5F11 Tweed Vibrolux... Coupling caps...

[Phil_Tre]

Hi !

This is my first post on this forum and I'm new to building amps...
I already built a 5e3 and a 5f11...

Ok, with the 5f11, I think that I will need a bit of help. The amp
works as it should but I would like more bass out of it. What about
doubling coupling cap value ? and since I'm not super used to what
cap does what job, I would also like to know which one(s) do I need
to change ?

I don't want the amp to be as dark as a Tweed Deluxe but just a
bit more bassy. I find the mids and hi freq. perfect with a Celestion
G10N-40 and I also have try a Jensen C10R with ok result but this
speaker is particularly bright without too much bass.

Thanks for your help, it's a great forum by the way...

Philippe

This is my "build post" from the Telecaster forum with a lot of detailed pics:
http://www.tdpri.com/forum/shock-brothers-diy-amps/447758-new-tweed-day-lots-pics-5f11.html#post5444915

[John]

Easiest thing to try first, is use alligator clips to clip in maybe a 10 bypass cap on the cathode resistor of your second tube; V2a. However, I'm not sure if that will affect the NFB loop coming from the speaker or not. Also, try bypassing the tone pot with a jumper. If that seems to boost your bass, play with different values of those little caps.

Either of these only require some jumpers with clips. For petey's sake, don't reach for your soldering iron on any of my recommendations!! 

[HotBluePlates]

... bypass cap on the cathode resistor of your second tube; V2a. However, I'm not sure if that will affect the NFB loop coming from the speaker or not. ...

That will ground out the negative feedback, and increase gain 2 ways. Since he didn't ask for more gain...

The 5E3 Deluxe uses 0.1uF coupling caps throughout except for in one spot. The 5F11 uses the same coupling cap values as the 5E3 Deluxe, except for a 0.022uF between the 1st and 2nd stages. Looking in the back of your amp, this cap is the 1st orange drop at the far-right of your board.

You have a 0.022uF, the Deluxe uses a 0.1uF. Try to split the difference with 0.047uF. If that's not enough (because the 5E3 didn't use the bright Celestion speaker), bump it up to 0.1uF.

Since your amp has such a pristine build quality, I'm sure you don't want to swap caps multiple times. Put alligator clips on either end of a 0.022uF and clip it in across the existing cap. That will put the total at 0.044uF (close enough for you to tell if this is the value you want). Keep paalleling caps until you find a total value that gives the bass you want.

[Phil_Tre]

Ok, fine !

Just to be sure, we are talking about the .022uF cap between the outer leg of the volume pot
and the pin #1 of the first 12AX7, is that ok ? It's the "far-right" anyway 

Oh and by the way, is there any side effect to this mod except more bass ?? Any treble loss
or something ??

Thanks !

Philippe

[HotBluePlates]

Just to be sure, we are talking about the .022uF cap between the outer leg of the volume pot
and the pin #1 of the first 12AX7, is that ok ? It's the "far-right" anyway 

Yes, that's the correct one.

You can, if you choose, increase the value of the other 0.022uF coupling cap, but that's already the same value as the bass-heavy 5E3 Deluxe.

Oh and by the way, is there any side effect to this mod except more bass ?? Any treble loss
or something ??

Nope. The only thing a coupling cap can do is reduce bass, and the smaller the cap the more it reduces low end. So making it bigger (in this position in the amp) will only increase lows and nothing else.

[Phil_Tre]

Just to be sure, we are talking about the .022uF cap between the outer leg of the volume pot
and the pin #1 of the first 12AX7, is that ok ? It's the "far-right" anyway 

Yes, that's the correct one.

You can, if you choose, increase the value of the other 0.022uF coupling cap, but that's already the same value as the bass-heavy 5E3 Deluxe.

Oh and by the way, is there any side effect to this mod except more bass ?? Any treble loss
or something ??

Nope. The only thing a coupling cap can do is reduce bass, and the smaller the cap the more it reduces low end. So making it bigger (in this position in the amp) will only increase lows and nothing else.

Ok perfect !

I placed my order for a couple of experimental caps and I will update as soon as I test those out.
You were right, it's won't be easy to squeeze a desoldering pump and a soldering iron in that position.
Now I know why it's "better" to lay down the filament wires against the chassis  At first, I wanted
to just tack a cap in parallel but I made this amp as neat as I could so I will just replace it the right way.

Thanks for your help, it's greatly appreciated...

