AA4 Guitar Amp

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AA4 Guitar Amp

Postby Sal Brisindi » Sun Jun 14, 2009 7:55 am

Last week I built a 4 tube guitar amp for my son for the heck if it. It is about 2-3 watts. The tubes are series filament string using 2-12AT6, 1-50C5 and one 50DC4. I fellow radio enthusiast designed it around the radio tubes.

He originally used a 35W4 in place of a 50DC4 with a 75 ohm filament dropping resistor. I put in a 50DC4 and no resistor. Here it is in the raw, I was to lazy to paint the chassis before I built it but my likes it this way.

The 1/4" jacks are high input, low input and the controls are volume and tone.

Sal

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Postby Geek » Sun Jun 14, 2009 1:11 pm

Cute!

I love little guitar amps like that.

"Only" 2-3 watts will be quite enough to make you regret building it sometimes though (lol)

Cheers!
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Postby TerrySmith » Sun Jun 14, 2009 1:53 pm

Very nice Sal! I'm glad you used an isolation transformer!

What brand of chassis is that? It looks better made than the usual Hammond unit.
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Postby Sal Brisindi » Mon Jun 15, 2009 5:57 am

Thanks,
I bought 4 of these chassis on ebay about 2 years ago on the cheap, I wish I bought more... Very well made.

Sal
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Postby dhuebert » Mon Jun 15, 2009 7:34 am

Good job! I have often thought about building a series string guitar amp. Could you post the schematic?

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Postby nyazzip » Mon Jun 15, 2009 9:54 pm

I have often thought about building a series string guitar amp.


what does "series string" mean? and what are the ramifications? i have examined a couple of antique and not-so-antique amps that i have, and the filaments appear to be in series. my initial and ignorant hunch would be: series equals quieter amp?
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Postby Sal Brisindi » Tue Jun 16, 2009 7:19 am

dhuebert wrote:Good job! I have often thought about building a series string guitar amp. Could you post the schematic?

Don


Thanks Don,
Here is the schematic, I cannot take credit for it, Joe Bento is the one who designed this little amp.

Like I mentioned, I used a 50DC4 in place of the 35W4 and removed the 75 ohm resistor in series with the filaments.

Regards,
Sal

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Postby Sal Brisindi » Tue Jun 16, 2009 7:56 am

nyazzip wrote:
I have often thought about building a series string guitar amp.


what does "series string" mean? and what are the ramifications? i have examined a couple of antique and not-so-antique amps that i have, and the filaments appear to be in series. my initial and ignorant hunch would be: series equals quieter amp?


Many many years ago when tubes were in the rage, Radio manufacturers wanted to build radios at a lower price for consumers. The most expensive part of the radio was the power transformer. To eliminate the power transformer, tubes were designed with to be wired in series so that all the tubes filament voltage would add up to 121 volts.

The typical AA5 (All American 5) tube radio had 5 tubes, 12BE6, 12BA6, 12AV6, 35W4 and 50C5 for miniature 7 pin tubes or octal tubes using 12SA7, 12SK7, 12SQ7, 35Z5 and 50L6.

These tubes mentioned had 150ma filaments. Later, to conserve energy, tubes with 100ma filaments were used.

Now in the 30's radio manufacturers used tubes that were available at that time that didn't add up to 120 volts so they had a 3rd resistance wire in the line cord to drop the filament voltage... now a days we call that a curtain burner.

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