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  1. sdn25

    How do you increase headroom in a 50w JMP?

    @Pete Farrington is this to be expected ?
  2. sdn25

    How do you increase headroom in a 50w JMP?

    It has increased negligibly on v5 compared to v4. Its actually weirder than I thought, when I strum a chord and let it decay, v4 goes from 180-190 to about 260 where on v5 when I let it decay it goes from 165 to about 110mV.
  3. sdn25

    How do you increase headroom in a 50w JMP?

    @Pete Farrington Since the change to a single 8k2 dropper, when measuring bias current through the 1 ohm bias test points, during playing it spikes to upwards of 270mV. Before the absolute Max was about 220mV. Is this right? Does it degrade the tube faster?
  4. sdn25

    How do you increase headroom in a 50w JMP?

    I think im getting a hang of it, I've gotta ask though, when the amp is cranked and is just a big square wave generator wouldn't the crossover distortion just blend in and disappear?
  5. sdn25

    How do you increase headroom in a 50w JMP?

    Okay so there are bias test points on the back of my amp which are connected to a 1ohm resistor to measure bias, Ive set it to where it reads 26mV at those test points using my DMM. With what you said it mind is the actual bias current only 21mV?
  6. sdn25

    How do you increase headroom in a 50w JMP?

    I measured the mains its at 239 right now
  7. sdn25

    How do you increase headroom in a 50w JMP?

    On the 230V tap it only reads 450V on the plates. Now I recall the 477-480V was on my old OT. The heaters also don't read 6.7V im not sure why. They only read 6.36
  8. sdn25

    How do you increase headroom in a 50w JMP?

    What do you mean by that
  9. sdn25

    How do you increase headroom in a 50w JMP?

    @neikeel @Pete Farrington @william vogel I may have found a super super cheap solution. I remember once I had the amp on the 230v tap with 240 from the wall and I remember measuring 477-480 on the plates. However, the heaters then ran at 6.7V I just wanna know whether 6.7v heaters are...
  10. sdn25

    How do you increase headroom in a 50w JMP?

    What voltage tweaks are you talking about here? Yeah the PT route is expensive, if I can avoid it that would be great.
  11. sdn25

    How do you increase headroom in a 50w JMP?

    Do KT88s last longer than EL34s? I ask since they cost about $130 for a pair without shipping 😭
  12. sdn25

    How do you increase headroom in a 50w JMP?

    Is my OT able to handle the KT88s?
  13. sdn25

    How do you increase headroom in a 50w JMP?

    My current PT sags about 65 volts when the volume is on 8. If the JTM45 PT is more squishy and has more sag wouldn't that make the low end kinda loose? or is the sag that makes the low end punch?
  14. sdn25

    How do you increase headroom in a 50w JMP?

    I’m using a suhr reactive load it’s a reactive load box and doesn’t attenuate signal to a speaker cabinet rather it creates a line level output to go into a mixer. The suhr is about as good as it gets in terms of reactive load boxes apart from the Fryettes
  15. sdn25

    How do you increase headroom in a 50w JMP?

    For sure, I checked the product page for the 290MAEX. The 2 primaries are 100/120 so I’m assuming to get 240 for where I live I have to use both the 120 leads ? From the data sheets I see both the 290GX and MAEX have a rating of 150mA, is that the current capacity you are talking about ?
  16. sdn25

    How do you increase headroom in a 50w JMP?

    Maybe, my goal is to try and get it as close to my needs as possible without external help and then work from there. I’m good for string guage I use 9-42
  17. sdn25

    How do you increase headroom in a 50w JMP?

    Mine is a jmp clone with a lay down PT.
  18. sdn25

    How do you increase headroom in a 50w JMP?

    Thanks for the reply, can you suggest a couple PTs to look out for this application ?
  19. sdn25

    How do you increase headroom in a 50w JMP?

    I see, I removed one of the 8k2 resistors as Pete suggested and now I hear a bit more clarity in the amp. A step in the right direction, more definition as mentioned before by somebody. But I gotta ask though, wouldn’t a bunch of small changes like the voltage, choke, filtering etc add up to...
  20. sdn25

    How do you increase headroom in a 50w JMP?

    I’ve found a Hammond 10H choke on mouser for $20, it’s rated at 50mA is that within spec for a Marshall choke ? @Pete Farrington @neikeel ?

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