Philippe

[HotBluePlates]

Now I know why it's "better" to lay down the filament wires against the chassis 

That, and only the 60's Fender amps had the filament wires in the air above the sockets.

The 50's tweed amps had the filament wires installed first (before the board or any other wiring), tucked into the little corner formed by the side of the chassis that the sockets are mounted on and the little lip at the open side of the chassis. Fender did that because it keeps the filament wiring as far from the rest of the circuitry as possible (the same is true of the 60's wiring with its different positioning of the sockets to the circuit board).

I don't know why so many people overlook that...

[Willabe]

I don't know why so many people overlook that...

It makes total sense the way you have explained it about keeping the filament wires away from the sensitive grid wires/eyelet board connections in respect to the placement of the tube sockets and eyelet board.

I can't recall reading that anywhere before whether in books (and I have a Lot of books  ) or on a web site. I don't recall KOC, Akien or Merlin ever commenting on it either. I do recall guys saying to tuck the filaments twisted pair in the chassis corner as it acts like a kind of shield to bleed away the radiated electro field to ground, but they didn't include about the grid wires/eyelet board part.


            Brad             

[HotBluePlates]

Well, the biggest issue is exactly what Phillipe said: if the heaters in the tweed amps aren't tucked into that corner, the chassis is just too cramped to get an iron and pliers in there to change out parts.

[Willabe]

if the heaters in the tweed amps aren't tucked into that corner, the chassis is just too cramped to get an iron and pliers in there to change out parts.

   Hey come on now HBP, every thing has it's +/-. So it's not a major benefit with respect to the layout, noise wise?

I don't have our friends amp in my hands but I've built a few and worked on a few old Tweeds and BF Fenders. I think if you took the soldering iron to 1 side of the heater wires and the solder sucker to the other side no problem. Just like working on 2 sides of a fence.

Yes his work is more than good/pretty as I've seen but it's way more than just pretty work to the eye, yes my words.


                     Brad              

  

    

[sluckey]

That really is beautiful work. The quality of workmanship reminds me of the blackface clones that blueznet was doing a few years back.

[Phil_Tre]

UPDATE

Ok, I have try different caps and I don't know what I was supposed to hear but
the difference is at best, faint. Yes it's a bit more bassy but not like boosting
the bass volume a couple of dB... It's more like if the bass became loose or less
firm, less "in you chest" feeling.

The Leo Fender design was probably ok as is, but it was an easy experiment
and now I know the difference.

So the "stock" .022 uF stay in and I will not have to mess with it... 

Now I need to build something else, any easy Voxy sounding amp suggestion ?
Something around 10-20 watts ??

Thanks !

Philippe

[Willabe]

Try a different speaker. They make a world of difference!


            Brad   

[HotBluePlates]

Ok, I have try different caps and I don't know what I was supposed to hear but the difference is at best, faint. Yes it's a bit more bassy but not like boosting the bass volume a couple of dB... It's more like if the bass became loose or less firm, less "in you chest" feeling.

I already built a 5e3 and a 5f11...

... with the 5f11 ... I would like more bass out of it. ... I find the mids and hi freq. perfect with a Celestion G10N-40 and I also have try a Jensen C10R with ok result but this speaker is particularly bright without too much bass. ...

So you heard likely exactly what you were supposed to hear.

Bottom-line, a 5F11 is voiced exactly like a 5E3, except for a single coupling cap that's not quite as big. And that voicing is midrangey with an alnico Jensen-type speaker. Yes, the 5E3 can also have some loose bass when pushed (depending on your tone control and volume settings).

Now you've added a Celestion speaker (the vast majority of which are midrangey compared to Jensen speakers), and you feel the speaker is bright.

I get the sense that what you really wanted out of the change to the amp was like having a Treble/Mid/Bass tone stack, but only turning up the bass control. The problem is, the 5E3/5F11 don't have a tone stack like that, and that type of stack creates a big mid-scoop. It's a big part of why a blackface amp doesn't sound like a tweed amp.

So you won't get the impression of bass boost without a circuit akin to a later Fender tone stack knocking the mids and treble down.

And what Willabe is alluding to is that you may not need to have that extreme tone shaping if you pick a speaker that gives what you want to start with. You may be fighting to counteract the speaker's voicing.

Anyway, long story short a speaker change is probably you best bet (do all you can to try before you buy). Outside of that, you probably need to change the amp into something it's not by creating a late-Fender/Marshall tone stack and fiddling the control values to give the response curve you are looking for; the "controls" could even be fixed resistors once you know the values that work for you. But the existing fiberboard won't help you do that.