George and I and others are getting well over that with the 6HJ5 (no top cap). George is putting over 600V on the plates of those without an issue. I'm doing more like 475V. The spec says it take take even more. 50W is easily attainable with this board and the right tube/B+ combo. I was seeing 80W.
Many people fear the cap, and would prefer not to use a tube with a plate cap. That limits your choices to two 24 watt tubes (that I know of) and several 18 watt tubes. Those are good for 75 to 125 WPC. All of the big sweep tubes have plate caps. Pete wanted me to build a higher powered version of his amp that would appeal to forum readers and potential builders. I asked what people wanted (a few pages ago) and the most common answer was a low cost 100WPC amp. I really don't think anyone can find a 100WPC amp that sounds as good as this one and costs next to nothing (using the Ebay power transformers). I will find a recipie for an Antek powered version soon, and probably build a bigger one if I can score some cheap OPTs.
I am not aware of anything that is on the current list that is drop in compatible.
The 6GV5 (plate cap) tube that Pete specifies in the very first post here was on the Dollar Menu at ESRC but I think we bought them all. It is however still $1 at vacuumtubes.net. It probably won't be for long now that I said something. 50 WPC is not a problem for the 6GV5. I think I stopped at 80 WPC with that tube. The limitation is not plate voltage with sweep tubes, it is plate dissipation.
I find the point where the tube just starts to show plate color under continuous sine wave testing. I set the amp up for maximum power at that level. The average power seen in music will allow for cool operation.
The board that I have been listening to makes 125 WPC on a sine wave using 6HJ5's at 600 volts and a 3300 ohm load. The plates just start to show pale redness in a dark room under those conditions. Running the amp with music hitting clipping on peaks does not run the tubes hard at all since the average power seen is probably in the 10 to 20 watt range. It is also rock concert loud with 95 db speakers.
The 6HJ5 is slightly more powerful than the 6GV5 but is NOT a drop in for the board. Modifications are needed.
Some dollar menu tubes with caps that look to be pin compatible or very close at least (similar to 6JN6, 6GV5 and 6JM6) are 21JZ6, 21GY5, 16GY5, 21KA6, 16KA6.
Obviously the odd filament voltage will have to be dealt with.
They all have the same size plate as the 6HJ5, but are only rated at 18 Watt. Their plate size is considerably bigger than the 6JN6 or 6GV5.
Obviously the odd filament voltage will have to be dealt with.
They all have the same size plate as the 6HJ5, but are only rated at 18 Watt. Their plate size is considerably bigger than the 6JN6 or 6GV5.
Funny you should mention the source for the 6GV5s, I sent August a PM about vacuumtubes.net having them for a dollar to keep them from disappearing...now look what you have done. They seem to be a very good value for use in this amp. I did purchase quite a few of them earlier this week after I found them along with a hand full of 12BQ6GAs.
no tube rectification but regulated B+ supply http://www.linearaudio.nl/t-reg-1.htm. Every channel has a dedicated B+, 150V and bias supply
I will use Fisher OPT's from an old receiver
The missing variable here is the load impedance. When using sweep tubes the actual tube being used makes little difference if it can handle the load. The main variables are B+ and load impedance.
Your OPT's came from a Fisher receiver. I would guess that would put them in the 6000 to 8000 ohm range. That should be in the 35 to maybe 50 watt range on 400 volts. If the OPT's have multiple output taps, AND enough inductance, you might be able to run them with an 8 ohm load on the 16 ohm tap for a 3000 to 4000 ohm load generating 50 to 70 WPC.
This morning I decided to crank some King Crimson and Triumvirat, so I flipped on the amp for warm up. If you listen closely to the speakers you can faintly hear something that sounds like wind chimes. It goes away after about 3 minutes. These sounds are generated inside the output tubes as they go from cold to hot in a few minutes. I heard this before at a friends house with high efficiency speakers on a DHT amp.
As George mentioned, it depends on your load impedance. I was using some 60W transformers strapped at 3300 ohms to get about 80WPC at 475V.
Well FINALLY I got it up and running. I did some adjusting and listened to it a bit through some small Optimus speakers that were used in our home theater setup. So far it sounds pretty good. I only had an ipod available as a source. I made up a board out of an old cabinet door to mount everything to for now I wanted to make sure I could move the board into my other room without having a transformer roll off and take everything with it. I just wanted to get all the kinks out before I even worry about the chassis. I am getting 580volts on the plates. To get the bias supply I wired the 44volt secondary and the 6.3vct winding in series, worked perfectly. I got exactly -60vdc. I forgot to measure the B+ going to the board but it should be half of the plates. I could smell something getting hot but I figured it was the CL90s. I put current limiting resistors on the primaries of the transformers and after the HV bridge recitifiers. I am kind of curious as to my lower B+ readings compared to George's...lower line voltage maybe? Anyhow here is the dangerous mess I had running earlier. I think I stood halfway across the room when I turned it on 
Even though the wiring is an absolute mess and it was pretty cobbled together there was no audible hum.
Even though the wiring is an absolute mess and it was pretty cobbled together there was no audible hum.Attachments
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If I remember correctly the 7018 model would put me around 440vdc. I should have picked up some of those while he had them for sale as well.
I have been plotting out a two level chassis with the board and OPTs on the top and the lower half containing the power supply. I would like to have an umbilical between the two for ease of taking it apart to fix or tweak it if need be. I have been having some trouble finding a decent plug system so what I am was proposing to do is on the power supply chassis installing an octal socket and from the the top chassis an octal base as the plug. Cheap and easy and keeps the HV from being touched.
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True the old schoolers used tube sockets for umbilicals. But why not use new safe plugs?
CONN PLUG CPC 7POS STD SER1 - 211399-1
Digi-Key - A1301-ND (Manufacturer - 206061-1)
These guys are good for 600vac and can be 4-whatever pin arrangement.
or
http://www.switchcraft.com/Category.aspx?Parent=845
http://www.switchcraft.com/Category.aspx?Parent=36
1500vrms
CONN PLUG CPC 7POS STD SER1 - 211399-1
Digi-Key - A1301-ND (Manufacturer - 206061-1)
These guys are good for 600vac and can be 4-whatever pin arrangement.
or
http://www.switchcraft.com/Category.aspx?Parent=845
http://www.switchcraft.com/Category.aspx?Parent=36
1500vrms
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Ive been told by the speakon people (nurtrik) that the switchcraft units are knockoffs and they can only say they "mate" with speakon connectors, since they cant use the speakon name.
That also means that the plugs are only rated for 250vac and have 4kv insulation. So heatshrink well and dont unplug while live.
That also means that the plugs are only rated for 250vac and have 4kv insulation. So heatshrink well and dont unplug while live.
Didn't see any of this this weekend. The Back Yard Speaker Lab was in operation this weekend. My line voltage varies from 118 to 124 volts. My amp is mounted on a piece of plywood not unlike yours. It has been in the living room connected to my latest speaker project. It sounds too nice to drag back into the lab. I haven't connected a meter up to it in 2 weeks, so I guess that I should check the bias. I'll test the line voltage, the B+ and the bias currents tonight. I have no resistance between the power transformers and the AC line. The only limiter is the CL140 that is on the board per Petes documentation. So far the amp is reliable and it sees daily use with the new speakers at low power levels. It is extremely loud with the volume control about 1/8 to 1/4 the way up.
Another old school possibility is something called Cinch Jones plugs and sockets. DigiKey used to carry them. I am using them in my 845SE. It runs at 1100 volts on the B+ and several amps on the filaments.