Wanted: Experienced Mk3 Poseidon user feedback.....

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

Wanted: Experienced Mk3 Poseidon user feedback.....

Postby crispycircuit » Wed Mar 21, 2007 3:44 pm

Here's my plan. I want to build Poseidon Mk3's to power my AR-11s (A 70's version of the AR-3). I don't play my music loud and 50 watts will do. The speakers are 4 ohm and like some power.
My questions are: Would some fast diodes help to keep the bottom tight? or would a tube rectifier be OK? Also should I use the SRS cap board or would more capacitance be better?
I will keep the UL hookup/mode. Which tubes, 6550, KT88 or KT90 will give a tight extented top and bottom?
While I'm at it, what coupling caps deliver this type of sound.??
I would enjoying hearing your likes and dislikes from experienced Poseidon Mk3 users.....Cheers!.
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Postby Shannon Parks » Thu Mar 22, 2007 5:27 am

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Postby EWBrown » Thu Mar 22, 2007 7:33 am

One comment (which I posted a while ago), if you use the C Chong cap board, and one of the Soundtastick chassis, there isn't enough clearance to use the supplied power switch. I don't know if the SDS cvap board allows enough switch clearance. (I went with the Chong Board and SS rectifiers)

For coupling caps, anything from Orange Drops to Solen Fast Caps, to the fancier ones like Auricap or Hovland Musicaps will all work nicely.
The Russian PIOs are also very nice sounding.

The original design calls for 12AX7 and 12AU7, but 5751 and 12BH7A cane be rolled in with no modifications, some folks prefer this combination, YMMV.

For output tubes, if you can use 6550s, then you can use KT88s as well, the Elektroharmonix are a great price / performance bargain, the Sovteks are from the same Russian manufacturer, they're just a slight bit lower on the quality scale (EHs are basically cherry picked, re-branded Sovteks).
The new "Mullards" and "Tung-Sols" are simply "rebranded" Russians, so don't get misled by the names.

I know, a lot of this is very "general", I built up a single amp, to experiment with, and eventually to use as the LF power amp in an HT system, someday. Right now, it's still a "lab rat" for tweaking and tuning purposes.

HTH

/ed B in NH
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Poseidon feedback

Postby EdStiles » Thu Mar 22, 2007 5:06 pm

You can look at several of my topics for additional info, basically, I rebuilt a pair of Dyna Mk2 as Mark 3s, adding a C354 choke and an SDS cap board (50/50/50/50 mfd). The SDS allows a 600v power supply, initially I used fast recovery diodes but was unhappy with the 560 B+ I was seeing, as well as the effort to get the other voltages right.

I went back to a 5AR4 and things got much better - my B+ voltage was dead on @ 518, but was still unhappy with the sound using a 5751 in place of the specified 12AX7, it had plenty of bass but didn't seem to have enough "punch" in the midrange.

As the 5751 was NOS, and I had experimented earlier with a NOS 12BH7 earlier, I decided to "rebuild" the unit to Ned's Tubezone version as posted on in the Poseidon section, it uses the 5751 and 12BH7.

At this time I have an amp that sounds like an Audio Research unit , very tight, almost crystalizes the sound. I have run it with a Audio Research SP9 preamp and a Marantz Model 7 which has been partially recapped in the audio section and has a totally rebuilt and upgraded power supply. The Marantz sounds more mellow, but is not as tight in the bass, its very listenable. The SP9 had awesome bass, but didn't sound right elsewhere - too crisp. I'm going to try changing R10/11 to a value between Ned's 47k and Shannon's 68K to see if that helps.

My music is mostly jazz, but also tested with Sting and Pink Floyd as well as some vocalists, male and female.

Speakers are KEF Reference 3s and Klipsch Fortes

Tube are NOS Sylvania JAN 5751 and RCA grey plate 12BH7s, KT88s are chinese, but also tried some EH which didn't sound much different. Bias is set at 68ma. Going to try using a scope to adjust crossover notch distortion as well.

Hope this helps, these are my experiences, your mileage may vary..........

Ed
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Postby crispycircuit » Mon Apr 02, 2007 11:21 am

Well after reading Gregt01 thread "Tube Pop" on tube arcing, I'll stick with a GZ 34 rectifier, an excellent read.... I received my boards and will be digging through my parts bin. I'll also go with the SDS MK3 cap board. As I slowly assemble I hope to get more replies to this thread......
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Postby WA4SWJ » Mon Apr 02, 2007 12:52 pm

Crispy,

I wouldn't be discouraged with solid state rectifiers. As I've stated a few times, I like 'em. The amps I have that use solid state sound punchier (if that's an audiophile term) probably due to their increased filter capacitance. I like them just a bit better, especially for home theater. The problem discussed in the "tube pop" thread is easily fixed with those resistors.

I use my Mark III clones (they're all new, not rebuilds) in my home theater. They are great for that and will rock the place. I use two eiclones for the surround speakers.

I think the poseidon driver is super. I use 5751's and 12BH7's. These amps work extremely well for music too.

Regards,
Ed Long
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Postby crispycircuit » Mon Apr 02, 2007 3:49 pm

WASWJ thanks for the reply. How much capactance are you using? What voltage is your B+? Did you change any resistors due to higher voltage? I have some 12BHA7's. Also what output tubes are you running?? I was looking at the Poseidon info I got with the boards and I didn't see the 680 ohm 2 watt (on speaker terminal) in the drawings but saw it in the part list??? Did you use it??
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Postby WA4SWJ » Mon Apr 02, 2007 5:19 pm

Hi Crispy,

I may have been slightly misleading. I use tube rectifiers in my poseidon Mark III's and I still place the resistors in the screen grid circuit. And yes, I did use the 680 ohm resistor you mention. If you look carefully at the original Mark III schematic you'll see it near the top of the schematic with one side connected to ground. I am running 6550's in these amps but I have some KT-88's that I just haven't tried yet.

As for solid state rectifiers, I use them in two Dynaco ST-70's and of course my ST-35, my eiclones and my 832 amp (at left). I use the screen resistors in the ST-70's and eiclones. I actually lost a set of EL-34's to arcing in my first ST-70 before I added the screen resistors. Once I put the resistors in I had no more problems whatsoever. I did not change any resistors in the amps due to the higher voltage and they work fine. The voltages are 45 or so volts higher and I didn't feel that was terribly significant.

Hope this helps.

Regards,
Ed Long
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Postby crispycircuit » Tue Apr 03, 2007 11:43 am

More questions.... The parts list calls for non grounded power cord. Any reason for doing this?? Ground loops, etc? I would guess that most builders would prefer a grounded power cord. .... The 9pin sockets for the circuit board. Triode has a 9pincerpcgold, are these correct and a decent choice?? Where did you buy yours?.... And the parts list grows!!
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Postby Shannon Parks » Tue Apr 03, 2007 11:52 am

crispycircuit wrote:More questions.... The parts list calls for non grounded power cord. Any reason for doing this?? Ground loops, etc? I would guess that most builders would prefer a grounded power cord. ....


This is a replacement for the original two-prong cord. Ultimately, I think you can get a 3-prong safety cord, try it, and keep it if the noise is low or disconnect it if the noise is high. A lot depends on your speakers and the rest of your system

crispycircuit wrote:The 9pin sockets for the circuit board. Triode has a 9pincerpcgold, are these correct and a decent choice?? Where did you buy yours?.... And the parts list grows!!


These are fine. I think I've bought the one piece ceramics from Handmade Electronics last time I ordered. Gotta spread the love around. :)
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