18w frankenstein - mid monster

[johannbr]

Hello guys!
Last weekend my former band got together and we played some songs for fun. I'm a little bit disappointed with my 18w. I built it in 2007 and made some changes during the years. It was born with an EF86 in the preamp and later I changed to 12AX7 and included a TMB circuit and added also a powerscaling circuit and PPIV MV. I believe I did all that before 2012.

While playing, our bassist recorded some songs and later I realized that this amp is a mid machine. Everything is pointed to the mids. It lacks low end, lacks bright, there is only MIDs.

I really need to get rid of that nasty exagerated mids and give it some low end and bright, preferably without losing gain. Yesterday I opened it and went through the night reverse engineering (lol) that beast. I draw this schematic attached. Here are some things that I noticed:

1. I'm planning to remove that marshally cathode config at V1 and stick some 22u/1k5 or something like this to tame mids, maybe I could stick a switch.
2. I don't know what I did in that tone stack. I really don't remember how I came into that but it seems to be a mess (LOL). I'm thinking about changing it to the classic TMB circuit and components from bassman 5F6-a.
3. I have read in the forum about using negative feedback (and also a switch for it), maybe it will help to tighten the low end.
4. Really don't know why there are polyester caps in parallel with filtering caps.

What do you guys recommend to achieve this?

Sorry for english mistakes, not my mother language.

Thank you all!

[Bieworm]

Hi there

First thoughts: what speaker are you using?

[johannbr]

I'm using mainly english voiced speakers.
Two Eminence GB12 in a 2x12 and I also have two 1x12 cabs, one with a bigger magnet with around 120w and other with a smaller magnet and around 75w. These speakers were built by a speaker maker locally in my city using some specs provided by me, trying to replicate G12H30 but with more watts.

The thing is, I also have a plexi clone with powerscaling and KT88 tubes and it sounds great, with tight and good low end using all the three cabs, obviously, better in the 2x12.

It is known that the EL84 can't reach the low end of a 6L6 or KT88 but in the past (I'm starting to remember things) I remember that I used a rotary switch in place of coupling cap in the output of the EF86 tube and this rotary switch has 6 positions, from 1uF to 1nF and when selected 1uF, I remember that this amp got huge uncontrollable low end. The guitar sounded like a bass in the low E. Pretty unusable but it proves that is possible to reach some good low end using EL84.

Thank you!

[JMPGuitars]

Your drawing is a little hard to read, but it barely resembles an 18W as drawn. Is that correct, 22nF for the cathode cap on the power tubes? Or did you mean 22uF? If you want tighter bass, we use between 1000 to 2200uF on the cathode cap.

Every circuit is different. If another amp sounds great with your speakers, that doesn't mean this will. Some speakers work with some circuits well, and others don't. That doesn't mean that there's something wrong with the circuits or the speakers, only that they don't get along well. If by Emi GB12 you mean GB128, then those are really punched in the mids, especially the mid and upper mid range.

[Bieworm]

Your drawing is a little hard to read, but it barely resembles an 18W as drawn. Is that correct, 22nF for the cathode cap on the power tubes? Or did you mean 22uF? If you want tighter bass, we use between 1000 to 2200uF on the cathode cap.

Every circuit is different. If another amp sounds great with your speakers, that doesn't mean this will. Some speakers work with some circuits well, and others don't. That doesn't mean that there's something wrong with the circuits or the speakers, only that they don't get along well. If by Emi GB12 you mean GB128, then those are really punched in the mids, especially the mid and upper mid range.

And additionally, it depends which G12H30 they try to copy. If it’s the 70th anniversary series then it’s no wonder the amp sounds off balance. That is by far the worst speaker I’ve ever had, period. The old 70’s or the Heritage series, those are real good!

[johannbr]

Your drawing is a little hard to read, but it barely resembles an 18W as drawn. Is that correct, 22nF for the cathode cap on the power tubes? Or did you mean 22uF? If you want tighter bass, we use between 1000 to 2200uF on the cathode cap.

Sorry, I forgot to write the value for the eletrolytic cap. It is a 1000uF but yes, there is also a 22nF in parallel.