Big speakers almost done

[jsn]

The big woofers are almost done, and are playing music. horn loaded
woofers sound really cool. definitely "effortless" like you would
think. And insanely loud. I measured 122dB in the basement. That
feels dangerously loud.

jsn

[robert taylor]

COOL!!! 

but it IS dangerously loud... 
'spcially cranked up in a basement...
hope you were wearing earplugs... 

(daily wearer of the annoying things). 
r

> Date: Mon, 13 Jul 2009 10:18:09 -0600
> Subject: Big speakers almost done
> From: j...@boozhoundlabs.com
> To: audio...@googlegroups.com

---

Lauren found her dream laptop. Find the PC that’s right for you.

[jsn]

Yeah I turned it up and was shocked how loud it was. Fingers went in
the ears almost immediately.

jsn

[robert taylor]

jason,

sorry, i spaced out sending you joe list info!
i think we were talking about balanced circuits?

http://mailman.io.com/mailman/listinfo/sound

has subscription info, and archives. 

r

---

Windows Live™ Hotmail®: Celebrate the moment with your favorite sports pics. Check it out.

[in...@rjguitars.net]

Hey guys,

I am near the end of another amp project and I need to know how to ground
the HV on a power transformer with no center tap. I have a 125-0-125 VAC
transformer with no center tap. I can make things work by grounding one side
or the other of the HV into the rectifer circuit but I know there is
something about putting a resistor from the AC-HV nodes tied to ground that
makes things better.

As I recall you use a pair of 100 Ohm resistors to ground for a 6.3V heater
supply when it has no center tap. Would the same idea apply and what value
of resistor to you suggest for the AC-HV nodes?

Thanks,

rjh

[Matt Wiebe]

Why not use a bridge rectifier, then you don't need a center tap.
Matt


On Nov 13, 2009, at 1:04 AM, <in...@rjguitars.net> <in...@rjguitars.net>
wrote:

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>
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[John Galbraith]

On Friday 13 November 2009 1:04:59 am in...@rjguitars.net wrote:
> I am near the end of another amp project and I need to know how to ground
> the HV on a power transformer with no center tap. I have a 125-0-125 VAC
> transformer with no center tap. I can make things work by grounding one
> side or the other of the HV into the rectifer circuit but I know there is
> something about putting a resistor from the AC-HV nodes tied to ground
> that makes things better.

I second Matt's response to use a full wave rectifier. I'm not aware of any
modern reason to use a half wave solid state rectifier. I read an article
once about some exotic Japanese designer liking half wave rectifiers, but I am
far from convinced. You get half the ripple with full wave, and it probably
has lower output impedance in some sense as well. And, you don't need a
centertap transformer, so the transformer can be made better.

> As I recall you use a pair of 100 Ohm resistors to ground for a 6.3V
> heater supply when it has no center tap. Would the same idea apply and
> what value of resistor to you suggest for the AC-HV nodes?

You would decide how much current you want in the branch; in the 6.3V case, it
would be 6.3V/(100ohm+100ohm) = 31mA, so the same current in the B+ winding
(in the US) would be 120V/31mA = 3.8K. That also dissipates 3.75W, so make
sure your resistors are big enough.

I've never quite understood how to pick that branch current well. In the
filament winding, losing 31mA is no big deal. But in the B+ winding, that
31mA can be precious and I would hate to lose it like this. So I would be
tempted to use lower and lower currents, but I don't know what happens sound
wise.

John

[John Galbraith]

On Friday 13 November 2009 8:27:52 am John Galbraith wrote:
> You would decide how much current you want in the branch; in the 6.3V case,
> it would be 6.3V/(100ohm+100ohm) = 31mA, so the same current in the B+
> winding (in the US) would be 120V/31mA = 3.8K. That also dissipates
> 3.75W, so make sure your resistors are big enough.

Uugh. Sorry about the BS in my response. These resistors are on the
secondary side, so you have to use the winding voltage, not 120V. Sorry about
my misleading mistake. DON'T put these on the primary side.

John

[rjgu...@gmail.com]

Atomic City Audio Nerds - Thank you guys... I feel a little dumb for not
seeing the choice for a full wave rectifier versus the half wave as the
solution for the no center tap problem.... I think the first real circuit
they taught us in High School electronics class was the full wave bridge
rectifer... so easy to do!

Matt, this amp is very much a tribute to you. It was so many years ago you
showed me the subminiature tubes. I always planned to build an amp out of
them, but I am so slow to respond that even I don't believe me when I say I
am working on it. Thank you very much for the inspiration as well as all the
assistance over these years!

The circuit is the Trainwreck Rocket (VOX AC-30 top boost channel). Tubes
are 5744 single triodes, 6021 dual triode, and a pair of 5902 output tubes.
Cathode biased and I think it might make 2 or 3 watts.

It all came together tonight. I was thinking I didn't care much for these
tubes when I was soldering them into place but after I got them tweaked into
shape I may have changed my mind. The amp was distorted but had potential
when I first fired her up. I tweaked the voltages and by the end of the
night this thing sounded awesome! IT cleaned up very nicely and has plenty
of headroom.

