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  1. johan.b

    Zound acquires Marshall

    Order your flat pack 1960 here.... do you want some surströmming with that? I have no clue what to think... just wanted in on the thread... J
  2. johan.b

    replacement for 490T in SG

    Gibson pickups are quite sensitive to what value pot you use... check what you've got. If you have 300k, a 500k might be all it takes and make all the difference...<~10$/€/£... Just a thought J
  3. johan.b

    Modifying a Marshall MOSFET output stage

    Solid state is NOT forgiving and might explode if set wrong. No need mess with the bias of it sounds good. Output is limited by tr4 and tr5 when current through r13 and r15 get big enough for the voltage drop to increase over 0.7 volt at the bases. Shunting signal to ground through tr4/tr5. I...
  4. johan.b

    Modifying a Marshall MOSFET output stage

    Again. It's an oversized opamp... As noted, Your ~600mV ([email protected] 1) turns to~ 20 volt(@2) for 20Vx20V/4ohm=100watt ... perhaps other ideas borrowed from the stompbox world could apply?... like diodes in the feedback?... or applying filters here?.. again, I let those brighter than me fill in with...
  5. johan.b

    Thermal noise in tubes

    You can probably take the heaters down a bit more if you want to... long time ago there was a Swedish manufacturer of mics for the tv and film industry, called Sela. They ran an 6ak5 at only 4.5volt on the heater. I was lucky enough to talk to one of the guys many years ago. He said the low...
  6. johan.b

    1977 Super Lead Mark ll 50w red plating.

    With only 3.5 volt on the bias feed, its probably the bias caps.. they are fed through a high resistance, so never did hard work in their life and likely to crap it after 45 years...
  7. johan.b

    Pedals that dont work out and why

    I basically agree with you here...But...The Marshall bluesbraker IS a good overdrive, even With The Latest Hype..set it for good crunch then push it with a clean boost and it gets a very fat, natural Sound...Only, I have yet to find a single example of anyone else doing that on YouTube...And...
  8. johan.b

    Modifying a Marshall MOSFET output stage

    Well, the inductor, as I suggested, would pretty much do the same... it sits in series with the speaker, so no current is sneaking around it. Same current as the speaker. . it just sits before instead of after, so the voltage swing is more in-line with the voltage feedback
  9. johan.b

    Modifying a Marshall MOSFET output stage

    .... or perhaps take an idea from the old valvestates amps
  10. johan.b

    Modifying a Marshall MOSFET output stage

    I was hoping for those two too... ha ha... This power amp is basically an oversized opamp. With R8,R6 and c3 being the usual "outside" gain/freq. Components... the main problem is the output devices having been unoptanium for 20years making extra caution necessary. The input is the differential...
  11. johan.b

    JCM 2000 DSL 100 1/2 Power and 1/4 Power Mods

    Look at the TSL schematic.. they had a ppimv switch to reduce output. The socket/connector for it sits on the DSL board too. J
  12. johan.b

    Modifying a Marshall MOSFET output stage

    You could possibly lift the right side of R8 and reattach it on the speaker side of the output choke... that would kind of make it current feedback. What happens to stability though, i don't know... wait and see what others say...(so it doesn't explode... ha ha.. ) J
  13. johan.b

    I took my DSL40cr to an amp tech and he couldn't fix the noise.

    I don't have the schematic and never worked on one of those, but if you're sure it's the lopp, perhaps it's easier and more cost effective cutting it out and replacing it with an aftermarket loop, like the metro no loss loop... just a thought... J
  14. johan.b

    NOO I DIDN'T.... yes i did. Turned my 5e3 into something AA1164-ish..(princeton reverb)

    This is the second 5e3 i built. I didn't like the first one and sold a few years later, I made some plans for a similar size amp and decided it was easier getting chassis and a lot of the small parts through another 5e3 kit It started as a regular 5e3 and with minimal changes to the...
  15. johan.b

    the current Digitech Bad Monkey situation

    Anything more than 150€/£/$ for a opamp/diode based, 9 volt powered stompbox is just silly... ok, take it up to 250 for the handmade by green eyed maidens in a sacret cave on a mysterious island somewhere near "Hy-brasil" boutique boxes... but there is no inherent magic in any make...
  16. johan.b

    Valvestate 80V choke replacement

    It isn't a real transformer. It is Open... it works more like an ignition coil. One winding around the core with a low voltage tap. And the same winding going on up to high voltage. J
  17. johan.b

    Peavey Butcher Adjustable Bias Installation Guide

    The VTM is basically a "Jose moded marshall"- copy... wait until people find out.. About 3/4 down J
  18. johan.b

    How to get the presence back on a PPIMV modded Marshall ?

    As i recall, the nfb resistor mustn't go to "0" though or it'll strangle the LTP. and that's where more experiments need to take place, to get the ratio change right.. myersbw's idea of going between the 4 and 16 ohm might be the right way if you, like you suggest, rebuild a pot to be small...
  19. johan.b

    Why does my late 80s 2204 sounds completely different compared to my late 70s one?

    This little part is often overlooked in the difference between JMP and later 800.(sitting between anode and cathode on first stage on 800).. then it's the state of tubes, caps and voltage
  20. johan.b

    Next best thing to original Mullard LP 12ax7

    I'd say... use the good stuff now when you're active and save the less good as spares for when you might not play as much anymore... but that's just me...