DIY PSU for Altec 150A (M11) Coke Bottle.

[MidnightArrakis]

[(I came across a video of a "PDF-To-GERBER" program) I just might go ahead and buy it!!!] -- I went ahead and bought the full program yesterday!!!

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[thecr4ne]

@rock soderstrom I've been thinking about this and I think I'm going to go ahead and build 2 separate PSUs for each mic. I think I've found a power transformer solution that's cost effective, but I need to confirm that this is sufficient to power this circuit. For about half the cost of a High Voltage + Filament Transfomer, I can get 2 separate transformers.

Currently looking at:
Triad N-68X (backwards for 115V pri:230V sec)
and
Triad F-313X for filament.
(Spec sheets attached)

(Based on a suggestion in this Vid: )

Is 230V enough to get +300VDC through your PSU? (If I understand this right, 230VAC RMS x 1.41=324V peak)
and
Is 600mA enough current for a single 6au6 filament through your PSU, or should I spec something higher?

Again, this would be for only one mic, not two. I'll just make a second PSU instead, with it's own transformers.

 

[thecr4ne]

@MidnightArrakis Thanks for all the useful info! Since you went ahead and purchased the pdf to gerber software, would you be willing to convert @rock soderstrom 's PSU pdfs and share them here?

 

[MidnightArrakis]

@MidnightArrakis Thanks for all the useful info! Since you went ahead and purchased the pdf to gerber software, would you be willing to convert @rock soderstrom 's PSU pdfs and share them here?

[would you be willing to convert @rock soderstrom 's PSU pdfs and share them here?] -- Send me all of whatever you have, OK??? While this program that I bought will output a PCB N/C Drill file, there -- HAS -- to be a PDF file containing at least the "images" of where the drill hits are located in order for this program to output a drill file. So.....send me whatever there is and I will see if there is enough -- PDF information -- within Rock's PDF file(s) to create all of what you need, OK??? Sound like a plan???

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[Khron]

Currently looking at:
Triad N-68X (backwards for 115V pri:230V sec)
and
Triad F-313X for filament.

N68X is rated for 50VA. FIFTY volt-amps. 115V @ 0.435A, of which you'll need 0.005A, if even that? Might wanna reevaluate a bit

Then again, what's wrong with the Gyraf G7 type PSU?

https://www.gyraf.dk/gy_pd/g7/gic_s.gif
I've put together a similar one (with a 9Vac 1A transformer for the heater, and a smaller 9Vac transformer in reverse), for a "stereo" PSU for two U67 clones (210V / 6.3V), but using discrete regulators.

Hint: dual primary (2x 115V) transformers allow for more flexibility...

Is 600mA enough current for a single 6au6 filament through your PSU, or should I spec something higher?

http://www.r-type.org/exhib/aam0079.htm
6AU6 needs 300mA (0.3A) for the heater.

 

[rock soderstrom]

6AU6 needs 300mA (0.3A) for the heater

In this specific case (with the rectification and the doubler), it is too little in my opinion. Double voltage means double current plus rectification.

Is 230V enough to get +300VDC through your PSU? (If I understand this right, 230VAC RMS x 1.41=324V peak)

In my opinion, the voltage is also a little too low, as you need a very clean B+ voltage and this requires large resistors (or expensive chokes) for the RCRCRC filters.

The current delivery capability can be much smaller, as Khron has rightly shown.

 

[rock soderstrom]

For one mic a 280V AC/6.3V AC transformer with 1A current max. would be good with my PSU. For two tubes/mics you need something like 1.8A current capability. (inclusive headroom)
B+ current for two mics would be something like 20mA. (LED currents plus mics with ample headroom)

For a classic LM317 DC heater a secondary of 9V AC and 500-600mA would be enough.

 

[thecr4ne]

Thanks everyone, forgive my thick-headedness. I'm 20+ years out of practice on doing circuit math, and I barely learned it to begin with. Figuring out current draw and voltage drops are far from second nature. I appreciate the patience and advice.

I'll look around and see what I can find that can get me in the ballpark a little better.

 

[thecr4ne]

I like that double transformer solution. That might be the way to go given the readily available transformer options I'm finding.

Then again, what's wrong with the Gyraf G7 type PSU?

 

[thecr4ne]

Closer, still overkill @ 15VA

https://www.aliexpress.us/item/3256801693563042.html

 

[MidnightArrakis]

Closer, still overkill @ 15VA

https://www.aliexpress.us/item/3256801693563042.html

Is the AC mains voltage in California now 220VAC? Has your esteemed Governor Gavin Newsom legislated a new law mandating (as California always does) that the California power-grid operates at 220VAC??? Because, that is what the primary input voltage for the transformer you have selected is rated at!!! See here in the photo below where it says: I/P: 0 - 220V.....



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[thecr4ne]

Is the AC mains voltage in California now 220VAC?

Listing says 110V Primary version is available. I messaged the seller to ask how to order that one, but haven't heard back yet.

 

[Khron]

Why not get whatever's in stock @ Digikey / Mouser / Element14?

Edit: At least the former two even offer free shipping orders over 50 bucks; surely you can figure out useful stuff to pad out a four-transformer order, AND receive it in days (as opposed to weeks or a month, from AliExpress)...

Edit no.2:
https://www.digikey.com/en/products...nczmhDPI0hFEIACY8M4dEoHfpWTgAT3Y+B4mFwaEkkiAA
Take your pick - VPP10 (parallel primaries, series secondaries) to feed the heater supply and VPP12 backwards (parallel low-voltage primaries, series high-voltage secondaries), and you're just a couple dollars under the free shipping threshold. Throw in some good-brand 105C capacitors and "problem solved-ed"

 

[thecr4ne]

Thanks @Khron. in the interest of expanding my horizons, I may try both approaches. I went ahead and ordered a pair of the Aliexpress transformers (~$29USD shipped for both). They'll prove useful for something if not for this.

