quad of kt88 is able to 200W , but how long will last?
http://www.lundahl.se/pdf/1620_3_7_9202.pdf
you might need to take this route
http://frank.pocnet.net/sheets/140/4/4-125A.pdf
http://www.lundahl.se/pdf/1620_3_7_9202.pdf
you might need to take this route
http://frank.pocnet.net/sheets/140/4/4-125A.pdf
Not sure how long output tubes will last but I play a 400 watt amp I built 4 years ago twice a week for several hours, cranked pretty loud. I've had the original sovtek kt-88s in there since the beginning without a hiccup and it still sounds loud and punchy. I have not used JJs before which is what is in this amp but I really doubt I will ever be playing this thing at full output. I have to get another 8x10 cabinet before I can even think about doing that!
Here is the schematic for anyone interested. I know there are a few small mistakes and I probably left out some changes I have made along the way but there it is. The pre and power amps are nothing amazingly complex but they do sound good and I used different style tone stacks on each preamp channel which make them act significantly different.
Here is the schematic for anyone interested. I know there are a few small mistakes and I probably left out some changes I have made along the way but there it is. The pre and power amps are nothing amazingly complex but they do sound good and I used different style tone stacks on each preamp channel which make them act significantly different.
Since this thread was started there is a dedicated place for awesome projects like this over in the Instruments & Amps forum. Tons of guitar guys over there now. Moving it there - I am sure it will get a LOT of attention.. 
I must say it is very impressive looking and of the highest professional caliber.
Some questions
Are those one-of PCB's you made? What made youdecide o use a PCB for a one-off amp?
Please tell us about the output transformers. What are you using? I don't think I've ever seen a 500W OPT that is flat from 15Hz to 20+ KHz
Finally what does it sound like?
They are one off PCB's that I designed and had manufactured. I decided to use PCBs because there is too much circuitry and not enough room to wire it point to point or with tag boards. There is still a lot of wiring in the chassis that you can't see. The heater wires for all the tubes and also the plate supply are not on the PCBs. They are wired to each tube socket on the topside of the boards. The tube sockets themselves are the highest quality I have ever seen and are made in Taiwan of all places. Each pin is machined from solid copper then gold plated and the pins on the octal tubes are replaceable. I got ones with bakelite housings but you can pay double and get teflon.
I am using 4 hammond 1650W transformers. 2 in parallel on each side. They are rated -1dB from 30Hz to 30KHz@280 watts. They are rather impressive for the price. At first I wanted to have 2 custom 500W toroidal transformers wound to keep it light as possible but the few manufacturers that do small quantities said my specs were too tight or it was not possible even with an EI so instead I went with the Hammonds and I'm glad I did. The only problem is they weigh 28 lbs. each!
As for sound - I have not played the amp at high volume yet. It still resides in my house, waiting for me to take it to my practice space. I just completed final testing yesterday evening but should be jamming through my swr 8x10 cab within the next week or two. I have played it extensively through the line out into another amp and I think it sounds great. There is zero hum in the line out or in the power amplifier outputs and the two preamp channels are distinctly different because of the difference in tone stacks. Channel 1 has a baxandall style stack which is more midsy than Channel two which has Fender/Marshall style which is a direct copy of the bassman tone stack. Channel two has the classic scooped Fender sound. You can assign either preamp channel to either power amp input via front panel control or with the foot switch and you can also drive both inputs simultaneously from input one or keep them separate and run a different instrument into each input. For all those bands with two bass players haha.
I am using 4 hammond 1650W transformers. 2 in parallel on each side. They are rated -1dB from 30Hz to 30KHz@280 watts. They are rather impressive for the price. At first I wanted to have 2 custom 500W toroidal transformers wound to keep it light as possible but the few manufacturers that do small quantities said my specs were too tight or it was not possible even with an EI so instead I went with the Hammonds and I'm glad I did. The only problem is they weigh 28 lbs. each!
