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A Lockin GU50 Push Pull Amplifier.
86.104.12.192 |
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Posted on August 11, 2020 at 06:11:04 | |
Posts: 32
Location: Guernsey Joined: January 6, 2008 |
This project started with A mate listened to my Kevin inspired Lundahl 300B XLS push pull amp a few years ago now. The usual "Wow get me some of that" how much, really! OK can you build me a cheaper version then. So I started with some used Standard Lundahl transformers and chassis and some GU50s and 6E6P-E of which I had acquired a lifetime supply of thinking that they would be a good investment as well as some great sounding valves/tubes for a future project. Lost interest myself and side-lined the project until the Covid19 lockin came along. This gave me time and renewed interest in this project. I am so glad I did. This amplifier is again Kevin inspired from his "Input Stage For A Two Stage PP Amplifier" Circa 2012. A Push Pull LL1682PP GU50 Triode @ 400v/95ma LL1671PP 6E6P-E @ 200v/22ma LL1540 input/phase splitter. Power is A Custom Toroidal, DSE12-12A bridge, with a 6CM3 soft start damper diode, Van der Veen EChokes & Motor Run Caps. The 6E6P Driver/voltage gain stage Kevin's Cascade Constant Current Sources & 13GF7 compactron series-pass one tube regulator on each channel. The GU50s have fixed bias supplied by the dedicated Van der Veen bias module. AC heaters with common mode filtration. OK so my hearing is getting a bit old now and so are the 300BXLS. I built this and my reference amp so I am a bit biased I guess, but I will try to avoid "Proud Papa syndrome". So with 30 hours on the above amp it to my ears anyway, bests my reference amp by a large margin, which I thought was already pretty good. This is a Push Pull LL1620PPAM 300BXLS @ 500v/65ma LL1671PPAM 6EM7 Drivers LL1637 Choke loaded 6SN7 LL1690 phase splitter. Separate power supply with Hybrid bridge and LL1638 chokes in common mode. As of Kevin's inspiration circa 2010 + CCS on the cathodes of the differential pairs & 6EM7 series pass regulators on Driver & Voltage stages. My test Speakers are Tannoy Kensington's and an Oppo BDP-105 source. Both amps have roughly 30 watts output but the GU50 amp sounds more powerful and with a much more detailed low frequency range. This manages to sound taut & tuneful but still natural & musical. The imaging is amazing and previously un-heard details just keep jumping out of familiar recordings. Recordings that used to sound confused are now more focused & beliveable. The background appears blacker with the ambience disappearing into a deeper sound stage. Instruments stand out with more tonal colour and are easier to define within the image, with more space around and better Micro & Macro dynamics. The high frequencies and particularly the soprano voice sound very smooth and detailed which can often offend my ears. Solo Piano is beautifully re-created you are there, with the right recordings of course. I also auditioned this GU50 PP amp against my well-regarded PSE 300b Monobloc amplifiers which sounded quite amorphous in comparison but typical of most single ended amplifiers, nice in the broard midrange but soft elsewhere. Guess which will be staying in my system. For a relatively budget design I am so impressed. In my opinion you will never know how good the standard PP Lundahl's sound until you have tried them with the ultra-accurate & quiet balancing of the push pull output stage by the Van der Veen Bias Module. And the shorter signal path 6E6P/6j49p/6j11p/D3a etc Drivers. With also the ultra-quiet Electronic Chokes doing great things with low ripple and rejection of intermodulation products in the time domain contributing to the inky black low noise background. I M H O If you want to take your Push Pull amps to the next level the above are the way to go rather than that expensive quad of output tubes. I have read that output valves/tubes make least difference to the sound of an amplifier on a cost basis that is. I am sure however that some will disagree. For $8.00/pair Triode conected GU50s sound amazing and are well worth experimenting with in this "Roll your own" Valves/Tubes push pull circuit, (thanks again to Kevin for shareing it with us all) but equally other power Valve/Tubes will benefit similarly. I guess that I will now have to build the 300BXLS with the Lundahl AM iron to see if this sound can be improved on further. It occurs to me also that a driver stage would be very interesting with the 6e6p and another fixed bias module, (as has done wonders for the output stage) would need an input/phasespliter transformer that could tolerate DC however, now there's a thought. Enjoy The Music And Please Keep Shareing Stay Well |
RE: auto bias details, posted on September 3, 2020 at 06:45:57 | |
Posts: 26
Location: Quebec, Canada Joined: December 28, 2005 |
Yes, correct. You need separate connections for each output tubes. |