Schematic recommendations for a PP KT-88 with the gear I have?

[laborer75]

Wondering if anyone can recommend a good Hi-Fi schematic for the transformers and tubes I already have?
I'm hoping to go KT88, 12AT7 and 12AX7 for the tubes in a push-pull configuration as I have many of these tubes.
I have a gutted Jolida JD302BRC case that has slots for 4 power tubes and 4 pre-amp tubes I am going to use for the build with the transformers already mounted to it.

My power transformer (Jolida SG-300A) specs is as follows:
6.3V (3.5A)
70V (100mA)
0-10-350-370V (500mA)
110V x 2
0-5-9V (5A) x 2

My output transformers (x2) specs (Edcor CXPP60-MS-4.2K) are:
60W
Primary: 4.2K ohms
Screen Voltage: 40%
Secondary: 4,8 and 16ohm

I was looking at a Jolida 502A Schematic and it looks pretty simple. Looking to max out wattage with these transformers. But wondering if there is a better way to go?
Any recommendations would be great.
Thanks in advance!

 

[quadtech]

You may take a look at Sheldon Stokes' version of the Dynaco ST70

http://site.triodestore.com/New_ST70_Driver_Board.pdf

https://www.quadesl.com/pdf/st70board_ef86.pdf

https://hifihaven.org/index.php?threads/dynaco-st-70-project.10975/

 

[laborer75]

Thank you @quadtech. I will take a look at that. 👍

 

[vinylkid58]

I have a gutted Jolida JD302BRC case that has slots for 4 power tubes and 4 pre-amp tubes I am going to use for the build with the transformers already mounted to it.

Unfortunately, the stock Jolida chassis isn't very good IMHO, because it's so shallow. This makes adding a decent power supply a real pain.

Have a look thru this old thread. Lot's of interesting ideas to improve the circuit. https://www.diyaudio.com/community/threads/opus-5-0-a-modern-mullard.161702/

jeff

 

[laborer75]

Thanks @vinylkid58. I do have a couple of Hammond cases to play with. I've done a few board builds but haven't gotten to casing the stuff yet. My latest was a 300b build I'm using on some Vandersteens, Sounds really good!

 

[hooman]

I guess 0-5-9 v........is 0-5-6 v !! 9 is not for rectifier tubes filimant /

 

[laborer75]

You caught a mistake on my part! Good catch. It is indeed 6V, not 9v. Thanks! I think I will take the advice of others and look into an ST70 build. Thanks again.

 

[Francois G]

Have a look at this design, based on an Eico HF87/89 Mullard topology. FWIW, I have both Dynaco ST70 and Eico HF87, and the Eico is clearly the better amplifier. If you would like to know more about Kevin Ward’s adaptation for fixed bias 6550/KT88/KT120 with UL 4300 Ohm output transformers with EFB modulated negative bias supply, read about it here: https://audiokarma.org/forums/index.php?threads/kt120-amp-mk-3.828722/

 

[laborer75]

@Francois G, I'll check that out! I do have a quad set of KT120's along with many KT88's. That build looks very versatile! Thanks for posting that information. 👍

 

[tubelectron]

@laborer75 : IMHO, the simplest basis with your elements would certainly be something like the well-known Dynaco MKIII, in a stereo version :

T

 

[Francois G]

As a caution, unless one uses the exact output transformer in building a schematic, it will be probably need some tweaking of the GNF components with the aid of an oscilloscope.

 

[laborer75]

I'd probably just splurge and buy some irons if needed and go by a known build's specs. I do have a scope but I'm not versed much in it. I have used it to track down signal losses along with a signal generator to fix a few things. Learning as I go. Wish I knew some old school amp guys locally I can shadow and learn from. Youtube has been my teacher. 🤣

 

[PurityAudio]

Hello Laborer
Did you ever follow through with this build? Curious if you still had that Jolida transformer and looking to offload it?