Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Other Topics => Topic started by: Cups on September 10, 2012, 01:40:02 pm
-
I took an old Spartan model #5348, from an electronics recycling bin. I'd like to reconstruct for guitar use but would like to keep all octal (I've never used octal dual triodes)
Naturally I'd like to get a schematic because there are a few things different that I'm not used to seeing.
Everybody seems to charge for the schems. Why is amp schem (and effect schem for that matter) so different as far as sharing freely?
If I have to I'll just trace it (I like doing this anyway) but there are a few things that I'm not familiar with. For example there are these square rectangular things protruding that I thought might be chokes but they have four leads coming out of it (three lead cap can?)
Thanks for listening to my rant. I bet there are a few tube radio cats around here.
-
> Spartan model #5348
Check that model number. I'm not finding anything quite like that.
Date? Tube-count? First tube? Power transformer or no?
> square rectangular things protruding that I thought might be chokes but they have four leads coming out of it
Two or three of them, with adjustment holes, yup. That's radio. IF cans.
-
It didn't show up for me right away either, because it's similar with a bunch of other models. Has a power transformer and 5 tubes. SE with a 6f6g and 5u4 rectifier. First tube is a 6sa7
-
Here's a link http://www.radiomuseum.org/r/spartoncan_5348.html (http://www.radiomuseum.org/r/spartoncan_5348.html)
25$ to join the website !!
-
Is a basic AM radio.
Radio waves are converted to IF, amplified, detected to audio.
Audio is amplified in the usual way. Volume control, hi-gain triode, power tube, speaker.
Compare with Champ: Champ has _two_ hi-gain stages and a power tube.
This radio's power tube is 6F6, the pre-improvements 6V6; 6SQ7 is like a half a pre-improvement 12AX7 (plus diodes).
"All" radios 1930-1970 were about this way. Main distinction is transformer or transformerless. Transformerless is bad for guitarists.
This radio has transformer and even has an external audio input.
You can try your guitar right into the Phono jack.
However it probably takes a quarter or a half a volt of signal to get the full 3-4 Watts of goodness, say 400mV. E-Guitar makes 20mV-200mV.
So you really need another stage. (Champ knew what it was doing.)
The simplest path is a clean booster-pedal in front.
If you can live without radio, you can triode-strap the 6SK7 IF tube as an audio stage.
Unusually, this radio has NFB around the audio. A little NFB is good, but too much may be bad for raw tube sound. Try increasing the value of R4 to 1.5K, 3K, or more.