You know that by doubling the power you only get 3db of additional volume.
Why would you need to push the speakers for testing the fidelity of the amp or speakers to 120W? Are you going to be listening routinely at that max level? Do you live in an auditorium? Need them for an outdoor public event? Do you have a power meter to verify the power/fidelty quality curve?
You should find a diagram for an amp of this class (good luck) and study the crap out of it until you understand it and then realize that building one "free hand" is not mysterious, it just takes some vision and planning for space, time, and component acquisition, tools, soldering skill, troubleshooting skill when you make a mistake and need to dig a 100K resistor out from a 10K's position....
You could build one without a chassis, too, just hang the circuit from the ceiling like a mobile.
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I am sure I remember seeing a 4CX250 variant which was set up for conduction cooling using a BeO block as an insulator to transfer heat to an external heatsink?
Not common and BeO is something of a hazzard all on its own, but external anode does not always equal large blowers and pressurised grid compartments.
But, if in fact you just want a couple of hundred watts, then half a dozen EL84 on each side of the iron is a much easier (And much more well trodden) way to get there.
Do however start with something very much smaller, 650V at an amp will 'have you if you do not know what you are doing, never mind the several KV at a few amps involved in what I would consider a large valve amp.
Regards, Dan.
Not common and BeO is something of a hazzard all on its own, but external anode does not always equal large blowers and pressurised grid compartments.
But, if in fact you just want a couple of hundred watts, then half a dozen EL84 on each side of the iron is a much easier (And much more well trodden) way to get there.
Do however start with something very much smaller, 650V at an amp will 'have you if you do not know what you are doing, never mind the several KV at a few amps involved in what I would consider a large valve amp.
Regards, Dan.
I would not use a tube amplifier for testing a variety of speakers. Most tube amp configurations desire a relatively flat speaker impedance to achieve flat frequency response.
You my hear unintended differences between speakers, just because of fluctuations in the impedance of the speaker. A solid state amplifier would not be suseptible to the same situation.
You my hear unintended differences between speakers, just because of fluctuations in the impedance of the speaker. A solid state amplifier would not be suseptible to the same situation.
Hi,
... or this way
The Champ CBA-20807 1000 Watt Amplifier - Part 2´
another 1000 Watter from the same guy. 20x 807 valves.
As far as I know the member "alexontherocks" made an 1,5kW Amp with two of the russian GU81. The real challenge with a high risk to losing money if something really ****** up while fiddling on the circuit. And 3kV is a term which speak for itself.
GU81 spec sheet:
http://www.mif.pg.gda.pl/homepages/frank/sheets/175/g/GU81.pdf
This valve is able to dissipate amazing 450W plate power!
73
Wolfgang
... or this way
The Champ CBA-20807 1000 Watt Amplifier - Part 2´
another 1000 Watter from the same guy. 20x 807 valves.
As far as I know the member "alexontherocks" made an 1,5kW Amp with two of the russian GU81. The real challenge with a high risk to losing money if something really ****** up while fiddling on the circuit. And 3kV is a term which speak for itself.
GU81 spec sheet:
http://www.mif.pg.gda.pl/homepages/frank/sheets/175/g/GU81.pdf
This valve is able to dissipate amazing 450W plate power!
73
Wolfgang
We don't know the final outcome for that one. The thread ended with fire inside one of the OPT's on initial power up. At this point his account is "disabled at the members request."
From my perspective it looks like Alex did things right, but his OPT designer didn't understand the voltages involved. The OPT in an amp will see twice the B+ voltage in normal operation. The voltage across the OPT primary can go well above that when the amp is pushed into clipping with a reactive load like a speaker. I have seen 2KV in a cranked guitar amp that has a 430 volt B+.
Good justification for a gas discharge tube across the primary - my 833 amp has a 6000V GDT in place just in case. According to Spice it will reach 4200V in normal operation at max power.
By the way, George, did you ever do the GDT experiments you were talking about a while back? As I recall you were going to evaluate them in your next high-power amp...
That was the plan, but life has a way of changing plans. I was about halfway through the design cycle on a 125 WPC sweep tube amp, also using a Landfall Systems chassis when I got word that my 41 year career at Motorola would end on Dec. 31 2013. That has now changed to March 31 2014, and may be extended again, but I won't know for a few more days.
That amp is designed for HiFi specs using Edcor OPT's but will see extreme duty use in a guitar rig / PA / DJ system. I will need some means of ensuring survival into an open speaker load. GDT's with an LDR to sense the GDT firing might be an option.
This has put all tube amp tinkering on hold for an indefinite time. Everything is being packed up for a 1200 mile move. Most of my tubes have already been moved. I'm not even sure where the GDT's are right now, so that isn't going to happen soon.
-1; all the more reason for a big tube amp. Sell it to your wife as being a space heater.
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