Originally Posted by Old Guy
All done with #the left side.
Very easy build. Lots of room in a monoblock chassis.
Note the distinct absence of output transformers. It's a relatively simply circuit. Pretty sexy.
Your neighbors called. They like your music.
All done with #the left side.
Very easy build. Lots of room in a monoblock chassis.
Note the distinct absence of output transformers. It's a relatively simply circuit. Pretty sexy.
Last edited by alancohen; June 8th, 2013 at 10:15 AM.
Well? Does it work?
Enjoying Altec Speakers since 1972
That's only the left side. I'm working on the right.
+1
Right on, all the early electrical distribution, electronics equipment I've seen were wired point to point with relatively stiff single conductor, so I consider a PC board just a durable wiring diagram.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Alan,
There are many choices and consequences one makes in audio. In this post I will address the use of output transformers and paralleling of Finals tubes.
An output transformer in a tube amp serves a very useful function, it prevents backwards EMFs from the loudspeaker motor from disturbing the Finals stage. The best-sounding tube amps ALL use output transformers.
When you elect to parallel tubes, ( four 300Bs ) you have a "choir" effect which is not as pure sounding as a single tube that is fit for the job.
With a well-wired DIY tube amplifier, having a good power supply, using a Altec 604 version driver, we certainly don't even need one 300B, let alone four, to drive it !!
So, the better-sounding 2A3 tube becomes the Altec tube of choice (for a Directly Heated Triode type....DHT ). The 2A3 will beat the 300B in all-out audio performance, no contest, it always has. I am talking "readily available" current production 2A3s, like a single JJ 2A3-40 or best-of-all, a single glorious-sounding EML meshplate 2A3.
The single 2A3 amp becomes the divine Altec listening experience !! Particularly when it is only two stages and direct coupled, the simplest circuit topology you can usefully apply to the Altec speaker in a home "high fidelity" listening environment. ( Realize, I am talking about purist and highest-fidelity home audio playback, certainly not movie theatre or PA applications.)
Google "Loftin White" ...... to get started in your journey of understanding.
'Just want to give you my opposite opinion to ponder, since you are a newbie and are not so experienced with all of this. But I encourage you to continue on, I LIKE your enthusiasm, and you are generally going in the right direction. Have fun.
LowOhms
Jeff, one question: have you ever heard an output transformerless amp paralleling 4 300B tubes? If not, you might want to reserve commenting on the sound until you have.
2nd, putting an output transformer between the final stage, basically 5 miles of wire without a direct connection, is certainly NOT the best way to get purity of signal. I can't think of anything that would muck it up more. You commented on solder joints being a poor connection...how about no connection, like in a transformer? The reason most of the well known amps use them is because designing an OTL circuit that works well and reliably is hard.
I'll let you know in a few hours what it sounds like.
Alan,
You are very defensive. I am not impressed with a 300B tube, and I would never elect to use one, ( much less 4 due to the "choir" effect.) I certainly KNOW what that paralleling sounds like, less pure and less pristine.
Your comments seem to ignore my point of backwards EMF from the speaker motor effecting the tube's operation, and in that respect,a transformer is beneficial. McIntosh makes solid state amps with transformers added, most likely for this reason.
There is a huge difference in signal levels, between unnecessary solder joints in a low level circuit ( such as a phono cartridge input stage ), and the fully amplified output stage of an audio amp.
I would question your assertion about output transformers: " The reason most of the well known amps use them is because designing an OTL circuit that works well and reliably is hard." OTL amps are no panacea Alan, they have been around for a LONG time. I owned a Julius Fiutterman OTL tube amp forty years ago, in the 1970s. I sold it. Harvey Rosenberg made OTLs in the 1980s ( NY Audio Labs) , but by the 1990s, Harvey "discovered" triode amps with transformers, and single ended topologies. There is even a dedicated OTL Forum for DIYers on Audio Asylum. OTLs are not particularly demanding to design. What is problematical to me is all the design compromises one must make, to implement such a circuit.
Give your amp at least 100 hours to break in, and more likely, longer to fully come into its own. Have fun, its always exciting to hear a self made amp pass a signal.
LowOhms
This is a fun thread.
The biggest pitfall of the 300B (I know because I've been listening to my PP 300B amps for years) is that they are terribly microphonic. I suspest that is what gives them their sound.
I personally believe it is due to the long grid and filament strusture.
I can hit the pause button on the CD when I have it up pretty loud, and you can literaly hear them ring and decay.
The attraction of them is the fact that they are a relatively low voltage high power DHT. SE can do 10 watts or so, and will rock and roll your Altecs...reasonably well.
I've never been a SE fan because I just need more volume (low end) than a 3w amp will provide, no matter how pure.
I really like and prefer my PP 6B4G amps. The 6B4G is the octal version of the 2A3 with a 6v filament. The only drawback to them is they only make 8W. Ohm will have a reason the 6v filament is not as good as the 2v filament. I simply never tried my amps with the 2A3. I don't have any.
My 6B4 amps are highly moodified Heathkit W5M amps, no global feedback, DC filaments and the peerless output transformers were some of the best ever made.
Ron
Enjoying Altec Speakers since 1972
OK, if you want to psychoanalyze each other...you are very dismissive, Jeff. Anything that doesn't agree with your model of what should be is bad. You dress up your comments in the guise of appearing helpful, but the self-righteousness just oozes out to the point that I'm just not listening to you any more.
If you want to use 2A3 tubes, go ahead. But there are plenty of great 300B based amps out there and to dismiss them out of hand shorts your credibility to ground instantly. It's like people that say Canon is better than Nikon or Fender is better than Gibson. When I hear a statement like that my mind immediately thinks, Well, there's millions of people out there shooting Nikons and playing Gibsons, can they all be wrong? Or maybe this one guy is.
To answer your question about EMFs and cone control, it's done with low output impedance. If the output impedance that the speakers sees is low enough, less than 10% of the load impedance, then the voltage drop across the finals stage will be minimal. Low output impedance is achieved with the required negative feedback to achieve the desired result. The trade-off, as you say, is there is not a hunk of iron and 5 miles of wire between your output stage and your speaker.
And I never said OTL was a panacea. That was you putting words in my mouth to avoid dealing with my assertion that a huge output transformer in the path of the signal is most definitely not the most transparent way to accomplish a task.
And as far as the amp goes, so far so good. I have a wiring problem in one that I need to sort out today, but I had a chance to hear them last night. Even after only 10 minutes of burn in, the difference in the 300B and my PP OTL is seductive. I was listening to Lyle Lovett's, "Baltimore" on the Joshua Judges Ruth album where he sings virtually a cappella. I heard the saliva in his mouth crackling very apparently. I hadn't noticed that before. So I went back to my 15W PP OTL and listened again. Sure enough it was there, but it felt like my ears had to reach for it. Back to the 300B and it was like I had a front row seat inside his mouth. Can't wait to break these babies in.
Last edited by alancohen; June 9th, 2013 at 08:01 AM.
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