26 is a lot better with 5x resistor. I always use at least 39K. I spent several hours trying all the alternatives from 22K upwards. Just kept getting better the higher the value. Especially it tightened up the bass, but it was just generally better.
In fact for quite a few tubes I try and use a 5x resistor.
If you use 39k as anode load for #26, for the estimated operating point must to choose high/er/ B++.
For example if the #51 post operating point (135V, 5.5mA) is OK, the B++ must be:
135V + 39k*5.5mA = 349.5V.
For example if the #51 post operating point (135V, 5.5mA) is OK, the B++ must be:
135V + 39k*5.5mA = 349.5V.
Yes, higher B+ is good. But it could also be worth decreasing the current a little if necessary, like 5mA or even a touch less. I found that 39K resistor load was important for cleaning up the sound.
Due to the big power transformer for filaments I had to change the primary fuse to 6A also changed the fuse holder for a biger one, fortunately can left the secondaries 1,6A fuses.
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6A a bit overstatement, the average is about 0.5A.
IMO 3A is more than enough .... but ... of course, if you want to weld .... 🙂
IMO 3A is more than enough .... but ... of course, if you want to weld .... 🙂
I do the maths 230VAC primary : 120VA = 1,91A + 10% tx regulation x 2, isn't correct to protect the primary?
Added 1R before the R.C. & reach nicely 7,5V
N.B. Just at the R.C. input used a 330uF as per Rod advice for two separate box (PSU & preamp) 1 meter between devices.
N. B. 2 Changed fuse 6A for 1,6A.
N.B. Just at the R.C. input used a 330uF as per Rod advice for two separate box (PSU & preamp) 1 meter between devices.
N. B. 2 Changed fuse 6A for 1,6A.
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Using cascode CCS both channels as anode load don't reach 20mA @ anode 234V, same CCS worked fine at 20mA for 12B4. Also left channel sound too weak. Voltage across filaments are aprox. 10V both channels. Voltage both filaments 7,5V.
N. B. Used SSHV2 with CCS set to 60mA.
N. B. Used SSHV2 with CCS set to 60mA.
Now two channels with hybrid mu-follower B+ anode both channels 234V as per schematic, right channel draws 17,39mA & left channel 16,3mA.
Filament resistor right 10,54V
Filament resistor left 9,96V
Filament resistor right 10,54V
Filament resistor left 9,96V
With both channels with hybrid mu-follower still same problem of weak level at right channel.
I will check all right channel connections inside the preamp.
I will check all right channel connections inside the preamp.
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Interchanged the tubes (of course adjusted again bias for B+ and filaments) it seems weak tube because now the low level channel is the left.😡
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Don't worry, this discrepancy is even within the "selected pair" title tubes zone. 😉
Check parameters shown this schematic.
Scribe your values (left/right) if its differ (mainly B+ and gyrator parts).
Check parameters shown this schematic.
Scribe your values (left/right) if its differ (mainly B+ and gyrator parts).
B+ before hybrid mu-followers 300V
B+ plate right 234,84V
B+ plate left 234,02V
Current plate right 16,46mA
Current plate left 16,91 mA
I use 1 Ohm for R1 R.C. regs.
I will check hybrid mu-follower parts
B+ plate right 234,84V
B+ plate left 234,02V
Current plate right 16,46mA
Current plate left 16,91 mA
I use 1 Ohm for R1 R.C. regs.
I will check hybrid mu-follower parts