1 watt tube amp

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9VOLT1967
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1 watt tube amp

Post by 9VOLT1967 » Fri Nov 04, 2011 5:10 am

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
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Re: 1 watt tube amp

Post by Jack Hester » Fri Nov 04, 2011 5:58 am

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
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Re: 1 watt tube amp

Post by M Fowler » Fri Nov 04, 2011 9:04 am

Here is something posted a few years ago.
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rdjones
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Re: 1 watt tube amp

Post by rdjones » Fri Nov 04, 2011 9:18 am

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/trans ... -PP-Output

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Cantplay
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Re: 1 watt tube amp

Post by Cantplay » Fri Nov 04, 2011 11:45 am

http://acepepper.com/ThunderTweakWeb/in ... ter_v4.pdf

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

It uses a fender reverb tranny.

John

9VOLT1967
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power transformer

Post by 9VOLT1967 » Fri Nov 04, 2011 12:52 pm

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!

9VOLT1967
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Voltage doubler circuit

Post by 9VOLT1967 » Fri Nov 04, 2011 2:33 pm

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
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Re: 1 watt tube amp

Post by xtian » Fri Nov 04, 2011 3:22 pm

I built a Firefly:

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

Very cool project, and good sounding amp.

9VOLT1967
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1 watt schematic with voltage doubler

Post by 9VOLT1967 » Fri Nov 04, 2011 8:15 pm

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
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Re: 1 watt tube amp

Post by renshen1957 » Fri Nov 04, 2011 9:11 pm

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/trans ... -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/hammonduniversalsingl ... rmers.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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Re: 1 watt tube amp

Post by Cliff Schecht » Fri Nov 04, 2011 9:54 pm

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..
Cliff Schecht - Circuit P.I.

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martin manning
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Re: 1 watt tube amp

Post by martin manning » Fri Nov 04, 2011 11:06 pm

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
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Re: 1 watt tube amp

Post by 9VOLT1967 » Fri Nov 04, 2011 11:10 pm

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
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Re: 1 watt tube amp

Post by martin manning » Sat Nov 05, 2011 12:20 am

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.

9VOLT1967
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Caculation of DC voltage

Post by 9VOLT1967 » Sat Nov 05, 2011 12:41 am

What formula did you use to obtain figure?

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