100 watt Marshall Power Transformer B+ winding really ~180mA?

[capehead]

I'm in the research stage of putting together a 100 watt Marshall style, non master volume amp using some of my 'spare parts' of which, I believe I have everything needed except for an appropriate power transformer. Partially motivating this project (aside from my always wanting a 100 watt Super Lead) is that I have been slowly learning about transformer winding and I feel as if I'm nearing the point where I could confidently construct a power transformer. I've been doing the research into all the various power transformer types Marshall had used in their 'classic era' and one startling/confusing bit of information I have come across is that the B+ winding on these transformers were in comparison to my previous experience of a much smaller current capacity (in the neighborhood of 180mA), that is if I read this information correctly. The conventional wisdom I have used up until this point is that for a 4x 25-30 watt output tube configuration, a B+ capacity of ~400mA is about right assuming at maximum a 100mA draw per tube. So am I missing something here? Is this 180mA rating wrong or as I have read, this lower capacity 'softens' the attack at peak levels? Any help/insight/previous experience on this topic would be as always, greatly appreciated.

[tubeswell]

The conventional wisdom I have used up until this point is that for a 4x 25-30 watt output tube configuration, a B+ capacity of ~400mA is about right assuming at maximum a 100mA draw per tube. So am I missing something here?

100mA per tube? Better tell us what kind of tubes you are thinking of, what voltages you are running them at, and what class of operation the output stage is going to be set up for

[J M Fahey]

Marshalls are fast punchy amps, not much "softness" in them, supplies were always (except, maybe, in early JTM45) quite stiff, well filtered, large caps, mostly silicon diodes.
180mA sounds a very low current capacity for 100W amps, remember 50W had a 500mA +HV fuse, 100W ones had a 1A one.
Granted, consumption is less than that, but not by much.

[capehead]

100mA per tube? Better tell us what kind of tubes you are thinking of, what voltages you are running them at, and what class of operation the output stage is going to be set up for

This is about the 'Fender standard' for a 4x output tube configuration (ie Twin, Showman, ect) and is generally ideal for many high gain designs. I did misspeak regarding the 100mA per power tube though; I meant it more as a loose guideline.

Marshalls are fast punchy amps, not much "softness" in them, supplies were always (except, maybe, in early JTM45) quite stiff, well filtered, large caps, mostly silicon diodes.
180mA sounds a very low current capacity for 100W amps, remember 50W had a 500mA +HV fuse, 100W ones had a 1A one.
Granted, consumption is less than that, but not by much.

Very true about Marshalls being punchy although when it comes to their filtering (referring up to the JCM800 era), it's actually fairly moderate in comparison to modern high gain amps like Mesa, Peavey, Engl, ect. This amp I'm looking to build will use more of a middle ground amount of filtering in comparison to the low filtering of the earliest 100 watts to that of the 2203/late iteration Super Leads; 40uF plates-(10-15H choke)-20uF screens-30uF PI- 16 and 16uF preamp. Speaking of plate/screen filter caps, the ones I've been using are these 600V caps from Weber: EC406-600 Capacitor and EC206-600 Capacitor I cannot recommend them enough for both their price and the usefulness of using 600V caps which with past projects has saved me both space and money in having to use caps in series. Anyways though, the research into the actual B+ current rating of vintage Marshall's has led me towards the conclusion that perhaps the experience gained by them using those giant Radio Spares PT's in their earliest 100 watt models (JTM-45/100) which had a B+ rating of 200mA, showed that the conventional approach established by Fender was on the conservative side which allowed Marshall to save some money on each unit. Here's a pic of that Radio Spares PT: http://www.merrenaudio.com/yahoo_sit...7.10123659.JPG

[J M Fahey]

I have been slowly learning about transformer winding and I feel as if I'm nearing the point where I could confidently construct a power transformer.

Cool, congratulations.

I've been doing the research into all the various power transformer types Marshall had used in their 'classic era' and one startling/confusing bit of information I have come across is that the B+ winding on these transformers were in comparison to my previous experience of a much smaller current capacity (in the neighborhood of 180mA), that is if I read this information correctly.

