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1 watt tube amp
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9VOLT1967



Joined: 26 Aug 2011
Posts: 36
Location: florida

PostPosted: Fri Nov 04, 2011 5:10 am    Post subject: 1 watt tube amp Reply with quote

I want to build a 1 watt tube amp using a 12AU7 for a power tube and a 12AX7 for the preamp. Does anyone know of any transformers that would work for this application?
Thanks

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Jack Hester



Joined: 05 Sep 2010
Posts: 101
Location: Roxboro, NC

PostPosted: Fri Nov 04, 2011 5:58 am    Post subject: Reply with quote

Do you have a schematic? What kind of B+ voltages are you looking for? SS rectifier or tube?

Jack
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M Fowler



Joined: 16 Jan 2008
Posts: 11199
Location: MN

PostPosted: Fri Nov 04, 2011 9:04 am    Post subject: Reply with quote

Here is something posted a few years ago.
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rdjones



Joined: 31 Aug 2010
Posts: 819
Location: Music City, TN

PostPosted: Fri Nov 04, 2011 9:18 am    Post subject: Reply with quote

For single ended you can use a reverb driver (one with an 8 ohm secondary).

Mojo has this one for push-pull:

http://www.mojotone.com/amp-parts/transformers-mojotone-project-output/Mojo-Clone-of-Wright-1580-10K4-8-16-12BH7-12AU7-PP-Output
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Cantplay



Joined: 22 Jun 2011
Posts: 913
Location: Ground Zero NYC

PostPosted: Fri Nov 04, 2011 11:45 am    Post subject: Reply with quote

http://acepepper.com/ThunderTweakWeb/info/HEAVYwatter_v4.pdf

This looks good, although I haven't built it myself yet.

It uses a fender reverb tranny.

John
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9VOLT1967



Joined: 26 Aug 2011
Posts: 36
Location: florida

PostPosted: Fri Nov 04, 2011 12:52 pm    Post subject: power transformer Reply with quote

I am ok with the reverb transformer for the output, but I would like to use a smaller transformer other than the Hammond type. I believe I can get by with a 350V rail voltage after rectifier and 1.2 a for the heater. Maybe 15-20VA. I am working on a schematic now. Thanks for all the great info!
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9VOLT1967



Joined: 26 Aug 2011
Posts: 36
Location: florida

PostPosted: Fri Nov 04, 2011 2:33 pm    Post subject: Voltage doubler circuit Reply with quote

Here is a transformer option, but need to use voltage doubler to obtain desired voltage. Hammond 262E6 18VA 120V secondary @ 87ma. 1.2A for heaters.
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xtian



Joined: 19 Apr 2010
Posts: 3270
Location: NorCal

PostPosted: Fri Nov 04, 2011 3:22 pm    Post subject: Reply with quote

I built a Firefly:

http://ampgarage.com/forum/viewtopic.php?t=11248

Very cool project, and good sounding amp.
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9VOLT1967



Joined: 26 Aug 2011
Posts: 36
Location: florida

PostPosted: Fri Nov 04, 2011 8:15 pm    Post subject: 1 watt schematic with voltage doubler Reply with quote

Here is my proposed schematic for a small simple 1 watt design. My understanding of the voltage doubler is as shown. 120VAC X 2.8 = 336VDC. Is there an easier way to achieve the same results? Are the component choices ok?
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renshen1957



Joined: 20 Feb 2009
Posts: 464
Location: So-Cal

PostPosted: Fri Nov 04, 2011 9:11 pm    Post subject: Reply with quote

rdjones wrote:
For single ended you can use a reverb driver (one with an 8 ohm secondary).

Mojo has this one for push-pull:

http://www.mojotone.com/amp-parts/transformers-mojotone-project-output/Mojo-Clone-of-Wright-1580-10K4-8-16-12BH7-12AU7-PP-Output


Hi,

A self-split 12A_7 design such as the Firefly was posted at the AX84 website.

I would suggest the Hammond 125 A push pull amp. Loads of options as to the primary/secondary, and I believe it runs about $33.00 from ebay.com or from Angela.

http://angela.com/hammonduniversalsingleendedorpush-pulloutputtransformers.aspx

Another option would be at Edcorusa.com

Their 10k primary 10Watt amp (yes, I know it is way over the 1W) is $17.22

http://www.edcorusa.com/products/354-xpp10-8-10k.aspx

Best Regards,

Steve
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Cliff Schecht



Joined: 30 Dec 2009
Posts: 2616
Location: Austin

PostPosted: Fri Nov 04, 2011 9:54 pm    Post subject: Reply with quote

Anybody here played with using 70V line transformers as output transformers? For a 1W application there should be no problem finding a CHEAP 70V distributed line system transformer. I have a few but have never played with this myself. I know that the right ratio for a tube output stage can be achieved with one but they aren't meant to handle static DC (SE amp). But at the same time, a 10W line transformer will have no problem handling the static DC from a 1W output stage..
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martin manning



Joined: 06 Jul 2008
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Location: Queen City

PostPosted: Fri Nov 04, 2011 11:06 pm    Post subject: Reply with quote

A full wave voltage doubler looks like the attached pic. If you want 100uF total for the first filter, make each of the two caps 100uF.
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9VOLT1967



Joined: 26 Aug 2011
Posts: 36
Location: florida

PostPosted: Fri Nov 04, 2011 11:10 pm    Post subject: Reply with quote

Re-drawn voltage doubler. This will cut my amperage in half, but still should have enough power only 2 tubes- 12AX7 and 12AT7. My secondary is 120VAC. With this configuration what will my plate voltage be?
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martin manning



Joined: 06 Jul 2008
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Location: Queen City

PostPosted: Sat Nov 05, 2011 12:20 am    Post subject: Reply with quote

9VOLT1967 wrote:
Re-drawn voltage doubler. This will cut my amperage in half, but still should have enough power only 2 tubes- 12AX7 and 12AT7. My secondary is 120VAC. With this configuration what will my plate voltage be?

Without knowing the series resistances of the PT, I'd guess about 310.
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9VOLT1967



Joined: 26 Aug 2011
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Location: florida

PostPosted: Sat Nov 05, 2011 12:41 am    Post subject: Caculation of DC voltage Reply with quote

What formula did you use to obtain figure?
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