2 years after ordering my Poseidon boards I have completed my Mark III clone! The only hiccup I had was arcing to the screen grids after setting the bias on the first amp I completed. I went back and added screen resistors to both amps. (See this topic - http://diytube.com/phpBB2/viewtopic.php?t=1455) This is a modification I would highly suggest for anyone building Mark III clones. After adding the screen resistors the amps have worked perfectly. Thank you Shannon for the nice Poseidon driver boards and thank you DerekVa for the 12AX7s!
Some pics:
http://diytube.com/phpBB2/album_pic.php?pic_id=55
http://diytube.com/phpBB2/album_pic.php?pic_id=56
http://diytube.com/phpBB2/album_pic.php?pic_id=57
Mark III clones completed!
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Mark III clones completed!
by patrickn » Wed Oct 08, 2008 8:42 pm
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by Ty_Bower » Wed Oct 08, 2008 9:01 pm
Really nice looking Mk3 clones. I've still got another year left if I want to finish mine faster than you. Dunno what's holding me back. I ordered "screen stoppers" from Mouser, but I can't recall what value I got. What did you use? 100 ohm?
I like those chassis. They're not exactly Dynaco original, but they definitely work for me. Did you drill / patch / replate originals, or is someone selling SS chassis with all the clever holes cut in the right places?
Those New Sensor re-issue KT88 are really good tubes. I'm using half the set I bought for my Mk3 in a single ended amp these days. I couldn't be happier with them.
I like those chassis. They're not exactly Dynaco original, but they definitely work for me. Did you drill / patch / replate originals, or is someone selling SS chassis with all the clever holes cut in the right places?
Those New Sensor re-issue KT88 are really good tubes. I'm using half the set I bought for my Mk3 in a single ended amp these days. I couldn't be happier with them.
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Ty_Bower - KT88
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by patrickn » Thu Oct 09, 2008 10:58 am
Thank you both. :)
Ty,
I did use a 100ohm resistor for the screen grids. I have not had any arcing problems after adding them. The chassis' were blank 9x9 steel from soundtastic on ebay. I put in all the holes. Some aspects of the Dynaco original chassis aren't great IMHO (like having the circuit board exposed for wandering fingers) so I wanted to make my own.
Yeah, the GL re-issues do like to conduct as some people here have mentioned. I started out with max negative bias and it didn't take much advancement of the pot to get to 70mA of cathode current. If I were to do it again I would consider using multi-turn pots for the bias adjustment.
Ty,
I did use a 100ohm resistor for the screen grids. I have not had any arcing problems after adding them. The chassis' were blank 9x9 steel from soundtastic on ebay. I put in all the holes. Some aspects of the Dynaco original chassis aren't great IMHO (like having the circuit board exposed for wandering fingers) so I wanted to make my own.
Yeah, the GL re-issues do like to conduct as some people here have mentioned. I started out with max negative bias and it didn't take much advancement of the pot to get to 70mA of cathode current. If I were to do it again I would consider using multi-turn pots for the bias adjustment.
- patrickn
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- Location: Seattle, WA
by FATMAN » Tue Nov 04, 2008 9:46 pm
those look nice! are the chassis stainless steel? I realy like the way you mounted your driver board and put the caps on the bottom of it. i just finished my set of MK3's today and I had no problems with the arcing. is that due to the type of tubes? I have electoharmonix they seem great. If I make another set i would like to get a chassis blank and make them mirror image and put the switch on the front or opposite side,with a indicator light. where did you get the bias meter that is nice too. Great work!!
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by patrickn » Wed Nov 05, 2008 4:53 pm
Thank you,
Yes, they are stainless steel. Not sure why some tubes arc in the Mark III and some don't. I assumed I would not need them because Dynaco did not see the need for them, but turns out they were needed in my case. I speculate it's because of the higher power supply capacitance with the SDS boards and the high transconductance GL re-issue KT88s.
What bias meter are you referring to? Are you looking at the pictures of my amp or a different amp? :-)
Yes, they are stainless steel. Not sure why some tubes arc in the Mark III and some don't. I assumed I would not need them because Dynaco did not see the need for them, but turns out they were needed in my case. I speculate it's because of the higher power supply capacitance with the SDS boards and the high transconductance GL re-issue KT88s.
What bias meter are you referring to? Are you looking at the pictures of my amp or a different amp? :-)
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by FATMAN » Wed Nov 05, 2008 5:27 pm
on the first picture there is a green badge type thing,I thought it might be a bias meter on the front. is that not a meter? How are the GL golden lion tubes, would there be much diference to a electroharmonix?
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by patrickn » Wed Nov 05, 2008 5:49 pm
The green thing is a lighted power switch from Mouser. The GL tubes are the only tubes I've tried so I can't give a comparison. I can say the amps sound fantastic. I've been very happy with them.
I have never heard an Electroharmonix tube so I can't compare them. It'd be interesting to try some other tubes, but may be a while - those KT88s are pricey.
I have never heard an Electroharmonix tube so I can't compare them. It'd be interesting to try some other tubes, but may be a while - those KT88s are pricey.
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by Ty_Bower » Wed Nov 05, 2008 6:02 pm
FATMAN wrote:How are the GL golden lion tubes, would there be much diference to a electroharmonix?
They talk about it here:
http://www.diyaudio.com/forums/showthre ... did=132289
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Ty_Bower - KT88
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