This tube/OPT combo keeps haunting me since I sold my 6AV5 amp years ago. I still have six or seven NOS Sylvania 6AV5GA left and a pair of 3k/8 25W XSE Edcor irons + a buffet of power transformers, chokes etc. 3k might be a bit low but my midbass horns are set up with 16 ohm drivers so that is not a problem. UL CFB output stage and pentode input with B+ taken from UL tap (E-linear) should result in enough power and damping factor to make the horns happy.
There are two sets of 6B4Gs on ebay at this time. So the legend is true. They appear to have been made for a military contract.
Matched Pair Jan 6B4G 6B4GA Sylvania Tubes USA 1975 $99 95 PR | eBay
Matched Pair Jan 6B4G 6B4GA Sylvania Tubes USA 1975 $99 95 PR | eBay
I had one of these tubes several years ago. It came in the lot of a zillion loose tubes that I got about 10 years ago. Unfortunately it had white getter disease, so I tossed it. It looked just like the ones shown in the Ebay ad.
$100 for a pair of rewired 6AV5's.....
I saw some of these listed on Ebay a few years ago for cheap because they tested bad in the sellers tube tester even though they were NIB.
I have some "6CW5's" that contain a much smaller tube inside. They last about two minutes in a SPP board.
Sorry to grave dig this thread up, but what load resistance do you guys find best for a pair of screen-driven 6av5ga? im building up an amplifier using cascaded differentials like tubelabs driver, and I have 14 6av5ga to dig through. I'm thinking B+of 400 to 550v, 6sl7 into 6sn7 with mosfet followers. I will be using feedback into the first differential pair to tighten things up.
Try 3300 ohms. That's what I was using for my small sweep tube experiments before tearing my lab down. A pair of 6AV5's can do 80 watts easy with 3300 ohms, higher impedance will give less power, 6600 ohms gave me about 45 watts.
Most of my recent experiments used 13GB5's because I got 150 of them cheap. They work about the same as the 6AV5. Oddly enough the driver board I was using runs a 6SL7 and a 6SN7, both connected as LTP's. There is direct coupling between the two tubes and mosfet followers to drive the screens of the sweep tubes. It is the exact same board I developed about 5 years ago in the 6L6GC in AB2 thread. I just changed a few resistor values and power supply voltages. The schematic is buried somewhere in that thread. Look for Chrish's final amp schematic.
http://www.diyaudio.com/forums/tubes-valves/133034-6l6gc-ab2-amp.html?highlight=6l6gc+ab2
I am not using any GNFB, but I use plate to plate feedback from the output tubes to the driver tube plates, as in Pete Millett's Engineer's amp.
http://www.diyaudio.com/forums/tube...p-p-power-amp-design.html?highlight=6l6gc+ab2
Most of my recent experiments used 13GB5's because I got 150 of them cheap. They work about the same as the 6AV5. Oddly enough the driver board I was using runs a 6SL7 and a 6SN7, both connected as LTP's. There is direct coupling between the two tubes and mosfet followers to drive the screens of the sweep tubes. It is the exact same board I developed about 5 years ago in the 6L6GC in AB2 thread. I just changed a few resistor values and power supply voltages. The schematic is buried somewhere in that thread. Look for Chrish's final amp schematic.
http://www.diyaudio.com/forums/tubes-valves/133034-6l6gc-ab2-amp.html?highlight=6l6gc+ab2
I am not using any GNFB, but I use plate to plate feedback from the output tubes to the driver tube plates, as in Pete Millett's Engineer's amp.
http://www.diyaudio.com/forums/tube...p-p-power-amp-design.html?highlight=6l6gc+ab2
I did a project with 6BQ6GAs, which are very much like 6AV5s (just a bit more Ip at Vgk= 0) Run them into 4K4 (P-2-P) and 3K3 (P-2-P) should also be good: a bit more power, and a bit more distortion, but it should still be OK. This type doesn't make much distortion, and what it does make is mainly h3 so all you need is enough gNFB to take the "edge" off.
6SL7 into 6SN7 is a good idea, but watch out for that CMiller or you might be losing your highs.
I don't think you need a VPP in excess of 350V here.
re-reading this thread I noted the interest in 12DQ6 / 6DQ6 etc by some above.
In OZ these were made by the Sydney AWV Tube Factory.
They (the tube factory) put out this application note for use in Class AB1 Audio
http://www.retrovox.com.au/6dq6aamp.pdf
Cheers,
Ian
In OZ these were made by the Sydney AWV Tube Factory.
They (the tube factory) put out this application note for use in Class AB1 Audio
http://www.retrovox.com.au/6dq6aamp.pdf
Cheers,
Ian
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