SE 300B and Folded Horn Fullrange Speakers

The SE bug hit me a long time ago around this time of the year.  I went into an antique store and heard Xmas songs playing and was pulled to the back of the store to find an old Philco Radio console.  I could not believe how nice it sounded.  It used an SE hooked up to a  45 output tube pair.  Just beautiful liquid sound.  I went back later and was going to make an offer and it was gone.    So not just a 300b but 45's and other output tubes will work as long as the system is efficient no matter if it is a folded horn or bass reflex with mid and hi freq horns. 

Alexc; the output transformers you show seem very expensive.  I'm sure the design on the philco radio was no where near that design but If you want to use them to mix on(as well as listen), it might be the way to go. 

In that price range I would look at these as well.

http://www.ebay.com/itm/300B-SE-tube-output-transformer-one-pair-Similar-Western-Electric-171A-for-91A-/121520933907

They look like they might be  good for the 300B application. 

I've always been tempted by this guy's adaptation of the WE91a:

http://www.timebanditaudio.com/james300b/91Aschematic.html

Seems like a simple enough build... bearing in mind EMRR's advice, maybe I'll see if I can find some bookshelf speakers for it.

Those WE clones look great, but man, there's so much snake oil in anything on the WE market I'd never trust anything from that camp without solid specs from real measurement equipment. 

So much potential inspiration out there, take your time parsing reality.  Think a lot about tube availability and cost.  I have a few too many 45 and 2A3/6B4G amps waiting for restorations, and can say from stockpiling old power tubes that it's a real crapshoot, and not cheap to do.  Among the commonly pursued tubes the 2A3 seems the most available in both used and new variants, though I get the strong idea with any of these types you need to stick with a certain manufacturer among the new makes as there are lots of little (and not little) performance differences that may preclude swapping of make.  Is anyone doing a SE 845 amp?  I have no idea.  Obviously the 'best' output transformer you can buy will affect more than anything else.  Choke plate load will do yet another thing, with same comments about choke quality. 

The only things I have in SE power land with speaker taps are RCA broadcast program amps that run 6L6 and 6V6 in 1W territory.  They are cool for quiet listening, and you see the WE crowd insist that 350B's make them better, you can also do some hacks and change to 6B4G without too much work.  I gotta worry about the pile of PP restorations first. 

emrr is right about the transformers.  Better make sure they are correct for the build before dropping a pile of money on something that is just marked WE.     

I saw those WE - like traffos for the guys WE style 300B. Looks nice but yep - what spec ?
If I had around 2Kusd to drop, the ebay WE amp guy would be interesting.

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I have got the big Edcor SE banging away in my current build, I am certainly happy with it's capabilities.

They don't disappoint in even a simple design, like mine, and I haven't even tried any fancy stuff
The price, makes it attractive to get into it.

I will use an Edcor psu feeding  a rectifier tube and 2x HV chokes per channel. Likely to include a regulated screen supply for each as well.

All that, top built on a 2RU chassis - no wood here, this is rackmounting, probably 11RU all up.
The other 1RU chassis to have the dual channels - basically a driver tube + 5x triodes.

8A of 6.3Vac heater and 300Vdc at 300mA of HV should do!
Thats 50VA of heater, 90VA of HV for around 150VA to feed this thing for 2x10Wrms output.
Around 18kg+17kg -> 35kg  of heavy, heavy metal.

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But I want to move into the next price league for the output transformer, over the Edcor units.

Which is imho, James transformers or ElectraPrint.

Beyond that is the mid high end - the classic vintage stuff we all love, the modern high end stuff - Magnaquest, Hashimoto, Lundahl, Sowter.

And then the  very top end stuff whose design I am not worthy to touch!  (WE, NE, Tango)

SO looks like James or Electrprint. And with parallel'd 9W triode tubes. 

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I think once you decide to parallel tubes, there's no point in staying with the 300Bs, 45s, etc.

I'm pretty sure the magic 'single tube' qualities disappear once you start paralleling.
So, a more utilitarian tube is probably no less magical in a parallel config.

I looked at the big triodes, the 15W platers, even 2 in a bottle  - 6AS7, 6080 and the other big psu series regulator triodes.

They are cool, except the heater gets pretty crazy pretty quick and you can't run a single envelope in parallel, according to the RCA app notes. Good for PP, or stereo etc.

So, in the true triodes, single stage envelope, I return to a pair of favs - 12B4A and 6S4A.

They like to be 250V @ 25mA plate for 6.25W dissipation (max 8.5W), so 4x for 100mA, 5 for 125mA.

Looks like that's the way I'll be going.

The driver will need some push to overcome the combined input capacitance of each set.  The pair of 6550s in the Edcor build is not small, but I'm not having any probs driving those to ruler flat response.

