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PostPosted: Fri Jul 10, 2015 7:31 am 
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Firstly, I still love my Tweed (Mostly). Secondly, I saw the snippet on Youtube about you guys and I think it was great. Good to see faces to match the names I always see.

I've had my Tweed now for 2.5 years and its a really great amplifier. It is probably going to get gigged quite a lot soon, mostly because it is smaller than my 18 watter with its 2x12 cabinet. It is very nearly the perfect rock and blues amp. I can see why people used them so much in the past and I can also hear why people don't anymore.

Some information, I have the VRM module in mine and I'm glad I do. It has a BBQ 12A125A speaker, which is not very efficient but even so, at full VRM it is rather loud. I certainly can't use it for practicing at my house at that volume. On the other hand, the full amp VRM sucks a bit. It makes the already spongy attack REALLY spongy unless the VRM is set to 2 o'clock or more, which means more volume. OK, this isn't the biggest of deals for gigging, I could gig this amp at full volume without much hassle I think, but it isn't an ideal situation. At full VRM the amp is a beast, it really loves my Les Paul through the bright channel. Bright and smooth overdrive. I love it like this.

So because of the volume, the pine cab and, I guess, the large amount of bass that gets through, my tubes rattle and my cabinet has a resonance in it, which makes the amp sound like its going to break apart on certain notes. (It probably will break apart haha).

How do I stop cabinet's backplate from rattling? How do people here stop that from happening? I guess the thing to do is to have some kind of soft cloth between the chassis and the backplate to dampen any vibrations there. Any tips to improve this would be most helpful.

Also, if I were to change one of the coupling caps to a 0.022uF, which one would be better to change? Earlier in the signal path or later? I think I only have one 0.022uF in my box. I'm considering this change in order to help the amp to be a bit tighter in attack at lower VRM, do you think this would help?


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PostPosted: Fri Jul 10, 2015 12:46 pm 
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To reduce sag in a power supply and "stiffen" it up you would typically use a bigger capacitor in the first stage of your power supply. The Tweed has a 16uF/500v cap in the first spot (C13). Bumping that to a 47uF/500v should stiffen things up a bit. Or you could get a couple more 16uF/500v caps and try running one in parallel with C13 for a total of 32uF. If that doesn't stiffen it up enough, you can parallel another 16uF in there or replace both with a 47uF.

Doing this will also give you more attack and tighten-up the bass, so you may not like the results. The smaller power supply caps are part of the whole package that gives the Tweed circuit its Mojo.

But, I don't know enough about how the VRM works to know if this still holds true with that in the circuit. I would imagine it does though.

Are you going to be gigging with a full band? You might find you will be turning your amp up louder than you think unless you get one of those sound guys who will walk out the door if you don't let him mic your amp. I am quite often maxed-out with 20-ish watts on stage. If not, then pretty close.

Also, is your cabinet open or closed back? If it's closed, try removing the back panel so your speaker can breathe. You could also try a speaker that has a tighter bottom-end to tame the bass.


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PostPosted: Fri Jul 10, 2015 1:08 pm 
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Remember that tube rectifiers have a spec for the highest value of the first cap it seems in the case of a 5y3 its 20uf so 47 uf might be a little taxing on it

need to build a chart with this info and add the value of first cap for the chart

Image


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PostPosted: Fri Jul 10, 2015 2:32 pm 
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47uF might be pushing it but 32uF should be safe. If you're worried about it, you can use a 5V4 instead of the 5Y3 rectifier as a drop-in replacement and it will be fine at 47uF.


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PostPosted: Sat Jul 11, 2015 8:10 am 
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Hi,

I don't really want to change the character of the amp too much. I already installed the 470k PI mod, to stop the nasty blatty distortion one gets when driving these amps hard. I see a lot of people like modding their 5E3s to have more headroom but I actually want the opposite. I'm one of those who use the amp cranked up and control the drive from the volume knob O_o I have a feeling that the amp will be better behaved with the smaller coupling caps, so that the useless bass frequencies get cut out, tightening up the sound a bit, making it cut the mix better and maybe even stop the cabinet from rattling itself apart. The sag is not so bad when the VRM is turned up, I have a feeling the sponginess is due to the preamp being starved at lower VRM settings.

I was just wondering how everyone else gets their cabinets to rattle less or if they do something to dampen them somehow.


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PostPosted: Sat Jul 11, 2015 2:54 pm 
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On various chassis designs, we started to add a tapped hole in the rear chassi lip. We use this to firmly attach the rear panel to the chassis ans stop the rattling. Current design has two, one in the top lip, one in bottom.

You can drill and tap that lip if you're cafeful.

In the olden days, I think they used guitar picks to wedge it so it wouldnt rattle.

On the coupling cap, change the first one(s) to.022uf.

Dont go beyond 32uf on the filter cap.

You can just scale the power amp if you prefer. You may need to adjust the voltage dropping resistors, but we havent tried it.

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PostPosted: Sun Jul 12, 2015 10:59 am 
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coco wrote:
On various chassis designs, we started to add a tapped hole in the rear chassi lip. We use this to firmly attach the rear panel to the chassis ans stop the rattling. Current design has two, one in the top lip, one in bottom.

You can drill and tap that lip if you're cafeful.

In the olden days, I think they used guitar picks to wedge it so it wouldnt rattle.

On the coupling cap, change the first one(s) to.022uf.

Dont go beyond 32uf on the filter cap.

You can just scale the power amp if you prefer. You may need to adjust the voltage dropping resistors, but we havent tried it.



Ah ok thanks. I'll change the first one and see how it goes. I must see if my chassis has that hole or not. I think I'm goin try and glue, staple or otherwise a piece of velvet or dustcloth or something in there to dampen the vibrations. I'm willing to bet that the rattling will diminish if I cut some of that bass too. I'll leave the VRM as is for now, it works, the amp just sounds better louder.


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PostPosted: Sun Jul 12, 2015 8:40 pm 
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Thanks, Stephen, for the tip about the hole in the chassis lip. I never realized it's there until now. I've been trying to get rid of the back panel rattle since I built the amp about 2 1/2 years ago. I tried padding the inside of the panel and jamming things in there but that didn't help much. The panel seemed to always need to be held closer to the chassis to be quiet, not farther away.

My chassis came with one 4-40 tapped hole on the top lip. I drilled and tapped a second one on the bottom lip today just to make sure, and I drilled a couple of corresponding holes in the back panel. With everything screwed back together the cabinet doesn't rattle at all. Even with low E's at near full volume!

Yes, the amp is a little bassy, but I like it that way. I've had no desire to modify the stock tone. It sounds really good with my Strats and the Jensen speaker I have in it.


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PostPosted: Mon Jul 13, 2015 2:44 am 
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I see from old pics mine has that hole too. I'll make a plan to get a hole and a screw in there.


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PostPosted: Tue Jul 14, 2015 6:01 pm 
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mitch, we did exactly the same thing and added the second hole as standard. 4-40 is the correct size.

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PostPosted: Sat Sep 12, 2015 3:16 pm 
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Just did another tweed and used those 2 screws. Really important to stop the rattle!

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