The 6HJ5's or 6GY5's should handle a 4.4K primary. The 6GV5 would need the 6.6K primary (and the 6HJ5 or 6GY5 should be fine there too for more power). Since the 4.4K OT is lower power rated, the 6GY5 would seem the best fit there.
(estimates based on cathode max DC current ratings: 6HJ5 280 mA, 6GY5 230 mA, 6GV5/6JN6 175 mA; The 6HJ5 is plate dissipation rated 24 Watts and the other two rated 18W, 17.5W)
(estimates based on cathode max DC current ratings: 6HJ5 280 mA, 6GY5 230 mA, 6GV5/6JN6 175 mA; The 6HJ5 is plate dissipation rated 24 Watts and the other two rated 18W, 17.5W)
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So would I !!!!! My 300Beast died a few years ago. One of the power supply caps shorted and fried the rectifiers. Then I stole the choke out of the power supply. The rest is on a shelf collecting dust.
I planned to rebuild it someday but it hasn't happened yet. The driver is still a wild card since I keep making new ones that work better than the previous one. In truth any of the drivers that I have made in the last few years would probably handle 300B's just fine. The driver circuit that I designed for the 300Beast was the best that I had seen....about 12 years ago. I have done better and simpler designs since I discovered mosfet followers about 8 years ago.
Still, some people don't want sand in the signal path, even if it does work better than a cathode follower, so I am still working on drivers of several flavors. If I had to do a push pull 300B amp today I would use the driver circuit I designed for the 6L6GC in AB2 thread. It is a good choice for a medium drive level tube like a 300B. Pete's new stand alone driver board is another good choice. I have even wired some 307A's into Pete's big red board, but I couldn't het the hum out since all of the heaters / filaments are tied together. I also have a few new designs, and I can steal the board out of the 300Beast.
I want to start building push pull amps with all sorts of tubes, big ones, little ones, common ones, and some that no one has heard of. So, how do I decide which driver board works best for a given output tube, and how do I drive the output tube, G1 or G2, or BOTH at the same time?
I build the mother of all breadboards, thats how. It is about half finished. It is a research project only, not for use as a finished amp. It contains a power supply for ANY driver board known to man, and maybe some alien creations too. All of my current drivers will fit in, and so will Pete's new one. It can fit up to 4 output tubes of 813 size, or 8 smaller ones (like sweep tubes) or lots of little tubes. The heater supply goes up to 50 volts and 10 amps, and the plate supply goes to 1000 volts at 1/2 amp, or more current at less volts. The mosfet buffer boards can source several hundred volts of drive at an amp of current and the bias can go from -200 volts to +300 volts.
It will probably take me a year to sort through all the combinations of tubes, drivers, and operating conditions that I want to try, but the 300B and 307A are on my short list. Once the breadboard is operational I will start a new thread. It will be a few weeks though, too many things to do, not enough time.
Just have to make a 300Beast now, can't wait? I thought I had a rather novel idea back when I made the Beast. I made an LTP out of an SRPP, remember SRPP's were rather in vogue in 1999. When I posted it on my web site the email ranged from "are you stupid, you can't do that" to "how do you do that". I was poking around this forum the other day and I found a post about a KT88 amp, so I followed the links, and there it was. An LTP SRPP circuit. It is very similar to the beast. It carries a 2000 date. I never posted my schematic, so at least one other person came up with the same idea.
See post #3 in this thread, follow the link and look at the amplifier schematic. About the only difference is the choice of output tube, my B+ is 400 volts and the plate resistors of my input tubes go to a 300 volt supply. My input tube is a 5751 and my drivers are 6FQ7's.
http://www.diyaudio.com/forums/tubes-valves/207372-great-sounding-kt88-amp.html
The 6L6GC design is here
http://www.diyaudio.com/forums/tubes-valves/133034-6l6gc-ab2-amp.html?highlight=6L6GC+AB2
I just orderd the board and a majority of the components so I can start stuffing. This is going to be a build for a friend (wedding gift)! My plan is to build it as an integrated amp (seperate volume pots and selector switch) so I also ordered 100K log PEC pots as well.
