AA4 Guitar Amp

[dynaco]

Hi all, this is my first post here.

Last June I built a simple 4 tube guitar amp for my son for the heck if it. It is rated about 2 watts output. The filaments are wired in series using inexpensive tubes from tube radios. They are 2-12AT6, 1-50C5 and one 50DC4. A 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 son likes it this way. I will be build another one to be installed in a home brew cabinet with speaker.

The 1/4" jacks are high input, low input and the controls are volume and tone. Below is a photo of the amp and schematic. I used a real small audio transformer and the larger transformer is a isolation transformer.

Regards,
Sal

[JHow]

Cool. The first piece of tube equipment I ever encountered was 1941 Philco "Five Tube" transformerless radio. I admit a soft spot in my heart for circuit with series filaments.

[paggerman]

That is a thing of beauty. I love the diagram - it's so simple. Your chassis fabrication looks brilliant. I am just starting on my first build and understing circuit diagrams can be confusing for a noob. But your diagram clearly shows the stages and I can spot teh coupling caps between them. I can do this because of what I have learnt on these pages, but I must commend your friend on his work in designing this. Of course, I have no idea what it would sound like, but I'm sure it's a 'proud' sound!

[Groover]

Where did you source your mains isolation transformer? and can you provide a part #?
I have an old tube intercom I want to modify for guitar amp use, and I need an inexpensive mains iso transformer to make it safe.

[dynaco]

Where did you source your mains isolation transformer? and can you provide a part #?
I have an old tube intercom I want to modify for guitar amp use, and I need an inexpensive mains iso transformer to make it safe.

You can get one from Allied at Triad Magnetics - N-68X - Transformers - Power Products - Allied Electronics

Regards,
Sal

[RWood]

Nice circuit and thanks for the link to the isolation transformer.

Is that a typo on the value of the reservoir cap: 220uF? On the spec sheet for both 35W4 and 50DC4 I am seeing a maximum value of 40uF.


RWood

[dynaco]

Nice circuit and thanks for the link to the isolation transformer.

Is that a typo on the value of the reservoir cap: 220uF? On the spec sheet for both 35W4 and 50DC4 I am seeing a maximum value of 40uF.


RWood

Yeah, I know the spec sheet says 40uf, I didn't have a problem with the way it was built but you can probably swap the 2 capacitors if you want.

Sal

[J M Fahey]

Real nice.
I bet it must be a killer amp to play "da blooz"

[dynaco]

One day I'll post a youtube video with my son playing through the amp.