Dynaco Mark IV to Scott 290

Another build, I am building a Mark IV into a Scott 290 (1 channel). I bought these a few years ago on BT knowing I was going to replace the chassis. The new chassis are SS instead of plated, I am using the Scott 290 driver circuit, except for the necessary feedback mod for different transformers,because of the 7199 tube problem,and going point to point.
I am using some nice SS plates I found on the auction site that are a perfect fit.
The can caps are from Hayseed Hamfest They were nice and sent me some factory defects to fill my can cap holes, I can't say enough great things about them,I am sure we will do business in the future.
The schematic is not finished, and just a starting point, and will be updated as the build is finalized
Some pics:
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schematic 2/16 added ultralinear
 
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Yours are mono blocks right, but the Scott schem says stereo? unless it only shows one channel... Just curious, and learning!!!
Your chassis looks great!
 
Yes 2 mono blocks with the schematic based on a Scott 290 with a few small tweaks.
Fixed the schematic title
 
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Also are you going to add the switch, volume and meter to the chassis?


Barney
 
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Thanks for the links... very nice work on all of them,,, you do the chassis work very well, just farming them out now to save time, I guess...
 
I have to get a good brake before I bend another one, I have the sheer. I bought the aluminum chassis, because Garey did an Awesome job on the previous one.
I don't have aluminum welding experience yet.
At the time I bought the Dynaco chassis, I had planned to rebuild it stock, but changed my mind.
I have a second pair I will rebuild with the Dynaco 70 II schematic which use 6GH8 for a driver splitter and point to point, with a SS plate also
 
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I decided to go ultralinear, a little more done.
If I split the cathodes on the output tubes and use q a 27 ohm resistor to get the 1.56 voltage reference Dynaco used, would it cause any problem?
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I decided to go ultralinear, a little more done.
If I split the cathodes on the output tubes and use q a 27 ohm resistor to get the 1.56 voltage reference Dynaco used, would it cause any problem?
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If I understand your question separate Rs you should be fine.
As long as you're not married to the 1.56 you can come up with a a more common value.
When I did my mk3s
I installed 10 ohm resistors (per tube as part of the Dynakit bias/balance kit
 
I was thinking of 1.56, as the chassis is marked for that. I am not sure if the resistor is more likely to pop or heat, as it is a higher resistance.
 
I don't see why two resistors vs one would be a problem, but apparently something about that common resistor reduces distortion compared to no resistor or individual resistors.
 
I'm not positive, but I think that is with cathode biased amplifiers, I have decided to go with the 10 ohm resistors, and modify the silkscreen.
 
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