Hello everyone. Well with this being stuck at home we need to use the spare time on at least something we find pleasurable. I am about to assemble a couple of Class-A 6B4G pp monoblocks for the hell of it. I'm using Pete Millet's version as basis as per www.pmillett.com/6B4G_push-pull_amp.htm

He talks of an output around 6W enough for home use with high efficiency speakers.

I am all a bit new to speakers side of things though having not played around with the things since the early 80s and magazines like Electronics Australia, ETI & Practical Wireless, which a lot of you i expect won't have a clue of what i just typed!

So i've scrounged around on the interweb looking at new commercial HiFi speakers and studied up on their Efficiency Spec & what all that means. I understand that retailers need to make their business profitable but i cannot help feeling i could so easily go blow a tonne of $ on something i just do not like the sound of that won't let my Class A toob things do their thing!

Yes i have a turntable albeit it a new Audio Research all things output direct drive but i also have a Dual sitting as another re'co project....

Once i have some space in my basement (long story.. but it involves the selling of one of my hobby vehicles once the new owner is allowed to come to Auckland) i can breakout the new drop saw, the planner & bench saw... and ruin some perfectly good plywood!

Seriously though i'm asking in a round about way what are my options are (maybe someone knows something vintage is about to turn up on good old Trade Me) or is there a kit that won't take another mortgage or at least are there some individual drivers & crossover info in the country that i a can get rid of some time on ?

So thanks for reading my post. Please tell me anything; even if it's that i'm flogging a dead horse & 6W audio is not worth the effort!

Moved to Speaker forum

Audio Research turntable ?

Do you mean Acoustic Research ?

A lightning fast comment, barely an intro ~

PM quotes:
5% THD at 8V RMS into 8 ohms (8 watts)
0.3% THD at 1W into 8 ohms

Who wants to listen through even 1W distortion at a reasonable volume level to suit the music?
We had the famous Leak Point One Stereo 20 in the late '50's - 0.1% distortion at 10 watts!

I would keep looking around further, read, as an autodidact, before even starting to window-shop.

But I'm just remarking. I also traded with a SI chap who loved his 6B4G amps, a different design.

As for high efficiency speakers, what?

In open baffle, whether with wings or not, or in cabinets, how shaped, what size etc. and or in horns?

A start opinion to read if not already: (lots to read out there, I'm sure others might chime in, but all I have time for;-)

www.troelsgravesen.dk/HES.htm

And now I remember again the Econowave ... another box speaker with a lightweight stiff 12" woofer that went full mid-range, and a horn flared tweeter. 90+dB sensitivity as I recall.

But low power even triode valve amps are a special breed, and indeed you do need to get suitable loudspeakers to reproduce their output.

So tread carefully! ;=})

All this is just still [spontaneous reaction, sharing brief impressions] a momentary comment.

Cheers in your quest! 

Regards.

Oct 13, 2021 20:14:13 GMT 12 michaelw said:

Moved to Speaker forum

Audio Research turntable ?

Do you mean Acoustic Research ?

For the record… (it’s been a long day). It’s a LP120XBT-USB-BK Audio Technica, nothing special other than it’s direct drive & has BT to a set of BT Bose cans that are simply just not loud enough for safety reasons apparently! 

So, any experience  on options of ‘super’ high efficiency speakers for low power 6W output Class A pp direct heater tubes amplifier? 

Hi Pete. Speakers are my thing (I've been designing them for friends for 45 years) as it seems amplifiers are to you. My take on what would best suit you could well be different from other members so listen to them also. First off you have to decide what kind - open baffle, ported box, sealed box and horn - and pick something that is appropriate for your room size and taste in music. For my tastes open baffle whilst sounding very open just don't produce enough bass. Again for my tastes horns are too complex to build and importantly, it is difficult to predict the end result. Many common wide range speakers can be put in either a sealed or ported box but the box dimensions will be different (mostly) for each type. The bass from ported cabinets will generally go lower but the bass from sealed cabinets will be tighter and too some ears, cleaner. The design of both sealed and ported cabinets can be calculated by using Thiele Small parameters (Q, Vas and fs) and fortunately there are accurate calculators on the web. If you decide on open baffle speakers, Lii Audion have quite a range from 8 to 15 inch and in this case the bigger the better. However for sealed and ported enclosure, bigger drivers really means bigger cabinets. Much bigger. Much much bigger. I think the best compromise is 8 inch so here are two recommendations - Visaton B200 (sealed cabinet 2 to 3 cubic feet) and SEAS FA22RCZ (ported cabinet of 2 1/2 cubic feet). The Visaton is a 6 ohm speaker whilst the SEAS is 8 ohm which would be better for your valve amp. The Visaton is of 96db efficiency whilst the SEAS is 94 db - the difference is an artifact of the differing impedance so they are essentially of the same efficiency. The SEAS has a whizzer cone (the Visaton doesn't) and a rising output with frequency. This necessitates the use of an inductor (.8 to 1.5 mH) and a paralleled resistor (around 10 ohms) in series with the driver. The Visaton starts rolling off at 12khz and the SEAS at 15khz so I strongly recommend the use of a super-tweeter with both driven through a single capacitor. Other drive units which you might like to explore come from Mark Audio, Dayton Audio, Tang Brand, Fostex, Lowther and so on. My pick would be the SEAS which is roughly US$140 (the Visaton is a few bucks more) and my basic reason is that SEAS is a well established company which has been making driver units for years, including for Audio Note (UK) and Wilson Audio (USA) and by consensus make the world's best bass units. If you have deepish pockets the SEAS Exotic F8 is another recommendation. Both pairs of SEAS are available from Image speakers (Trade Me) at respectively for $785 and $2995 and I know that they have a cabinet for the cheaper pair for around $1k. I have successfully driven both with a 3 1/2 watt SE 6A3 so you would have no trouble. However if you have the know-how and gear to make your own I would strongly recommend that you consider 15mm Baltic Birch Plywood as the material of choice. This is available from West Auckland at about $180 per sheet. I can give you the plans which are on the application notes with each speaker anyway. Send me a PM if you would like to discuss your options further or have a chat. I live in Auckland and am guessing that you do too.

