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Just finished my Poseidons rev2

PostPosted: Tue Jan 03, 2012 7:44 pm
by K4ECA
I built these a few years ago and always felt they lacked something. The amps where just upgraded, mostly the power supplies. Now filter caps have: 60-110-75-50uf and 800v. Also changed Sovtek KT88's to Electro Harmonix 6550's. These new (?) amps kick ___ . They are capable of 80 watts RMS, with 535V B+, (measured with true rms meter and oscope, 4 ohm load, 4 ohm tap). Using hammond 1650R's, 100w OTs. Bottom end seemed loose, uncontrolled, but now the bass is very impresssive. I am currently listening to Maroon 5, Mickey Maddon's bass finally has authority. [:)
Shannon, Love the Poseidon boards. Here is a pic.


PostPosted: Wed Jan 04, 2012 11:12 am
by TomMcNally
Nice looking amps Bob! I built a pair a few years ago using Triode's
transformers, Soundtastik chassis and GZ-37 rectifiers. They kicked azz!

PostPosted: Wed Jan 04, 2012 7:34 pm
by K4ECA
Thanks Tom, I'll probably just road test them for now. If I still think they are as good a month from now, I'll make the next upgrade cosmetic, maybe a wood chassis with box joints.

PostPosted: Thu Jan 05, 2012 7:13 pm
by Thermion
Bob, great job on the amps. I've been very happy with my Poseidon MkIII's. I think the 1650R was a good choice of output transformer for your amps. A little extra headroom over a 1650N. What did you use for a power transformer? You may be able to get a little more power with a quad of KT-120s. I have been using a quad of KT-120s in my Ikes biased at 90 ma a tube and love the sound, especially the bass.

I like the look of wood bases also. I think they go well with tubes.


PostPosted: Thu Jan 05, 2012 8:20 pm
by K4ECA
Thanks JT,
The PT's are dyna replacements from Triode Elec. The B+ is high because the line voltage is some what high here, never below 123, some times as high as 128. I had the 1650R's left from a project that went horribly wrong. Sortof an over grown st70 with the worst sounding front end ever built in the history of man(!), the RCA tube manual is not always right. I've learned a ton since then.

1650R Primary Impedance

PostPosted: Sat Feb 04, 2012 1:52 pm
by maynard999

I just ordered the same transformers as you and am looking forward to pulling this project together. I did notice that the 1650R has a higher primary impedance (5000 vs 4300). Did you make any changes or just drop it in?

PostPosted: Sat Feb 04, 2012 5:04 pm
by K4ECA
I stuck with Shannon's schematic and parts values for the Mark III build and stock transformers with one exception. I found the power supply resistors R16 (100K) on the Poseidon board and the 6.8K 2W resistor on the can cap needed their values to be adjusted due to the higher than spec. B+ and the voltage divder resistors on the power supply board I used in place of the can cap. The voltage divders draw enough current to drop the voltage at point J and K so the resistors I am using are: The 6.8K is now 12K 3W and R16 is now 56k 1/2W. I now have 325v at point J and 425V at point K with about 535v B+, close to perfect. Note the original schem. shows 480v after the choke and 430V at point K only 50V drop, mine is 110v drop so double resisitor value needed, 6.8K to 12k.
Happy to help if needed, or if you want details just reply. Let us know how it goes. Like to see a pic or two if you can.

PostPosted: Sat Feb 04, 2012 5:12 pm
by K4ECA
I forgot to ask what tubes your planing on using, brand and type.
Remember the Posiedons, like Ben and Jerry's, come in many flavors!


PostPosted: Sun Feb 05, 2012 10:31 am
by maynard999
Plan on putting Shuguang Treasure Kt-88's in there. Heading to China in two weeks on business. Can snag matched quads for $70 total.

Only other difference in my setup is I'm getting a Hammond 300BX power transformer. Using the extra 5V tap (converted to 12VDC) to run a backlit VU meter and driver.


PostPosted: Sun Feb 05, 2012 10:55 am
by maynard999
Forgot....also ordered the quad cap upgrade from Curcio (Dynaco-Doctor).

Re: tubes

PostPosted: Mon Feb 06, 2012 8:45 pm
by Ty_Bower
maynard999 wrote:Plan on putting Shuguang Treasure Kt-88's in there. Heading to China in two weeks on business. Can snag matched quads for $70 total.

How many quads are you allowed to bring back in your suitcase? By the way, I'm first in line if you are taking orders. ;)

PostPosted: Mon Feb 06, 2012 9:05 pm
by SteveH