You are about to talk about a certain Emperor's clothes ... keep reading

The conventional wisdom I have used up until this point is that for a 4x 25-30 watt output tube configuration, a B+ capacity of ~400mA is about right

Yes, so far so good.

assuming at maximum a 100mA draw per tube.

No, it's not that, it's more complex.
Besides, you are not saying much about those 100mA ...
* is that at idle?
certainly not, each tube would have a static dissipation of ~450V * 100mA=45W ... good to create nice glowing metal puddles inside the envelopes or to cook chicken exposing it to the infrared emitted.
* is that peak? ... neither, peak current reaches above 200mA each tube.

So am I missing something here? Is this 180mA rating wrong

I'm certain of that.
Just out of curiosity I just checked HV current rating for a number of "Marshall 100W" PTs, all were nonsense, even the one by respected Hammond (Canada) .
The rating for a 100W JCM900 PT was even worse, a ridiculous 150mA
All I can think of is that somewhere an amp was imbued with magic powers (say, EC or JH or JP used it in some mythical recording) and all others quote same spec, for fear of devout believers not accepting that.
Or something similar.

Where am I basing this on?
Well, Electronics 101, what else?

1) a class B no loss textbook example power amp, is 75% efficient, so for 100W output needs 100/0.75=133W (DC power).
Since amps are usually Class AB (so we have a little waste at idle, which of course comes from and substracts from power supply capability) plus active elements are not perfect "controlled resistors" , since transistors have a minimum voltage drop of 2 to 4 volts and tubes 60V or worse, conventional wisdom is to rate DC power supply capability as 150% of rated RMS power.

In fact, it's worse for tubes: high saturation voltage, resistive loss in the OT windings, important current passed through screens which is wasted, does not contribute to output power (except in Ultralinears, this explains at least in part their increased power out).

So there's 2 ways of understanding this: either 100W amps do not produce nowhere near to 100W ... but nobody says so because it sounds bad and kills marketing or transformers are actually rated higher than officially stated, but nobody says so ... maybe because all want to match "vintage/original" specs ande although all see the King/Emperor naked nobody dares open their mouths.

Am I certain?
You bet, let's see some "official specs" .... remember we need AT LEAST 150W DC power to get 100W RMS Audio.
I'll be very generous and accept 150VA rating (although we'd need an even higher rating for that)

* "100W Marshall" : Marshall 100W Power Transformer for JCM 800 and JMP
HV specs: 350VAC*290mA=101VA <-- good for a 75W "perfect" amp, some 60W Real World.

* "100W Plexi upright" 100W Plexi, JMP & JCM800 Power Transformer with M-6 and flux band upgrade
HV specs: 350VAC*290mA=101VA <-- good for a 75W "perfect" amp, some 60W Real World.

* "100W JMP&JCM800" Marshall 100W JMP & JCM800 Style Transformers By ClassicTone
HV specs: 350VAC*290mA=101VA <-- good for a 75W "perfect" amp, some 60W Real World.

as we see, so far it's the same basic design, just with different mounting hardware.

now for more modern spec amps:

* "100W JCM900, 100W 30th Anniversary, JTM60 and JTM600" Marshall 100W JCM900 Style Power Transformer, T5826
HV specs: 360VAC*450mA=162VA <-- NOW we are talking, a reasonable spec, good for a 121W "perfect" amp, some 100W Real World.
How come all others are nonsense and only these match Math , or what PS calculators state?
Only explanation I can imagine is that all want to "match" some mythical, probably mistyped or imagined "vintage spec" which is very wrong .
Of course JCM900 is the bastard child, the despised one, and nobody wants to be associated with it ... although 4 x EL34 or 5881 require the same electrical "food" here and in China to produce 100W.
Another funny fact is that it shares specs with the very expensive, top of the line, 30th anniversary !!!!!

