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FDP Forum / Fender Amps: 1985 - Current / Blues Jr. - Middle Cap ?



Feb 2nd, 2007 06:32 AM   Edit   Profile  


I took my amp into Dabeck yesterday (he's very local for me) and I asked him (David) to fix a serious rattle going on in my BJ and perform your mods (I already did the Twin mod, but he is going to do the Tone Stack and upgrade power caps). He initially suggested using a .047uF cap for the middle replacement. He said that would give more of a Bassman feel (hey, I'm all about that). That however, goes in the opposite direction you mention on your site (taking it from .022 to .015uF). I had your schematics up on my phone and showed him your reccomendations. He said he would use .015uF if that's what I wanted. I'm not the expert, I was just curious what your thoughts are of increasing the mids cap to .047 vs. decreasing it to .015. I like more of a Bassman feel vs. a Twin, but only from testing them out at GC. I play Blues (SRV, BBKing, Freddie King) at home, so that's my environment. What are you thoughts on that?

Contributing Member

New Jersey, USA

Hey! What exit?
Feb 2nd, 2007 07:07 AM   Edit   Profile  

A smaller mids cap gives you more mids, not less.

Remember that the tone stack mod is designed to overcome the boxy tone of the Blues Junior, not imitate another amp. It works in the context of a big speaker in a small cab.

In terms of mids, the .015 mids cap and TwinStack work opposite one another. One gives you more mids overall, the other lets you take them out. The result is a bigger tonal range and more flexibility.


USA Dallas TX

You call THAT music ????
Feb 4th, 2007 01:08 PM   Edit   Profile  

I had David do my BJ mods as well. He used a .047 cap in mine & while I'm not an expert, like Billm, I was quite happy with the change. The best description I can give is it "smoothed out" the mids. Could be that it just worked well with my replacement speaker, a Hellatone 30.



Feb 5th, 2007 09:02 AM   Edit   Profile  

So, by doing the TwinStack mod I can achieve roughly the same thing as increasing the mids cap, but at the same time having the capability of cranking UP the mids by reducing the cap to .015uF? Is that what you mean by flexibility?

Contributing Member

New Jersey, USA

Hey! What exit?
Feb 5th, 2007 09:14 AM   Edit   Profile  

Gryffandor, your tech removed mids. Might be just the thing for that Hellatone 30, which is nothing more than a broken-in CelestionG12H30, which has fairly strong mids.

Oscar, yes, the .015 cap giveth mids and the TwinStack taketh away. The net result is that you can have more mids when you want them and less, right down to none at all, when you don't.

Contributing Member

New Jersey, USA

Hey! What exit?
Feb 5th, 2007 09:44 AM   Edit   Profile  

I should probably mention that I've done a "TwinStack Plus" mod on a couple of amps, increasing the mids control from 25K to 50K, for more mids when you want them--they're really where the distortion lives in the the Blues Junior, so the 50K control with the TwinStack jumper gives you an even bigger mids range.

In conjunction with the modded tone stack, of course.

And don't forget that the bass cap has a role in this, too. One of the joys of a modded Blues Junior is the ability to have strong low bass and few or no mids, like the Twin Reverb.

Rick Plays The Blues


ooops I changed that tube again ...
Feb 5th, 2007 09:56 PM   Edit   Profile  

your idea of the Twin Stack Plus is interesting.
I guess, this is doing something similar to what I have been thinking of maybe doing to my Concert Reverb's drive channel: I thought of maybe adding a bypassable (switchable) ca. 250k to 1Meg resistor between ground and the mids poti.
Of course, my other ideas are, making a switch to totally disconnect the tone stack from ground, or the deluxe version, having an additional poti between the mids control and ground - e.g. a 250k log poti .....
of course, all these ideas go in the same direction of increasing mids and overall level and disabling the tone stack - getting a raw, direct and mid-focused drive sound .....
Already today, I usually turn up the mids to 10, reduce the treble to zero and set the bass to somewhere in the middle .....

