Submini Tube Amp Project (Edited w/ more questions)

[Kevin Mitchell]

Quick question if anyone could answer it;

I'm thinking it may be a problem if I were to use a 12volt 500ma PSU to the SMPS - possibly being not enough current to drive 4+ tubes as I would eventually be doing.

So I'd likely have to modify the SMPS and upgrade my wall wart 

Any validation or suggestions would be super. Thanks guys.

[amptramp]

if you get game enough to start it up again, measure the voltage across the 18R resistor, from end to end (it doesn't connect to ground, does it?)

then do ohm's law - P=V*V*R - and tell us what you get.

Sure about this? P=V*I=V*V/R

[thomasha]

four russian tubes in series parallel at 12V each pair will need at least 800mA. The SMPS will draw a little less.

I use a 2A 12v Wall wart, and you can find some cheap ones. For my superfly, with only 2 tubes I use a 12v 1A switched wall wart.   

[Kevin Mitchell]

four russian tubes in series parallel at 12V each pair will need at least 800mA. The SMPS will draw a little less.

I use a 2A 12v Wall wart, and you can find some cheap ones. For my superfly, with only 2 tubes I use a 12v 1A switched wall wart.   

Yes I've noticed. I actually paused your submini marshall video to read the specs on the adapter 

So the adapter I have now may not even drive 2 russian tubes   

The first Superfly used a 12volt 500ma adapter for 6112/7327 pair I believe. This makes me skeptical on what the current draw of my setup will be. But hey I'll give it a shot when I'm only running 2 tubes.

[MetalGuy]

I solved my PSU issues by ordering some PTs from the local transformer shop. This way you have a real power supply, not some crappy SMPS. I used SMPS in some tube pedals but for an amp I prefer the good old PT.

[Kevin Mitchell]

Thanks, MetalGuy.

Since I'm building a small amp head and very likely not using an encosure it may be ideal to use a power transformer in my case. Though I'm a bit nervous about messing with line voltages. I have no experience with transformer outside of octave fuzz pedals.

Could you please share some ideal specs for a PT for my case? I can't special order any parts here... So purchasing from an online US vendor is ideal for myself. I'm also making this a budget build. Or at least I'm trying  I would like a PT that could work for the superfly on breadboard and also not be a problem as I go on adding to and modifying the circuit. Likely a 6 tube minimum project. So I'd have to take in consideration the current needed - increasing by ~300-400ma for each tube I add if I understand correctly.

[MetalGuy]

I could recommend you many options but mainly from an european vendor with local primary voltages. They have an US version as well but it's the only one:

http://www.tube-town.net/ttstore/Transformer/Power-Transformer/Toroidal/Toroidal-30VA-US-Version::6842.html

This will be enough for max of 5 tubes though.

[Kevin Mitchell]

Thanks for the timely reply! I was meaning to mention I have a "120" transformer from a Frontman 15G and I'm unsure if it would be of any use here. I can't find a datasheet on the transformer but here's the amp's schematic with some details "+16, 0, -16". My guess is not good or not good enough.

I'm trying to wrap my head around PT specs for what I would need. I'm clueless on this topic.

[Metaldestroyer]

As far as US suppliers for power transformers, Antek has a large selection of transformers that would work well:

http://www.antekinc.com/

Depending on your tube complement of course. You might find them to be a bit large compared to the size of the amp you want to build though. For an amp using only preamp tubes I would lean toward a 2A 12v wall adapter and MAX1771 SMPS like Thomasha's mini jcm800, but I'm obsessed with miniaturizing things so that's just me.

[Kevin Mitchell]

Thank you very much! The SMPS is within my comfort zone though I'm trying to be practical here. I suppose it wouldn't hurt to build the 555 SMSP or perhaps even the MAX1771 version and see how far it can go. As I've mentioned I'll eventually need enough current to run 6 tubes at the least.

[LightSoundGeometry]

I solved my PSU issues by ordering some PTs from the local transformer shop. This way you have a real power supply, not some crappy SMPS. I used SMPS in some tube pedals but for an amp I prefer the good old PT.

iron and tube 

[Kevin Mitchell]

Okay... I've been absorbing info on power transformers and using submini tubes.

From what I've gathered I know I'd need a power transformer that pushes ~200v and also has a 6.3v filament connection with as much as 3-4 amps (400ma per tube) for the heaters - may that connection come as a dual secondary.

It's difficult sourcing a PT in the US that fits the bill and wont break the bank... But I'm taking my time and learning allot - appose to learning along the way as I have been. There's so much more to dig up before anything starts to look like an amp... I also should stock up on a variety of higher wattage resistors considering the current consumption on the heaters and anodes -res. to B+ - if I'm not mistaken. I thought my 12v 500ma adapter would suffice to experiment a little but sadly not without halfing the voltage with better resistors for the heaters (need more current and 1/4 watt wont be enough) I was actually expecting the 1/4 watt to burn up but that didn't happen. Nothing happened.

