I have dabbling with fixed bias output stages in an attempt to get more power output for less sensitive speakers. The EICO HF60 caught my attention, since it has a 6SN7 phase inverter, as opposed to the high gain Mullard 5-20. Here is a schematic of the circuit:
This article (http://tronola.com/html/hf-60_with_6550s.html) discusses possible improvements and modifying ideas. I used some of them in this build. The power supply is my own design (regular bridge/cap/inductor/cap) PI filter.
Mars 100 by Karel Mars, on Flickr
After a bit of to and fro', the sound is settling beautifully. The EF37's were chosen in stead of EF86, since I recently acquired a whole hoard of EF37's that begged to be used. KT66's were handy, since the 6550's are still on order. A very appealing sound. If you like music loud, this may be the way to go.
This article (http://tronola.com/html/hf-60_with_6550s.html) discusses possible improvements and modifying ideas. I used some of them in this build. The power supply is my own design (regular bridge/cap/inductor/cap) PI filter.
Mars 100 by Karel Mars, on FlickrAfter a bit of to and fro', the sound is settling beautifully. The EF37's were chosen in stead of EF86, since I recently acquired a whole hoard of EF37's that begged to be used. KT66's were handy, since the 6550's are still on order. A very appealing sound. If you like music loud, this may be the way to go.
