Author Topic: New low voltage tube amp project. Runs on 12v walwart 62v inside. not to scary.  (Read 39633 times)

solderburn

Do the tubes glow? ;D
Frequency Centrals murder one glows, but with sublimini tubes. I dont know if the bigger tube means less/no glow.
Dan

blackcorvo

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Here's a thought I just had for an alternative power supply for this mini amp:

If you used a 24v+24v 12VA PT, wired it for a half-wave voltage doubler from rail to rail (that is, grounding one of the 24v leads and feeding the doubler with the other one), and connected the 12AU7 and 12AX7 filaments in series (wired for 12v), you could use the center tap to feed the filaments, and the voltage doubler would give you over 130v unloaded (probably more if you use large values for the voltage doubler and filtering caps).

What do you think? Worth a try?

[EDIT]

Here's a schematic to help visualize what I meant: http://imageshack.com/a/img855/7152/4wu0.png
« Last Edit: February 08, 2014, 05:23:55 AM by blackcorvo »

sajy_ho

if you have access to step down transformer they work to. a 120 to 12v coupled to a 12v to 120 for b+ works well from what i hear. i havent tried it yet but should.
Thanks, that would be something like Real Mc Tubes, but I don't want to use transformers becouse of their weigth and size. How about a SMPS design using LT1054?
Life is too short for being regretful about it.

zambo

@ solderburn- they glow but not a ton. led light in the center of the socket works good though.
@ Blackcorvo- Sounds good, but when the voltage goes above 70v or so they get to loud for a quiet amp all of a sudden.

@Sajy ho- thats what the current ps is. you could use smaller 10uf 100v caps, just dont add more stages to it or you could have a blow up. I only used 160v because i was selling them to someone else. more of a cover your a$$ type of thing. 
I wonder what happens if I .......

sajy_ho

@Sajy ho- thats what the current ps is. you could use smaller 10uf 100v caps, just dont add more stages to it or you could have a blow up. I only used 160v because i was selling them to someone else. more of a cover your a$$ type of thing. 
:icon_mrgreen: Sorry my bad, I thought SMPS is only called for those with a MOSFET switch!!
Life is too short for being regretful about it.

Scruffie

I wouldn't say this is a SMPS, it's a charge pump or switched capacitor voltage converter if anything.

Frequency Central did a SMPS design using a MAX1044 if you search the forum.

psychedelicfish

I wouldn't say this is a SMPS, it's a charge pump or switched capacitor voltage converter if anything.

Frequency Central did a SMPS design using a MAX1044 if you search the forum.
It is an SMPS in a sense, because it does chop up the DC input at a high frequency in order to convert it to a higher voltage. It differs from a boost converter in that it increases the voltage by putting the chopped up DC through a voltage multiplier rather than pulsing current through an inductor.

A boost converter would be better, I think, because the output would be regulated, but the current design is simple enough and seems to work fine.
If at first you don't succeed... use bigger transistors!

smurfedelic smurfberry

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blackcorvo

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@ Blackcorvo- Sounds good, but when the voltage goes above 70v or so they get to loud for a quiet amp all of a sudden.

You could always just make it a half-wave rectifier instead, still using both 24v leads to get 48v AC. I'm guessing it would give a B+ of something around 60v.

solderburn

How are the Power supply caps supposed to be oriented?

I have Polarized capacitors, Will they work, and if so how am i supposed to orient them? ???
Dan

solderburn

Anything?
« Last Edit: February 19, 2014, 04:33:46 AM by solderburn »
Dan

sajy_ho

How are the Power supply caps supposed to be oriented?

I have Polarized capacitors, Will they work, and if so how am i supposed to orient them? ???
All the upper lids in the schem are positive. Something like this:http://i210.photobucket.com/albums/bb292/frequencycentral/ValvecasterHead.jpg
Life is too short for being regretful about it.

zambo

yes exactly like that. thats the exact power supply. Thank you Sajy!
I wonder what happens if I .......

solderburn

I got the voltage multiplier to work with polarized caps the other day and today I wired up the rest of it, and I Works!! :icon_cool: Sounds like a crunchy Marshall.

The sound is great accept it has absolutely no headroom. It instantly clips, But I play Hi gain stuff mostly but for the sake of versatility how could I decrease gain without affecting volume?
And when I play a chord, say a G major or E 5 It has a extreme loss of volume, kinda think a wire might be loose. Is there anything else that would cause this to happen?

