Power scaling in a tweed deluxe?

[K-man]

Has anyone installed power scaling in a tweed deluxe? I was thinking of building one from a kit and installing power scaling for home use.

Where do you mount the power scaling and drive compensation controls? Also do you need to install a fan or is the heatsink adequate?

Thanks.

[K-man]

Anybody?

[57paf]

Dear K-man:
I've been thinking of having a large tweed (Bassman or Bandmaster) custom built for me with power scaling too.
My ideal would be to make a custom silk-screened, one off chassis.
If you have a real tweed, I wouldn't change it to preserve its historic value. I only vaguely recall what a tweed champ looks like, but what I would suggest is:
1. Eliminate the ground switch/death cap and replace with a 3 prong cord;
2. Remove the fuse holder and install a simpler type with two clamps at the ends rather than the fancier barrel type; &
3. Install your scaling pot in the ground switch hole & install the drive pot in the fuse holder hole.
I presume that you are not going with whole amp scaling, but are going with the 2 knob type. Please let me know which way you decide to go. I only scaled the power tubes on my plexi clone, thus have a post-PI master volume. John Suhr uses a pre-PI master volume on his Badger because he liked the sound better.
Good luck.

[57paf]

I forgot to answer your 2nd question.
Cooling fans or a 2nd MOSFET were required for 100 watt amps running at bedroom levels. If you run your scaling about 50%, the MOSFET doesn't get real hot. A champ is kind of a tiny amp and some may question the need for scaling something this small.
You could ask Kevin O'Connor if you need to be reassured, but I don't expect that it would get too hot. Although I would mount the MOSFET on the transformer side where air can move vs the interior board area where no air circulates.

[GuitarsFromMars]

Power scaling for an 18 watt,twin 6V6 amp seems like a really large waste of money.Why not buy a Bad Monkey?

[Dave]

Power scaling for an 18 watt,twin 6V6 amp seems like a really large waste of money.
Why? If you're looking for volumes say, as low as an acoustic guitar, an 18 watt amp is really loud. Hell, a 5 watt amp is really loud.

[Trout]

Why? If you're looking for volumes say, as low as an acoustic guitar, an 18 watt amp is really loud. Hell, a 5 watt amp is really loud.

If you need volumes that low, why pollute a perfectly good amp with sand?

Get a headphone amp Like a Rockman.
Back when all the great music we all love was recorded, Those guys didnt use power scaling or any other gimmick, The used the amps that are highly sought after even today.

Trout

[Bussman]

...Back when all the great music we all love was recorded, Those guys didnt use power scaling or any other gimmick...

Those guys used plenty of gimmicks. And if today's technology would have been available to them they would have used it too, as a matter of fact they are using it now...

[vibroverbus]

Those guys used plenty of gimmicks. And if today's technology would have been available to them they would have used it too, as a matter of fact they are using it now...

Absolutely. The irony always strikes me when some guy will b*tch about purity and not polluting an amp, then run a tube rig with a bunch of boxes on the front end. Ever looked inside a stompbox? The cheapest, lowest grade components you can buy, running on a crappy 9V battery that will be quickly running below voltage spec. And basic concepts of amplifier design - any noise or distortion on the front end is exponentially worse than something downstream, which is why you can live with microphonic tubes in a PI spot but not V1/V2. So if you want amp purity, you better be against using effects... like Jimi or Jimmy or Jeff or Carlos or Eric etc. etc. did.

Criticism based on 'not putting SS into my amp' misunderstands what the PS kit is. Power scaling is a pretty clever design actually, using SS components to adjust the power supply voltages while leaving the basic signal path intact. No transistors used for signal amplification (or attenuation), just to 'scale' the supply & bias voltages. So it's not "adding sand" really any more than having a diode rectifier is.

The criticism one might have would be that using SS voltage control could be overly stiff... I haven't seen a detailed schematic of the circuit, but if it does over-regulate the supply for your taste, adding sag-emulation resistors, in the form of either big plate or screen supply resistors is an easy way to 'soften' the supply up. In fact, doesn't KOC offer that as a kit as well?

[Dave]

Criticism based on 'not putting SS into my amp' misunderstands what the PS kit is.
+1
Exactly why I didn't even bother to reply.

[Trout]

Absolutely. [rant] The irony always strikes me when some guy will b*tch about purity and not polluting an amp, then run a tube rig with a bunch of boxes on the front end.

I own NO Stomp Boxes, Never Have. Some think power scaling is a viable answer, But I feel running the tubes outside the proper voltages Meaning Starved is not a solution. Its a Band Aide.

I have seen several detailed schematics and variants, Not saying they do not work, But no way in hell they are going to produce or reproduce the tone of the amp exactly like running at optimum specs.

I can see if its a 50W or better amp that needs to be used at home, But there will still be trade offs on the end tone.

Trout

[vibroverbus]

no way in hell they are going to produce or reproduce the tone of the amp exactly like running at optimum specs.


Troutman - Obviously you're right on that point - pretty much "nothing sounds like a cranked Marshall stack except a cranked Marshall stack" (insert Fender/whatever).

