SMPS PSU for tube power amp heater - 10A

[rock soderstrom]

Hi guys, I'm thinking about the time after Corona when I want to start my small, intimate "DJ sets" again, which are more like a radio show in front of about 50 people.

For this I would like to build a tube power amp that has a good sound and a spectacular look as part of the show.

For this reason I'm thinking about 811 transmitter tubes, because they really shine bright and give a really good show.

My intended tube setup would be 2x 6SN7, 2x 6V6 and two 811(a), resulting in a current consumption of about 10A on the 6.3V rail. Probably sand rectifier for B+.


I've already done some research on this topic here in the forum, the tube mixer guys have similar requirements, Ian writes here for example how he approaches this topic.

https://groupdiy.com/threads/poor-mans-tube-mixer.73216/post-980523
Here are my questions:

1. I would like to heat with 6,3V, are there SMPS suitable for this, or at least which are so flexible that they can be adjusted to 6V? 12V would also be possible, but I would prefer 6V.

2. according to Ian's suggestion, I would size the power supply to 20A, something like this:

20A Meanwell SMPS

Does this fit?

3. how would a suitable filter stage look like to filter noise and possible switching residues? Is further ripple filtering necessary? Do I need a base load for inrush?

Cheers!

PS: Attachment shows 811 thorium-tungsten heater in action - not my pic

 

[moamps]

So you moved to the dark audiophile SET side?
811 is a DHT tube, so a lot of attention should be paid to the power supply for heaters of these tubes. I think using a single power supply for all tube's heaters isn't a good idea.

 

[rock soderstrom]

So you moved to the dark audiophile SET side?

Ha ha, so true!
Yeah I know the DHT heater thing, maybe I will isolate the end tubes from the 6SN7 and 6V6. I'm still looking for a good solution, 8A alone for the two 811a is a lot of current and heat.

I am new to the SET/ DHT church!

 

[emrr]

One theory

http://www.bartola.co.uk/valves/dht-filament-regulator/
There are several commercial products and some diy boards.

 

[rock soderstrom]

Thanks Doug, I will check this!

This project uses a SMPS for the 811s but they do not show what kind of SMPS they use.

https://grabcad.com/library/811a-stereo-amplifier-1
The solution in the link from Doug seems more sophisticated, though.

 

[Bo Deadly]

With a two-diode drop capacitance multiplier it would be just right I'd say. As long as you really are using 10A at all times. Any less and you might get output modulation.

Even with the CM I would check the inrush currents and adjust the power switch accordingly. Might even justify adding some component(s) to assist with inrush.

 

[dom]

Capacitance multipliers are nice in that they have some natural amount of inrush limiting inherent in the design (due to the slow RC charge-up of the base capacitor). So, additional inrush limiting may not be necessary.

One thing to watch out for with a cap multiplier in this case is that your overall voltage of 6V is pretty low compared to the cap multiplier drop (about 1.2V or so). So, your load regulation and stability over ambient temperature may vary quite a bit in terms of percentage of overall output voltage (few hundred mV or so). So, keep that in mind when biasing and give yourself a bit more headroom than you think you need to account for that variability.

To answer the question of how much and what type of filtering is necessary, I would just start with your bare power supply module and your amplifier circuit and test it without any filtering first. If it sounds noisy, then add filtering.

 

[rock soderstrom]

Thanks dom for your input!

 

[beatnik]

1. I would like to heat with 6,3V, are there SMPS suitable for this, or at least which are so flexible that they can be adjusted to 6V? 12V would also be possible, but I would prefer 6V.

I was wondering if you have further explored any options for 6V / 6.3V SMPS

I am about to embark on a project that has heater current requirement of 8.4A @ 6.3V (no DHTs are involved)

No luck in finding adequate SMPS with 6V / 6.3V output they are either too big / powerful / expensive

12V SMPS have a lot more choice but I must stick to 6.3V tubes.

I am thinking maybe a good compromise would be getting a 7.5V SMPS like the one you linked and adding regulation stages with a pair of 1084 or similar LDOs

An alternative would be powering the bulk of 300mA tubes with a 100V series string, but I don't think this could be done with an off the shelf transformer since it also needs another high voltage winding for B+, a low voltage winding for relays and another 6.3V winding for the remaining tubes with a different heater current.

 

[rock soderstrom]

I was wondering if you have further explored any options for 6V / 6.3V SMPS

No, unfortunately not. I haven't tackled the issue yet. The whole thing is not really trivial from my point of view (which also has to do with my inexperience with SMPS), I am still looking for a simple and stable solution.

An alternative would be powering the bulk of 300mA tubes with a 100V series string

I'm not a big fan of Christmas tree lighting ;-)

 

[scott2000]

and another 6.3V winding for the remaining tubes with a different heater current.

https://ampgarage.com/forum/viewtopic.php?t=26372