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eRiCdWoNg 23rd July 2004 03:42 AM

Amp for a beginner
I love audio and I try all aspects, old and new. My last venture was a 3bx-ds dynamic range expander. Pretty intersting stuff, I stuck it on my DJ/PA system aka the ridiculously loud, undetailed system. I never used tubes before. The only thing I have had even slight exposure to was from Audio By Van Alstine's kits.

Anyway, these would be driving a pair of Magnepan MGIIIA's or Polk LSi9's. Doesnt have to be super powerful but should be able to drive those speakers to a decent volume. For super loud, I have solid state still.

I am willing to try DIY, however it cant be too expensive. Im willing to do a few hundred US $. Anything of vintage (or present) worth getting? Is there a tube FAQ around here?

I tried to collect as much info as I can here and on the net. I have pretty good hands on skills and basic EE skills. So I dont need to learn ohms law and stuff like that again.

Ive found these threads:

BHD 23rd July 2004 07:40 PM

In my experience with them, I found Maggies need an amp with a bit of power to "get going" as it were.

There's a 150W monoblock amp design that uses a pair of EL509 output tubes detailed in Bruce Rosenblitt's book "Audio Reality". He gives the schematic, the ideas behind the design, parts lists and how to build and test it. I haven't heard one, but his products are pretty well regarded.

Good luck!


cadman 23rd July 2004 11:15 PM

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Eric, BHD,

I've attached a pic of my version of the Rozen SC150 amp. What I did was combine two monoblocks, the grounded-grid preamp, gas-regulated supply and an active 3 band EQ into one unit with microprocessor control, LCD display, motorized pots for remote (and Cadillac pearl paint!), etc.

If you want loud, this amp will deliver it! But, notice I'm not running the EL509/519s. Even though they're fairly inexpensive and readily available from ebay/russians, they have a tendency to crack (because of the basing and stress the modern production sockets place on the pins) AND flashover when the going gets tough. Trust me, I had to redo part of my output stage because of components literally catching fire when one of the 519s bit the dust (and early in its life). I must've gone through 5 tubes b/w of short-term (day or two it would appear) cracking and flashover

Both of these problems are not unheard of at all with the quality of these tubes these days. Because of that, I changed the outputs to EL34s, running the plates at absolute max ratings, and screen voltage of 400 (IIRC). All together it sounds great, but Bruce's designs have a tendency to be very clarical, more of a solid state, detailed sound. A different preamp would probably make a difference in this regard.

I love the fact that there is absolutely no hum whatsoever, even with your ear to the speaker. You'd be hard-pressed to know it's on. My PP 6L6 has that great tubey sound, but the idle hum drives me nuts.

Overall, the most expensive part of the monoblocks are the Hammond 150w transformers. Mine are actually vintage off of ebay (new are $$). You wouldn't necessarily have to run these if you went with different output tubes like I did (converted I should say). Go nuts, use 4 per stage in parallel push-pull and have SS power with the tube advantage!


fdegrove 24th July 2004 12:26 AM

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they have a tendency to crack (because of the basing and stress the modern production sockets place on the pins) AND flashover when the going gets tough.
Because of many people just use the wrong type of socket (not saying you did):

Magnoval and Neonoval (AKA Novar) are not the same socket even if they do look suspiciously similar.
The EL509/519 requires a Magnoval type of socket, when force pushed into a Neonoval one the glass base CAN crack.

