The Fender 400-PS FAQ
The Fender 400-PS FAQ
The Questions:1. Is the 400-PS a Bass or a Guitar amp?
2. I've heard that the 400-PS is very problematic.
3. Why do I have to use those high priced GE-6550A's?
4. Are all 6550's the same?
5. What test equipment do I need to setup a 400-PS?
6. How much TRUE R.M.S. power does the 400-PS really put on the speakers?
7. Why are there three 145 watt speaker outputs on the back of the 400-PS?
8. What are the best speakers to use with a 400-PS?
9. What are the best speaker cabinets to use with a 400-PS?
10. Can I get all the power of the 400-PS on one cabinet?
11. What's so special about the 400-PS experience?
12. Can I ship my 400-PS to you for repairs?
13. Is there some way you can help my amp tech repair my 400-PS?
14. How can I find out when my 400-PS was made?
15. How can I find out what my 400-PS is worth?
16. Are there any mods that can be done to the 400-PS?
17. I found a broken down 400-PS for sale. Do you think I should buy it?
18. What are the best basses to use with a 400-PS?
19. My solid state amp blew speakers often. Will the 400-PS do the same?
20. Did any famous bands use the 400-PS amp?
21. Are there any Do's and Don'ts I should know about when using a 400-PS?
22. What is the advantage of having a 400-PS over an SVT.
The Answers:1. Is the 400-PS a Bass or a Guitar amp?
(This email was found in my mailbox, speaks for itself)2. I've heard that the 400-PS is very problematic.
Subject: Re: Fender 400PS
Date: Wed, 16 Feb 2000 08:45:10 GMT
From: "ALAN THOMPSON" <zambiwoof@xxxx.com>I had the pleasure of hearing Albert King blazing through one of these monsters years ago at an outside concert in Phoenix (the amp was supplied by the local promoters). Imagine Albert with a screaming Hendrix tone and that about nails it. Awesome. Taj Mahal was sitting next to me, he was jumping up and down and yelling all through the show.
At one point Albert held a sustained note through the complete twelve bars of a song, and then deftly bent it down into a cool turnaround, the audience was on the edge of their seats through the whole thing and reacted crazily when he finally completed
the lick.What a show! It's hard to remember now, but I think they had it
going through a couple of Dual Showman cabs, so it was only using 2/3 of the available power.A.T.
Used as a keyboard amp, the 400-PS is just amazing with the full range JBL Showman speaker cabinets.
I have found that it is most often the users and amp techs who cause
the problem, in the 400-PS to appears to be problem-matic.Users, don't want to be bothered following the rules that go along with owning and operating a 400-PS. They seem to think that the same rules that apply to owning and operating a 100 watt Fender Bassman or even the 300 watt Ampeg SVT, automatically applies to the 400-PS. Mistakenly thinking, that the 400-PS is in the same class of amplifier.
They, couldn't be more wrong, and...
Amp Techs, seem to think that if they know how to work on a 100 watt Fender Bassman or even the 300 watt Ampeg SVT, that this automatically qualifies them to work on the 400-PS. Thinking, that the 400-PS is in the same class of amplifier.
They, couldn't be more wrong.
It is for this reason, the 400-PS amplifier gets it's undeserved problematic reputation.
The 400-PS is a one of a kind amplifier, with its own set of rulles to follow.
When you understand and follow these rules, the 400-PS is no more problematic than a Fender Bassman.
3. Why do I have to use those high priced GE-6550A's?It's like anything else, when specific things are designed to work together to yield the "maximum" in performance with long service life. This is the case with the 400-PS with the original Tungsol 6550, as well as with the even higher performance GE-6550A.Likewise, the high performance Musicman amps were designed to run the Sylvania 6CA7 tube, because of their well known superior performance and service life.
In both cases, no other tubes were considered for use in these amps. Not even, as a substitute replacement tube.
A year or so back, I had a 400-PS owner stop in with a set of the Russian 6550WE tubes to be installed. I really had to play games with that 400 to get those tubes to run. This was their best day right out of the box for these tubes, and the best they could do was 124 watts per load at 100 Hz for a 372 watt total output from a conservatively 435 watt rated amp.
