Submini Tube Amp Project (Edited w/ more questions)

[printer2]

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.

Not sure if this refers to the Hammond 229C12 I suggested as an alternative. This one easily supplied the power, 6V and high voltage, to build a 3W 5E3. It was a good match for a 1960's 10" speaker and a full size guitar speaker (much louder). I am hoping to trade back for the amp to come home. If you need more than what the transformer delivers then you are not making a mini amp. Getting suitable sized transformers inexpensively was not an option for me at the time so I used the Hammond.

[Kevin Mitchell]

What really confused me was you suggesting to use a primary tap as a secondary. Could you perhaps share a drawing? I'm just seeing caution signals in my head     Maybe this is something I would find useful as power alternative.

I'll be working up a submini amp for my record player since apparently these things only put out phono or line level signals     I'm thinking a stereo champ amp for a super simple amp build. The only thing is... would very likely need two output transformers for stereo amplification & output.

It's time to put this project back on the breadboard!

[printer2]

Darn computer froze on me when I tried to post my message, it was probably too wordy anyway. Here is the wiring diagram, 1-2 and 3-4 are the 120V coils, parallel them for 120V or series for 240. Because these windings are on their own plastic bobin they are 100% isolated from each other  and not like a normal transformer where the one winding would be wound one the other.







I I flipped the transformer so the pins faced up rather them stuck in a circuit board. Because of the plastic that supports the pins is in the way of a bolt through the mounting holes I had to file a flat on the side of the bolt head. I bought it as it gave me a flattened transformer to to put in a shallow case. I think if you live in the U.S. there are more options for a regular transformer for tubes. Shipping and brokerage fees kill me at the border.

[Kevin Mitchell]

So the unused primary becomes the high voltage secondary? Could I regulate this supply for 180V - 240V DC? I'm curious to if that tap is sufficient without any drawbacks being used as a secondary and if so - I would certainly snag a few of those transformers. This info is new to me and with my limited experience with power transformers I wouldn't consider thinking outside the box so much.

[printer2]

Yeah that is me, outside the box. 

I looked up the 5E3 6AK5 amp I built, I used a 70V transformer that had an 1/8 watt tap and I used that as a 16k load for the tubes. I biased them at their plate dissipation limit.

No info on the transformer. I have a few scavenged from renovation at work. This transformer is an oddball as all the other transformers I have are like the ones you are familiar with. The tubes want to see 10k in SE so I went for the highest ratio, for the two tubes it should be 16k with the 1/8W tap. The speaker is across the 1/8 watt tap and the common, the way it is photographed it looks like the lugs are shifted over.

    For the power transformer, for a 1:1 power transformer Hammond (I am guessing others also but since I have not tested any I can not say for sure) winds the secondary with more windings than the primary to make up for losses in the transformer. Since in the above transformer both the 120V windings are suppose to be connected to the line their winding turns are the same. When you use one for the line and the other as a secondary the losses creep in and even unloaded you do not get 120V out.

    Now when you take a AC voltage and multiply it by 1.414 you are calculating the peak voltage of the AC waveform. If you have a rectifier and a capacitor making dc and you have no load on it this is the voltage that will end up on the capacitor. If you draw a reasonable amount of current from it you really only get from 1.1-1.2 times the AC voltage. Also with using the transformer as I had you are loosing half your primary winding so your losses will be magnified.

    Can't remember what the voltage was but say we take 110V AC, multiply it by 1.1 you get 121V and then double it you have 242V, pretty close to the 230V I ended up with. Using the transformer the way I did is far from ideal in terms of what the manufacturer intended, it just works out nicely for my application. The transformer does not have the VA rating that it would have if used normally but it has enough for my little one watt tubes.

I reduced the cathode resistor on the 6AK6's to about 360 ohms. Power supply had SS diodes using a doubler circuit and capacitance values of 22uF. This then fed a 22uF which was the plate supply. I had 230V on the plates and 192V on the screens with a 4.7k and 22uF. Through a 22k to a 22uF I had 140V for the preamp triodes. I had 112V on the cathodyne plate, 29V on the cathode. The second stage triode, 96V on the plate and 0.78V on the cathode. The input stages have 75V and 83V and the cathode with 1.1V on them with just a single 820 ohm.

Looked up a transformer I suggested for an amp like this, think it might be cheaper than the Hammond.

https://www.tubesandmore.com/products/transformer-fender-replacement-power-stand-alone-reverb

And these little buggers I like.

https://www.tubesandmore.com/products/6ak6-pentode

Beats having a triode output tube.

This is my buddy on the amp, he never played a 5E3 so he didn't know how to play with the controls. Ignore the Microsoft sign up window.

http://1drv.ms/1hDNpt3

Oh yeah, going through an old 10" out of a stereo console.

[Kevin Mitchell]

Sweet! Now I want one of those for myself 

I've done a fair amount of searches trying to learn the in and outs of phono preamps and came across a nice little circuit called the Mini Me. It's a stereo phono preamp using 4 6N16B tubes. I'm going to experiment with this and try my hand in designing an output preamp and amp (an integrated amplifier) using 6N16B or 6N17B triodes and 6P30B pentodes in a push-pull setup for higher output.

I've found a few projects using these tubes but no schematic that I could work from. I could replicate a low voltage (meaning around 200v) guitar amp since the 6P30B are very similar to 6v6 pentodes and tame it down for the cleanest result.

Now just have to find a couple of decent output transformers that fits the bill.

[Kevin Mitchell]

You might not get the full 24VA out but should be fine for a couple watt amp.

Not knowing for sure what the "120v secondary" would be rated at how would I know what primary fuse would be appropriate? Would I have to calculate the current consumption needed for B+ to get the ~VA for this improvised secondary winding? Could you suggest a fuse that would be safe using?

