300B Board design rating

[Rod Coleman]

Do you think this would be better?

No - this is a voltage regulator -- It will interfere with the music signal. The feedback to the regulator cannot tell the difference between the dc voltage-feedback (for setting the output voltage) and the voltage of the music signal, across the filament.

This will make it sound worse than a simple CRC rectified DC. A real current-driven filament regulator is the better solution.

are Rod Coleman's dht heater boards - I've used dozens of them.

Pleased to hear they are giving good service, Kevin.

 

[Rod Coleman]

Some more design notes:

A transformer rated for 2A RMS {shown on your drawing) is not enough - it will get very hot. The RMS current in the transformer is ca. 2.5A RMS, for 1.3A DC , and some margin is required - 5A rating is the minimum usable.

Also, don't use a winding on the transformer for the anode supply. There is no screening to prevent rectifier noise from the filament supply getting into the anode supply; this is very audible.
The noise is increased by using the type of bridge rectifier in that drawing - Schottky diodes should be used instead, as Mr. Valve has already suggested.

There is plenty more information on designing the Raw DC supply for filaments in the manuals for my filament regulators.

 

[Deva009]

Some more design notes:

A transformer rated for 2A RMS {shown on your drawing) is not enough - it will get very hot. The RMS current in the transformer is ca. 2.5A RMS, for 1.3A DC , and some margin is required - 5A rating is the minimum usable.

Also, don't use a winding on the transformer for the anode supply. There is no screening to prevent rectifier noise from the filament supply getting into the anode supply; this is very audible.
The noise is increased by using the type of bridge rectifier in that drawing - Schottky diodes should be used instead, as Mr. Valve has already suggested.

There is plenty more information on designing the Raw DC supply for filaments in the manuals for my filament regulators.

Hey Thanks For the valuable information! Would you be able to give more details about your filament regulators? I tried to find them on your profile

 

[Deva009]

Yes that would be better, don't forget to add two diodes over the regulator chip. one from adjust to output and one from output to input.
Also rectifier diodes you could try a bridge consisting of SB530 or 1N5828 or those have lower forward voltage than a normal bridge

LT1085 dropout is around 1.2V so you need 6.2V minimum under the ripple of rectification to make this work from a 6.3V winding.

PSUD2 shows you dont get there with that 4A bridge. I took 1n5400 to simulate that 4A bridge and im getting 5.5V under the ripple with 6800uF If i change this to SB560 and 15000uF we get the required 7V under the ripple.

Another option is the MIC5156 regulator IC. I have boards for those. Feel free to use the schematic as you see fit. Ive updated the mosfet to IRL540N. The MIC5156 really makes a nice scalable regulator IC for DC power supplies. The only downside is the added complexity for the mosfet drive voltage. Ive added gerbers for the boards im selling to this post if you want to use these.

Shameless self advertising, swapmeet post can be found here: https://www.diyaudio.com/community/...6-based-tube-amp-upgrade.382265/#post-7113502

Thanks! This is very good information, I will test stuff so I see what's best, you won't be mad if I made pcbs myself If I decide to use yours?

 

[PRR]

give more details about your filament regulators? I tried to find them on your profile

Kevinkr already gave the link in his reply #16.

Rod Coleman's dht heater boards - I've used dozens of them.
https://www.lyrima.co.uk/dhtreg/dhtRegIntro.html
They are very reasonably priced, I recommend them.