Fender 400PS on a diet

[CoolBlueGlow]

How do you get all 435 watts out of a Fender 400PS without lugging those gigantic folded 18's around?

Here's one way I found to do it.



2 x K110 JBL wired parallel, and 1 x dual voice coil Infinity Kappa 12 are used to engage all three of the 145 watt output jacks.

This amp has been gigged weekly for three years without a single failure or problem. The Princeton in the background gives you a size reference.

So, to all you doubters out there, here is proof that a 400PS can be used in practical applications.

That is, if you don't mind springing for the six GE 6550A, six 7025, a 12AU7 and a 6L6GC.

Cheers,

CBG

p.s. Just the filaments in a 400PS draw 13 amps at 6.3 volts.

[StephaninMelb]

I had to laugh reading this 1971 advertisement for the Fender 400PS after seeing all the threads complaining how heavy Fender Twins are:

And don't be fooled by its 210 lbs (combined weight of the amp and speaker). It was designed to be very portable. The casters on the bottom and handles on the back make moving easy. Additional back casters mean easy loading and unloading.

[CoolBlueGlow]

Yeah, "don't be fooled"... it's ONLY 210 lbs - with ONE folded W cabinet! What are you whining about? Why that's no more than a Hammond B3, which you move all the time!

Hence my 400PS half stack. I call her "Golden Girl".

Actually, you can't see it very well in my picture, but there's a little script badge on the front of my cabinet. It says "Manitowoc". That badge came from a 1950's era Manitowoc refrigerator...sort of my inside joke/homage to these big 1960's and 70's leviathans.

:-)

[StephaninMelb]

I have never seen one of these 400PS monsters. It is a really nice looking rig. I bet it sounds killer...I like the Manitowoc logo. Did these amps have a crushed ice and cold water dispenser option?

What the single 6L6GC is used for? Don't tell me it has a SE low-power practice or tuning mode?

I've retired my Mesa Boogie 400+ but haven't had the heart to get rid of the ole gal. These days mainly using a EBS Fafner II or TC Electronics RH750, both which sound really great.

[gypsymoth]

dual voice coil? are you running two outputs into that, and one into the pair pf JBL's? I 've got those in my little Musicman 65 - not sure of their ratings, but I guess I could use just one safely.

three eminence delta/ kappa pro 12's would work well too.

[Chris Winsemius]

Originally Posted by StephaninMelb

What the single 6L6GC is used for? Don't tell me it has a SE low-power practice or tuning mode?

The 6L6 (+ extra outputtransformer) is used as phase-inverter. Some very old Gibson amps used this "style" too.

[WireLine]

Uh...what planet are you filling with that rig? :)

I can't imagine such a clean beast...and what would happen if the volume knob shorted to full.

[StephaninMelb]

Thanks for the info. I thought the 6L6GC might be a phase inverter but without looking at the schematic or specs I wasn't sure. I will have to track down some YouTube video to get an idea how they sound. I am thinking full-on late 60s - early 70s rock bass rather than funk machine. How do you describe the tone?

[CoolBlueGlow]

Thanks wireline. I expect you'll think I'm nuts, but this setup is actually quite docile. The tone of the thing has to be heard in person to be believed. Warm, smooth, commanding, very even up and down the fretboard, dead quiet and trouble free. A nice amp.

Gypsymoth - re: dual voice coil. Yes, each voice coil in the Infinity is 4 ohm. 4" voice coils, each driven by one of the 400PS outputs. Physically, the cabinet is port tuned to maximize the efficiency of the Infinity 12 from 32-350Hz. At 350Hz the dual K110 (4 ohm total load) take over, providing the mid bass and above articulation and typical JBL clean punch. So that's 290 watts on the Infinity and 145 on the JBL 2x10. It really does sound great.

Chris - re: 6L6 - Yes, of course - interstage transformers were used on several other amps, including some Fenders - but the 400PS design is unique in that this interstage transformer is driven by a 6L6GC operating in Class A triode mode. This is the secret sauce of the 400PS. The 6550A output section operates as a class AB2 amplifier. The way you can get 435 watts from six 6550A is to drive them class AB2, and the best way to drive a Pentode into class AB2 is with an interstage transformer of sufficient size that it can swing the kind of current (at the low impedances required) to drive the grids of six 6550A. THIS is how a 400PS achieves 435 watts output from six 6550. No disrespect to other designs, but a long-tail phase inverter 12AT or 12AU7 can't even come close to swinging the kind of current compared to the 6L6 triode strapped and pushing big iron in a 400PS

So, in spite of what other scofflaws and ignorant posters might insist about 400PS "wattage exaggeration" they are wrong. I've personally measured this amp loafing along at 390 watts, with plenty of headroom left. In my experience the 400PS is a fabulous and nearly bullet proof design...but you have to understand the science behind the design or you are going to have trouble with it.

Glad everyone likes Golden Girl. :-)


Cheers

CBG

[CoolBlueGlow]

Stephen - actually and quite surprisingly, it IS a funk machine. The "Guitar" channel (which is basically a Twin Reverb front end with some additional e.q. shaping) features a broad smooth tone with lots of slappy, poppy sparkly highs like you'd expect out of a JBL equipped hybrid. It's almost like a Twin Reverb for bass! In this configuration, Golden Girl easily reaches down and articulates that low B note on a Marcus Miller 5 string with alacrity. No flapping out, farting or problems at any useful volume. (Of course, if you dime it, things get crunchy - but why do that?)