After 72 hours of running time and a re-adjustment, that 372 watt total figure dropped by almost 50 watts.
It's one thing to print the specs for a tube, and quite another to make the tubes that live up to those specs.
Here, are the GE-6550A data sheets for you to see if the other so called 6550's measure up to the high performance GE-6550A standard.
High performance with long service life is the hallmark of the GE-6550A.
With the way tubes are being made in other countries today, there is little chance of any of the same type of tubes being the same.There are no unifying standards behind what they produce. There simply are no unifying standards to cover their manufacturing methods, material standards, or electrical performance characteristics.
In the USA, we had electronics industry standards and practice to follow. The rest of the world's countries have what ever they think a tube is, for a tandard. This, most often can change from production run, to production run.
Therefore, the problems we have with vacuum tube performance being all over the map today.
For example, if they can't even make a tube with the right size pins for our tube sockets,... would you expect them to have the correct electrical characteristics dead on spec for a a Sylvania or GE of the same branded type tube.
If industry standards were on the minds of those who make the vacuum tubes from off shore, I would not have had to re-base these tubes to fit the sockets made in the USA, and you would not have these pictures to look at on this FAQ page.
5. What test equipment do I need to setup a 400-PS?TEST EQUIPMENT REQUIRED:1- 0 to 150 volt 60 Hz A.C. voltmeter 2% accuracy
1- G.R. Variac type W10M, 13A 0-140v.
1- Weston 0-10 Amperes Iron Vane R.M.S. meter model 1944-2%
1- H.P. 120B oscilloscope (or equivalent)
1- H.P. 200AB Audio Oscillator (or equivalent)
1- General Radio 546 Micro voltmeter (or equivalent)
3- 4 ohm 160 watt load resistors
3- Weston 1942 series 0-25 volts 2% accuracy rectifier type A.C. meters
3- Heavy duty cables of #14 flexible wire (5 ft. maximum) and associated
connectors for output hookup
1- Dummy load for reverb test (consisting of actual reverb input coil
assembly mounted in box with two (2) phono connectors for output
hookup.
1- H.P. 400 E RMS meter (or equivalent)
1- Weston model 1241 D.C. volt-ohmeter (or H.P. 412 V.T.V.M. if in house)
plus necessary shielded cables for input, reverb, etc.NOTE - The above list was required by Ed Jahns in 1970, for the original factory final testing and setup of the 400-PS that came off the assembly line.0
6. How much TRUE R.M.S. power does the 400-PS really put on the speakers?
From Step 29 of the Fender factory test an setup procedure,....29- Connect audio generator to Bass input "1"; increase signal to be certain that output of over 25 volts (156 watts) at 120 line voltage is available.....
(actual power output available exceeds 190 watts R.M.S. per channel at 80 Hz per channel and is 145 watts R.M.S. at 5% T.H.D.)Step 29 is a three part step, with three power levels to be observed on the three loads used on a stock 400-PS.
The first total power level on the three loads is 468 watts R.M.S. with the previous EQ settings on each channel with the audio generator set to 500 Hz.
When the generator is now plugged into the Bass channel, and the audio generator is changed to 80 Hz., due to the previous EQ settings, the power output to the three loads can go up to 190 watts R.M.S. per load.
Which, would give a total yield of 570 watts R.M.S. for the three loads.
Then, the signal level is reduced till 5%T.H.D. is reached, which yields a musician's super clean 435 watts R.M.S., as a very clean conservative final power rating figure.
To put it simply. What this all means is...... the stock factory 400-PS setup correctly is more a 500+ watt amplifier, than a low 400 watt amp in the hands of the real world bass player.
7. Why are there three 145 watt speaker outputs on the back of the 400-PS?It was a totally different world in the early years of speaker development. For the longest time during this time period, JBL and Altec Lansing were the only high power speakers in the musical instrument amplifier game.Through the 60's and up until the mid 70's, the power output of the amplifiers were governed by the power limits of the speakers available to soak it up, without blowing up. This, is the main reason for the three 145 watt speaker outputs on the 400-PS.
When JBL gave birth to their K series of speakers, JBL jumped out front in the power game big time. Remember, we are talking pre and post 1970 here.