Thanks all of you for your help. This is not my best effort cosmetically but
functionally it came together very nice and has great potential for a kit
amp. The "everything including the tubes mounted on the circuit board" is a
Jason idea that he planted in my head a couple years back.

thanks again,

rjh

[Matt Wiebe]

5902s, you gotta love. Those were the P-P outputs on my 955 acorn to 5902 that I had with me at the Mesa get together years ago. Nice work Bob, looks like a fun build, I like the daisy chained heaters. Not that you want to know, but I know you like tube rolling, the Russian 6P30B has been drop in for 5902 in the circuits I build with, and better for your kit building you can buy in lots of 50 to 100 pretty easy. The 6N16B subs for 6021, even if you exceed its plate voltage max. As usual Russian tube specs are extremely conservative. 

I take it you are going to offer a circuit board at some point. I recommend going with octal tube sockets because octal plugs are so easy to get. It makes tube swapping easy. Keeps us informed as you get used to it. Looks like a fun build for my boy.

Matt

<Dwarf Rocket - Tubes and Board.jpg><Dwarf Rocket - Front View.jpg>

[rjgu...@gmail.com]

Matt,

 

Thanks a ton for the info on te Russian equivalent tubes. As I've watched over the past year or two, the 5902 tubes have become really hard to find. I was thinking that there is no way to offer a kit if I couldn't get tubes.

 

Is there a tube equivalent of the 5744 or the 6112 tube? These are the Hi-Mu triodes. I see a lot of 5744's (single triode) but not so many of the 6112's (dual tirode).

 

I definately agree that a tube socket is the only way to deal with these... when I was soldering in the tubes I thought to myself that  this was not a good way to do things.

 

thanks again for all your help.

[Matt Wiebe]

Bob,

I assume you have called the usual suspects in Florida for large lots of 5902s. I still see lots of 20 to 50 come up every once and awhile on eBay but their popularity has dried up supply.

You may want to build a breadboard of this amp with octal sockets so you can plug and play and start having a look at all the Russian subminis on the market. I wire everything to a 6SN7 base. For quick spec' http://www.russiantubes.com/tubes.php?r=12

For 6112, try 6N17B-V mu 75 max V 200V,  6N21B mu 82 max V 200V, 6S32B Gm 2.2-4.8 mA/V Mu 80 to 120, 200V, 6N33B  mu 70 max V 100V. I use these in phono preamps, as well as the 6112. 

I don't know the hi Mu single triodes very well, but you can look at 6S7B-V Gm 3.1-4.9 mA/V Mu 70    250V. 

There are other options for US NOS little tubes.

I don't think soldering these tubes directly to a board is bad, it is just that I think guitar guys swap tubes frequently and wiring to tube bases makes this possible.

Matt

[rjgu...@gmail.com]

Matt,

 

I found one of the Florida vendors with a good stock on the 5902 tubes and bought 26 of them. I also bought 100 of the 6112 tubes on EBAY. I will compliment those with a couple smaller orders of the Russian equivalents and eventually expect to sell a kit using them.

 

I'll have excess 6112's to sell if anybody has an interest in them. Audionerdz can have them at cost.

 

EDCOR made me a great deal on power transformers that will be perfect for all pencil tube amps and maybe useful for the 7 pin projects I have in mind as well. 125-0-125 AC @ 125mA with a 3A heater winding.

 

thansk for all your help... and thanks to everybody else too.

[Matt Wiebe]

That's great luck, but I expect you will need more 5902s at some point. I've got quite a few 6112s but maybe knowing you are flush I will dial up the plate current. I sure would be nice to lower Rp just a bit. It's funny, years ago it was hard to get Edcor to take DIY seriously, their pro business kept them as busy as they wanted to be. I wonder what changed? I find them much easier to deal with now, and they were never hard to deal with. But they seem to really reach out to DIY. Sounds like your kits are really coming together nicely.

Now if you get a good deal of Cree Schottky Diodes, 600V 2A, you will have my attention. 

Matt

[rjgu...@gmail.com]

Yes,

 

I'll no doubt want more 5902's, but I was so pleased to find them. That will let me repeat the same output tubes and such as my prototype amp. I'm planning to look at the Russian equivalents for comparison later. My plan is to make up a dozen of the mini amp kits as a starting point, then see if more are warranted in the future.

 

I have some capacitor questions for you. The guitar world has not really embraced the paper in oil coupling caps. Is this because we are following the lead of the old guitar amp companies who were very cost per unit aware? Any clue how a PIO will impact the tone of a guitar amp? My plan is to buy some russian PIO caps and try them out but I was curious about your thoughts in how they might compare to the orange drops?

 

Also, what is a PETP cap? They seem cheap enough. Is that a completely different material or technology than an orange drop is made from?

 

Soory, no Schottky Diodes of any flavor, although you never know. The Black may have what you want. I did pick up an old set of 6l6GC's for $1 each the other day. The prices are all a little bit better these days.

