Certainly Transformers make a difference, but knowing takes some experience. Since I am not aware what karrrang is, if you could be more specific maybe I could have some insight since I have had 2 originals. The late 60,s amps were not as bright as 72.
Heybour makes a Drake replica spot on part 784_139. Also, every old Marshall pots measured above the marked resistance and the cf valve was stronger. The slope resistor varied as I have seen 33k, 39k, 47k, 56k.
Try first replacing the NFB resistor with a 100k pot, if youmwant to make permanent I use a locking nut pot. Turn and play, the lower you go the less feedback and will add additional high harmonics.
Next replace the slope resistor with a 100k pot again. Adjust down and check your eq settings as you'd like. When you find what you prefer, measure the pot and install the closest resistor value. I have always preferred 33k. Anyway it is your ears.
If you have a master volume and it is a PPIMV, this will reduce the effectiveness of the presence when turned down and the amp will dull some, and this is why the NFB adjustable pot helps.
If jumping channels, either make a y cable so both are plugged into high inputs or you can google how to rewire the jacks. This makes a difference.
Output transformers can improve or change the tone, but if what you have going to it is not the tone you want it will not magically make it so.
Also consider it is common practice today to use silver mica pf in tone stacks, but the originals had ceramic. It is different sounding. Mustard caps, real ones make a difference. Sozo yellows work well.
Having the bias set correctly on EL34s is more important than other valves IMO. Set you dissipation at 60% and play, recheck. Increase, recheck and play. Keep running them hotter, but make sure you are not beginning to redplate. Do it by ear, but know your 70% dissipation ma.
If you have some real winged c or nos tubes these sound correct. EH from what I am told sound best but that is opinion. I only use NOS Mullard tubes, cause I got them when they were affordable.
Surely the speaker makes a huge difference, but you should still hear what you want. If you don't your tone you want is not at the power tube plates.
Try these suggestuons in order and that Mercury Transforrmer will work just fine. And try to find a NOS Mullard 12AX7 for v1 and a good strong NOS for v2. Get a balanced new production 12ax7 for the PI. I use gold lions simply because they seem to hold up. I prefer burned in prior to balance sections. You can also balance using resistors if you have a scope, but a inbalance does not really hurt anything.
If the amp is too loud and you are using a master turned down a lot, get a 12ay7 fot the PI. A 12ay7 has a much closer tone, with less gain.
If you do the 12ay7 and like the voume control, but miss the gain you can easily get it back increasing the plate load resistor on v1b if that is where your. 68uf/2.7k bypass is. Also make sure the coupling cap after this is a. 0022. I have seen many with a. 022 like the first bypass cap.
Finally, the bright cap before the grid of v2 should be a 500pf ceramic. If it is silver mica and you do not have any ceramic, just keep it there. After you do these things one at a time, let us know if tou get any karrag.
Topic: 1987x OT Replacement - Much to be gained? (Read 3769 times)