For example:
The K-110 was rated 75 watts RMS with a sensitivity rating of 99 db
The K-120 was rated 100 watts RMS with a sensitivity rating of 102 db
The K-130 was rated 125 watts RMS with a sensitivity rating of 104 db
The K-140 was rated 150 watts RMS with a sensitivity rating of 99 db
The K-145 was rated 150 watts RMS with a sensitivity rating of 99 db
The K-151 was rated 150 watts RMS with a sensitivity rating of 100 dbIn other words,.... compared to the speakers of today, those JBL speakers would perform just as loud with less power applied. Or, they would perform a lot louder with the same power applied.
Don't take my word for this. Compare today's high-tech, high power speaker's sensitivity ratings to these old JBL's. Then do the math, and discover how little is really gained with the "power piston" concept, behind today's bass amplifiers.
For another example, to help add better understanding to the above, from the old school real world, note the picture below.
Billy Cox is using six Guild Quantum Bass cabinets with two JBL 15" speakers in each of them. Each cabinet is powered by one of those four Showman amps, a Showman Reverb, and a Twin Reverb. The total power Billy has on his speaker cabinets is ONLY 600 watts for a concert level stage rig.
How do you think today's popular four 10" bass cabinet with the same 600 watts is going to perform in comparison on that stage. Imagine, yourself with this 4x10" cabinet of "Power Pistons", trying to replace those six Quantum cabinets on stage, with that same 600 watts for power.
Clearly you can seethat this isn't going to work out too well. A single 4x10" cabinet with ONLY 600 watts! The reality is, you will be placing a 150 watts on each of those 10" speakers, while Billy is only placing 50 watts on each of his 15" JBL's.
Billy could easily double his power delivery without risk of speaker failure.
Now, stop and think,... about how many more ADDITIONAL watts of power are you going to NEED, to jack up above the 600 watts you already have on this 4x10" cabinet, to equal the performance Billy previously had going on that stage.
But,... you say, that's not fair. Because, you only have one cabinet.
OK, assume you have two 4x10" cabs now. You still have to pile on a lot more watts on those TWO 4x10" cabs, over the 600 watts Billy originally started with to equal his performance.
By the time you have reached 1200 watts on those two 4x10" cabinets, you now have 150 watts per speaker again, and Billy is still kicking your ass filling that theater with his full ranged sonic delivery system.
With the JBL K-130's 1 watt at 102 db rating, how loud will each JBL speaker be with Billy's 50 watts placed on each of them?
That, would be an approximate 120 db of Sound Pressure Level, or SPL
All the high power piston bass speakers have lowered sensitivity ratings due to the increased mass weight of their assemblies for the high power handling.
One of the popular Eminence 10" bass speakers is rated at 95 db.
Which, would require an approximate 250 watts for it to reach the same 120 db SPL produced by Billy's JBL's. But, you only have 150 watts per speaker, that can't reach Billy's 120 db SPL.You still, don't have enough power to come close to Billy's gear.
Do you see now how inefficient this modern "Power Piston" game is, for the sake of a few db increase in SPL per speaker.
Remember, a 3 db increase in SPL, requires twice the power.
So,... you have the old school method of using more cabinets, with very highly efficient speakers, at low power levels per cabinet. Which, is why the 400-PS was designed with its three separate 145 watt RMS speaker outputs.
And,... with the correct wiring, one 400-PS could replace all six of Billy's 100 watt Fender amps, and will provide the same VACUUM TUBE tone and power to those six Guild Quantum Bass cabinets as before.
With the weight of a Shoman Reverb head being around 40 lbs., and the 400-PS being 84 lbs.,... the gear weight reduction is a substantial 156 lbs too.
The "Power Piston" concept used of today, with its inefficient speakers, forces the use of those very high power levels. This recipe's artifacts from solid state clipping, solid state switching power supplies, semiconductor noise class of operation, with horns for better "noise" reproduction, along with theRISK of Hang Time cooking the speakers, etc...
These "Power Piston" speakers that are far from the full ranged fidelity REQUIRED to reproduce the full spectrum of the natural sounds found in the bass instrument.
