At which supply voltage and bias?
KT77 A.F. BEAM PENTODE
Base: OCTAL
Uf=6,3 V
If=cca 1,4 A
Typical characteristic: Ua=250 V
Ug2=250 V
-Ug1=15 V
Ia=100 mA
Ig2=10 mAS=10,5 mA/V
Ra=23 KΩ
μ=11
Attachments
ygg-it,
What is the DCR of your 16 Ohm speaker?
That might explain the better sound when it is connected to the 8 Ohm tap.
The damping will be greater on the 8 Ohm tap than the 16 Ohm tap.
The load at certain bass frequencies will 'appear' to be lighter on the 8 Ohm tap.
The load at certain mid frequencies will 'appear' to be lighter on the 8 Ohm tap.
It all depends on the particular loudspeaker design.
What is the DCR of your 16 Ohm speaker?
That might explain the better sound when it is connected to the 8 Ohm tap.
The damping will be greater on the 8 Ohm tap than the 16 Ohm tap.
The load at certain bass frequencies will 'appear' to be lighter on the 8 Ohm tap.
The load at certain mid frequencies will 'appear' to be lighter on the 8 Ohm tap.
It all depends on the particular loudspeaker design.
I am sorry for going back to the early Posts, Modification # 10 . . .
If it sounds better, it is probably related to the low quality of the output transformer.
Consider the capacitance of the plate end of the primary, to the secondary.
If you ground one end of the secondary, you have more capacitance from the plate to ground through that primary to secondary path.
But as you already know, safety has been compromised.
Safety First!
Ground the output transformer's secondary common wire.
Prevent the "Surviving Spouse Syndrome"
If it sounds better, it is probably related to the low quality of the output transformer.
Consider the capacitance of the plate end of the primary, to the secondary.
If you ground one end of the secondary, you have more capacitance from the plate to ground through that primary to secondary path.
But as you already know, safety has been compromised.
Safety First!
Ground the output transformer's secondary common wire.
Prevent the "Surviving Spouse Syndrome"
Last edited:
Attached My final modified circuit A10+CCS.
With Toggle SW and 2 color LED lamp.
(EL34 is lit Green, KT88 is lit Red.)
Hello there
Have you rated the new circuit in terms of power output compared to the old 2x12w one?
I just bought the same amp and I will definitely follow your modifications.
Br
A question for A10 owners: Does anyone have the spec. for the 'uprated' OPTs and Power Tx?
I'm sure that the quoted output of 12wpc is optimistic, so are the OPTs 5w or more?
I have got my hands on a bare A10 chassis and want to have a go at building an improved version, ideally with the same OPTs or slightly higher rating, but same footprint as the chassis is pre-drilled.
The uprated OPTs are potted, someone must know where I can get them from!
Douk wanted an arm and a leg, more than the cost of a whole new A10 infact...
I'm sure that the quoted output of 12wpc is optimistic, so are the OPTs 5w or more?
I have got my hands on a bare A10 chassis and want to have a go at building an improved version, ideally with the same OPTs or slightly higher rating, but same footprint as the chassis is pre-drilled.
The uprated OPTs are potted, someone must know where I can get them from!
Douk wanted an arm and a leg, more than the cost of a whole new A10 infact...
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