After searching around for output transformers I'm back to this thread doing the math to use line transformers
Trying to understand how to get ~6k from this line matching transformer for a couple of 6P30B pentodes. This is something I have neglected to do last time I was picking at this project. Gonna take a few more read-throughs 

[amptramp]

If you were doing single-ended outputs, it would be easy.  You use the equation P = V*I = V*V/R so R = V*V/P

Your 70 volt (actually 70.7 volt) outputs gives you a V*V = 5000 so if you have a 1 watt tap, you have 5000 ohms, if you have a 5 watt tap, you have 1000 ohms between the black (common) lead and the tap.

With 25 volt taps, your V*V is 625.

Push-pull operation gives you the problem of trying to balance the inputs.  The black common lead goes to one plate and you have to pick a centre tap and the opposite plate tap.  In this case, you can get push-pull operation from the 2.5 watt and 0.625 watt taps but the impedance is too low and although the voltages between the common and 0.625 and the 0.625 and the 2.5 has the same number of turns, the winding resistances will not be balanced.  The transformer in your link seems to be drawn wrong.  The highest power taps are closest to the common and the lowest power taps are closest to the opposite end from common.  See this:

https://www.alliedelec.com/m/d/d8292cf7f11c601de4c651a61586c0eb.pdf

for how it should be.  Use the tap with 4 times the power of the other plate tap as the centre tap so if you follow the Hammond drawing, you could use a 4 watt tap as the centre tap and the one watt tap as the opposite plate tap and get 5000 ohms plate-to-plate.

[Kevin Mitchell]

Thank you for breaking that down once more, Amptramp.

I have not settled on what format I'd like to use these tubes in but I'd like to avoid SE so I can get the most out of the setup though for the sake of tinkering I might try SE on breadboard to see how it sounds. Maybe it'll be loud enough for what I'm after.

In another forum I guess someone had gotten close to 15W out with a 3K transformer in ultra linear format. I assume that was in reference to plate to CT.

A week ago I had no idea what that meant. Just so you know where I'm at  So now I'm trying to find an OT that's okay for any format I may throw together on breadboard.

[printer2]

You might not get the full 24VA out but should be fine for a couple watt amp.

Not knowing for sure what the "120v secondary" would be rated at how would I know what primary fuse would be appropriate? Would I have to calculate the current consumption needed for B+ to get the ~VA for this improvised secondary winding? Could you suggest a fuse that would be safe using?

After searching around for output transformers I'm back to this thread doing the math to use line transformers
Trying to understand how to get ~6k from this line matching transformer for a couple of 6P30B pentodes. This is something I have neglected to do last time I was picking at this project. Gonna take a few more read-throughs 

A 0.25A fast blow fuse on the primary should be fine.

[Kevin Mitchell]

Off the subject of line matching transformers (I've read they could have low freq response which is suitable for guitar but not sure about a hifi stereo design)
I have found this OT for a reasonable price


I feel this could work fine with a push-pull design with 6P30B pentodes.

EDIT:

Also I'm starting to get a little skeptical about the improvised PT having drawbacks. I may need ~2A at 12V for the entire filament circuit which a little higher than it's secondary rating so I'm unsure if pushing this and using that 120v tap as an extra secondary would be safe. But I could just be uninformed on the matter of current tolerance in this situation.

But I've also found this
After rectifying the taps I'd use this one should be perfect. And it's a couple bucks less 

[Kevin Mitchell]

Once again I took a different route on my project goal and again I have a full blown amp 
Super proud of this one.


Now that I have a better understanding of all of the possible circuit configurations I'm very much interested in creating a submini version of this amp with smaller output transformers and powered completely by a SMPS.

Always itching to tinker.

[vigilante397]

Wow, Edcor transformers and everything

[Kevin Mitchell]

Good observation.

If you can point me to a couple UL output transformers with close specs for less money then I'd see your point. These have 20 - 20khz frequency response which is more than I needed for a hifi amplifier. Not a guitar amp - a hifi amp. Most output transformers wont even list their frequency response rating - for a reason. With so much time invested into designing and building, why the hell would I cheap out and cut corners?

Final note - I got a deal on these compared to anything else that comes close. Do some research, man.

It's okay to be jealous.

[vigilante397]

It's okay to be jealous.

And I totally am I don't remember the frequency response of the cheap Chinese transformers I used in my hi-fi amp, but it sure as hell wasn't 20Hz-20kHz. Edcor isn't expensive just because they're Edcor, they're expensive because they're high quality stuff. And frankly they are reasonably priced compared to some of the other brands out there

Legit question though, did you choose the chassis color before or after you got the transformers? It's a very aesthetically pleasing look Any plans for a cabinet/grill over the top?

[Kevin Mitchell]

The transformers took so long to process I had plenty of time to pick at stuff. I had the whole thing painted, built and waiting for the transformers which I received two days ago - ordered in mid January. The aesthetics where designed around the transformers really.

I want to keep it open to show it off. Mostly to have a reason to talk about electronics when I have guests over. I did consider using tube guards but thought that was a bit much 

The amp is a version of the Poddwatt circuit if anyone is curious.

[thomasha]

That looks awesome! Imagine small edcor transformers! I think they have a 22k 3w like the fender/hammond?

if you're going the submini route, you definetely want to take a look at this>

https://www.audioasylum.com/forums/tubediy/messages/13/edit/13824720080311181501.html

or this one
https://blog-001.west.edge.storage-yahoo.jp/res/blog-33-56/matsu_kat/folder/837569/15/56212415/img_0?1229346383
https://blogs.yahoo.co.jp/matsu_kat/folder/837569.html?m=lc&p=5