Built me a Bucker

Nasty day today, so went digging for an indoor project. Found an old power strip and transformer and got to it.

Simple 120v primary - 6.3v secondary transformer rated at six amps.

Tada!



First thing I noticed is the ST120 biased up quite a bit lower than without the bucker. Went from the usual 55mA down to 48mA, so there's a definite drop on the B+. I've got it idling away right now without load and I'll give it a go later tonite. So far, the transformer is staying nice and cool.

Should be an interesting experiment. I've heard folk going on about how much better their stuff sounds when you get the power down to what the designs originally called for.

I built a bucker for my little Chinese novel amp with a 110 volt tranny . Was running way too hot . Used one with a 12.6 volt Secondary . Line is down to around 107 volts now . The amp likes it .

Nice Job sKiZo. But is not the ST120 designed with the intent of higher voltages of today then the amps of yesteryears?

You'd think ... but from what I gather, the Dynaco clones are just that ... reproductions of the original designs. Those designs were made for wall current of 115-117vac. It's not something to lose sleep over, but I'd say fits in the category of improved components like filter caps and chokes and such ... not required, but every little thing and all that, when it comes to improving sonics and performance.

Maybe we can get Bob & Co. to chime in on this?

Anyway ... I just spent a couple hours shuffling thru some of my favorites and first impression is ... just when you don't think it can get any better, it does! I now understand what the bucker brigate are talking about when they refer to an amp driven with high vac as "pinched". I'm noticing quite a bit more detail all across the spectrum - best way to describe it is that I'm now hearing more that I never missed before. Individual voices instead of a chorus, sub-harmonics that previously blended in - it just feels like the amp isn't working quite as hard.

I did have to also boost the volume - without changing my old settings, I was down around 3-4db. No biggie as I had been throttling the pre signal back quite a bit anyway. Once I boosted it up back to room resonance, it was like the amp had to retrain itself for a few minutes, then it blossomed similar to what you'd experience with breaking in new tubes. Hard to describe - like a veil lifting seems apt. All subjective of course ...

I did check the bucker after about an hour and it was barely heating. No discernable effect on the big iron on the amp itself. What I should do is double check some of the internal voltages, especially the B+ to see where those are at, but those were always a bit on the high side, so I expect they're back more to middle range now.

PS ... I also installed a thermistor back when I built the amp. Those are meant to give a slow start as they're made to  pass reduced current until they heat up. Thing is, they never really go completely open, and you can expect the line voltage to drop 1-2vac with one on the AC line. That would put me at around 115vac running off the bucker. Something else to meter out and verify.

I was just reading about these. I like the look of yours. I just recently caved and bought a variac for the same purpose.

The power strip mod seems to be quite popular. I only needed the one outlet, so plenty room to mount the transformer with pop rivets. Already has a breaker and switch too, which is handy. Only "problem" with this one is the indicator light is burned out. Don't need it anyway.

I did have a dOH! moment when I realized the socket was bass ackwards and I wouldn't be able to plug in my GFCI adapter for manual restarts on power outages. Ah well ... would have been handier on the bucker, but for now I just plugged the bucker into that. Same thing, only different. I get bored, I'll pull it apart and reverse the socket.

I've got a variac, but it just looks right at home on the bench ...

Can you post how you wired the tranx  in your setup.............thanks

using a Varick to lower the ac volts..... is one of the best thing i have done with any tube amp ............tube last longer..........sound is sweeter...b+ at 460-80...tops
but it hard to tell other...it like if you dont go ...you can know!




thanks for the site Bob....

I live to serve ... would you like fries with that?   



Pretty straight forward hookup, especially with a simple transformer with one primary and one secondary winding. Mine is 120v in by 6.3v out. The breaker and switch wiring didn't change on mine - that's all on the hot side of the AC connection to the wall. As you can see, I just cut out a couple sockets on the power strip to mount the transformer.

- Neutral side of the AC wall feed goes straight through to the socket.
- Hook the neutral side of the transformer's 120v winding to that straight through feed.
- Hook the other side of the transformer's 120v winding to the hot leg of the AC wall feed.
- Hook one leg of the secondary winding to the hot leg of the AC wall feed also.
- Hook the other leg of the secondary winding to the socket.

Just tack the secondary winding wires in place temporarily until you verify that you've got those right with a VOM in the socket. If you've got it right, you should see the voltage drop. If the voltage goes UP, reverse those two wires and check again.

Gets more complicated with more windings as you have to figure out which leads are which. I've seen a few examples where folk have both 6v and 12v taps, and have wired those up to provide different output voltages to multiple sockets. Gives them some flexibility, but I'm happy with what I got, mostly because it's doing the job, but also because it doesn't take up much space in the rack.

Great idea! I use a thermistor for my ST-35 for a little soft start-up, but also to knock down the high voltage a little bit at my place. It seems to "eat' two or three volts. Today I noticed the wall voltage to be 125, so I'm probably getting about 122V at the primary of my power transformer - with the thermistor in place. I want to knock it down even further.

