'68 JMP50, screen grid resistors, grid stoppers ???
Posted: Fri Jan 22, 2021 7:51 pm
So, after much looking & wishing, I finally scored my "grail" amplifier, a '67/'68 JMP50 (1987, serial No.11225) in decent condition, all original iskras, mustards & RS SM's, red lacquer/dye still on 90% of the solder joins, original iron.
The previous owner had it outfitted with NOS Mullard (60's era) CV4004 12AX7's & a matched duet of '65 Rohen Telefunken winged plate "00" getters EL34's.
I also have a NOS closely matched duet of matching date code (B2J3) 1962 Blackburn Mullard "00" getters xf2 EL34's & a few matched duets of 70's era Blackburn Mullard "0" getter xf2 EL34's.
Now I know that old production valves of this calibre can cope with the stresses of being run without screen grid resistors (or grid stoppers), as was done in the early EL34 Marshalls. My question to the good, knowledgeable folk here is,
Would it be prudent to fit suitable (Ohmite or Welwyn) screen grid resistors in the interest of safe & prolonged service life of the output valves, also possibly (Iskra) grid stopper resistors for stability, or simply leave "as is" in the interest of originality? What say ye?
Any opinions greatly appreciated. Cheers
The previous owner had it outfitted with NOS Mullard (60's era) CV4004 12AX7's & a matched duet of '65 Rohen Telefunken winged plate "00" getters EL34's.
I also have a NOS closely matched duet of matching date code (B2J3) 1962 Blackburn Mullard "00" getters xf2 EL34's & a few matched duets of 70's era Blackburn Mullard "0" getter xf2 EL34's.
Now I know that old production valves of this calibre can cope with the stresses of being run without screen grid resistors (or grid stoppers), as was done in the early EL34 Marshalls. My question to the good, knowledgeable folk here is,
Would it be prudent to fit suitable (Ohmite or Welwyn) screen grid resistors in the interest of safe & prolonged service life of the output valves, also possibly (Iskra) grid stopper resistors for stability, or simply leave "as is" in the interest of originality? What say ye?
Any opinions greatly appreciated. Cheers