The "Bass" channel has that 70's mid-bass growl. I don't use it much. Not my style.

Cheers!

CBG

[Ringo]

I like the gold tolex, is it metallic gold like the old Zodiac Naugahyde they used on the Kustom amps?

What are you playing through it, bass? guitar? both ?

I remember reading an article about the guy who designed that amp, he would interview techs before he would tell them how to work on the amp because of the complex design of the circuit.

[CoolBlueGlow]

Hi Ringo,

Thanks!

Yes, that covering is grained like regular Fender black - but it is a gold iridescent finish. Kind of hard to photograph. I should try to get a better picture of it.

The player plays a Marcus Miller 5 string Jazz bass through it. She loves the tone and the pretty gold iridescent tolex. She's happy with the gold because she thinks it looks feminine. :-)

I wish I could get more of that gold. It's out of production and I think I bought the last five yards on the planet.

Thanks again,

CBG

[Piotr]

CoolBlueGlow, I am pretty sure you do owe us a sound sample ;) I'd LOVE to hear that beast with bass and/or guitar.

[Bard2dbone]

Hear, hell. I'd love to PLAY through that sexy beast.


I love 400PS's. I quit looking for one becasue of the weight. But back in the day I didn't mind it so much. I once had an Acoustic 360 rig. Before that I had an SVT. I figured if neither of those had killed me, one of these probably wouldn't. Then we quit gigging regularly and I started realizing that I was getting old. My main rig for the last few years we gigged was an Acoustic B4 into an Acoustic TC210p and a Randall 2x15. That is a monstrous sounding ring. But it was also 300 lbs.

My current SWR Redhead into an SWR Triad is a grat rig. But I went to it because it's lighter. It's still 200 lbs.

I mostly dream of something like a 1x15 and 1x12 neo cab with an LMII on top. Low, loud and light. But now and then, back in the depths of my brain, I think about those monster rigs from the '70's and want one bad.

[CoolBlueGlow]

Bard,

Yeah, as you know these anachronistic rigs can be quite an unique experience. This setup just has a magical vibe about it. Honestly, it's not about being the absolute loudest amp...and it is not totally visually dominating on stage because of this small package I've built it into. It just has a commanding tonal authority. When the player drops down into that first couple of octaves on a five string bass, it has to be heard to be appreciated. Like I told Stephan earlier in the thread, this amp has the same effect for a bass player as when a guitar player plugs a Tele into a Twin Reverb. You don't HAVE to blow everyone away on stage. But, as with a Twin Reverb, you never have to wonder if you're going to be able to hold your own.

Yes, the head's fairly heavy at 86 pounds, but the cabinet as loaded with two K110 and the Infinity dual VC sub is only 67 pounds - and very carefully built from void free birch with pine bracing - I took many extra time consuming weight saving steps with this cabinet - so the whole rig is fairly light as these types go. I spent a lot of design and testing time tuning the cabinet both by listening and by measuring. Just one example of that tuning for efficiency - Many square bass cabinets have serious standing wave problems due to internal parallel surfaces. The typical solution is to stuff them with acoustical absorption. (a cost-effective and practical solution which is also wasteful of amplifier and loudspeaker energy) So, rather than throw away the extra acoustical energy present inside the cab by stuffing it with absorption, I tuned and shaped the cab in such a way that it needs almost no internal damping material. This design has no significant internal standing waves simply because there are no internal parallel surfaces. That took a lot of work, but the payoff is a very live, open sound that is extremely smooth with no lumps, bumps, and dead spots.

Of course, you can't see these goodies, but inside the cabinet are also extensive lightening efforts. All the internal bracing is shaved to minimize mass. It's finger jointed, corner braced, glued and screwed. The back panel and front panels are cross braced like a guitar top and they connect via loaded struts placed to eliminate resonance by coupling front and back. All screws are 10/32 SS backed with T-nuts. There are 40 of them just for holding the back in place. :-)

Of course, the other usual goodies like ultra high-grade jacks, extra high capacity speaker wiring, heavy duty American made casters, etc.


Anyway, thanks for the compliments.

Cheers,

CBG

[entresz]

Wow, what an amazing amplifier. I've always been fascinated by the super high powered amps of the 60's and 70's. The 400PS to me is like the holy grail! I remember reading in a magazine about Albert King using one at a concert once, and apparently he sounded pretty fierce...!

[Piotr]

Originally Posted by CoolBlueGlow

Yeah, as you know these anachronistic rigs can be quite an unique experience. This setup just has a magical vibe about it. Honestly, it's not about being the absolute loudest amp...and it is not totally visually dominating on stage because of this small package I've built it into. It just has a commanding tonal authority. When the player drops down into that first couple of octaves on a five string bass, it has to be heard to be appreciated. Like I told Stephan earlier in the thread, this amp has the same effect for a bass player as when a guitar player plugs a Tele into a Twin Reverb. You don't HAVE to blow everyone away on stage. But, as with a Twin Reverb, you never have to wonder if you're going to be able to hold your own.

OK, so although everybody is drooling now, the kind request for a sound sample still stands

[CoolBlueGlow]

:-)