With the inclusion of HORNS in the common everyday bass rig of today, to compensate for the lacking highs from the speaker,... is this additional horn is really going to provide the full spectrum of the natural sounds found in the bass instrument, with the WARMTH of a speaker?
This bass rig has the full ranged fidelity REQUIRED to reproduce the full spectrum of the natural sounds found in the bass instrument, with the warmth and harmonic richness only vacuum tubes can provide.Welcome to the 400-PS experience.
8. What are the best speakers to use with a 400-PS?For Bass or Guitar:Any single or group of full range speakers of the highest possible sensitivity rating, with a total power rating no lower than 200 watts RMS, to equal 4 ohms per speaker output line of the 400-PS.
9. What are the best speaker cabinets to use with a 400-PS?
For Bass or Keyboards:Any ported compression cabinet tuned for the lowest frequency to be reproduced.
For example:The Sunn 200-S, 2000-S, or 215 two 15" cabinets.
The Guild Quantum Bass cabinet.
Any properly tuned "W" bin.
Any properly tuned "Scoop" cabinet.
For Guitar:Any extension cabinet designed of guitar applications with properly selected speakers for the 400-PS.
10. Can I get all the power of the 400-PS on one cabinet?
Not, without a custom made output transformer, and output stage circuit modification.
11. What's so special about the 400-PS experience?
I guess I'll let one of the guys from the 400-PS club answer this question.Subject: Re: [400PS_group] Re: Steve! what year....
Date: Sat, 22 Feb 2003 02:22:02 EST
From: BARTTHOM@AOL.COM
Reply-To: 400PS_group@yahoogroups.com
To: 400PS_group@yahoogroups.comSES,
I USED TO PLAY A G&L B1000 THROUGH A PEAVEY MK IV w/ 1810 CABINET. YEAH, I'M A BASS PLAYER; BUT, WAIT, IT GETS PERTINENT!I PURCHASED A BCRico BASS & FOUND MY SOUND IMPROVED DRAMATICALLY! THEN, IT HAPPENED; THE THEFT OF A LIFETIME.
I WAS ABLE TO RECOVER THE G&L AND I SUPPOSE THE 1810 SPEAKER WAS TOO HEAVY; CAUSE I GOT TO KEEP IT.
HAVING ALWAYS UNDERSTOOD THE AMPEG SVT WAS TOPS, I SEARCHED FOR ONE.
WHAT I FOUND, FOR WHAT I COULD AFFORD & WHAT THE SALESMAN TOLD ME, WAS A FENDER
PS400: "THE DESIGN AMPEG BASED THEIR SVT AMP ON!" RICH HAS SINCE FELLED THAT MYTH !
HOWEVER, I GOT LUCKY, ONCE THE G&L WAS RECOVERED: OH BABY - TALK ABOUT SWEET SOUND!!!
THE PS400 IS AWESOME!! I WAS MERELY PLAYING ONE
CHANNEL AT THE TIME - AND STAYING UP WITH OUR DRUMMER WITHOUT FLEXING or MAXING ANYTHING.NOW, 14 YEARS LATER; WITH THE SAME PS400 & PEAVEY 1810, I USE A VERY SWEET BCRich MOCKINGBIRD BASS WITH ACTIVE ELECTRONICS & I GOTTA TELL YA "I'M ON TOP OF THE WORLD"!!!!!!!!!!!!!!
THE PS400 WILL DELIVER !!!!
THE PS400 WILL SURPRISE!!!!THE PS400 WILL GIVE YOU TONES THAT YOU DID NOT KNOW WERE POSSIBLE!!!!!
HEY, THE BETTER THE INSTRUMENT, THE MORE YOUR DISCOVERY WILL BE!!!!!!!!!!!!!!!!!
HAVE FUN!
ROCKWOOD
12. Can I ship my 400-PS to you for repairs?
No problem. Through the years, many 400-PS amps have broken the backs of the delivery man with Time Electronics on his route. The best thing to do is call for special packing instructions. There is only one way to pack a 400-PS to make the round trip without mishap.
