Tube amp questions

[maxhifi]

Originally Posted by JohnCT

Good catch. Here is an article on it:

https://www.vintageguitar.com/20982/...l-dobro-6107a/

As an audio amp, probably sounds like crap. This also uses an electrodynamic speaker.

John

Yeah but all guitar amps sound like crap if you use them full range. That's too cool, there have got to be very few surviving nearly 90 year old guitar amps! Nice find on the article! I'm surprised only 6W from a pair of 2A3

[JohnCT]

Originally Posted by maxhifi

I'm surprised only 6W from a pair of 2A3

B+ at 220V would limit it's power a bit. Or, they didn't want to drive the outputs too much. It would be many years before distortion would be a *good* thing for guitar amps..

John

[maxhifi]

Originally Posted by JohnCT

B+ at 220V would limit it's power a bit. Or, they didn't want to drive the outputs too much. It would be many years before distortion would be a *good* thing for guitar amps..

John

220V appears to be downstream of the field. I bet the field drops a good 50-100V, so B+ is probably in the 300V region as you'd expect it to be. That votage divider resistor in the power supply is sure old school! I really do wonder how it sounds.. 1930s guitar music is definitely interesting in it's own right.

[JohnCT]

Originally Posted by maxhifi

220V appears to be downstream of the field. I bet the field drops a good 50-100V, so B+ is probably in the 300V region as you'd expect it to be.

You're right - the 220V is indeed after the field coil. The output of the field coil (220V) is drawn closer to the rectifier, so that's where I goofed. Not all that clear on my phone, but on my desktop is much easier to see.

John

[mr_rye89]

This is very interesting to say the least. I'm not about to poo-poo building an amp designed in the 1930s because I use one every day. My homemade stereo amp is loosely based on the Western Electric 91A and makes 8 watts per channel. The biggest issue I see is the interstage/phase splitting transformer, But I'm sure Lundahl makes one though.

I'd also drop the first stage,I don't think it needs that much gain.

[JohnCT]

Originally Posted by mr_rye89

I'd also drop the first stage,I don't think it needs that much gain.

Makes one wonder about how much signal a 1930s guitar pickup would have?

John

[willy3486]

Originally Posted by maxhifi

Yeah but all guitar amps sound like crap if you use them full range. That's too cool, there have got to be very few surviving nearly 90 year old guitar amps! Nice find on the article! I'm surprised only 6W from a pair of 2A3

I rebuilt a amp close to 90 years old that was a 1938 Correct amp that was made in Germany. It was for a music performer that his dad used it in the 40s and 50s to perform "Hawaiian steel Guitar" as he called it. He remembered his dad playing it. I could not find any info on it but was really easy to rebuild without a schematic. I got it going but had to look up Hawaiian steel guitar as I had no idea what it was. When I found some references to it the music was like the music used on the spongebob cartoons. So when he picked it up I played a spongebob soundtrack through it. A very happy man to hear his amp play for the first time in probably 50 years. These older amps have a really neat sound and from the ones I have seen are easier to fix than newer ones.