First monoblock question?

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

First monoblock question?

Postby Blair » Sat Mar 10, 2007 10:39 am

I have printed the preview of shannons manual and see there are two different blocks available to be built from this board. An EL34 and a 6550/KT88 amp. What are the bennefits and or tradeoffs between the two. I recently built shannon's st35 kit and love it, but am looking for a bit more overhead. Thank you for any impressions of the sound differences.

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Postby TomMcNally » Sat Mar 10, 2007 11:46 am

You can use the Poseidon board in a Dynaco MK-III or new clone, which is 60 watts with 6550 type tubes (I used KT-90's) or you can use it in an original or clone of the Dynaco MK-IV, a rare mono block which uses EL-34, and was 35 watts or so, and pretty much half of an ST-70.

There are pics of a pair of Poseidon MK-III clones on my website using the Sountastick chrome chassis at: http://mcnally.cc/amps.htm

The choice is all about power ! Also, from a practical standpoint, the parts for the MK-IVs will be cheaper, but I don't think there is a pre-made chassis, but you can get them for the MK-IIIs.
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poseidon stereo

Postby Blair » Sun Mar 11, 2007 10:26 am

Hey Tom,

As usual, you have replied to my questions with positivity. I am not overly concerned with the monoblock version versus power as you stated, but here is a question you may be able to help me with . I found a toroid tranny that is 400 vct at 500ma with a 12.6vct winding. Assuming I change the rectification to SS and use a small tranny for the SS rectification, do you know of anyone who has built a stereo version of this amp? Will this work?

Thnak you ahead of time for any info,

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Postby Blair » Sun Mar 11, 2007 11:34 am

Sorry, that is 800vct.

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Postby TomMcNally » Sun Mar 11, 2007 1:25 pm

Hi Blair ...

I'm not sure what you mean about a transformer for the SS rectification ? If you want to build a stereo (one chassis) amp, why not go with the ST-70 board and a pair of EL-34's ? One of the reasons people go with "monoblocks" is that the weight gets out of hand with huge transformers. But, to pick a power transformer for a stereo amp, find something with the proper voltage for one side, but with double the current. I suppose if you only had a 12 volt filament winding, you could put sets of EL-34's in series and run them on 12 volts, and the driver tubes are already two 6 volt filaments inside the tubes, so you could strap them for 12 volts.

I don't think I've seen anyone build a stereo Poseidon, it would be BIG !

... tom
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Postby Shannon Parks » Sun Mar 11, 2007 1:44 pm

TomMcNally wrote:I don't think I've seen anyone build a stereo Poseidon, it would be BIG !


Howabout something like the Soundtastick chassis with a Poseidon driver, MKIII build, KT88s and one of the Antec toroids? Probably would use Hammond 1650Ns though they aren't as cheap as they once were. Viola - a very cheap modern Eico HF89 along with the chiropractic bill. :)
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Postby erichayes » Mon Mar 12, 2007 12:55 am

Hi All,

Just a FWIW: my first two (had to build a second to make sure the first wasn't a fluke) prototypes of the 2046--which is an HF-89 with minor modifications and my iron--weighed in at 46 pounds and were built on .050 Al Hammond chassis. Talk about 46 lbs of jello! Bottom plates made them a little more stable, but you an see the OTs leaning in toward the center of the chassis. I'll send pix when I have a chance.
Eric in the Jefferson State
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Postby sorenj07 » Mon Mar 12, 2007 8:55 am

Congratulations on the build! Basically, the problem you just mentioned is why I'm going to try and afford a couple custom jobs from a metal shop down in Dorchester. I'm just too lazy to draw out in CAD the layout for the tubes and transformers and stuff, but if I did, it'd be pretty sweet. My cheap Unibit-knockoff for the octal sockets kind of chews the metal...
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Postby Blair » Mon Mar 12, 2007 8:55 am

separks wrote:
TomMcNally wrote:I don't think I've seen anyone build a stereo Poseidon, it would be BIG !


Howabout something like the Soundtastick chassis with a Poseidon driver, MKIII build, KT88s and one of the Antec toroids? Probably would use Hammond 1650Ns though they aren't as cheap as they once were. Viola - a very cheap modern Eico HF89 along with the chiropractic bill. :)


Hey Shannon,

I like building my own chasis so that is not an issue. Antek, as you suggested has a 800vct 500ma per winding tranny with two 6.3v secondaries, and EDCOR has some OPTs : CXPP60 that will work for the application. Weight is not an issue. I'm young and do not mind toting around a 65lb amplifier. The Antek is 10lbs and I assume the EDCOR are about 7 each so it should not weigh more than 50 pounds anyway. Will this 800vct tranny power both channels sufficiently? Will I need another small tranny to drive any of the additional tubes? I know I can run the KT88s and the 12AU7 and the 12 AX7 off the Antek, but what about the rectifier tube? Any suggestions or is SS a better option?

Thank you

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Postby TomMcNally » Mon Mar 12, 2007 9:21 am

Soren -

Have you used cutting oil with the UniBit ? It's messy, but it helps. I have a quart I got at Ace Hardware. I use an old Mouser catalog to soak it up.
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