Oct 13, 2021 22:45:33 GMT 12 Pete Bronlund said:

Oct 13, 2021 20:14:13 GMT 12 michaelw said:

For the record… (it’s been a long day). It’s a LP120XBT-USB-BK Audio Technica, nothing special other than it’s direct drive & has BT to a set of BT Bose cans that are simply just not loud enough for safety reasons apparently! 

So, any experience  on options of ‘super’ high efficiency speakers for low power 6W output Class A pp direct heater tubes amplifier? 

A friend had a pair of Wavelength Cardinals 8wpc SETs which did sounded best with his Martin Logan CLS  

CLS would require much more if my fading audio memory agrees

ML CLSs would present an impossible load for an 8 watt SET - I'm presuming 300B. Here is Stereophile's take on them.
"Sidebar 1: 1987 Measurements
Looking at the amplifier load factor, the impedance curve (fig.1) is typically "electrostatic." Low at low frequencies, and with no visible signs of the 50Hz diaphragm resonance, it climbs steeply to a harmless 33 ohms by 1kHz. Above this level, the load is almost purely capacitive, falling with frequency at 6dB/octave, reaching 2.5 ohms at 10kHz, and finally bottoming out at a value of 1.6 ohms at 20kHz. Wide-band synthesizers played at high level will not do the amplifier-speaker combination much good, while this load non-uniformity will cause more treble balance variations than usual with different cables and different amplifiers. In fact, one or two power amps may not be too stable with this load under heavy transient drive."
Horses for courses.

Yes 300Bs.

Friend had the later CLSIIz - much more benign than earlier CLS'

Magic in a small room, at modest volumes.

Troels Gravesen has a lot of interesting things to say about high efficiency speakers (wide range speakers are a subset of these) including some classic designs.
www.google.com/search?client=firefox-b-d&q=troels+graveson+high+efficiency+speakers
www.troelsgravesen.dk/tannoyMG15.htm
www.troelsgravesen.dk/JBL_L100.htm
Good reading during lockdown.

Oct 13, 2021 20:36:05 GMT 12 RdM said:

A lightning fast comment, barely an intro ~

PM quotes:
5% THD at 8V RMS into 8 ohms (8 watts)
0.3% THD at 1W into 8 ohms

Who wants to listen through even 1W distortion at a reasonable volume level to suit the music?
We had the famous Leak Point One Stereo 20 in the late '50's - 0.1% distortion at 10 watts!

[Slight snippage to your post].

Perhaps the PP 6B4G pete millett design having such concerning THD figures is a tradeoff to it being based on an early approach with what was available from, i assume the 1930s with directly heated triode tubes? Add to that the distortion is vacuum tube so as they say 'easy on the ears'. A figure of 5% by a semiconductor circuit would i'm certain be harshly obvious & annoying. I actually cannot wait to get at least one circuit up and working & then run a few bode plots on the thing as a start to see response at least. I will not be holding my breathe because after all i am using the Hammond 1615 which in itself was expensive enough but not extreme HiFi.

At the end of the day when i was a teenager in the 70s, i had an obsession with an already 10+ year old big quad ECL82 per channel amplifier i'd bought at the local junk shop with all the money i had from mowing lawns. It was a chassis only and i'm certain a Sony but i have never found info on it today. It had huge output transformers compared the power supply one.

It's that special valve sound that amplifier made i'm chasing. Sure, the sounds were interpreted by my then teenager brain & ears the latter having been somewhat damaged since & those few LPs that i still have from then that i hope i can recreate that sound or close as, or at least 'die trying'. My interest in using valves for audio has only recently become a thing, probably because when i began my career as a trainee technician everything had them & the Tech Institute block courses i did covered them along with these great new things bipolar transistors...

Another vote here for the SEAS FA22RCZ. 👍


If you follow Pete 0c's very precise help. 😎



I have some hearing difficulties including a sensitivity problem - but I'm most pleased with the way it's going so far.

Check out Lii Audio for plans for their drivers

Things are changing virtually daily around me. Working From Home served up a curve ball that resulted in a urgent 12hr effort on my part and no i am not complaining, glad to still be employed!

At last though i have some me time and the search of speakers sensitive (thus efficient enough) to give my push-pull 6B4G units once i have yet to have one assembled & operational. I must say i am impressed with what Pundit has given me as a starting point & once i have some time i must make contact.

For now i have to balance temptation to play around with the newly arrived 3D printer/laser/cnc and the DRO kit to install on my milling machine, work on repairs for fiends & actual work. One project, the restoration of a very sad Luxman LV-107u that i have designed a new driver PCB to replace the burned out one is halted in China, DHL do not have a flight to NZ.

Maybe over this Labour Day weekend i can begin the on the valve amps...

Well, seriously off topic