13. Is there some way you can help my amp tech repair my 400-PS?Only under four conditions.1. As Ed Jahns had tested my background and electronics knowledge on the 400-PS over the phone, so will I test any amp tech who seeks my help. There also must be total understanding of the concepts and use of line current observation, as it applies to amplifier function and analysis.
2. Digital pictures of all the test gear required to work on the 400-PS must be made available to me before we speak, and the test gear ready with the 400-PS on the bence when we speakon the phone.
3. The amp tech picks up the phone bill.
4. A donation is made to cover my time off the workbench.
14. How can I find out when my 400-PS was made?Through the use of the EIA source codes, found on the components used in your 400-PS, you can date it's birth. CLICK HERE for a great web site that applies these source codes to vintage amplifiers.
15. How can I find out what my 400-PS is worth?
Perform a search on Ebay's completed past 400-PS auctions. That, is always a great place to start.
16. Are there any mods that can be done to the 400-PS?
Most of the standard Fender amp mods that involve the pre-amp, tremolo, and reverb stages, can be performed on the 400-PS.There are power increase mods too.
17. I found a broken down 400-PS for sale. Do you think I should buy it?
Ed Jahns was from the old school of product design, and designed the 400-PS to be as strong as a bullet proof brick shit house. I NEVER found a 400-PS that was beyond repair.Yes, 400's will put on a light show with a good smoke screen. But, let us not forget that UL sticker that resides on the back panel of the 400-PS for one second.
Ed and I talked a lot about the tests the UL people would subject the 400-PS through, in order to fry the damn thing up. Many times Ed would get a 400 back from UL a complete mess.
Yet, all he had to do was clean up the mess, replace any smoked components, broken tubes, etc... and the 400 was back up and running. Then, Ed would send it back for the next round of amp torture that UL would put the 400 through.
I got my 400-PS for dirt because the so called amp tech at the store said the transformers was blown. I replaced the fried parts, installed a fresh set of tubes in it, and it fired right up without a problem.
As a matter of fact, the melted tube on this page, was one of two side by side melted tubes that was in my 400-PS, when I drove it home from that store.
I have yet to find a 400-PS on my bench with an actual blown tranny.
It's just a matter of how cost effective the selling price is, to make the resurrection from the dead worth while.
18. What are the best basses to use with a 400-PS?
Fender amps were always designed to make Fender instruments sound the their best through Fender amplifiers. So, logic would have it that, the Jazz Bass, P-Bass, and Bass VI would be the basses to use with the 400-PS.19. My solid state amp blew speakers often. Will the 400-PS do the same?However, you haven't lived till you've heard a Gibson Thunderbird IV, Explorer, or EB-2 Bass on a 400-PS rig.
Solid state amplifiers, when a square wave is introduced anywhere in the signal chain, will produce speaker *hang time*. Which, is a slow death for any speakers connected to that amp. 600 watt speakers are easily toasted by a solid state 300 watt amp run in hang time.Vacuum tube amps can't produce enough DC current to hold speakers in hang time, like a solid state amp can. This, is due to the nature of the output transformer in a vacuum tube amplifier.
20. Did any famous bands use the 400-PS amp?
Heart, Poco, Chicago, Ike and Tina Turner, and Albert King are a few I've been told about.21. Are there any Do's and Don'ts I should know about when using a 400-PS?I'm always looking for 400-PS sightings in old concert photos.
1. Always make sure all speaker cabinets are properly connected to the output jacks, BEFORE turning on a 400-PS.2. Always warm up the tubes for a few minutes before playing.
3. Always let the tubes cool to room temperature, BEFORE loading out the 400-PS.
4. Never let an amp tech without prior 400-PS experience work on your 400-PS.
5. Always use the best output tubes possible. If you have read this far,, you already know which tubes they are.
6. NEVER think of using a tranny toast (power attenuator) on a 400-PS.
7. Only connect 4 ohm loads to the speaker output jacks. Otherwise, you are looking for trouble.
The power to weight ratio favors the 400-PS big time!!!!The weight of the Ampeg SVT head on my scale is 82 lbs.
The weight of the Fender 400-PS head on my scale is 88 lbs.ONLY,... a 4 pound difference!
© Copyright R.K.Koerner 2001 All Rights
Reserved.
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