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PostPosted: Wed Feb 25, 2009 5:54 pm 
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sorry couldn't resist :lol: :lol:
Ha still can't remember how to get this email going :lol: :lol: :lol:

I think you should wait until Coco gets his PT and buy his !! :wink: :wink:
Ya know it'll be the best and make "The Chimp" GREAT! :wink: :wink: :D :D
Have fun
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PostPosted: Mon Mar 02, 2009 3:22 am 
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hi there, was wondering if one of you knows where i could find a schematic involving one 12ax7pre, one 6aq5power and one 6x4 rectifier.
i found a cool little amp in my stock of old thingies and i would really like to make a little minimalist living room amp out of it, think it was a phono amp back in its days....im thinking, one volume and one tone.
heres some pics of it, its pretty old :oops:

Image

Image

Image

maybe some of you might get an idea what to do with it :idea:
i was thinking about some kind of champ derivative, the less parts involved the better, power transf is good, got bout 325v and only 6.2v heater circuit(ok with 6x4 me think)....also, i cant figure out how what is the impedance of the OT, so i can choose speaker accordingly :?:

btw, sorry for hijacking that tread, i figured it was the best place for a little SE infos :oops:


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PostPosted: Mon Mar 02, 2009 8:46 am 
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ok, i looked at schematics all nite long(im a night guy) and the only thing keeping me from going forward is the 6v6/6aq5 pinout wiring, cant seem to figure it out. and the values of caps that would go with it....
at least i think i could get by without using the old capcan, wich is a good thing as i plan to build another chassis even smaller, sort of a micro amp :twisted:

i think i grasped how to wire the recto too.
damnit, i almost lost interrest in building pedals since getting in thoses forums, amps are much more tone worty addiction :lol:


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PostPosted: Mon Mar 09, 2009 2:07 pm 
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coco wrote:
Be sure to get a big ass SE OT. Not some wimpy little Champ reissue style.

How big of an ass should I be looking for? Here are the specs for 4 possible OTs:

Allen
    T010B
    2.5k --> 2/4/8 ohms
    5k ----> 4/8/16 ohms
    60mA

    T011c
    4k --> 4/8 ohms
    8k --> 8/16 ohms
    95mA
Musical Power Supplies
    OT10SE
    2.5k/3.5k --> 2/4/8 ohms
    5k/7k ------> 4/8/16 ohms
    60mA

    OT20SE
    2.3k/3k --> 4/8/16 ohms
    4.6k/6k --> 8/16/32 ohms
    90mA
The way (I think) I understand it, the primary impedance is a function of the pri/sec winding ratios and the speaker impedance.
A higher primary impedance reduces max output and clean headroom, lower impedance does the reverse. Too low, and the power tube gives it up in a showy, yet unsatisfying, fashion.

According to many Internet sources, a 6V6 likes a higher impedance than a 6L6...but, opinions vary widely as to the specifics.
In fact, a chart on Musical Power Supplies site indicates the opposite:
"6V6 Family 4500 Ohms 30 - 45mA"
"6L6 Family 5500 Ohms 40 - 54mA"

WHAT-da...??? :bugeye:

So.....Assuming we have a single 6L6/6V6 SE amp with ~350v at the plate...
    -What is an appropriate primary impedance range for a 6V6?
    -What is an appropriate primary impedance range for a 6L6?
    -Are there any tonal considerations between higher/lower impedance other than clean headroom?
    -Is there any benefit to a 90mA rating vs. a 60mA rating?

Thanks for the help,

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PostPosted: Mon Mar 09, 2009 10:58 pm 
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For SE & PP impedancdes check out this: viewtopic.php?p=6188#6188

5K is about right.

10 Watt minimum would be my recommendation for good bass response. The OT10SE 5k/7k for 1 6V6 or OT20SE 4.6k/6k for 1 6L6 looks promising.

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PostPosted: Tue Mar 10, 2009 6:23 pm 
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Here's a good possibility for the faceplate....

Image

I did this in CorelDRAW.

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PostPosted: Tue Mar 10, 2009 6:28 pm 
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Cool! Would be nice to have the chimp in reverse video - white chimp on black background. But, I'm no artiste!

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PostPosted: Thu Apr 02, 2009 9:54 am 
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I like the Hammond 125ESE for single-ended amps. It's a nice and beefy OT, with strong low end, and is good for up to 20W. The 125DSE is also pretty good.
b0b0 wrote:
I'm still trying to work out the B+ voltages. I was originally considering a 310-0-310 PT thru a tube rectifier. If I'm thinking correctly, this now works out to ~400DCv since there's no voltage drop across the diodes.

Around 300V -350V DC is about right for a small Class A SE amp running a 6V6 or 6L6 (or even an EL34) tube. You don't really want to go much higher than that.
elegy wrote:
hi there, was wondering if one of you knows where i could find a schematic involving one 12ax7pre, one 6aq5power and one 6x4 rectifier.