Flashovers? Hmmm...Never seen any with those tubes, these are about as tough as a boot AFAIK.


cadman 24th July 2004 12:55 AM


Good point about the sockets! Regarding flashover, I was referring to the new production Russian EL509/519s as having that tendency, at least in the SC150 amps. I never had those problems with the NOS Admirals I picked up sometime back. The quality control of these new ones aren't the greatest and with plate voltage at over 700v, bad things happen. When my first channel went up in smoke I visited the Transcendent sound forum and found I definitely wasn't alone on this one. A lot of those guys were running Bruce's hardware and had the same cracking problems. They were with the new tubes but regarding sockets, I have no idea. I picked my magnovals up from triode elec (ceramic with floating pins) and see that they've replaced them with a different (saddle-less) style now. For all I know they could've secretly been Novars. All I know is, you can't go wrong with octal :smash:

G 24th July 2004 01:02 AM

Go get yourself a Dynaco ST 70 on Ebay. Make sure that you like the sound with the original design and then you can rebuild and modify to you hearts content. You can get any part for a ST 70 that you can possibly need including new boards. Get your feet wet with something easy. I tried to dive in over my head when I first started out and ended up spending more money and time and frustration than I had to because of discouragement , ignorance and indecision. Find out if "Tubes" are the sound you are looking for first and then go from there. That's my 2cents. A good thirty five watts of tube power should make your Maggies happy.

fdegrove 24th July 2004 01:10 AM

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I was referring to the new production Russian EL509/519s as having that tendency, at least in the SC150 amps.
Blame the infamous tube branders for this one...see, the EL509 and EL519 aren't one and the same even though a lot of tube vendors would have you believe otherwise.
While you could safely use a true EL519 instead of a EL509, the reverse certainly isn't the case, the EL519 being kind of a super EL509 if you'd like.

AFAIK, the Russians never have made a single EL519 and I even suspect their so called 509s to be only acceptably similar much in the same way their 6SN7s and 6SL7s would.


All I know is, you can't go wrong with octal
Yup...we're all waiting for a true octal EL519, aren't we?


P.S. Note the pic shows the EL509-MK2.

PrairiePete 24th July 2004 01:43 AM

From what I remember of the Maggies (20 years ago), you need a ton of power to make them sing. Talking SS, a Bryston 3B (100w) sounded fine. A Bryston 4B (200w) made the bass rise from the grave so to speak (as Maggies go). It made the 3B sound anemic by comparison. My Bryston 2B (50w) could hardly get them going. In a tube sense your talking alot of power into a 4 ohm load. It sounds exciting to do, but your still talking a lot of power.
On a side note, the best movie I ever heard was on a movie channel that used the FM band for stereo (before stereo TV's) through the MGIIIA's. The back wall was right behind the couch. I was looking behind me on more than one occasion. Who needs multi-channel surround.?

DigitalJunkie 24th July 2004 01:37 PM

When I was listening to my first tube amp,I was constantly looking around the room.."What was that?!" the sound was everywhere!
That little 10wpc PP 6V6 amp has plenty of "balls" to get my inefficient speakers pumpin..Not to mention that little amp smokes any SS gear *I've* ever heard.
There's certainly something about toobz...

The amp is from an old Sears Silvertone colsole stereo set..I got the power amp,and preamp,and decided to give it a listen "in the raw" (before I replaced anything,or made any mods)
My first impression was *ACK!* Horrible!...then I disconnected the preamp,and used the pre-out of my Sansui AU7900.. MUCH better,it seems it *would* be worth the time to I did,from the chassis up! new paint,parts,and tubes..
Then it came time to flip the switch and press play...
Fleetwood Mac's greatest hits came on,and my jaw dropped,I'd never heard anything *SOO* good! Stevie nicks was Singing *in my room*..not just from the speakers..she was *there*!! :eek:
It was worth every minute/penny it took to rebuild!!
The rest is history.

So,my advice is,If you aren't sure if you'll like tubes,and don't wanna spend lots on a nice old ST-70,or Marantz 8B,W5M's etc.. Get an old console stereo or something,rip the amp out,and rebuild/tweak it to your hearts content. Don't let those old ugly consoles fool ya,There might be a worthwhile amp in there!
But be warned..You may never look back! (I Havn't)

eRiCdWoNg 24th July 2004 03:21 PM

yea these speakers do need quite a bit of power to get going~ I thought about starting up another system, with horns or something with high efficiency.

As for the model, the ST 70 chassis looks appealing, plenty of mods and the "right of passage" tube amp :)

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