(haven't checked out the square wave and all those optimisations yet)

I'll definately build up a prototype before drilling the finals' metal work!

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Anyway - for now, I look for nice wood and  prepare to purchase some Audio Nirvana units.

I don't mean to scare you off here at all, just tell a funny story:  There's a 1980's-1990's school of thought in vintage amp collector world that parallel tubes are bad; they can't say why, but they think those amps are always inferior somehow.  I could see chalking it up to the increased input capacitance.  They might like SE or PP, but not PSE or PPP.  Always funny to me, maybe because I have PPP amps in both 45's and 2A3's.  In a lot of ways a 2A3 is a pair of parallel 45's, so you could just load the PPP 45 amp with PP 2A3's.  Would it be better?  There's a bomb to drop into your local vintage hi-fi hangout!  I do have some Gates program amps that are SE output with 6SN7 paralleled.  They sound just fine to me!  So long as you plan it properly, I think it's a fine way to go to avoid the esoteric tube prices. 

Can't help but thinking, emrr, that your 'to do' pile would be fantastically interesting to interview

Auditioning some SE 2A3 or 45s and then some PP s then some PPPs and PSEs and making notes!

Trying to work out which you like .. slightly more.

Even my humble pile is growing - each build means there's another, even more interesting one to try right after  

I have to admit, the PSE Edcor build has renewed my enthusiasm for PSE 'powerdrive'.

And this little 6L6 SE single tube stereo just sounds very nice - in a 'have on all the time' kind of a way.

The  6L6 at  360Vdc and 63mA certainly toasty at 22.5W quiescent.  But does sound so nice.
8" + tweeter + port small bookshelves with 92dB or so sensitivity.
Good for low volumes - awesome mid and with pleasantly strong woof too.

And it has crappy ebay noname output traffos. Not great but well .. good.
I would say $30usd type of thing from 10years or so ago.
Main issues are poor low extension and quite inefficient.

I am planning on replacing these with some 'Transcendar' SE 10W types.
Modest priced stuff but nice, as an alternative to what I've previously used.

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One thing I would say - if you haven't heard some even modest SE tube amp with higher sensitivity speakers, you're missing out!

It's so very alive - I'm glad some of you have experienced this too.

It's very much like as a guitarist, when you finally get around to putting together a 'Champ'.

From then on, you just know.

My weirdest speakers are some cheap european oval shaped car audio speakers that are 800 ohm.  The nice thing is you can build up an array of them maintaining 800 or 200 ohms, and get higher gain out of low power amps with line level speaker taps.  You can go all series and run a 4K stack with cap coupling off a plate circuit.  They'll give a nice auratone quality plugged directly into the output of a console or DA converter.  Totally different angle than what we are talking about, but similar nonetheless. 

These things are never apples to apples, it's always too different to make direct comparisons, and still all about whether a systems works, or doesn't, for the application. 

The PPP 45 amps are about 60lbs/27kg apiece, 6RU, and deliver a doubtful paper spec of 25W peak power.  We'll see how good they actually are one day. 

One of the most satisfying listening experiences I've had was a Altec A7's powered by a MacIntosh 30Watt. Granted the horn was changed to a TAD and it had a new crossover but what a sound. If i had the room I'd get a setup something like that. I wouldn't want to work on that setup but listening is really fun.

After almost 15 years of valve hi-fi diy, I'm happiest with 807PSE Pentode with partial feedback driven by 1/2 6SL7(100k plate resistor off the bottom of the Audio Note output transformers).
It does away with the over rosy 2nd harmonic signature of triode SE and probably leaves a whack of 3rd but nothing much else.
The PSU is separate in a rebuilt Fluke 407DR, with a Broskie Janus regulator for the screen voltage.
AC heaters,silent.

I'd love to hear it working a cinema horn setup,(done Lowther Acoustas/9710s) but my living room is tiny and for the electronic music alongside the contemporary classical I mostly listen to, the bass bins would need to be gigantic.
So the above 300Hz goes to the PSE and some 87dB/W Opera Minis and below 300Hz through a 50W Tripath into some old Fisher closed box 10".
Too loud for my neighbours generally.

Active crossover hi-fi is imho the real step but it's something very few bother to do.

Robert

Parallel SE 807 has to be the beginnings of a good amp.  I've heard some very large horn PA systems with the lows driven from SS and the highs driven from low power tube, I remember it working very well. 

I don't think I've been terribly clear on one perception aspect with the La Scala.  Yes, the math says they don't go so low, and need to be much larger to do real bass sort of flat.  Yet it doesn't take much EQ to get the bass there at all, and even without it there is more of a sense of low bass impact because it's a 15".  It's moving more air than any small box speaker possibly can, and you feel that, even if it's lower in level than a flatter small box speaker with an 8" or 10".  Kick drums actually give a sense of vibration.  When I switch back to my small boxes, they have more of a hyped low mid bass that suggests more than is actually present, and there is no vibratory experience at all.  Apples and oranges, again. 

