I'm glad a few of us now have working models. Mine has been in my system now for several months and I'm hugely satisfied. It has been trouble free and is easily the best amp I've built in 30 years. It drives a pair of infinite baffle columns of around 21 litres with Mark Audio Alpair 10s (Mk.1).
Here are the schematics - three stages with the first stage (line) in a separate chassis with its own power supply. Every tube is in filament bias and has a DC filament supply with choke input and a Rod Coleman regulator. So three outboard boxes, each containing a pair of supplies.
Here are the schematics - three stages with the first stage (line) in a separate chassis with its own power supply. Every tube is in filament bias and has a DC filament supply with choke input and a Rod Coleman regulator. So three outboard boxes, each containing a pair of supplies.
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Here's my crazy contraption. Looks a fright, works a delight! Actually very quiet on my ~95dB/W system. The low gain helps.
Not shown is the filament supply. One 6.3V winding goes to the rectifier tube, the other goes to the 6SN7 and the regulator for the 4P1L filaments. The 4P1L cathode shown on the schematic is the middle point of the filament. 1R is just there to measure current.
Bias on the 6SN7 is set with 2 red LEDs in series, or about 3.4V Bias on the 4P1L is 2x9V in batteries in series with 2X AA (1.5V) batteries.
Not shown is the filament supply. One 6.3V winding goes to the rectifier tube, the other goes to the 6SN7 and the regulator for the 4P1L filaments. The 4P1L cathode shown on the schematic is the middle point of the filament. 1R is just there to measure current.
Bias on the 6SN7 is set with 2 red LEDs in series, or about 3.4V Bias on the 4P1L is 2x9V in batteries in series with 2X AA (1.5V) batteries.
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first test 4pl1
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PC900 4pl1- really good mixAn externally hosted image should be here but it was not working when we last tested it.
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driver is a PC900 used as RF amplifier tvNow that's a stacked amp! I like it.
What's the input tube?
very good tone!!
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I'm just making a back-up 4P1L PSE amp for the one I use every day. I use a modular system with top plates 4mm thick alu, 275mm long. Widths are 50mm, 70mm or 100mm. Here's my output stage on a 50mm strip. It has four loctal sockets wired up to the filament bias resistors which are parallel 2x 25ohms, 25W on top and underneath, series 2x 1.2ohms 7W, Welwyn W22. So 12.5 plus 2.4 = 13.9 ohms for bias. These get hot so are well within ratings, in fact passing about half spec. (50W rating for 25W actual) They should have 19v bias on them. Current is about 1.3A. Plate voltage should be about 260v, giving 240v across the two tubes for about 30mA each. The two 1.2ohm resistors under the chassis can be fine tuned in size to alter the bias.
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Here's the present amp. Audio Note Trans-152 OPTs. On the extreme right are two glow tubes giving 180v on the input stage of 4P1L into Hammond 126C. This is all fed by my 26 preamp, as shown in the schematics a few posts back. For the new amp I'll be using O-netics OPTs. The front of the amp is made up of standard 19" subrack parts - two horizontal rails, top and bottom, with an anodised sheet of aluminium in between. All the top plates screw into the horizontal rails with the usual 2.5mm screws. I can change any of them as needed, and I have a LOT of spare ones with various project bits on!
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#26+4pl1
behind hedlund horn
Lowther DX4 speakers
power
sounds nice and very detailed
having fun
do it yourself
An externally hosted image should be here but it was not working when we last tested it.
behind hedlund horn
An externally hosted image should be here but it was not working when we last tested it.
Lowther DX4 speakers
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
power
An externally hosted image should be here but it was not working when we last tested it.
sounds nice and very detailed
having fun
do it yourself
know little orthodoxy but,,, funnyA masterpiece!
thanks!
more pict.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