But now, reading your idea, I think, that this might be an option as well ..... I am thinking of a 50k or 100k logB poti (currently, there is a 25k lokB) to replace the mid poti ......

Hm, what do you think? I would prefer if I don't need to add any switch or poti, and e.g. a 100k poti is almost like having the original range in the lower half of the mid control, and having a nasty boost above ...

I really have to think a lot before I start, because my amp is not so easy to modify .....

Contributing Member

New Jersey, USA

Hey! What exit?
Feb 6th, 2007 06:02 AM   Edit   Profile  

Rick, have you tested your idea on Duncan's Tone Stack Calculator? It would give you a better idea of the effect of a large mids pot, but the final proof is in your ear--I guess you'll have to dig into that amp one more time!

Duncan's TSC



Feb 6th, 2007 09:11 AM   Edit   Profile  


Thanks for the input on my mids cap question. If I hadn't done the TwinStack mod, I probably would have gone with the .047 cap. I like the flexibility idea....I should get it back this week, I'll post and let you know what I think. I'm probably going to pick up a Swamp Thang or Texas Heat if I need more, but I wanted to see how it sounds stock before I drop $75.

Tele Vince

United States

Dec 5th, 2016 12:18 PM   Edit   Profile  

Has anyone experimented with changing the mid tone cap at all?

I’ve changed my bass cap from 0.022uF to 0.1uF. Happy with that change.

However, I also changed the mid cap from 0.022uF to 0.015uF, per BillM’s specs. Now, I find the mids to be muddy (too many 150-400Hz, not enough 700-1,000Hz).

Would it make sense to put the 0.022uF mid cap back in? Or maybe go all the way up to the 0.047uF that many Fender amp’s use?



Since I already had the part, I tried just putting a 0.022 mid cap back in. Seems to have removed the muddiness. (Yay!) I do understand though why BillM recommends the 0.015. That definitely sounded fuller when clean. So, it's a trade-off: more fullness will bring more mud . Since I play more overdriven than clean songs, the less muddiness was a larger priority. (If I was playing mostly cleans, I'd probably leave the 0.015 cap in.)

Either way, increasing the bass cap was still the way to go. I'm happy with the 0.1 I have in now, but I bet a 0.047 could be a good choice compared to the stock 0.022 too.

(This message was last edited by Tele Vince at 10:52 AM, Dec 9th, 2016)


usa metro detroit

Dec 9th, 2016 09:25 PM   Edit   Profile  

I'd go with a .022uf cap. I like it better than .015 value. I find the .015 almost squishes the tonal dynamics out of the tone stack, clean or driven.

I went for a Tweed vibe. (Total Tone stack mod w/Sprague caps) The standard "Twin tone stack mod" (IMO the twin mod took the El84's mid tones out... very clean and chime'ish I like indeed.) Heyboer Trans, Mojotone reverb tank, Eminence Cannabis Rex, 12ay7 gold pin & ECC83S w/ some Mesa El84's power tubes

The amp is super quiet and sounds as good as any Princeton RI does. I love my Blues JR.. Not hard to mod these amps at all.. and if you do a little research.. you can come away with a really nice amp. Also no Princeton gets as good overdrive as my Blues JR does now I get guys at jam sessions all the time.. Asking "What did you do to that amp?"

Same with my HRDeluxe, I've modded the tone stack of that too. Now the Drive/More Drive channel sounds as good as the clean channel (same EQ dynamics in quality of tone ) Now it's very much like a pushed 59 Bassman/Early Marshall Plexi.. sounds really close. I just heard a Deluxe Reverb RI and said to myself "Meh?" My HRDeluxe Clean sounds as good and on the Drive channel sounds better than that pushed Deluxe RI.

Little research, a little solder, little know-how combined with Fender goes a long way...

(This message was last edited by pcalu at 11:34 PM, Dec 9th, 2016)

FDP Forum / Fender Amps: 1985 - Current / Blues Jr. - Middle Cap ?

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