Submini Tube Phaser Project --- The illusive Tube-O-Vibe

[Kevin Mitchell]

Well it's in the works! After a good deal of effort researching the few tube phaser schematics out there I finally found a documented project worth tinkering with. A while back Scott Schwartz published an article is a magazine called Vacuum Tube Valley about a 12AU7 based phaser stompbox with anode voltages at 235v. Though I don't have much experience with high voltages I feel it's time to bring this project to light equip with some upgrades. First being the power. I want a stompbox so a switch mode power supply will be ideal apposed to a power transformer. This makes things less difficult for my efforts and makes the circuit much more simplistic. But now to get it to work... I have a 4 stage version on breadboard with B+ at 12 volts. There is some very, very subtle phasing with little distortion. So I guess the next step is to increase B+.

Here's my schematic which holds the exact values as the original which used 3 12AU7 tubes with just 4 phase stages. I have excluded the original power supply circuit as well as the "improved univibe LFO" and added in 2 more phase stages.


I have some questions before I snag the BOM and work on the SMPS.

Are the resistor power ratings crucial? Are they rated higher to allow more current flow as well as handle the high voltages? I ask because other tube projects with high voltages seem to use 1/4 watt resistors at the plate and cathode.
Any favorite SMPS circuits? I'd like to try a max1771 based one that has been used on similar submini tube projects. If it's good for a russian submini combo, it's good for this.

Many people have been looking for the Tube-O-Vibe project and have no way of obtaining the magazine. I have luckily found a photo copy of the issue which holds this project. I'd gladly share it openly if I wasn't worried about upsetting the designer of the circuit and the publisher of the magazine - I am not familiar with these legal grounds. I give credit to the designer at heart and have no intent of displeasing anyone.


I've learned a great amount looking into the workings of all sorts of phase shifter designs as well as the oporations of a tube. The only thing I've been reluctant to dig into is all the math that is likely to come 

Any comments are very welcome. I can't wait to get this beast running and boxed up.

[idiot savant]

I'm just eyeballing everything, but some things to consider.

Assuming a B+ of 235v, each phase shift stage eats ~3ma at idle, the first gain stage a little less, and the CF at the end about double-ish. So say around ~30ma total at idle, passing signal it will be more, best to plan for better then 35ma.

Those 27K, and 24K resistors are burning around a half watt each, so 1W is good for those.

Remember that your cathodes are sitting at half B+ or so, so make sure you don't breach the safe Heater to Cathode voltage of the tubes.

Leave extra juice in your power supply for the cold start-up surge the heaters need. You have 800ma of heaters the way you wired it, so you should plan on providing at least 2A for those and what the switching supply needs.

You could scale your voltage down a bit if you want to use less power and smaller parts. At a B+ of 100-120V your current consumption is drastically reduced, and you can go down to half watt and quarter watt resistors. You might have to make those 1K5 bias resistors a tiny bit bigger, say 1K8 or 2K.

good luck! BE SAFE!!

[bluebunny]

Will be interesting to see how this develops.   

good luck! BE SAFE!!

Aren't these two things mutually exclusive?      

[Kevin Mitchell]

Thank you very much for your suggestions! I will certainly try what you have said. You mentioned some facts that I wanted to know but couldn't figure out how to question clearly. I also had no idea of what the current consumption would be for each tube section. So thank you!

Leave extra juice in your power supply for the cold start-up surge the heaters need. You have 800ma of heaters the way you wired it, so you should plan on providing at least 2A for those and what the switching supply needs.

The other night I was currious to see how far my wallwart can go (talking about powering the 6n16b and 6n17b heaters in series. Rated at 12V, 3A I stuck about 18 tubes in there! In doing so I've learned that the 400ma rating is true when the heaters are warming up. But once they're going each pair pull about 340ma or somewhere around there. I've learned this when wondering why the heaters wouldn't go until I allotted the appropriate current to start with. With the wallwart I have on hand I very likely wouldn't have to worry about that when it comes to the complete build. Though I would like to consider the option of a daughter board for more phase stages. This may require a slight rework of the SMPS - a more powerful inductor I'd guess. I've been eyeballing Frequency Central's max1771 design thats floating around. I'll gather all of the parts next week which gives me enough time to design the board for once I'm through with the breadboard prototyping.

Soon we can talk LFOs. I may use a lm13700 based one.

[J0K3RX]

http://desmith.net/NMdS/Electronics/NixiePSU.html

[Kevin Mitchell]

http://desmith.net/NMdS/Electronics/NixiePSU.html

Yes that's the one that Frequency Central redrew. I have to stock up on multiple inductors to see what works best for what is needed here.

[Kevin Mitchell]

Tube phaser circuit by Scott Schwartz


I may not go the submini route but I'm back at this. I've got the few ECC82 tubes on hand waiting for a purpose in life.

I'm developing a layout in eagle and will share the progress on this thread. This being my first printed board for a tube circuit I would appreciate advise on anything that may be improved on. I hope to share the transfer files or even send them out for fabrication if there's enough desire for such an effect.

I would like to use an SMPS. Though part of me is leaning towards picking up a power transformer. If anyone has a layout for a decent SMPS and maybe a BOM to share for a home etched board that would be super useful  If it works well enough I'd like to include it in the circuit. I did not manage to get my own SMPS layout workings at all.

[Kevin Mitchell]

To whomever removed the schematic I put up - Scott asked for them to be hidden over a decade ago when money was still being made off of the Vacuum Tube Valley magazines. Since then the editor had passed away and had arranged for them to be free to the public. Please observe this link

Aron/Peter

If the above refers to the design that was published in Vacuum Tube Valley and was authored by me, I would respectfully request this not be posted.

I was paid for article, VTV needs to sell magazines to pay authors, etc.

I'll put up my own drawings when I get a chance but thought I should point out there's no reason to take them down unless Scott still has a problem with it - which I would respectfully persue the project in the dark.

PM me if I'm doing something wrong. Thanks.
-KM

[PRR]

To whomever removed the schematic I put up -

No one removed *your* image.

Problem is, it was hosted on postimg.org which has been caught in some dispute and gone dark. All the same stuff (including your image) is available if you replace ".org" with ".cc".



https://postimg.cc/image/4gqevpphn/
https://s9.postimg.cc/e1a1iletp/Phase_Shifter_Circuit.png

[Kevin Mitchell]

Oh

I've received a voltage booster recently and had breadboarded the circuit. It sounds very nice though there's a bit of distortion that probably shouldn't be going on. I've tried dialing the B+ supply to see if that would clear it up but I haven't had much luck.

I'm working with a tap tempo chip using the attiny85 -info at SabroTone- and will steer the project back to using 4 submini tubes (6 phase stages) so I can get it all into a reasonably sized enclosure with more taste.

I'm working on a revised BOM and will share my progress with the layout some time this week. I still need to find a working SMPS layout for this since the booster module takes up a bit of space.