My question is should the 100K log pots replace the 100K input resistor (R64) or should it be wired in series between W28 and R61 (keeping R64 as is).
http://www.pmillett.com/images/DCPP.h1.gif
I know, total newb question so TIA!
My question is should the 100K log pots replace the 100K input resistor (R64) or should it be wired in series between W28 and R61 (keeping R64 as is).
http://www.pmillett.com/images/DCPP.h1.gif
I know, total newb question so TIA!
R64 remains. You should hook up the pot in parallel with(infront of) it, that will give you an input impedance of 50k, which should be easily drivable. R64 remains just in case your pot opens up. Its kinda the max size you can get away with connecting pin 1 of the input tube to ground. You can go lower. In your case your adding another 100k. If you had a really powerful source you could go really low, like 1k 
I thought about it just because I have quite a few motor run caps still sitting around from another build but the size of the chassis with all the capacitors and four transformers is just too large. I am still debating of whether I want to use two of the 15lb ebay transformers or if I can make a pair of tektronix transformers I have from a 585a scope work. Either way it will be a back breaker.Im waiting for George's evil twin to show up with and all motor run cap version thats doing 600v on the red board alone
In order to make my amp smaller and lighter I decided to use one 15 pounder for the main power transformer and an Antek toroid for the boost transformer. It's all still mounted to a piece of plywood but works quite well.
My amp currently has a 470uf 450volt electrolytic across each power supply output. I used them because I had them. I got some 1000 volt film caps to try, but I am currently 1200 miles away from the amp so it will have to wait.
My amp currently has a 470uf 450volt electrolytic across each power supply output. I used them because I had them. I got some 1000 volt film caps to try, but I am currently 1200 miles away from the amp so it will have to wait.
Good evening!
I´ve started reading this thread after listening to my corner bass horns powered by a wide range of amplifiers, from 1W SETs to commercial 300W solid state amps. Awkward as it may be, the transistors won this time... Probably not by being transistors but by offering more power and lower output impedance, something that must be achievable with tubes as well...?
Push-pull connected pentodes with Schade feedback seems like an logical alternative to SS amps in this application.
The tubes and transformers that I have in my junk box are either too small or too big (6AQ5 and 15W Edcor transformers vs PL519/40KG6 and 120W Hammond transformers) but since the horns seemed perfectly happy with the 2x300W amp I´ll give the big stuff a chance...
The OPTs are 1,9k p-p and B+ will be 400-440V. Anything I should know before I start sacrificing expensive components to the gods of fire and smoke?
I´ve started reading this thread after listening to my corner bass horns powered by a wide range of amplifiers, from 1W SETs to commercial 300W solid state amps. Awkward as it may be, the transistors won this time... Probably not by being transistors but by offering more power and lower output impedance, something that must be achievable with tubes as well...?
Push-pull connected pentodes with Schade feedback seems like an logical alternative to SS amps in this application.
The tubes and transformers that I have in my junk box are either too small or too big (6AQ5 and 15W Edcor transformers vs PL519/40KG6 and 120W Hammond transformers) but since the horns seemed perfectly happy with the 2x300W amp I´ll give the big stuff a chance...
The OPTs are 1,9k p-p and B+ will be 400-440V. Anything I should know before I start sacrificing expensive components to the gods of fire and smoke?
I was using my red board with a set of EZ-10 horns. The red board can still sound nice with the average power under 1 watt. My horns really liked this amp. They sound nice with a SET on simple music, but if you want to ROCK build an amp like this one.
I haven't experimented with the 40KG6 since I only have 1 or 2 of them. I don't know if a pair of them would be happy with a 1.9K ohm load, but they might be OK at 400 to 440 volts. Most of my experiments were at 600+ volts.
My only sacrifices were due to dumb blonde moments on my part, like running 600 volts through a 450 volt cap and 650 volts through a 250 volt cap! No other parts met their maker.
