The Vet 10's should be a decent mix with the blackbacks, definitely not taking over from the 12's. Some JMP:s use 22k after the choke (ore double 10k). The platevoltage to PI and the preamp is very important for the feel and sound of your amp. Here's a pic from the mounted board (before I changed to double 16uF).ĮDIT: A component you didn't mention is the B+ resistor after the choke. When I use my Mullard xf2 I can push them with much more bass freqs and still the bass is tight. But it also depends on what power tubes you choose (and probably the OT - I use the nice Marstran). In some cases 0,022 will do better, a little bit tighter bass. I use it in all my Marshalls, even my modified 6100 But in the JMP I use a 56k/390pF combination, to get a little bit more aggressive in the treble freqs. First lowered to 32uF and then to double 16uF (in parallell, 32uF) in the preamp! That's the sound I like! Much better response and feel (my taste). long cabels across the chassi and cloose to the high ac voltage area - a source for hum.) But I felt the sound was to stiff with the 47uF. (I don't understand why Marshall put the second cap can so far away from the PI. Let the first cap can remain as it was, double 50uF. I started with four single 47uF filter caps mounted on the board. But i also depends on the sound you want to get (I'm a little bit freaked about the 1987 circuit). It's a little bit easier to convert it to 1986 spec if you want to, than the other way (from 1998 to 1987). I dont't know how you are going to build, designing your own board? But go for a 1987. I've rebuilt my -83 Marshall JMP 1987 to a ptp. I agree with almost everything neikeel suggests. Thanks in advance for any advice, recommendation or straight tip. I'd like to take the bull by the horn and hopefully find the path to the right direction. That makes building a 50 watter unclear and could becom a long story to nail it. In reality the amps have other parts and components in use as shown in standard schematic diagrams. I know above mentioned information can vary from amp to amp of different years and so. preamp filtering: single/dual 32uF, 40uF or 50 uF? screen filtering: single/dual 32uF, 40uF or 50 uF?
main filtering: dual 32uF, 40uF or 50uF? rectifier diodes: 2 or 4, 1N4007 or FRED? My questions or what do you recommend for? presence control: 5k pot/0.1uF (common in reality: 25k pot with 4.7k/0.68uf) negative feedback resistor: 47k at 8ohm-tap of output tranny (common in reality: 100k at 4 or 8ohm-tap) tone stack, slope resistor/tone cap: 33k/500pF
2nd stage V2A cathode circuit: 820R/0.68uF bright cap on bright volume: 0.005uF (common in reality: no cap) 1st to 2nd stage coupling cap on bright channel: 0.0022uF
negative feedback resistor: 47k at 8ohm-tap of output tranny (common in reality: 27k) tone stack, slope resistor/tone cap: 56k/250pF mixer bypass cap: 500pF (common in reality: 560pF) 1st to 2nd stage coupling cap on bright channel: 0.022uF shared cathode circuit in 1st stage: 820R/320uF To start from scratch the key data are according to schematic diagram from G+W Unicord Incorporated as follows:īasically 1986 Bass amp has similarities to JTM45! Some very informative websites together with this forum I found here: Probably Marshall assembled what they just had, later some were tweaked and some were repaired and had their specific parts. There are many different buildings even for 1986 and also for 1987. It could be an assortment from both side of 1986/1987. I prefer old blues rock style as Allman Bros, Lynyrd Skynyrd, Rory Gallagher etc. So far I'm not sure which one I will go for. Soon I'd like to build one Marshall 50 watt head.
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