Harman Kardon Citation II Rebuild
- Thread starter mayfly
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If he's at no load except the capacitors as filters (ie, capacitor input full wave, non-bridged, power supply), then it should drop about 25vdc or so, give or take, with the idle current of the output tubes as additional load. Make that about 70milliamps or so. You'd say... OMG, that means at full tilt its gonna drop another 50 volts! Strangely, they dont do that. Once you have a real DC load on them, of any real magnitude, the power supply will settle down, and only vary by the copper losses in the secondary... almost none.
mayfly
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More progress:
The first channel is almost complete - except for a missing 6.8k 1/2 watt resistor.
I did not replace the preamp tube sockets, or the wiring harness. Beginning to regret not doing these. The preamp sockets are a PITA to solder to (but I'm getting it done with cleaning and additional flux). The wiring harness is another matter - still having issues with insulation breaking down at the ends of the wires. fortunately there is enough slack in the wires that I can cut them back and re-tin - but I'm a bit concerned about shorts developing in the harness at other heat points. Currently there are none (I beeped it out), but it's a worry.
Oh - and I'll clean up the wire dress in a bit.
Anyway, onward and upward!
The first channel is almost complete - except for a missing 6.8k 1/2 watt resistor.
I did not replace the preamp tube sockets, or the wiring harness. Beginning to regret not doing these. The preamp sockets are a PITA to solder to (but I'm getting it done with cleaning and additional flux). The wiring harness is another matter - still having issues with insulation breaking down at the ends of the wires. fortunately there is enough slack in the wires that I can cut them back and re-tin - but I'm a bit concerned about shorts developing in the harness at other heat points. Currently there are none (I beeped it out), but it's a worry.
Oh - and I'll clean up the wire dress in a bit.
Anyway, onward and upward!
mayfly
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Alright,
It's running and passing signal through both channels!
But there is a problem. When it got hot, a short developed in the B+ rail somewhere. I was monitoring the mains current, and it slowly crept up from 2 amps, to 3 amps, then to 4 amps, then the smoke came. I shut it down quickly.
I replaced 3 B+ wires and the main bias wire in the harness with wires running directly point to point. After this was done I could run it with a test signal for an hour with no issues.
This means I'm replacing the harness <sigh>
But hey! at least it runs! and the three prong cord that I put on it paid for itself many times over....
It's running and passing signal through both channels!
But there is a problem. When it got hot, a short developed in the B+ rail somewhere. I was monitoring the mains current, and it slowly crept up from 2 amps, to 3 amps, then to 4 amps, then the smoke came. I shut it down quickly.
I replaced 3 B+ wires and the main bias wire in the harness with wires running directly point to point. After this was done I could run it with a test signal for an hour with no issues.
This means I'm replacing the harness <sigh>
But hey! at least it runs! and the three prong cord that I put on it paid for itself many times over....
Most if not all of electronic components, including and especially transformers, come from the factory, prefilled with smoke. when the smoke escapes, you either gotta buy more smoke to refill it, or usually buy a new component.
and no, cigarette smoke will not work, they use some special kinda smoke
and no, cigarette smoke will not work, they use some special kinda smoke
mayfly
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Spent some more time testing the unit. It reproduces input waveforms very accurately - much better than any guitar amp I ever worked on. It also really cranks the power. Have not run it through a speaker yet - that will wait until after the harness is replaced.
Also, on one channel the waveform was a bit messed up. Turns out one of the preamp tubes (of which I'm running the originals) was bad. Shocking I know.
So in summary it's running pretty good. Tomorrow I'll work on the harness.
Also, on one channel the waveform was a bit messed up. Turns out one of the preamp tubes (of which I'm running the originals) was bad. Shocking I know.
So in summary it's running pretty good. Tomorrow I'll work on the harness.
Return of Guitlouie
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Do yourself a favor, when you get this thing up and running, and you have the Rega running into it, the first piece of vinyl you should lay down is a 180 gram copy of Ravel's "Bolero" performed by Ernest Ansermet with Orchestre de la Suisse Romande. I know that sounds weird coming from a die hard rock and roll fan such as myself, but trust me on this, there is nothing else in the world of music like that piece jamming through a kick ass system at too-loud volume. It's a good test of the range of amp/speaker setup as well.
mayfly
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Here's the speakers that will be first built for this unit.
http://diy-nation.blogspot.com/2007/01/proac-25-clone-project.html
Some other vintagy ones will follow, but the advantage of these speakers is that the project is already underway.
My buddy is now sweating over crossover issues (whatever! it's all passive!) :icon_jokercolor:
http://diy-nation.blogspot.com/2007/01/proac-25-clone-project.html
Some other vintagy ones will follow, but the advantage of these speakers is that the project is already underway.
My buddy is now sweating over crossover issues (whatever! it's all passive!) :icon_jokercolor:
mayfly
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Out with the old harness:
In with the new:
The system is stable and runs at full power. I had it running for over an hour into dummy loads, just playing with it. Mains current never rose above 2A.
I offer the following two images:
only a little bit of phase distortion - but check out the frequency it's running at!
I ran it up to 50KHz with no loss of power. This thing could be an AM radio transmitter!
In with the new:
The system is stable and runs at full power. I had it running for over an hour into dummy loads, just playing with it. Mains current never rose above 2A.
I offer the following two images:
only a little bit of phase distortion - but check out the frequency it's running at!
I ran it up to 50KHz with no loss of power. This thing could be an AM radio transmitter!