As for sound - I have not played the amp at high volume yet. It still resides in my house, waiting for me to take it to my practice space. I just completed final testing yesterday evening but should be jamming through my swr 8x10 cab within the next week or two. I have played it extensively through the line out into another amp and I think it sounds great. There is zero hum in the line out or in the power amplifier outputs and the two preamp channels are distinctly different because of the difference in tone stacks. Channel 1 has a baxandall style stack which is more midsy than Channel two which has Fender/Marshall style which is a direct copy of the bassman tone stack. Channel two has the classic scooped Fender sound. You can assign either preamp channel to either power amp input via front panel control or with the foot switch and you can also drive both inputs simultaneously from input one or keep them separate and run a different instrument into each input. For all those bands with two bass players haha.
I have just finished an 80 watt valve amp and I used a pcb.
It sort of worked ok.
I was getting some positive feedback and when I looked at the pcb the input circuit to the first gain stage was far too long.
I had also forgot to star ground the output valves return path but luckily this was one cut and one link to fix.
At least with a pcb it is harder to get the wiring wrong as it is already done for me.
I had organised the amp to be a guitar amp with volume and gain controls but it doesn't have enough distortion to give a solid rock music sound.
So I use it with my mp3 player and it sounds very detailed compared to SS amps.
It sort of worked ok.
I was getting some positive feedback and when I looked at the pcb the input circuit to the first gain stage was far too long.
I had also forgot to star ground the output valves return path but luckily this was one cut and one link to fix.
At least with a pcb it is harder to get the wiring wrong as it is already done for me.
I had organised the amp to be a guitar amp with volume and gain controls but it doesn't have enough distortion to give a solid rock music sound.
So I use it with my mp3 player and it sounds very detailed compared to SS amps.
Careful thought to layout is critical when doing a PCB tube amp and there is nothing wrong with using a PCB so long as it is designed properly. I've seen some pretty awful designs in mass produced guitar amps. And I had several mistakes on mine as well that needed to be corrected. Even after looking it over numerous times and trying to contemplate everything before manufacturing. I work in the automated test equipment industry and deal with circuit boards all day long. I know of very few new PCB designs have been perfect on the first run except for simple circuits. So you hack it up and modify it until it works the way you want it to then respin the board. In this case though that was not an option since I was well invested after stuffing all the boards with sockets and components.
Not a problem getting sufficient power; all you need is a 20-amp 110 outlet, which uses 12 guage wire for short runs. Or there's a 30-amp standard common on large wall air conditioners. 50+ amps are usually Hubbell twist-lock.
I usually plug my multiple solid-state power amps into a 220v clothes dryer or electric stove outlet...via a small fusebox and multiple 110 outlets.
I usually plug my multiple solid-state power amps into a 220v clothes dryer or electric stove outlet...via a small fusebox and multiple 110 outlets.
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The output is not bridgeable. I originally wanted to do this but it turned out not to be possible reliably the way I wanted so it is stereo only. Each output is selectable between 2 and 4 ohms and there are also separate standbys for each power amp so it is possible to run one side only which is probably how I will use it most of the time...that is until I get another cab.
Aw shucks. Was dreaming of a 1kw toob amp to drive my fEARful 1515/66+1.
http://greenboy.us/fEARful/DL/1515+66/fEARful 1515+66.png
Still 500w is pretty awesome. Maybe a pair of the 12/6's [excursion limit is about 533w] with mirror baffles.
Kudos for an awesome build. I hope all your dreams come true.
http://greenboy.us/fEARful/DL/1515+66/fEARful 1515+66.png
Still 500w is pretty awesome. Maybe a pair of the 12/6's [excursion limit is about 533w] with mirror baffles.
Kudos for an awesome build. I hope all your dreams come true.
Thanks! Yeah I really wanted to do a bridged output but I would need to have the exact same signal going to both power amps for that which is not feasible in my design with the stereo preamp. But it will do stereo tremolo or ping pong a signal back and forth between left and right channels with a variable rate. I don't know how useful that is to most people but was easy to implement with the circuitry used to control the channel switching and it sounds kinda cool
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