I would like to put together a test build using one or so of the russian tubes for an overdrive or distortion running at low voltage. This will be an actual effects pedal. After developing a nice preamp I can experiment with higher voltages and eventually throw on an output section and the reverb thus creating a legitimate submini tube amp.

This project is on-going and very much open for discussion. I have much more to learn. Still wrapping my head around what I just wrote here 

[MetalGuy]

I thought my 12v 500ma adapter would suffice to experiment a little but sadly not without halfing the voltage with better resistors for the heaters (need more current and 1/4 watt wont be enough)...

If you're going to experiment you can connect 2 tubes' heaters in series (a 12v 500ma adapter will be good only for that). This way your voltage issues are automatically solved.

[Kevin Mitchell]

Thanks, man! That's something I didn't consider. I checked that out last night and the two tubes glow nicely reading 6v with .4A draw between them.


If I have time this weekend I'd like to breadboard a tube-vibe. I guess I'd use the two tubes for the phase stages and a nontube buffer since it's unlikely I could use more than 2 tubes with the 12v 500ma adapter though I'm unsure to how much current would be left to work with. Since the heaters have a minimum rating of 5.7 @ .4A I don't think there's any tricks I could pull here without gathering more parts and an appropriate transformer/wallwart.

[Kevin Mitchell]

I forgot to drop this in;

Vintage Vibe" Low Voltage 6111 Submini Tube Vibrato - You're the man, frequencycentral!

This inspired me to work up submini tube effects pedals. So I'm going to do a tube-vibe!

[Kevin Mitchell]

Thought I'd check in. It's been a few months and I've been between a few projects absorbing the experience. I grow stronger with every 230v zap.... I've got a 555 SMPS working smoothly. Though I may source a power transformer once I work out the chassis and speaker spacing.

Tonight a reverb tank + transformer came in. I've added it to a Superfly-like circuit I've had on breadboard and it works okay at the moment. The amp is way too gritty and all the controls seem to react with each other. Not too pleased with that. I have to fine tune allot of things and pretty much rework the entire circuit - while also aiming for it to resemble a Deluxe Revert amp.

The output transformer I've chosen works alright. I may find a better one for more power. I've got some 6P30B tubes on the way hoping that using those output pentodes improve the output level and clarity.

So for now I'll be cleaning it up, adding a fender tone stack and then work on the vibrato. It's finally coming together 

[thomasha]

Nice update!
It looks like this will be an awesome small tube amp with reverb an all.

hoping to see how it turns out.

[Kevin Mitchell]

What I wanted in the beginning was to build a mini-moog clone. But I had nowhere to start. I'm a guitar player who absolutely loves to play with keys and synths. I get lost in playing with those much easier than with guitar.

I'm still alive and kicking. In case anyone was curious 
I'm posting here because I knew I've mentioned my DIY goals somewhere on the site. Though I do not yet have a finished submini amp, I have went the extra mile and built a deluxe reverb from scratch. Here are some photos taken a while back when I was finishing it up.




And for my recent endovour... Minimoog clone - eurorack format designed by Guinguin Instruments.


Happy holidays everyone.
-KM

[printer2]

Anybody looking for an alternative for a power supply transformer if you don't have the option of something cheaper. Hammond 229C12.

https://mouser.com/productdetail/hammond-manufacturing/229c12?qs=sGAEpiMZZMvwUzoUXIIvyQPvPmwnNFGy8%2FbWRSe3AqI%3D

229C12
24
12.6V C.T. @ 1.9A
6.3V @ 3.8A

What you do is use one 120V winding to go across the line  and use the other 120V winding as your secondary. I used this one to make a mini 5E3 with 6AK6's for output tubes. You can get away with using the high voltage winding as a secondary as the two HV windings are electrically isolated. You might not get the full 24VA out but should be fine for a couple watt amp.

[Kevin Mitchell]

Thanks for the info. Though it sounds strange and these submini amps should be getting at least 170 volts at B+ (depending on the tube) from what I have learned if you're after shrinking a classic amp circuit.

If one were to use a power transformer that's not a wallwart why not just get one that supplies B+ rather than using a power transformer with insufficient power and/or an smps? Seems a bit silly.

I'm going to dig out my submini tubes and get back on this since I need a couple of audio amps for projects and SS amps kill my buzz (hehe  ). I believe I left off building an smps on veroboard and it didn't work out. So I need to dig that out and pick at it or perhaps as a solid alternative I could find an appropriate power transformer.

I shall return.
-KM