Let's see others, some of which are even worse, others sing the official song:

* "100W Plexi" Mains transf. for Marshall 100W Plexi lay-down type - Mains Transf.
HV specs: 350VAC*300mA=105VA <-- good for a 75W "perfect" amp, some 60W Real World.

* Mercury Magnetics: no real specs on them, they are sold based on "1967 spec" , "model used by Dokken and AC/DC" , "improved" , and similar "hot words" , or to be more precise, they do state on some the stack thickness, mainly to compare to Fat Stack versions.
Meh

* My biggest dissappointment was with Hammond, because they are a true Transformer winding Company, who does nothing else, and is not centered on gueetar amps or Mojo (Jimi Hendrix never used them anyway) but on well made products ... yet their specs are nonsense:

* "Hammond 100W JCM900" (remember the specs I posted earlier) https://www.amplifiedparts.com/products/P-T290JX
HV specs: 361VAC*150mA=54VA <-- good for a 40W "perfect" amp, some 30W Real World. REALLY?
Datasheet: https://www.amplifiedparts.com/sites...s/p-t290jx.pdf

I thought maybe they were confusing specs, that this was actually for the 50W version , but no, went straight to the Hammond site which confirmed the above posted and showed:

* "Hammond 50W JCM900 PT": http://www.hammondmfg.com/pdf/EDB290KX.pdf
HV specs: 330VAC*100mA=33VA <-- good for a 25W "perfect" amp, some 18/20W Real World.

I pulled data from Hammond datasheet, downloaded from thir own site.

I am without words to describe this.

or as I have read, this lower capacity 'softens' the attack at peak levels? Any help/insight/previous experience on this topic would be as always, greatly appreciated.

As you see every day, what you read in Forums is usually wrong, with very few exceptions, what's crushing me is that data from suppossedly serious manufacturers is also junk.
Oh well.

Oh, and the Emperor IS naked .

[frus]

* My biggest dissappointment was with Hammond, because they are a true Transformer winding Company, who does nothing else, and is not centered on gueetar amps or Mojo (Jimi Hendrix never used them anyway) but on well made products ... yet their specs are nonsense:

* "Hammond 100W JCM900" (remember the specs I posted earlier) https://www.amplifiedparts.com/products/P-T290JX
HV specs: 361VAC*150mA=54VA <-- good for a 40W "perfect" amp, some 30W Real World. REALLY?
Datasheet: https://www.amplifiedparts.com/sites...s/p-t290jx.pdf

Maybe they just state that the secondary voltage is 361V when the amp is drawing 150mA (pretty much the idle condition)?

[pdf64]

Maybe they just state that the secondary voltage is 361V when the amp is drawing 150mA (pretty much the idle condition)?

That was my thinking, ie it's just an indicative point on the curve, rather than the limiting value for continuous load.
But the info sheet shows a drawing with the label, which gives a total VA figure that is the sum of the winding VA.
So, it's a mess!

[J M Fahey]

It IS a mess, that's no way to rate a transformer, anywhere.

Proper is actual voltage at full rated current which is the max you can pull without improperly overheating it or having way too poor regulation (too much voltage drop under load).
Typically (but not always) makers wind extra 2% to 5% to better meet rated specs under load.

Really, a mess; doubly so because *some* post the real value in *some* transformers (say one version of JCM900).

FWIW my own transformers (and most real ones) for SS amps, my bread and butter product, which have no filaments and preamp draw is tiny, are rated 50% above RMS rating.

Most used one: 30+30VAC for +/- 42V rails (unloaded) , 2.5A , which adds up to: 60*2.5=150VA , what the Doctor ordered, by the way, and what *everybody* uses: Valvestate 80/100 , Peavey 80/100/120 , Crate 100/120 , Hartke 140 , Fender FM212 , Ampeg 100/120 , Laney 80/120 , Randall RG80/100 , most old Kustom, Acoustic 118/120//125/126 , Sunn 100W mixers, GK150/200 , 1000 more.

Japanese 80/120W amps tend to use slightly higher rails, +/-45V to even +/-48V because they normally use BIG output transistors whict they probably pay cheaper than us, but power transformer ratings follow same rules.

