Marshall 2204 with kt88 build

[jcm-jmp]

ok
2204 with kt88s


OT: Hammond 1650TA
120W
1.9k primary
403ma per side
4,8,16 ohm secondary


PT: Hammond 290JX
360@450ma
6.3v@7a
43vct@250ma


Are these transformers a good choice?
Or
Should I go with a higher voltage PT?
And is there a better OT selection for 2 KT88s biased at 70%?

[pdf64]

70% of what?
30W may be a reasonable estimate of the design centre plate limit for KT88.
Run them hotter and you’d need to take account of the 100k grid leak limit. Which would load the output from the LTP, such that it may become a problem to drive the power tubes to their full ab1 power.
A 1k9 load impedance seems low, how does the load line look?

[PRR]

....A 1k9 load impedance seems low, ...

Sounds like FOUR big tubes. Not two.

[DummyLoad]

Hammond 1650NA OT

Hammond 378CX

will need series stacked filters for at least the plate and screen supplies. PT will provide around 550V B+

the 60W OT will work well for 100W guitar amp.

can wire output stage as UL/tetrode switchable.

can use up to 220K for KT88 grid leak if bias is set at <=35W per tube.

--pete

[jcm-jmp]

PRR


The 1k9 isn't best choice for 2 kt88s?
What primary is best for 2 kt88s in push pull?

[jcm-jmp]

I have loaded jcm 800 2204 with kt88s before with just a bias mod. I really enjoyed the huge sound that the kt88s produced in that amp. However that marshall pt and ot ran extremely hot.


I'm trying to wrap my mind around a build with a proper sized pt and ot.


I'm not clear on the process of empedance selection of an ot. I'm hoping someone can explain this process in terms my feeble mind can understand.

[sluckey]

DummyLoad suggested a good set of transformers.