Poseidon is HOT ! Upgrade or build new - Listen First !

for Dynaco Mark II/III/IV and DIY PP monoblocks

Poseidon is HOT ! Upgrade or build new - Listen First !

Postby TomMcNally » Thu Mar 16, 2006 7:26 pm

OK - I stared at the hot looking Poseidon board all day at work, nice job Shannon ! Decisions, decisions ... time to listen.

When I got home - I hooked up my Dynaco MK-III's - they have the "Brand N" boards - in fact - my MK-III's and ST-70 are the poster children on the "T" web site. No boutique parts - just the Xicon caps.

Test conditions for all amps ... bass heavy music from my new favorite source - a Polk XM tuner on Channel 84 - "XM Chill" which is like slow electronic something or other ... I like it. Feeding my Adcom GTP-500II with the contour button in and out for testing, but tone controls out. Into a pair of Klipsch KSB 3.1's No, I didn't warm each one up for an hour or anything ... just plug and play for 10 minutes.

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MK-III's - Well - they sound pretty nasty - tubby, vibrating bass and not very clean at all. The worst out of all we will talk about here. Pillows over the speakers compared to the others. Probably time for new tubes - the Magic Marker on the sides says 6550 6/18/73 ... might be accurate ! (and it won't wash off) I rebuilt everything else - but no new tubes.

Next:

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Dynaco ST-70 with the "Brand N" driver ... just as tubby bass, not all that clean. Low on the list. The EL-34s are new Valve Arts.

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DiyTube ST-35 ... better bass, more open sounding than the old Dynacos.

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Dynaco ST-35 - better bass than the ST-70 or MK-III's ... but not as clean as the DiyTube ST-35

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Dynaco SCA-35 - sounds pretty much like the Dynaco ST-35 - probably a little cleaner. I replaced the coupling caps and put new JJ EL-84's in it recently. Pretty good sounding. Not as much bass as the others.

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DiyTube ST-70 clone with Heathkit AA-100 iron and new 7591's ... ahhh ... more like it - cleaner bass - open sounding - more listenable. # 2 place Obviously a lot of kick.

The winner ... and who knows why ...

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832A push pull amp I built recently ... solid bass - no tubbiness - clean midrange - very listenable. The bass seems to have a faster release time (to use an audio processing term) All around more kick and less muddiness.

OK - while I'm at it - I'm going to hook up my big azz 60 pound 300 B amp ... I know it's not PP - but it's here in the room already.

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I'm back - I will agree with Eric in McKinleyville to an extent - complex music gets muddy. Solo instruments and voices sound pretty good. Solo bass compares well with the ST-35's. Still a pretty listenable amp. Disclaimer - this thing cost a small fortune to build, I may be biased.

While I'm at it - I'll drag the huge Velleman K-4000 up here ...

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It's actually lighter than the 300B ... PPP Svetlana EL-34's ... mids and highs are nice - bass is pretty tight. This one ranks pretty high, lotsa kick - I guess so, they call it 95 watts per channel. First time upstairs on these speakers - pretty nice. Bass still isn't as clean as the 832A.

No real reason I did all this - I just couldn't believe my MK-III's sounded as bad as they did ... so I kept going. Bottom line - I need to learn to tweak ... I'm on the way.
Last edited by TomMcNally on Thu Mar 16, 2006 8:17 pm, edited 1 time in total.
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Postby WA4SWJ » Thu Mar 16, 2006 8:11 pm

Tom,

Ordered my poseidons from Shannon today. I'm building 3 Mark III clones from scratch with all new parts including dynaclone Mark III transformers from Triode. I can't wait to get them built. My transformers arrived just today along with some Sovtek 5AR4's. I also have a set of transformers coming from Eric that I REALLY can't wait to see. I'm going to use some old eiclone boards as drivers for those but I haven't made up my mind on output tubes yet.

Also can't wait to get my 832 amp done to hear what you've been talking about. I've sort of stalled on it because I've been very busy at work and spend too many hours there! But I'll get it done. I even bought some tung oil to finish the wood base with.

Love all your amps! Since some are muddy and so on, might be a fun thing to do some analysis and tweak them using some of Shannon's suggestions.

Have a great weekend everyone!
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Postby TomMcNally » Sat Mar 18, 2006 3:21 pm

Three Poseidon based amps sounds like a nice project. What type of chassis are you using Ed ? I looked at the remakes on eBay, but to be honest, the tubes are too close together on the original MK-IIIs and I'd prefer wider spacing for better cooling. They do have the advantage of much faster assembly and do look great though. I did order a pair of the red boards too, but am thinking I might look for some unique output tubes ... maybe some big Triodes ! Anyone have any thoughts for something unusual and cool looking ?

