Lee Jackson says those white chicklet caps are prone to cracking and failing, he changes them out as a matter of course. Interesting regarding that .47 presence cap, I know some people swear by a .68 there too. Cheers mate, I'm getting a better understanding of these circuits from your well-explained vidz. Not inspired to do most of the mods as I love the low-ish stock gain structure, although I'm thinking about a switched Resistor/cap combo for the second cathode just for when I want to use the low input, which really is too low for me.
I have a1978 100 watt factory 1/12 combo, bit of an odd sort, has four input normal preamp volume and lead preamp volume and has a factory master volume on front panel as well. Had my tech disconnect the master volume as I think they add unwanted tone and although he said it's a much different beast it functions much like a 1959 non master volume and is probably my best sounding 100 watt head
I cannot understand why people take out the brightening circuit on these amps.. you lose gain and presence and all those swirly things and harmonics going on in the real marshall sound. thank you for properly condemning this outrageous practice! lol
I left my bright cap out when I first built my 2204, just so I could experiment with values, which I did, starting from 100pF, now it's settling in nicely I've put the stock 1nF value back and yeah, like you say, "swirly things" galore ;) really made it richer, loving it. Cheers.
the EH 7025 is a pretty low gain tube. the 12ax7b's are high gain. I just never had enough gain using those 7025's. Id be more inclined to just put in regular EH 12ax7's
You know what I hate when guys mod? Is when they use on of the inputs instead of putting all the pots on the back of the amp allowing for the regular 4 inputs to still be used and the modded circuit to be controlled from a back mounted pot, any additional mod switchs unless they are small batwings should be mounted on the back do you agree?
Yeah, you GOTTA check ALL components in these old amp and what I posted a couple times in the forum. They drift soo much, really, I fucking hate them and would prefer to just replace everything with modern day components to get the amps in spec and this is why people say you have to go thru a bunch of these heads to find one with really good tone (because of drift in component values)! Likewise, it's been 43 years and the amp has been gigged and modified. Who knows what abuse has been done. Although may sound better....I am not digging the tone! I assume you checked all components for drift?? I wonder if any damage was actually done to the Output Transformer over the years? Being 43 year old, all components need to be checked for drift, probably needs a cap job, seems like you found issues with the tubes and really in my opinion, this total redo needs to be done on most and as I communicated previously, check them diodes and make sure working 100%, because the diodes of days gone by suck and I have had to replace all of the components on more than one amp to find it was the diodes causing the issues all along!! :O Lessons Learned Not sure why he wanted and if it was wise MODifying a vintage JMP to JEL-spec?!?? First, a vintage amp holds value and if want JEL-spec....just get a cheaper JCM800 and do it to that and really, JEL is just a JCM800 with the fatter 3rd gain cap (i.e. - VH cap)!! It's mostly a JCM800 and not much more!
I sure like see all those tube on a tube tester and see which one was bad. New tube do make a big difference. Those White chicklet caps I have heard are not very good.
When modding an amp, why run it through that rig you have. Your masking it's true tone. You should play it as is with speaker cab, amp and guitar. Guys make demos of modded amps through recording software and then sugar coat it. Lets hear the amp, not the rig.
I disagree and have an alternative view. The direct recording process exposes the true sound of an amp, rather than "in the room boominess" of all the lo-fi mobile phone demos out there.
