Wow, this is a REAL AMPLIFIER !!!!

The problem with using transmitter tubes like 813s is the huge, 2500 volts here, B+ supply. You need a monster, custom, high-ratio, 5KV insulated output transformer, and it's hard to get good HF response from that.

John

Yeah, but once you're old enough to be able to afford one, you can't hear up there anyway. ;)

Cheers

Phil Hobbs

MSA260 Variable Switching Frequency PWM Amplifier

9000 Watts 6.6" x 9.8" Just add power supply.

but at max 50KHz pwm I doubt it will do full audio range frequencies ;)

something like this:

2400W@4R 20-20KHz, 9.8" x 6" x 1.8" with power supply list price 309euro ...

-Lasse

Or you wind a new coil for the speaker. Done it once but never, ever again. I think that was the episode where I used more cusswords than all the rest of my life. It was a huge speaker from a circus that had folded and I needed it to get to a few hundred ohms.

Guy plugged in his E-guitar ... *TWWWAAAIIINGGGG* ... thwok ... darkness. The 230V/16A breaker had popped.

I guess one could also buy a boatload of small speakers and string them in series but I didn't have that kind of money as a student. The added risk with my amp was that there could be up 900V riding on the speaker coil so nobody was allowed anywhere near it. I am still amazed it didn't arc over because back then I didn't pay much attention to dielectric properties and stuff.

--
Regards, Joerg

http://www.analogconsultants.com/

I was wondering where they get the transformers?????? They must be custom made and very costly. The power transformers might be made for large transmitters, but the output xformers almost have to be custom made.

Just curious why the HF response would be poor? Is that due to the thickness of the insulation in the xformer?

Now, if I was building this, there would eight output tubes instead of four. Putting out over 2000 watts, and four (quad) channels. Over 8000 watts would make a kick ass stereo (quad) sound system. Of course there is no point in having that much power, but I like to dream about excessive shit like this.

I recall reading somewhere that the Woodstock Festival had a 10,000 watt sound system. So my 8000 watt amps could liven up many acres of land and probably get me arrested for excessive noise :)

Typically one would buy them used and rewind them if necessary:

It's actually not poor at all. I was mighty surprised when I had to test some aircraft designs here, so I needed a stiff power source up to

440Hz. Vary the frequency, apply nasty surges, the works. Generator ->

big Kenwood amp -> ordinary 60Hz line transformer. After completing the tests I became curious. Now how high would it go? To my surprise this

60Hz transformer easily did several kHz without the core heating up much. And above a few kHz you don't really need much power for audio purposes.

However, back when I built my amp there was no Ebay and I couldn't even buy a kilowatt-sized mains transformer. Those cost too much. So I generated slightly over 900VDC from 230VAC, Cockroft-Walton style. In a country where wall outlets where not keyed and you could plug them both ways. Woe to those who didn't measure first and plugged in the "wrong" way ... -> Hint to readers: DO NOT do this! (I was young and foolish back then).

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

I have some 4-1000Z tubes around here. Some new, some only used a little.

Maybe I should Ebay them. I don't think I'll be doing much with them in my life time but I wonder what kind of an audio amp they would make?

I got these from a place where they used them in EDM machines to operate the quill at 400hz. I also have a supply and output transformer..

Jamie

The toob side impedance is high, so winding capacitance starts to matter. And the HV insulation encourages leakage inductance.

John

Not really. Tube amps can have remarkable frequency response and when you are dealing with kilowatt-range stuff the impedances are not very high. Just a few hundred Ohms. It take lots of capacitance to mess with that.

The trick was to massively parallel color TV flyback driver tubes. That's how I built my first one. They run really nicely between 600V and

900V. IIRC my 930V was a bit over the limit but they hung on. Later I built an RF amp the same way (copied someone else's published plan though) but in order to remain legal I had to back off to five tubes.

--
Regards, Joerg

http://www.analogconsultants.com/

Those were 6KD6 or the European equivalent? There were a lot of sweep-tube linears built over here in the 70s. Some of them were even passably linear.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant

Oh yeah, used to make CB amplifiers out of them in my younger days, some where mobile :)

Jamie

Yes, PL509. The really old PL36 from the early 60's B/W sets was very good as well but harder to find. Surprisingly my RF amp had better linearity than some expensive commercial ones with the big tubes. The audio version before that, I don't know. That was more like a highschool buddy competition and only power output mattered. The music back then, Jefferson Airplane or Led Zeppelin, didn't sound particularly linear anyhow :-)

Oooh ... a friend did that but they caught him. What really did him in wasn't the big amp per se but the fact that he had a police crystal in his rig. So they took it all away from him. "Otherwise we'd just have taken the amplifier", they said.

--
Regards, Joerg

http://www.analogconsultants.com/

That's only 200W, but it is uglier.

Push-pull parallel 807s?

..20KHz is good enough for us old fogies..

I did a 0-10kHz 72V 9A cont./15Apk class-D servo amp with Apex parts and some help from folks here.

No way to get that thing over 10kHz BW. Well, maybe it would be possible if I ever get to understanding the z-transform...

It bugs me though, that it's usually a choice of DC to a few kHz, or AC coupled audio amps that go to 20kHz or better, but without the ability to configure in current mode and configure with DC coupling.

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_____________________
Mr.CRC

Max switching frequency 50 kHz. That's not gonna cut it for broad band audio applications, although it would make a hell of a subwoofer amp.