I currently use my 6BM8 SE amp (just short of 1W per channel) to drive the horns AND the front speakers in // with enough SPL for my listening habits, what´s lacking is bass control. Schade-style feedback seems to do the trickaccording to what I´ve read here and on other forums.
Bruce Rosenblitz has designed an amp ("150W super compact amplifier") that uses a pair of EL509 (6KG6) and a Hammond 1650T OPT fed with 700 volts.
Not sure though if the OPT is wired for 1,9k in that amp but I think so.
I´m not comfortable with 700V on the top caps, neither do I need 150W so I´m planning to stack a 340V PSU on top of a 80V heater PSU.
Thanks to my infinite lack of impulse control the chassis for this project (monoblocks) are almost done already. While the steampunk style with exotic woods and polished copper is nice for SETs I decided do go for a more industrial look this time, resulting in a pair of big gray aluminium boxes that looks like some Soviet military equipment from the early Cold War years. Not in everyones taste perhaps but I like it, will post pictures later on.
Bruce Rosenblitz has designed an amp ("150W super compact amplifier") that uses a pair of EL509 (6KG6) and a Hammond 1650T OPT fed with 700 volts.
Not sure though if the OPT is wired for 1,9k in that amp but I think so.
I´m not comfortable with 700V on the top caps, neither do I need 150W so I´m planning to stack a 340V PSU on top of a 80V heater PSU.
Thanks to my infinite lack of impulse control the chassis for this project (monoblocks) are almost done already. While the steampunk style with exotic woods and polished copper is nice for SETs I decided do go for a more industrial look this time, resulting in a pair of big gray aluminium boxes that looks like some Soviet military equipment from the early Cold War years. Not in everyones taste perhaps but I like it, will post pictures later on.
No, my amp is pretty much the same as Pete Milletts Red Board amp. The actual amplifier topology is similar (but with different tubes and component values) but the power supplies are a bit different. I´ve hardwired everything on aluminum sheets with some small pieces of veroboard for the solid state parts.
I built a point-to-point version of the DCPP, and fired it up in July 2011. It had multiple faults, the worst of which was a huge AC signal getting to the output with no signal in. I put it aside for vacations, and lo and behold a year has passed.
I returned to the scene of the crime a week ago, and had to relearn everything about the amp to troubleshoot it. One mysterious clue was that the bad behaviour was the same in both channels. I tracked the problem to the output tubes (i.e., it went away if I removed the tubes and ran a resistor load across the gaping hole created by removal).
Anyhow, finally a bolt of inspiration came to me - I had managed to cross the feedback wiring to create positive feedback from plate of one output tube to grid of the other (within the same channel). Fubared both channels in identical fashion. By switching the wires to the plate cap of the 6GV5s in each channel, suddenly my Schade was negative feedback and there was no AC on the outputs. I feel like a dope to have lost a year to this screw up.
After balancing the various pots, I hooked up speakers in place of the dummy load. Powered up, but heard nothing from the speakers. At that moment I was sure I had blown up my output transformers, having abused the Hell out of them with positive feedback a few times (before removing them and using power transformers as outputs to troubleshoot). My next test was to try a little music as an input, to see if maybe the speakers were just being really quiet. Lo and behold, out came music.
The sound was incredibly punchy and clean. This through "basement speakers" bought in 1974 for small money. I immediately dialed up Marcus Miller, Jaco Pastorius and Victor Wooten, and was rewarded.
My amp uses 3CB6s and 6GV5s. Power supply is a conventional 340-0-340 to 6CE3s for rectification, running through to cap-choke-cap filter that uses motor run caps. Screen supply is straight out of Pete Millett's schematic. C- power comes from a separate transformer (I forget the spec on it). The feedback resistor is replaced by a small triode (6SL7) wired as a resistor (this is similar to a Schade design I saw years ago called a "super triode" or something to that effect -- I have used this in previous designs, single ended and Class A push pull).
My other departure from convention was to use non-inductive wirewounds rather than carbon comp resistors as the grid stoppers (lots of them in this amp). My initial impression is that the amp has an unusual level of clarity.
