JTM-18 EL84 Build Suggestions

[Rontone]

I've had these Elstone transformers for a while from a 2x EL84 Push Pull cathode biased amp with 3x preamp tubes and EZ81 rectifier, they test ok and in fair condition for their age, then a chassis and head cabinet that was perfect turned up recently, so they would do nicely for an 18w JTM preamp and LTP into a cathode biased EL84 power section

Mains TX is 300-0-300 100mA, 6.3V for EZ81 Rectifier, and 6.3V w/CT for heaters

Output TX is 7200 ohm : 16 ohms

Choke is ~300 ohm, I believe around 10-20H, and its big enough so I'd say definitely over 50mA





Would anybody see a problem doing this, considering the 100mA HT rating and cathode biased output stage?

I've made a .sch file schematic and a DIY Layout along with JPG and PDF for each, if anyone can see any obvious wiring or connection errors in the layout please let me know

There are values I have not settled on, such as power dropping resistor values and maybe heater elevation, cathode biasing values and pot/cap values/voltage ratings, so they may differ between schematic and layout while I refine the idea a bit

[Rontone]

Here is a Schematic JPG and a Layout PDF

[Rontone]

Some updated Schematics and Layout, a few mistakes corrected and parts added

Need to get the Presense control worked out

[tubeswell]

The B+ should drop quite a bit with cathode biasing of the EL84s (compared to fixed bias from the same HT winding) - but don't be too gentle with the cathode biasing of the EL84s - or the B+ won't drop enough. IMO you want the B+ around 300, and preferably under 320V - unless you're running old stock EL84Ms which can take higher voltages. Under these conditions, they can afford to be biased at 100% - Others may have other opinions.

[Rontone]

Slightly updated Layout File

There was an unnecessary filter cap in the middle of the board, now removed