Hammond has a 166 series for filaments which have various ratings. Single primary and secondary (to keep it simple), and the one I was looking at - the 166RS - has 115VAC primary, 5VAC secondary and rated output of 8 amps. I know I don't need that high amp rating, but I might use it for my phono amp, turntable power supply and Quad ESL-57 speakers. I don't mind spending the loot on higher ratings if needed. Am I in the right track?

Going a bit beyond the research I did, but it looks like the 115vac rating of the Hammond's primary winding would be essentially ignored, and the wall current would pass unaltered. This could create additional heating? Anyway, if what I've seen is typical, the actual output you'd get with the 5v secondary winding in series would be around 120 with your current ... er ... current, +/- 1-2v. That leaves you with 118v other side of the thermistor.

Here's another option?

http://www.mouser.com/ProductDetail/Hammond-Manufacturing/166Q6/?qs=zAx27f%252bWkoElcPca8RQ65g%3D%3D

Now we're talking 10a with a 6.3v secondary. More reserve, more drop. More money too, but another $10 sounds reasonable enough, especially if you're gonna be feeding several boxes. Still a workable size too, so it should fit most anywhere.

Bonus ... this looks like it'd be a real nice power strip for ya ...

http://www.ebay.com/itm/UL-Listed-3Ft-6-Outlet-Power-Strip-Metal-Case-/321015668144?pt=US_Surge_Protectors_Power_Strips&hash=item4abe065db0

Hadn't realized how hard it would be this day and age to find a decent metal case power strip. Should leave you at least three sockets once the dirty is done, but you might be able to mount the transformer other side of the power switch and save em all ...

It looks like the 166Q6 has a rating of 6A, unless I'm not looking at the table correctly. Anyway, that should be plenty, if I choose to use it. I have a SurgeX sub panel that would house this transformer, eliminating the need for a separate box.

ooPs! My bad ... try this.

http://www.mouser.com/ProductDetail/Hammond-Manufacturing/166S6/?qs=zAx27f%252bWkoEUfLAYE7FTaA%3D%3D

166S6 63va    115V      60 Hz.     6.3 C.T.    10a    C14H

Thanks Skiz.   

How is your bucker wired?  There are a few different methods.  The reason for asking if you have more than 0.5A at 120V in the primary of a 63VA tranny it could burn up or possibly saturate the core and you would loose bucking ability.

Skizo has a picture and description in post 8.

He's bucking 6.3 volts with a 6A rating which would be approx 38VA. If he's not drawing more than 6A with his amp (which is unlikely), he should be okay.

I was going to use a 5V, 20A rated transformer which would give me 100VA. More than enough. The rating is for the amount of current you're bucking, is it not? At least that's what Rod Elliott of WestHost states here:

http://sound.westhost.com/articles/buck-xfmr.htm#s30

BUCK BUCK NUMBER ONE!!   

Finally got around to doing some readings, and as expected, all down across the board. Driving a quad of KT120's on my ST120 using a GZ37 rectifier ... I also double checked with a good 5AR4 without seeing any change.

At the rectifier >> Pin Number - With Bucker  (recommended range)  Without Bucker {Bypass Thermistor}:

#6 = 393 (400-425) 420 {398}

#2 = 470 (490-530) 502 {474}

At tube sockets:

#3 = 463 (470-520) 497 {474}

So ...

- All low, but I figure close enough for an ex-government worker. These readings were all taken with house current "normal" at 124+vac.

- I could pull the thermistor, but I do like the extra level of protection, and doing so doesn't make that much of a difference anyway.

I think Captain Nut is on the right track with the 5v secondary ... with that, I'm sure I'd still have readings above the minimum ... once again, on a "normal" day here. Truth be told, if the transformer I used was actually to spec, that'd probably work too. As is, I'm seeing a bit over a 7v drop from a 6.3 winding ...

PS ... I also measured the AC line current past the thermistor. 116.6 in, 114.3 out. More drop than I expected to see using a CL90 ... then again, all thermistors aren't created equal either.

BUT ... it still sounds mighty fine ... that's the important part!

Looks like you may have hit one sweetspot...........the Varick well let you find a better spot!...maybe

just saying.....befor you get the next Bucker tranX.........

Whats the heaters V runing??............

thanks for your time....


thanks for the site Bob...

http://sound.westhost.com/articles/buck-xfmr.htm#s30 wrote:

Nice link and thanks. The diagrams help understanding a lot. Just a fixed voltage auto-transformer of sorts. Very clever and I like the "Yankee" ingenuity. As the article states it has been around since transformers were first developed.

zx wrote:Looks like you may have hit one sweetspot...........the Varick well let you find a better spot!...maybe

just saying.....befor you get the next Bucker tranX.........

Whats the heaters V runing??............

ooPs ... forgot to list that ... 6.5vac, with or without the bucker ...

Control grid reads out at -56, also with or without the bucker.

Also forgot to mention - bias is set at 55mA. I suppose I could fudge the rest of the numbers up a bit by setting that lower, but I like it like it is ...