2021 Monkeymatic Black Butte SMPS version!

[xtian]

I bought one of the switchmode DC supplies mentioned elsewhere on ampgarage.com: https://www.ebay.com/itm/333261621359

I'm going to build one of my Black Buttes using this PSU instead of a heavy hunk of iron, and see where it gets me.

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Input voltage : 12VDC

Output high voltage : 150V-420VDC, 1.25V-12V DC filament voltage regulator is adjustable. (Chip voltage regulation, there is a little pressure drop.)

Output Current: High Voltage: 30mA; Low Voltage: Max 3A

First step, I'll see how the PSU functions at 400v with 25mA load, checking for AC ripple and heat. Or, it would be my first step, if I had any high-wattage, high resistance loads. 400v / 0.025A = 16K, 400v * 0.025A = 10 watts.

Hmm. What's a monkey to do?

[xtian]

Hey, will this PSU work with one EL84 and one 12AX7? I'm aiming for 350v plate-to-cathode, and about 20mA (60%). But that's current at idle, and it may swing way over 30mA when pushed, right? Maybe I'm barking up the wrong PSU.

[xtian]

Now here's a thing: https://www.aliexpress.com/item/1005001631716069.html

For under $40, this PSU is mains powered, and claims:

Size: 100mm 43mm 40mm (L*W*H)
Filament voltage: 6.3V, current 7A, high voltage [300v] current: 300mA

I don't know, guys. Is it worth the journey? Might as well buy a Quilter, huh?

[pdf64]

Hey, will this PSU work with one EL84 and one 12AX7? I'm aiming for 350v plate-to-cathode, and about 20mA (60%). But that's current at idle, and it may swing way over 30mA when pushed, right? Maybe I'm barking up the wrong PSU.

There’s a few SE HT voltage - load impedance options in the Philips info https://tubedata.altanatubes.com.br/she ... e/EL84.pdf
But to get down to 30mA, the HT would need to be around 230V

[xtian]

Well, I ordered that high power unit. May take a month to get here...

[maint_tech]

Now here's a thing: https://www.aliexpress.com/item/1005001631716069.html

For under $40, this PSU is mains powered, and claims:

Size: 100mm 43mm 40mm (L*W*H)
Filament voltage: 6.3V, current 7A, high voltage [300v] current: 300mA

I don't know, guys. Is it worth the journey? Might as well buy a Quilter, huh?

Curious as to how the connections work. I see 5 screw terminals.
Two for AC input and three for dc out? Is it filament and HT or filament or HT?
Does filament and HT share a common?

[xtian]

Great question. Guess we'll find out in a month!

[xtian]

So, 150W SMPS arrived, and the connects were explained to me by the vendor: "3P terminal, the side close to the indicator light is 6.3V, the middle is the ground wire, and the left is the high voltage 300V. 2P terminal is 120V input."

I started to test it in my JCM 800 build, then realized I cannot create a negative bias voltage without an AC source! I found this:

https://www.electronicspecifier.com/pro ... -converter

Is there a suitable, prebuilt buck converter out there?

[bmx]

Cathode bias?

[xtian]

Cathode bias?

Yes, that's the obvious conclusion. Just disappointed because for my 15w, cathode-biased amps, this SMPS unit is no less expensive that a traditional PT, and not much smaller. I was really hoping it could replace the 10-pound 50w PT in a larger build.

[bmx]

I see! The 300V B+ is a bit low for 50W with the usual output transformers. Ho would you tackle that? Re-label the secondaries to reflect a lower primary impedance?

Really interested to hear of your results. Has anyone discovered the schematic? Maybe it could be modified to deliver ~477v B+? (first things first of course)

[xtian]

I see! The 300V B+ is a bit low for 50W with the usual output transformers. Ho would you tackle that? Re-label the secondaries to reflect a lower primary impedance?

Really interested to hear of your results. Has anyone discovered the schematic? Maybe it could be modified to deliver ~477v B+? (first things first of course)

I had imagined the 300v SMPS would result in a lower-wattage amp with earlier breakup. It never bothers me to lose efficiency in a 50- or 100-watt amp.

[xtian]

OK, I'm having a go at this. Parts organized, and a first layout drafted. Finished dimensions 11" wide x 6.25" deep!

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[ViperDoc]

Cool, man!

[xtian]

I did the headphone trick, and I cannot hear any radiated noise from the SMPS. That's one thing less to worry about in layout out this amp.

With the 12v/3A AC adapter feeding the SMPS, it's drawing just under 2W at idle.