Ceriatone OTS 100 vs more traditional dumble ODS designs

[jmrckr]

I'm on the path of building another ODS amp. I already built a 124. I'm going into high plate territory for sure. That being said, I'm pretty interested by the ceriatone OTS circuit (pretty much high plate skyliner with some twists ?). But the power amp looks different from, let's say, the 102 or the 124, and the power supply as well. The output transformer is 2,35K primary instead of 2k primary, the signal resistance on power tubes pin 5 is 3k3 instead of 5k1, the resistance on pin 4 is 1k instead of 470R, the B+ is higher (700V ct winding for power transformer instead of 640ct). What these diffences do to the sound ? I'm wondering if I build a ceriatone OTS preamp with a 124 power amp, would it still sound pretty much like the OTS ? Or I could build the OTS preamp and power amp as they are but with the fender twin power transformer (640vct) ?

Let's say that I build an OTS just like it is with the "right" transfos, these are less common ... there are mercury magnetics tranfos but they are much more expensive.

For the output transfo I could go with hammond 1750D. The OTS choke is 3 henry and the fender twin (hammond 194B) is 4 henry ... I guess it would still work with the hammond. But for the power transformer there is no direct fit with hammond. What do you suggestions ?

Yeah, a lot of questions.

Thanks !

[jmrckr]

ok ... found these Edcore transformers that could do the job ...

power : https://www.edcorusa.com/xpwr173 (there is no 60V bias tap ... only 100v winding. Maybe some modifications to the bias circuit could do)

Output : https://www.edcorusa.com/cxpp100-22k

[martin manning]

ok ... found these Edcore transformers that could do the job ...

Those transformers will be fine, a good option in fact. The 100V winding will work nicely for the negative bias, just tweak one resistor. And (bonus!), you have a 12V winding for relays. A 4H Twin choke is standard Dumble part, and the other circuit changes you mention are minor, so I wouldn't worry. Just build to 102 or 183 spec, and/or season to taste.

[jmrckr]

According to the calculator on this website (https://thesubjectmatter.com/calcptcurrent.html), the amp should draw about 433.77mA with a 350-0-350 transformer, 4 6l6 and 4 12ax7 ... at 400mA rating for the edcor it is theoretically not enough ... maybe this could cause unwanted voltage sag when the current demand is near max ? Ok, maybe it does not happen often, maybe never at all (we never run an amp at full throttle ...). But, it kind'a makes me wonder if it is still ok ?

Also, the rule of thumb that I know is :

P=VI, so 100watts = 479.5V plate voltage * I
I= 208mA , and you need 2 times that ... so 416mA, and that is still higher then the rating of the Edcor PT.
What do you think ?