Usually I go for lower filtering and medium gain tones, but since I already have plenty of the early JTM45-style preamp amps, I decided to go for something different this time. My 12-series build has ended up with late-'68 specs (50uF mains, 16uF screens, 100uF PI filtering, and 490-500V plate voltage), which means it's not as compressed and gainy as most people's 12-series amps, who usually go for EVH tones. I'm more after late period Hendrix tones or Trower tones, so those specs suit me well. To make this amps stand out even more from my 12-series though, I decided to go for the more aggressive '69 specs vs the earliest split cathode 50-watters, which still had 50uF mains filtering, and usually 40uF each for screens and PI.
This new amp has 100uF mains, 50uF screens and 50uF PI filtering. I went with 32+32 for the preamp as that is correct for a '69, but I also wanted to maintain a bit of touch sensitivity/compression, and I think going to 50+50 in the preamp kills a bit too much of that. Preamp is a stock '69 style, but with 820R/0.68uF for the cathode on channel 1. I'm not sure when (if ever?) the 50-watters went to 2k7, but there are photos of what looks like a '69 (probably early '69) with WIMA red cathode caps and 820R cathode resistors for both V1A and V1B. Negative feedback is 47k on the speaker jack. RS silver micas, mustards, WIMAs for the 0.68uFs, Iskra resistors. I'm still looking for another Iskra 82k and a 15k for the bias circuit, but other than that it's all good. M e r r e n 784-139 clone and C1999 3H choke clone, Marstran 1202-118 PT clone. Sparky front panel, Valvestorm rear panel and bits. Castelco front switches. Still looking for a head cab, but am talking to Chris Uff and will probably order from him. I currently have a pair of RFT 60s short base EL34s that I got from Andy (setneck) - superb tubes! Waiting for some more preamp tubes, but tested the amp yesterday with a Tungsram in V1 and V3, and Tesla E83CC in V2. It sounds exactly as I wanted it! Bridging the channels, it gets a fat, searing, articulate lead tone almost right from the start, even with no bright cap! By bringing in channel 2, I can control the amount of "fat", and even introduce a little bit more sag right at the end of the dial, where the gain makes the amp compress and breathe. I like it even more than I would have expected, very fun amp to play and very "liquid". The high filtering means there's no ghosting, but it doesn't feel too stiff like I think some 100-watters with high filtering can do. Cleans up to a sort of cutting clean tone, quite a different feel to the clean tone versus the earlier amps, but very useful nevertheless. I can see why this is Doyle's favourite 50W Marshall spec, even though it's hard to bump the 1986 off the throne for me...
Here are some photos - enjoy!
- chassis1987.JPG (114.14 KiB) Viewed 4652 times
. Mine has virtually as much gain in plexi mode as it does when cascaded. 