Just build it into a regular Tweed Champ or Tweed Princeton. You can follow their schematics pretty closely, using the transformers you have there. The one thing that will be different is the power tube's cathode resistor. So use the same value resistor as your amp has right now. For the OT, first test that it's OK. There's an article about OT testing on geofex.com. If you then *carefully* connect the OT primary to 120V AC supply, you can measure the voltages on the primary and secondary, which will give you the turns ratio. The impedance ratio is the square of the turns ratio. 6AQ5s typically run with a 5k primary load impedance. so the speaker impedance should be somewhere around 5k divided by the impedance ratio.

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PostPosted: Thu Apr 02, 2009 12:20 pm 
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Bobo and others, I hate to introduce a little "shameless commerce" here - but in an effort to possibly help a brother builder, I have a brand new Hammond 125ESE such as Zaphod recommends. I abandoned a single-ended project about a year ago and would be happy to sell this a bit below the best price you can find from a vendor. No sense in letting it just sit on the shelf...

Jim


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PostPosted: Mon May 18, 2009 8:45 pm 
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:shock: ...it actually works..... :shock:

I finally dusted off the soldering iron and pounded the Chimp into submission. Initial tubeless power-up produced no smoke or sparks, so I put in some sacrificial tubes and lit it up. Still no fireworks!! As I had suspected, the voltages came out a bit higher than I would like, but they're pretty close to what's present in a Champ....so I went ahead and brought the MV and gain up. The only real surprises were that it fired right up and that I only burnt myself once! It's definitely a little gain-monster. It starts threatening some high-pitched nastiness at about 75% gain, but all-in-all I'm VERY pleased with the initial results. I'm still gonna be tweaking it a bit to bring the B+ down before I put the good tubes in. Sure would like to put in a VRM, but there's very little available real estate....the chassis I used is only 6.5" x 12.5".

Many, many thanks to all who contributed with their expertise, moral support, and/or basic interest in the project.....expecially coco and zaphod (obviously), without whom......

It's been very gratifying to see the interest in the thread. Once the final tweaks are in place I'll update the schematic and layout.
Next project: TC-15

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PostPosted: Sat May 23, 2009 12:56 pm 
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that's 1 angry chimp


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PostPosted: Sat May 23, 2009 1:08 pm 
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The VRM only takes 1.5" sq foot print + the pot.

As for the voltages, put in a Zener on the B+ liek we did on the TRIWATT for the 6V6 selector. Works great.

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PostPosted: Sat May 23, 2009 11:55 pm 
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Would it work to put a Zener between the PT center tap and gnd?

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PostPosted: Sun May 24, 2009 10:42 am 
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No the zener goes on the B+ rail. For this amp I would suggest using 5W zener. See the TRIWATT schematic for ideas

http://www.trinityamps.com/ForumGallery/trinity/triwatt/TRIWATT_v1_schematic.jpg

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PostPosted: Sun May 24, 2009 2:31 pm 
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Yah....I figured. I was just hoping I could avoid messing about with the board. My theory was that a properly oriented Zener on the CT would effectively reduce the voltage of the 1/2-wave pulses from the secondary leads.

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PostPosted: Fri Apr 01, 2011 8:35 am 
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Hello b0b0, can you send me the final schematic / layout so this thread will be complete, & I'll post them. Can't get to your links. click email button below

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PostPosted: Sat Apr 02, 2011 12:56 pm 
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Documents sent........sorry bout that, I killed off that web server & forgot about the schematics.

I wound up using a JAN Philips 5751 at V1, Tung Sol 12ax7 at V2, and a Tung Sol 5881 at V3 & it sounds very tough. Kind of a one-trick pony with stacked gain pots……dual or dual-concentric is somewhat more flexible. The single tone control actually works pretty well, but I don't seem to move very far either direction from center. I had a small chassis on-hand with room for 3 controls....which is what dictated the single tone and stacked gain pots.

*edit*
The original links should be working again. These will get you to the most recent versions:
http://burntmonkey.net/chimp/ChimpSchem1_1.jpg
http://burntmonkey.net/chimp/ChimpLayout1_1.jpg
http://burntmonkey.net/chimp/ChimpReverse1_1.jpg

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PostPosted: Sun Apr 03, 2011 9:16 am 
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Links aren't working


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PostPosted: Sun Apr 03, 2011 2:48 pm 
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jharasym wrote:
Links aren't working

:damntech: hrmmm.....I've tried a couple different computers & the links work fine for me. Could someone else give it a try please?

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PostPosted: Tue Apr 05, 2011 12:23 pm 
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Hokay.......the idiot sysadmin (who shall remain nameless, but whose username may rhyme with shm0b0) blew the firewall config. Links should be good now.

sorry :oops:

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