GU13 813 SE smps psu

[artosalo]

Redrawn Schematic:

Quite low load impedance (3k5) with 900 V +Ub. This means high THD.
Is this intentional ?

I once tested GU13, also as a SE triode with 850 V +Ub and 100 mA anode current.
With Rload = 3k7 the max. output power was some 18 W and THD about 9%.
With doubled load impedance (7k5) the max. power dropped some 1.5 dB to 13 W, but THD dropped more than 5 dB to 5%.

 

[claudiomas]

this amp its for the beauty of these GU13,
if i wont low distorsion high quality its better to use real triode like GM70
and good IT
said this i use 4ohm output for 8 ohm speacker, i just need few watts
please do not get miss the pleasure of a new amp with problems calculations etc etc ,
its nice amp sound pretty good and make nice music
i repair a 845PP made by guru and its not better festival of harmonics
the GU13 SE load 8ohm but 4 ohm output:

 

[claudiomas]

Quite low load impedance (3k5) with 900 V +Ub. This means high THD.
Is this intentional ?

I once tested GU13, also as a SE triode with 850 V +Ub and 100 mA anode current.
With Rload = 3k7 the max. output power was some 18 W and THD about 9%.
With doubled load impedance (7k5) the max. power dropped some 1.5 dB to 13 W, but THD dropped more than 5 dB to 5%.

you see 14.3W or more only 2.5% THD all harmonics
look both channels engaged
of course if 8ohm output THD up to 6%
i just realize i forget to write, its UL connection by 1630SEA Hammond

 

[artosalo]

i use 4ohm output for 8 ohm speacker

That explains good result since now Rload = 7k.

 

[jazbo8]

Schematic with UL connection:

 

[claudiomas]

last upgrade :
816 RCA and two 1H 240mA and 110uF 900V (two 220uF 450V in serie)
i was surprised to have 50Hz from the 2.5V of valve heather,
normal noise come from screen G2.
with triodes i never get noise, only need one small choke
so for GU13 need one more choke and cap to filter the HT.
also the 2.5V transformer 266M5 its 2X2.5V so no central tap, so the best its from two 22ohm resistor. i order a 266M2 2X1.25V 3A for central tap .
also two 5W24V zener on screen and bias pushed to 130mA, HT its little lower, so -65V bias.
power increase to 15V sinusoidal , measurement to come next .
sensibility its very good, -10db or so for max power so 100K log volume alps pot
beatyfull amp

 

[claudiomas]

night time