way lower than a Plexi should be, so I removed a 10k resistor that would normally be in series with the 8.2k between screen and b+ on my drawing. This got my B+ node to 299, about 20V less than the Plexi values I've found, but probably close enough.

    For whatever reason my screens were also running higher than my plates. So I added an 8.2k from choke to my screen junction and got that down to 308V.

    As far as sound, well it sounds like rock and roll! And idle noise without a guitar is pretty good, even without heater elevation, except when channels are jumped. I'm going to try to kill the oscillation/feedback with the 7pf cap (probably will be a 10pf), elevate the heaters and shield the cab before I pull my hair out installing rg174. I also might swap the 33k tone slope resistor to a 47k or 56k. Another common Plexi mod is to remove the 500pf that parallels the 470k mixing resistor going into V2A. I dunno. I'm gonna try to quiet it down and then fool with mods later.

    Anywho, I'm about to start 7 days a week, so I'll get a full voltage chart down the road sometime and some pictures.
     
  8. wtk0315

    wtk0315 Tele-Holic

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    This is my power section before the 10k got removed and the 8.2k to the screens got put in. Black wires toward the bottom are choke wires. Plates and grids aren't hooked up yet in this one.
    IMG_20190901_093511328.jpg
     
  9. wtk0315

    wtk0315 Tele-Holic

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    Oh almost forgot. My plates are running a touch higher than what Peavey lists on their schematic (332V). I'm about 345 or so, but I've got the bias close to 70% (I need to double check everything.) I don't want it to be a mesa style tube eater. I could always put another dropping resistor between the parallel reservoir caps. And then of course my screens would probably be too low so I'd have to change that too. I'm going to order a grab bag of 3 watters when I order the 10pfs so I can maneuver the voltages.
     
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