It's very weird what Mojo loaded tube amps "spec" .

[capehead]

I'm certain of that.
Just out of curiosity I just checked HV current rating for a number of "Marshall 100W" PTs, all were nonsense, even the one by respected Hammond (Canada) .
The rating for a 100W JCM900 PT was even worse, a ridiculous 150mA
All I can think of is that somewhere an amp was imbued with magic powers (say, EC or JH or JP used it in some mythical recording) and all others quote same spec, for fear of devout believers not accepting that.
Or something similar.

One might think that the reason someone would be looking for a replacement PT for their JCM900 would be for the reason that the OEM specs were wayyyyy underrated to begin with, so why would a no-nonsense type of company with a reputation of over-specking their products design and sell a replacement of the same faulty specs? It's either Hammond put the underrated specs on the box/data sheets in order to not scare away non-electronically oriented musicians looking to replace their burned out JCM900 PT (many people do not know that you can go over the stated current value) while in reality the PT has been beefed up (to prevent future failures) or this well respected company is letting their marketing department dictate to the engineers how things should be done.

So there's 2 ways of understanding this: either 100W amps do not produce nowhere near to 100W ... but nobody says so because it sounds bad and kills marketing or transformers are actually rated higher than officially stated, but nobody says so ... maybe because all want to match "vintage/original" specs ande although all see the King/Emperor naked nobody dares open their mouths.

It's not very often the most desired request of someone who plays through a classic '100 watt' amp is for it to be louder; although I have heard this a few times from players who use an overdriven preamp/clean power amp configuration but this was mostly a frequency thing (ie. lack of midrange!).

... although 4 x EL34 or 5881 require the same electrical "food" here and in China to produce 100W.

That is a fantastic analogy!

Let's see others, some of which are even worse, others sing the official song:

* "100W Plexi" Mains transf. for Marshall 100W Plexi lay-down type - Mains Transf.
HV specs: 350VAC*300mA=105VA <-- good for a 75W "perfect" amp, some 60W Real World.

* Mercury Magnetics: no real specs on them, they are sold based on "1967 spec" , "model used by Dokken and AC/DC" , "improved" , and similar "hot words" , or to be more precise, they do state on some the stack thickness, mainly to compare to Fat Stack versions.
Meh

I don't know about what to feel about MM; it's obvious their prices are massively inflated and with some of their OTs I've heard, I was not all that impressed. In fact I had one of my modded Marshall type amps that used a Laney AOR OT versus a similar amp with a MM that simply killed it in the context of playing with a band at volume; the MM sounded dull and somewhat 'artificial'.

* My biggest dissappointment was with Hammond, because they are a true Transformer winding Company, who does nothing else, and is not centered on gueetar amps or Mojo (Jimi Hendrix never used them anyway) but on well made products ... yet their specs are nonsense:

* "Hammond 100W JCM900" (remember the specs I posted earlier) https://www.amplifiedparts.com/products/P-T290JX
HV specs: 361VAC*150mA=54VA <-- good for a 40W "perfect" amp, some 30W Real World. REALLY?
Datasheet: https://www.amplifiedparts.com/sites...s/p-t290jx.pdf

I thought maybe they were confusing specs, that this was actually for the 50W version , but no, went straight to the Hammond site which confirmed the above posted and showed:

* "Hammond 50W JCM900 PT": http://www.hammondmfg.com/pdf/EDB290KX.pdf
HV specs: 330VAC*100mA=33VA <-- good for a 25W "perfect" amp, some 18/20W Real World.

I pulled data from Hammond datasheet, downloaded from thir own site.

I am without words to describe this.

Yeah, this is a load of crap in one sense or another; referring to what I mentioned previously about Hammond.

As you see every day, what you read in Forums is usually wrong, with very few exceptions, what's crushing me is that data from suppossedly serious manufacturers is also junk.
Oh well.

