@nzoomed,
You will want to seperate the volume control between the sub and main amp. There will be times you get sick of your chest thumping from the sub and want to focus on the main speakers only. At these times you will be glad you seperate the volume control.
You will want to seperate the volume control between the sub and main amp. There will be times you get sick of your chest thumping from the sub and want to focus on the main speakers only. At these times you will be glad you seperate the volume control.
OK, ill consider that, your probably right. Only issue is i have to reach down to the sub and turn the knob on the sub itself.
If im happy with the sound i get from my amp, i will probably not bother with a sub if i get enough lows from it.
If im happy with the sound i get from my amp, i will probably not bother with a sub if i get enough lows from it.
Since this thread is still alive, I built a cheap little amp with these ECL82's and found that they responded very well to cathode feedback and ultra-linear. Was the easiest way to get the most power out of them cleanly. Better than plate to plate feedback in this case.
Shoog
Shoog
Thats good to know, i will have to get some custom wound transformers for ultra linear though. Are you aware of any major brands that produce these? I dont think hammond make them.
I used some salvaged console SE transformers which have a ultralinear winding (not strictly designed for UL - rather for modulating some of the radio circuits). relatively small but still very sweet sounding for what they were. Good for a few clean watts.
Shoog
Shoog
Well thats the type of transformer im after, im not too sure where i will find such a transformer, i might be able to get some wound locally though.
Im at long last working on this amp build and will post some photos when complete.
Couple of questions - the large 680 ohm 5W wirewound resistor on the HT supply, is this supposed to act as a filter choke?
Each ECL82 will draw 35mA of current. So at 270V, it would be running at 9W of power per channel on the HT supply. Would this resistor run rather hot? Should I use a larger power rating?
Couple of questions - the large 680 ohm 5W wirewound resistor on the HT supply, is this supposed to act as a filter choke?
Each ECL82 will draw 35mA of current. So at 270V, it would be running at 9W of power per channel on the HT supply. Would this resistor run rather hot? Should I use a larger power rating?
Assuming that the wirewound resistor is between two capacitors, then it acts as part of a low pass filter to reduce ripple. It is not a choke.
At 70mA current the resistor will dissipate about 3.3W. It will get hot, but they are designed to cope with this. You could use a slightly bigger resistor, which will then run cooler.
At 70mA current the resistor will dissipate about 3.3W. It will get hot, but they are designed to cope with this. You could use a slightly bigger resistor, which will then run cooler.
OK, sweet.
Nothing to worry about then. Dunno whats up with my calculations, but im allowing 35mA for a single ECL82 from the datasheet, multiply that by 270V, and i get about 9.4W.
Nothing to worry about then. Dunno whats up with my calculations, but im allowing 35mA for a single ECL82 from the datasheet, multiply that by 270V, and i get about 9.4W.
You may want to have some closer look, as the ECL82's maximum plate dissipation is rated at 7 watts. What are the voltage drops over the cathode resistor and the OT's primary?
Best regards!
Best regards!
35mA times 270V gives 9.45W dissipated in the ECL82 - which may be slightly too much for it. Some of that may be in the triode and some at the pentode screen grid, so the pentode anode may just be within spec.
The 680R resistor carries 70mA. It will drop 48V, and dissipate 3.3W.
The 680R resistor carries 70mA. It will drop 48V, and dissipate 3.3W.
Question to nzoomed: Did you build your amp according to the schematics shown in the very first posting? This leaves something unclear: Do you feed one or both channels via the 680R/5W resistor? Where do you measure 270Vdc? At the right (PSU) side or at the left (charge) side of it?
Best regards!
Best regards!
This datasheet even has a higher current rating than the one i got my figures from.
http://drtube.com/datasheets/ecl82-philips1969.pdf
Says current on the anode is 41 mA, and 3.5mA on the triode so is 44.5mA going by that, which would even mean more power!
As you say, thats more wattage than the plate dissipation, but perhaps there is some losses on the output?
Page 2 of the data sheet you linked says 41mA at 170V. Also says max 7W anode dissipation in the pentode section. At 270V that means max anode current of 26mA.
OK that makes more sense. I missed that bit.
Anyway, that maxes out at 7W like you say.
Dont think it will be an issue as i would have to have it cranked up at full volume to be an issue.
Anyway, that maxes out at 7W like you say.
Dont think it will be an issue as i would have to have it cranked up at full volume to be an issue.
No, the very contrary. A Class A output gets hottest with no signal; it is coolest at max volume.
Zero volume: 7W DC in, 0W AC out, so 7W dissipation.
Max volume: about 7W DC in, 3W AC out, so 4W dissipation.
Zero volume: 7W DC in, 0W AC out, so 7W dissipation.
Max volume: about 7W DC in, 3W AC out, so 4W dissipation.
OK, thats true, forgetting about that.
Its a big problem with Class A amplifiers.
Ive got an amp i built with an EL34 and the plate will glow hot when idle. Im trying to increase the resistor on the cathode to try and make it use less current.
Its a big problem with Class A amplifiers.
Ive got an amp i built with an EL34 and the plate will glow hot when idle. Im trying to increase the resistor on the cathode to try and make it use less current.