[Matt Wiebe]

Bob,

I never liked paper in oil caps for stereo, too veiled, but I kept hearing good things about the  Russian K75-10 and the K40Y. Having purchased a few I still think they suck. The Russian teflons are so much more to my liking. I don't know how they would impact guitar tone however, but people claim they are close to Vitamin Qs if you know that one, and I will agree with that. Before you buy any send me some values you are looking for and your address and I will post some over to you. I don't imagine I will be using mine at a very fast rate.

PETP, Polyethylene Terephthalate, is just another film and foil cap, you just have to try it a see what you think. They are different from Orange drops but I couldn't describe the difference. The only cap I would suggest you also want to listen to is a tin foil cap, made by Solen, Relcap, Mundorf and other other maker that escapes me. A big step up from an Orange drop for audio, but not nearly as good as Teflon.

I haven't been to the Black Hole since Ed died, I was wondering about the pricing over there. Ed was never that concerned with inventory turns.

Matt

[John Galbraith]

On Tuesday 17 November 2009 6:07:41 am Matt Wiebe wrote:
> PETP, Polyethylene Terephthalate, is just another film and foil cap, you
> just have to try it a see what you think. They are different from Orange
> drops but I couldn't describe the difference. The only cap I would suggest
> you also want to listen to is a tin foil cap, made by Solen, Relcap,
> Mundorf and other other maker that escapes me. A big step up from an
> Orange drop for audio, but not nearly as good as Teflon.

Matt, how do you feel about the different positions for capacitors? I'm
assuming that you are talking about coupling capacitors above. Can you also
hear the difference in bypassing rolls, such as filtering voltage dividers or
zener based references, such as in bias, current source, or regulator
circuits?

What about in the power supply, can you hear the difference between good
electrolytics, poor electrolytics, and plastic capacitors either before or
after a choke?

> I haven't been to
> the Black Hole since Ed died, I was wondering about the pricing over
> there. Ed was never that concerned with inventory turns.

My experience has been so far that the prices are down, and way more
reasonable than they were under Ed. I bought a couple of lab cabinets for $20
each that were identical to two others I bought from Ed for $50. The second
(cheaper) set I had to work out some dents, but I cleaned, painted, and
rebuilt both sets. I've also been buying power resistors and aluminum for
prices that seem quite low.

I think his stock is down, however. The stuff I've been snagging, for
instance, is pretty much picked over and out.

John

[rjgu...@gmail.com]

You guys are a great resource... I ordered 50 of the PETP .047uF caps today,
let me know if you want some to test.

I was wondering about using the IC sockets for the mini tubes? I'd like to
mount them directly to the boards and then either have the tube plug in
directly or maybe solder it into an 8 pin carrier. What do you think?

http://cgi.ebay.com/100-pcs-8-pin-DIP-IC-Sockets-Adaptor-Solder-Type_W0QQitemZ150382508960QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item23037efba0

Lastly - I am wondering how you determine the right cathode resistor for the
5902 tubes? I chose 470 Ohms for the pair because I was relatively sure
that I wouldn't red plate them at that value. I can go back and play with it
until my ears think I've made a good choice but I want to understand enough
to be in the ballpark rather than just guess and change parts.

In one of my books the author suggests you reduce the resistance (increase
current) until they redplate then back it off a notch.... while this was the
procedure given for a fixed bias amp, I suspect there might be a better
method and that same strategy might not even apply to a cathode biased amp?
This will obviously expose me for not knowing how to use the spec sheets,
but maybe I'll absorb more this time than the previous 2000 times Jason has
showed me how load lines work and such...

thanks,

rjh





----- Original Message -----
From: "John Galbraith" <bar...@cybermesa.com>
To: <audio...@googlegroups.com>
Cc: "Matt Wiebe" <mwi...@unm.edu>
Sent: Tuesday, November 17, 2009 9:28 AM
Subject: Re: Power Supply Question

[Matt Wiebe]

Bob,
I used IC sockets on a few sub-mini phono amps I built, they work
real well. Though my female connector in the socket was round, and
they were harder to get out of the socket then I liked. The only down
side is they are ugly so they are a below deck, way below deck,
option. There are three other options here,
http://pacifictv.ca/socket.htm#submin
Though the flat press tubes are always difficult.
For a kit I think go till it melts and back up a few is not the best
approach. You have to remember that 10 extra mills of plate current
will make almost no difference in power output, but it will in tube
life. I would shoot for plate diss about 10 to 15% below book max and
call er quits. However, I run my little tubes above book spec and I
have yet to have one fail because of it. But they do get tired fairly
early. To calculate plate dissipation it is just ohms law. Voltage
measure plate to cathode, times plate current and that's plate diss.
What your books author said is fine for personal use, but building
for others I would be way more conservative. Plus its very hard to use
this approach on sub-minis because its hard to see the plate from the
filament when the tube lettering takes up most of the glass. Reducing
plate resistance by over running the plate suggests you have only one
tube to play with. If you need lower plate resistance pick a tube with
lower plate resistance, there are lots of tubes.
Matt