Id like to fix these problems soon because I did not paint the chassis :icon_rolleyes: So, I have to disassemble a lot of it. and Id like to have the peace of mind that i got all of the issues worked out.
Ill post pics when I'm done too!
Dan

thomasha

Hi,
i have build a similar amp with the same problem, I think the problem is that the charge pump can't maintain the B+ voltage because bassy notes require more current to move the speaker.
Try to play very agressive but only hiting the sixth string and you will see the same thing happening, and the sound getting louder after that. I don't know if that's was sag supposed to be, but my amp bass gets really flabby.

Look for the voltage at the charge pump and if all the capacitor's are working properly, maybe adding a larger reservoir capacitor will correct that.

At lower volume setting the problem disappear right?

solderburn

I tried again, had the same problem and wiggled a cathode wire by accident, And it fixed volume loss the problem accept for when i plugged my homemade Telecaster in(tuned to E with single coils) and ripped on the low e string it lowers the volume a little bit, not much. Which is weird because i plugged my strat knock off in (modded with humbuckers and tuned to Eb) ,Dean ML (also with humbuckers tuned to A#) and my bro's Epiphone (P-90s tuned to D) there was no volume loss, but with the Dean it was a little flabby, i think i can facilitate this by changing the cathode capacitor somehow. I made a Big Muff Pi and had almost the same problem, then re did the off board wiring thus fixing it. I narrowed it down to adjusting cathode caps and poor off board wiring.

But still the lack of headroom is a little annoying.
Dan

zambo

Adding a reservoir cap will help the volume sag a ton! I noticed it on mine when its cranked ( hahaha cranked ...) all the way up. a 20uf worked. I dont play it turned all the way up though. im a halfway guy and use a pedal for super gain. If you want more headroom, dont bypass the cathode on the power tube. It will distort less. you wont notice a ton of volume loss. If you want more headroom, you need more voltage. thats all there is to it. Im going to modify one to use this voltage but use an el84 power tube. I dont know if it will work out well but... yeah. im going to try it any way haha.  If you just gotta have more headroom and you used all high voltage parts, the 13 dollar 1364 smps from taylor electronics works and has enough ma. still needs the reservoir caps though. Remember, this was built for quiet nighttime practice. Borderline headphone material.
I wonder what happens if I .......

psychedelicfish

Im going to modify one to use this voltage but use an el84 power tube. I dont know if it will work out well but... yeah. im going to try it any way haha.
I've tried something like that on my breadboard, only using a 6AQ5 (7 pin mini 6V6 equivalent) and a 32V supply. It worked, and more importantly sounded good, but the volume was a little on the low side (ok, scratch that, it was a lot on the low side). With your 62V supply you should have no problems with volume. I think a 5k load should work nicely, but you should play around with this if you can. At this low of a voltage you don't have to worry too much about the valve's max dissipation, and I seriously doubt your supply can put out 12W to overheat the anode anyway.
If at first you don't succeed... use bigger transistors!

thomasha

Hey,
why don't you use a Max1771 circuit instead? 240V and it's pretty loud;

I made one, and it's too loud to crank at night, but headroom is a little better.

take a look:



Based on Frequency Central Obsession amp
« Last Edit: February 22, 2014, 11:14:59 PM by thomasha »

solderburn

I reinstalled it yesterday and gave it a good testing today and both problems i had before are fixed! They where caused by bad terrible off board wiring. I was excited to see what it sounded like and went way to fast. But i re wired it and all is good, It sounds great!! no headroom issuses or volume drop. I'll post pictures tomorrow. the only two anomaly's are when i plugged my strat and tele in the low end is flabby/farty, but when i tried a LP with P-90s (tuned WAY lower i may add) the flabbyness was eliminated. OD did Stop the flabbyness with the strat and telecaster. Could this be fixed by adding a buffer or by changing Cathode cap values? And when i drive the amp hard with a pedal and take my hands off the strings it makes a for a lack of a better term a hissing/tire deflating noise. his one has me stumped. Both of these minor issues don't really bother me cuz it sounds so good with a little OD, but i would be nice to fix'em.

thomasha- Thanks for your suggestions! the BMP tone In the circuit gives me ideas! And did you make the amp in the video? it looks great!!

And thanks zambo! this is by far my best piece of gear I have ever made! :icon_mrgreen:
« Last Edit: February 23, 2014, 01:05:24 AM by solderburn »
Dan