I've done a couple of SE 845 amps. It is a relatively cheap tube but I'm not sure I would recommend it to beginners because of the high voltages. I used 1100V on anode and got 25W in class A1.
I've also done SE amps with SV572-3 and Siemens Post tetrodes in triode mode. How ever my next tube amps are definitely going to be 300B based because availability issues, and actually PP, not SE, because I want to use amorphous iron output transformers and get really wide bandwidth and inaudible distortion levels without feedback. 

Gosh I'd drive a long way to have a chance to do an 845 SE amp 

Especially one made by someone with skill and craft.

So nice - those Altec ones .. way nice. 

And from Japan, some of the hand built Tango stuff is so .. art.
Fine art, I say.

Some amorphous transformers, like those high end Lundahls would be just .. high art.

One can imagine an end-to-end chain of audio - two channels - done with such care and expense.

So very nice.

And yes - I draw the line,  these days,  at 500Vdc 

Jonte Knif said:

I've done a couple of SE 845 amps. It is a relatively cheap tube but I'm not sure I would recommend it to beginners because of the high voltages. I used 1100V on anode and got 25W in class A1.
I've also done SE amps with SV572-3 and Siemens Post tetrodes in triode mode. How ever my next tube amps are definitely going to be 300B based because availability issues, and actually PP, not SE, because I want to use amorphous iron output transformers and get really wide bandwidth and inaudible distortion levels without feedback.

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I'm intrigued by these SE 845 amps. Do you have any schematics you'd recommend for an 845?

Which 300B PP schematic are you thinking of building?

That 845 I did was my own very simple design with an interstage transformer and ECC99 driver. Nothing special, fixed bias for the 845 and a couple of dBs feedback. I recommend DC for the 845 filament. It was a long time ago, I was young and foolish.

The 300B push pull I have designed to start with an ECC88 differential stage feeding a 6H30Pi differential stage, all stages capacitor coupled and the tails fed from simple resistor and -200V source, no real constant current sources needed here.  Output tubes are probably going to have DC heaters and fixed bias. I think there are some schematics on the web similar to these. There are not many ways to skin these cats after all, but perhaps the devil is in the details... 

There's plenty of 300B designs around the web.

My personal fav would be a transformer coupled front end combined with low2 sensitivity - the kind of thing I like to drive from my DIY studio rack builds - with a nominal +4dBu signal with plenty of available headroom.

A simple grounded-cathode-stage for voltage gain, but using a plate load choke and quite a beefy tube there too.

All that driving the 300B which of course has the direct heated cathode arrangement.

Other possibilities for me would be the options for :

-  parallel'd finals allowing add another 300B when your wallet allows and needs dictate, for a max around 12W, 150mA operation

- using an interstage traffo instead of a plate load choke.

Given my builds are always a one-off deal, I'd probably experiment with a bunch of things before settling on the simplest

Vacuum Tube Valley article on the 300B>

https://web.archive.org/web/20131122141304/http://www.jumpjet.info/Pioneering-Wireless/eMagazines/VTV/VTV03.pdf

VTV on Klipsh>

https://web.archive.org/web/20131122141738/http://www.jumpjet.info/Pioneering-Wireless/eMagazines/VTV/VTV13.pdf

alexc said:

I do like the 'point source' idea - my main 'studio' (music room!) monitors are Tannoy System 8….
The bottom end is there but takes some serious power to move them.

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I have a pair of those and used to use my Phase Linear 700B with them.  That was a great combination with lots of headroom!

You chaps in the USA are very lucky with the range of valve amps available.  In the UK we have lots of Quad IIs, a few Leaks, Radfords & the like, but they are all in collector territory and unaffordable for most

I think the last place in the UK to have a decent stock of valve amps was BBC Bush House.  When I worked there all the line amps in the control room were valve units hung in floor-to-ceiling 19" racks with rep coils the size of a small loaf.  Quite a few studios still had LS10 monitors which had valve amps in the bases.  I wonder where they all are now?

The BBC lease on Bush House ran out in 2012 and External Services (foreign language broadcasts) moved out after being there 70 years.  The building was built by Irving T Bush, a name that will mean more to you than to us over here

Nick Froome

EMRR:  What bass EQ are you using on the LaScala ?  Sounds like a simple bass shelf would work for this.    I have a Pair of Altec 604's in  EV Patrician corner cabinets.  I use a Fisher tube amp with some low boost on the bass control.  It gives me that kind of meaty bass response your talking about.  Just curious if your using a graphic or shelving eq.   

Happy New Year everyone.