Except regarding "optimal"... running tubes at different voltages isn't per se wrong, just have a look at any tube datasheet - operating point is a designers choice. Nothing empirical says that a 6L6GC should be run at 400V vs. 250V or 150V. The PSK basically gives you control over where that is set. Higher voltages were mainly chosen to give the most clean power output by original designers, long before we decided overdrive clipping was cool.

Now as you say, a different operating point won't necessarily sound exactly the same as the real-deal stock setup, but it is likely a far better approximation than a lot of other bedroom-level solutions.

BTW & FWIW I don't have nor have every installed a PSK, no reason to be a proponent but I don't think there's much wrong with the concept...

[GuitarsFromMars]

I own NO Stomp Boxes, Never Have. Some think power scaling is a viable answer, But I feel running the tubes outside the proper voltages Meaning Starved is not a solution. Its a Band Aide.

I have seen several detailed schematics and variants, Not saying they do not work, But no way in hell they are going to produce or reproduce the tone of the amp exactly like running at optimum specs.

I can see if its a 50W or better amp that needs to be used at home, But there will still be trade offs on the end tone.

Trout

That what i was referring to,you stated it differently than I did.My sensibility(with 35 years of recording,gigging,and playing) is that a tweed deluxe is a small amp known for not having a lot of clean headroom,and that if you need to put something that is a potential electrical problem,in a classic tube circuit that has survived,on it's own,since 1957,you need to be looking at an alternate piece of equipment.I can see looking into it with a 50 watter.The amp guy here in the neighborhood was asked to do the power scaling on a BFDR,and he refused,said it's not a safe mod,and that amps that small were not designed for something like that.

[tommytomcat]

Any kind of PSK is going to be a tough fit inside the normal 5E3 chassis... if not impossible. Maybe an external 8ohm attenuator might be the ticket. I have a 5e3 homebrew that has a post PI MV and triode/pentode switch built in. One or a combo of both gets me decent tone at bedroom levels.

[vibroverbus]

electrical problem,in a classic tube circuit that has survived,on it's own,since 1957,you need to be looking at an alternate piece of equipment.I can see

See OP.

He said he's looking at building a new one from a kit. There is no vintage amp.

[GuitarsFromMars]

See OP.

He said he's looking at building a new one from a kit. There is no vintage amp.

I got it.I was referring to the original 5E3 circuit(from the Western Electric circuits which Leo used...)which it will be built from.Still very little headroom and a marvelous low volume tone which will be there without any assistance.It's still a waste of money,imho.YMMV.It's the model A of guitar amps...

;)

[mark norwine]

I could be all wrong, but if I recall correctly......

....The one {and only} time I had a Maven Peal amp on my bench for repair, I seem to remember that, aside from the power attenuation circuit, the amp itself was just a 5E3....

So, yes, if I recall correctly, there is a tweed deluxe with power scaling...

[K-man]

I wasn't asking for opinions on the merits of installing power scaling in an 18 watt amp (which by the way John Suhr has done very successfully).

57paf thanks for the ideas. I'm going to look into getting a custom chassis built, but if not I'll probably build it per your suggestions. I wanted to build the kit from Mission amps, which has the chassis laid out for an on/off switch, fuse, standby switch and pilot light. What I think I can do is use a dpdt switch as an on/off/standby switch, put the fuse in the extra speaker jack or internal to the chassis, and then use the holes for the fuse and the standby switch for the PS controls. Do you see any problems with doing that?

As far as the fan goes, on London Powers website they say you may need a fan in a 100W amp or a cathode biased amp. I'll email Kevin O'Conner and see if he thinks I'll need it in the deluxe.

[Scottone]

I've heard good things about this guys power scaled tweed circuits.

http://www.daviesaudio.com/build.html

[57paf]

K-man:
Sorry, for some reason I thought you meant a champ. What you propose makes sense.
There are different ways of scaling the amp: Output tubes only w/post PI drive (what Kevin usually recommends), output tubes plus PI w/pre-PI drive (John Suhr told me this is what he uses on the Badger), or whole amp (Kevin says it sounds like a variac--Cory Davies says it sounds "tweedier").
Scottone, thanks for finding Cory Davies site. Cory is the best guy to talk to about power scaling a Fender, particularly tweeds. He even helped me 2 yrs ago when I commissioned a powerscaled 69 plexi clone. Cory told me that you should listen to the different scaling configurations and see which one you like better. It may be very complex to try to install a switch to scale it different ways--check w/Cory.
I would appreciate if you could post what you find out. Good luck!

[57paf]

John:
I don't think that I mentioned this to you when I called last month to inquire about your power scaling topology, but everyone in the store that heard your Badger was just drooling over the wonderful tones that they could get at all volume levels. Two of the guitar teachers were playing it and just couldn't stop. I told Dan (the store owner) that your amp is probably the first that is going to make power scaling a sought after feature because you have executed it so well. It is so easy to get jaw-dropping tones.
Since K-man is intending to power scale his amp, I was wondering if you could volunteer your impressions on the different tonal effects that you got with the different scaling methods you tried. How would you compare post PI drive, pre-PI drive, & did you try whole amp scaling?