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Instruments and Amps Everything that makes music, Especially including instrument amps.

12" feild coil speaker "WOW"
12" feild coil speaker "WOW"
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Old 22nd June 2012, 10:46 PM   #11
Printer2 is offline Printer2  Canada
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Originally Posted by tubelab.com View Post
I started out in this hobby making guitar amps out of old radios and TV sets in the 1960's. I did build some guitar amps using field coil speakers. A field coil speaker works very well on a tube guitar amp when used well within its power ratings (which were pretty low) and as some have found sound pretty good. I even used some 15 inchers from old organs for bass guitar.

I found out that a field coil speaker and a solid state amp doesn't work too well if the amp has good low frequency response. These old speakers with phenolic spiders are very easy to bottom out. I made a SS amp in high school using the Li'L Tiger (SWPTC) power amp design. The preamp was copied from a popular SS guitar amp of the day (Kustom or Acoustic probably) the amp destroyed two 15 inch field coil speakers due to bottoming. I finally spent the money on a real Utah guitar speaker. The amp sounded slightly less "alive" but lived on for several years without incident.

Back then I used SS rectified and filtered wall outlet to power the coil with a big green power resistor in series. That was over 40 years ago so I can't remember the value. Today we know that an isolation transformer would be needed to avoid frying guitar players.
Still have my home built Li'L Tiger from the mid 70's. When I have time I am going to make a small guitar amp out of it.
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Old 23rd June 2012, 03:03 AM   #12
Tubelab_com is offline Tubelab_com  United States
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I made probably 100 total of all the Tigers from the LiL up to the Universal through out the 70's. There was a group of us who worked in the Motorola plant that made them for everything from guitar amps to car stereo amps. Never made a TigerSaurus though. Sometime last year I found a box full of the old boards and parts. I gave some of it away on the solid state forum and tossed the rest.

I put the Li'L Tiger in a combo amp with a 15 inch speaker back in 1969 or 1970. I played it for a few years and gave it to a friend when I made something better. After I put the Utah speaker in it never broke. I think it had about 15 watts.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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