As I piece things together for an order for the remaining components for the PSU(s) I'll throw in a few of those triad VPPs and give that option a whirl too.

I think I'll look into trying to layout a PCB for the audio section too. Would be cool to have this all on PCBs, but I'm down to do it point to point if need be.

All the help is appreciated!

 

[thecr4ne]

I've been thinking about this some more, and I may take a different direction for the PSU PCB. Will keep you posted as that progresses.

In the meantime, I got my pair of 15W, 110V: 6.3V+ 300Vct Aliexpress transformers. I have yet to test them. Seller's page says 6.3V @1.5A, 300V (150-0-150) @ 30mA. They're a little bigger than the transformer in Alctron style tube mic psu.

I've been fiddling with KiCad today. As a learning project, I've done my best to recreate the Altec M11 schematic. I've attached it below. The Component numbering doesn't match the original, and some things are positioned slightly differently. Also the power transformer doesn't have the 6.3v center tap so I omitted the lamp as well. I'm hoping to use this as a starting point to adapt to a few variant designs. Separate PSU and Audio PCBs, All on one PCB, maybe even one with off the shelf pc mount transformers on the PCB as well.

Anyway, I'd appreciate any feedback on this. I know it's nothing special to copy a schematic, but it's a starting point.

 

[rock soderstrom]

Without judging what you are doing in detail, I think it is good that you are tackling the matter yourself. Good luck!

 

[thecr4ne]

I decided not to re-invent the wheel, and just adapt an existing PSU rather than building something from scratch.
I bought a pair of the t.bone Retro Tube II PSU's from Thomann and a pair of 110V:300V+6.3V power transformers from Aliexpress and plan to use those as the backbone of the project. The PSU chassis has enough room inside for an output transformer, which is not the case with the apex 460 psu form-factor. The mounting screw holes on the new transformer also line up perfectly with the original's so that's nice.


Insides Stock


New Transformer:


The t.bone PSU is a variant on the Apex 460 psu design, despite the different chassis. Pics and schematic below. Notably it has an L7806CV voltage regulator for the heater supply, which can put out 6VDC from as little as 8VDC input voltage. With the new power transformer, I get more like 8.5ish VDC rectified.


(Schematic adapted from Stellar CM2 PSU schematic)





The high voltage caps are only rated 400V so they'll be replaced as the 300V winding rectifies to about 425VDC. I have tested with the stock caps and so far haven't fried anything, but that's not reason to leave things as is. Without any mods, the high voltage side puts out about 150VDC, which is set by the zeners.

I also got some of the correct 8 pin cannon connectors for the coke bottle mic.

I replaced the original power transformer, and removed the mains voltage selection switch, as the new transformer only takes 110V.

(will add image here later)

I removed the 7-pin XLR connector and drilled out the hole with a step bit and cut a notch with a dremel to accommodate the Cannon connector.




I removed and disassembled the 9-position polar pattern selection switch, drilled a 1/16" hole in one of the plates and put a screw through it to act as a stop so it's now a 3-position switch to be used for the roll-off.


didn't get the hole as straight as I'd have liked, but it works.

I added 2 more zeners of comparable value in series to test and got it to 296VDC. Nicely in the ballpark for the mic's needs. The voltage drop across each of the original zeners is 79V and the others I had on hand measured 69V.



Still need to figure out some stuff to get the polarization voltage and screen voltage, and the audio side of things. As always, suggestions, advice, constructive criticism welcome.

 

[thecr4ne]

Considering just using different value zeners to get the 265V and 270V for the screen and plate voltages. That is, using say, 3 or 4 zener diodes in series as in the above pic, but with values 91V, 87V, 87V, 5V, or 135V 130V, 5V and then tapping off each side of the 5V zener to feed the Plate and Grid.

Would this work? Is there any interplay between the two I should worry about or additional filtering needed? Pros and cons to this approach vs the original design?

 

[thecr4ne]

Please provide any feedback you may have.
I've attached a schematic that I think is a functional mish-mash of the t.bone PSU and the Coke Bottle PSU.

Items of note:
Original t.bone transformer replaced with the Aliexpress Transformer discussed previously.

C6-C14 are to be rated 450V. Corresponding stock caps in t.bone PSU are 400V

Zeners are 2x 68V and 2x 82V all in series as in my test.

Heater voltage is DC elevated referenced to 150V at Zener center tap to reflect original Coke Bottle PSU heater design. This will require some modification to the stock t.Bone PSU pcb. The trace connecting ground on the heater side to ground on High voltage side will need to be cut to isolate. See:




I decided to keep the schematic original to get from 300V to 270V and 265V instead of trying to tap the zeners. I'm leaning toward adding the additional 5 components to the PCB if I can do it cleanly.

I have some small-ish prototype board which I'll use for the audio side of things, and may mount to the rear of the Roll-off switch. At least for the first go. If I get a better handle on KiCad I'll try to design a PCB for that.

If I'm reading the original coke bottle schematic correctly, the polarization voltage is coming from the R1, R5, C2 junction. I think it would be cool to use the cardioid Altec capsules (28 and 29 series) with the coke bottle mic. Those capsules use 60V for polarization instead of the 200V the 21 series capsules require. To accomplish this, I replaced R5 (125K) with R2 (90K) and R3 (39K), and switch SW2 to select different taps on the resulting voltage divider. I don't know if that works the way I think it does, and I'm unsure of how C2 will interact in this configuration.

Thoughts and Suggestions welcome.

 

[AboveAndBelow]

Thank you, this is really useful information about the Retro II PSU.