I returned to the scene of the crime a week ago, and had to relearn everything about the amp to troubleshoot it. One mysterious clue was that the bad behaviour was the same in both channels. I tracked the problem to the output tubes (i.e., it went away if I removed the tubes and ran a resistor load across the gaping hole created by removal).
Anyhow, finally a bolt of inspiration came to me - I had managed to cross the feedback wiring to create positive feedback from plate of one output tube to grid of the other (within the same channel). Fubared both channels in identical fashion. By switching the wires to the plate cap of the 6GV5s in each channel, suddenly my Schade was negative feedback and there was no AC on the outputs. I feel like a dope to have lost a year to this screw up.
After balancing the various pots, I hooked up speakers in place of the dummy load. Powered up, but heard nothing from the speakers. At that moment I was sure I had blown up my output transformers, having abused the Hell out of them with positive feedback a few times (before removing them and using power transformers as outputs to troubleshoot). My next test was to try a little music as an input, to see if maybe the speakers were just being really quiet. Lo and behold, out came music.
The sound was incredibly punchy and clean. This through "basement speakers" bought in 1974 for small money. I immediately dialed up Marcus Miller, Jaco Pastorius and Victor Wooten, and was rewarded.
My amp uses 3CB6s and 6GV5s. Power supply is a conventional 340-0-340 to 6CE3s for rectification, running through to cap-choke-cap filter that uses motor run caps. Screen supply is straight out of Pete Millett's schematic. C- power comes from a separate transformer (I forget the spec on it). The feedback resistor is replaced by a small triode (6SL7) wired as a resistor (this is similar to a Schade design I saw years ago called a "super triode" or something to that effect -- I have used this in previous designs, single ended and Class A push pull).
My other departure from convention was to use non-inductive wirewounds rather than carbon comp resistors as the grid stoppers (lots of them in this amp). My initial impression is that the amp has an unusual level of clarity.
Can we see a schematic of how you have this wired?
"The feedback resistor is replaced by a small triode (6SL7) wired as a resistor (this is similar to a Schade design I saw years ago called a "super triode" or something to that effect -- I have used this in previous designs, single ended and Class A push pull)."
"The feedback resistor is replaced by a small triode (6SL7) wired as a resistor (this is similar to a Schade design I saw years ago called a "super triode" or something to that effect -- I have used this in previous designs, single ended and Class A push pull)."
A triode makes a great resistor (for AC) by simply inserting a resistor at the cathode (rk), for the bias, and connect the grid to the opposite end of that bias resistor. Dynamic resistance equals the triode's rp plus (mu + 1) * rk for this unbypassed triode. The plate connects to the plate of the output tube.
I needed a lot of resistance here, but wanted to use a simple triode. 6SL7 has a mu of 70 and an rp of 44000 (by the book - I am not sure I fully agree). 44000 plus (70+1)*2200 (2200 being my bias resistor) yields 200,200 ohms. Somewhere there is an old Tubecad article that talks about this, I think in Broskie's excellent article on plate to grid feedback (or partial feedback). See The Tube CAD Journal, A Virtual Resistor
There is every chance that this upsets Pete's distortion cancellation, so I am prepared to abandon it. But, it sounds good at first blush. (I like my amps to have lots of tubes - 12 in this one).
I will try to post a schematic excerpt to show this, but I have never posted anything but words so have to figure it out.
I needed a lot of resistance here, but wanted to use a simple triode. 6SL7 has a mu of 70 and an rp of 44000 (by the book - I am not sure I fully agree). 44000 plus (70+1)*2200 (2200 being my bias resistor) yields 200,200 ohms. Somewhere there is an old Tubecad article that talks about this, I think in Broskie's excellent article on plate to grid feedback (or partial feedback). See The Tube CAD Journal, A Virtual Resistor
There is every chance that this upsets Pete's distortion cancellation, so I am prepared to abandon it. But, it sounds good at first blush. (I like my amps to have lots of tubes - 12 in this one).
I will try to post a schematic excerpt to show this, but I have never posted anything but words so have to figure it out.