I know I sound fanatical about the 832A amp - but it has something magical going on - maybe it's the effect from both plates being in one bottle. The clarity, kick and sizzle is amazing. High shock and burn factor too. Do get a fan for yours ! The almost silent Whisper fan seems to do the job.
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Postby WA4SWJ » Sun Mar 19, 2006 7:01 am

Tom,

I have three of the reproduction Mark III chassis. I like the idea of them being a little smaller than my eiclones. I keep the amps in the open so I am not too worried about cooling, although it would be nice if the output tubes were a bit farther apart. But I am proceeding. I'm going to run some Electro-Harmonix 6550's to start with just because I have some. I will likely obtain some KT-88's eventually. Either JJ's or Sovtek. Not sure quite yet.

I'm going to use these as L-C-R amps for my home theater setup. I currently use my three eiclones for that but I'm addicted to this stuff and I wanted to build something that looked just bit nicer than my home built looking eiclones. Granted they sound excellent and work quite well for music and for home theater. They have plenty of power. Just something a little better I guess. I'll use the eiclones in the basement.

I haven't worked on the 832 amp much lately. I've just been busy with work. I hope to get back onto it in a couple of weeks. After your reports I am anxious to hear it!

All for now ....
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Postby TomMcNally » Sun Mar 19, 2006 4:27 pm

Ed -

Do you think the Poseidon boards could be mounted slightly below the chassis in those repros so that a cover plate could be made, and just the tubes and maybe a little socket could stick through ? I'd rather not have the exposed high voltage, and the cages are kinda pricey. That might be a way to go. I've seen perforated covers, but flat metal work is about the limit of my capability.

... tom
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Postby WA4SWJ » Sun Mar 19, 2006 6:01 pm

Tom,

I plan to leave them open. I have no kids, no pets, no spouse and my ladyfriend knows all about high voltage. Granted, it's always better to cover up exposed high voltage, but I don't have metal working facilities at all. I thought about some perforated covers but I like the looks of them better open.

Once I get one of them built I'll post some pictures.

Regards,
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Postby TomMcNally » Sun Mar 19, 2006 8:45 pm

Hi Ed -

What I meant, was * I * was thinking of recessing the board - and was asking your opinion, since you have all the stuff ... do you think there is enough clearance under the chassis if the components except for the tubes and maybe the bias trimmers were mounted on the bottom. I like the look of the boards too ... maybe I would make covers out of thin plexiglas.

... tom
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board clearance

Postby Shannon Parks » Mon Mar 20, 2006 7:17 am

TomMcNally wrote:Hi Ed -

What I meant, was * I * was thinking of recessing the board - and was asking your opinion, since you have all the stuff ... do you think there is enough clearance under the chassis if the components except for the tubes and maybe the bias trimmers were mounted on the bottom. I like the look of the boards too ... maybe I would make covers out of thin plexiglas.

... tom


Hi Tom,

Both the ST70 and Poseidon boards were designed with recessing in mind, so definitely yes. The double silk screen makes this a snap. Even with the coupling caps poking downwards, you'll be fine - clearance-wise - even in a stock MKIII chassis. To get an idea of how recessed you want it, compare it to the standoffs in the ST35. You maye want it a hair more or less.

Shannon
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Postby craigtone » Mon Mar 20, 2006 9:27 am

Shannon,

I just purchased a set of Poseidon boards from you. One will be to restore/upgrade a Mark IV, the other to build a Mark III from scratch using a new repro chassis with updated punches (eliminates quad cap, rocker switch, 5-ways, etc.). Looking at the design and the fact that the chassis is the same depth as the ST70 chassis, using a 1/4" standoff and placing the coupling caps on the bottom will allow a flat cover plate to be used. I'll be posting pics of mine in this configuration when I start building.

Another question is the coupling caps. I plan to use the Mark III as a subwoofer amp and was wondering what value you would recommend on your board? You know the circuit better than anyone ... could I get away with 0.47uF? I am not concerned with THD/Freq Resp. about 300Hz, as long as bass is clean and tight.

TIA ...
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Postby TomMcNally » Mon Mar 20, 2006 11:18 am

hey craigtone -

Do you have a link to those MK III chassis you have ? I'm thinking about what I wanna do here. I have a set of MK-III's - but a new project would be fun. The Poseidon boards are on the way.

Thanks

... tom
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Postby craigtone » Mon Mar 20, 2006 11:35 am

I put a link in the topic about the chassis I posted in the preBay section ...
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