It depends on the forum I suppose, this forum for example is top notch and on the polar opposite side forums such as rig talk and the HCAF. In regards to old Marshalls though, I've found the metroamp forum to be a great resource; although this is the source of much of the talk about (non tube rectifier induced) power supply sag through the use of low mA HT supplies.

Oh, and the Emperor IS naked .

Or at the least, a debate can begin on whether or not he is in fact naked

[pdf64]

.. talk about (non tube rectifier induced) power supply sag through the use of low mA HT supplies..

I think it should be considered that the PTs for these classic amps were designed in an era when tube rectifiers were the norm and B+ winding were probably expected to included sufficient series resistance to accommodate them without the need for external resistors.
So B+ windings had to be saggy, have poor regulation, and get hot during sustained heavy loading.
Even 100 watt (well, nominal) / 4 tube amps might use tube rectifiers, eg http://bmamps.com/Schematics/Selmer/selmer_pa100.pdf
Just because the Marshall PTs didn't have rectifier tube heater windings, I don't think we should assume that transformer designers would immediately develop / implement a whole new set of 'ready reckoners'. Rather I suspect they would still use the old design templates developed for tube rectified PTs, in regard of winding AWG, window size etc.
So for the classic response, a saggy B+ may be pretty much essential, whether or not tube rectifiers are involved.
And the lower than expected B+ current ratings may just be reflecting that somehow?

[nickb]

I would hazard a guess that the justification for using such underrated transformers is that the average power output in normal use is much less than maximum. Competitive price pressures no doubt have something to do with it.

I see this a lot in PA and powered speakers whose continuous power output is 2-3x the instantaneous. In these it is a sound engineering approach as they have limiting circuits to ensure operation within the limitations.

[Justin Thomas]

SO! That's the real reason Marshall wanted master volumes - so they could fool players into thinking they were putting out a lot more power than they really were, because of the loads of distortion? So since you don't have to crank it to 10 anymore, we can use cheaper parts!

Being sarcastic... but honestly, I think Marshall was probably the first company that DID expect us to turn their amps up to the point of distortion...

[Leo_Gnardo]

SO! That's the real reason Marshall wanted master volumes - so they could fool players into thinking they were putting out a lot more power than they really were, because of the loads of distortion? So since you don't have to crank it to 10 anymore, we can use cheaper parts!

Being sarcastic... but honestly, I think Marshall was probably the first company that DID expect us to turn their amps up to the point of distortion...

My best guess is Marshall reverse engineered what some early mod guys had done to their 4-input amps. Fender tried to do much the same with their master volume models but they sounded like poo when you cranked the pre and cracked the master. Marshall definitely won that battle.

And Ampeg's one page mimeographed owner's manual: "If you hear distortion, turn down the volume control". Sure Ampeg, we'll do that.... A cranked Jet or GemI or Reverberocket is sonic heaven!

[capehead]

SO! That's the real reason Marshall wanted master volumes - so they could fool players into thinking they were putting out a lot more power than they really were, because of the loads of distortion? So since you don't have to crank it to 10 anymore, we can use cheaper parts!

Being sarcastic... but honestly, I think Marshall was probably the first company that DID expect us to turn their amps up to the point of distortion...

I'm more inclined to think that the master volume was something that was being sought by players who weren't performing to large audiences, which was/is approximately 98.6758% of guitarists. Marshall did eventually thin out their standard power supply circuits, but that wasn't until the mid to late 80's; as far as I know both the 1959 and 2203 (and likewise for the 1987 and 2204) shared the same transformer/filter arrangement during this 1976-1981 period. Being that Marshall up until this point was basically 'winging it', I believe they deserved the benefit of being forgiven for their technological shortcomings because what we got in exchange was an iconic sound which had never before been possible.

[Justin Thomas]

I was being silly with that... but I'm probably one of the 0.083% of guitarists who likes their distortion to come from a cranked up amp, be it 1W or 180W...
I've never had the pleasure of playing a non-MV Marshall, but I did get to try a 76 JMP 100W... it was awesome! I'm just sorry my only cab is 100W & a 2x15" so no cranking on 10...

Justin