Category Archives: Harman Kardon

Harman Kardon | A30K | A300 Tube Amp | SOLD

Harman Kardon A30K | A300 | Integrated Tube Amplifier
Harman Kardon A30K | A300 | Integrated Tube Amplifier
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Item location: Italy | Ships to: Worldwide
This listing has ended.

 

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This is a very nice Harman Kardon A30K amplifier, serial number 6041830. The 30K is the kit version of the A300 amplifier. Electrically the 30K and 300 are identical. I never put power to these amps without first replacing the electrolytic and coupling capacitors and diodes. It is strongly recommended (Google ‘recapping radios’) that the electrolytic and coupling capacitors be replaced in old tube units. For the A300 there are a total of seven electrolytic capacitor sections in the power supply and a total of eight coupling capacitors to be replaced, which I have done. After restoration I also verified the B+ voltages and critical components are to specification. I also replace the rectifying diodes with more modern units that have fast turnoff/soft recovery, characteristics that provide a little less noise– makes for a cleaner power supply. No change in the sound of the amp, only just a cleaner power supply.

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These restorations do not modify the wonderful ‘tube sound’–no real modifications, but rather put back the way the HK engineers designed it, only make the unit safer and more reliable. See pictures, showing new components and before and after chassis refurb. (bottom cover removed for picture).

In addition to replacing the electrolytic and coupling capacitors, using premium 716 Series Sprague Orange Drops for the coupling capacitors, I have tested all the tubes on my B&K 707 tube tester—and replaced any that were marginal. I also have cleaned the tubes, tube sockets, controls and switches (Deoxit D5 contact cleaner for the tube sockets and switches, F5 Fader Lube for the potentiometers). The output tubes are performance matched Sylvania 7408’s with identical date codes of 1962, 26th week. The 7408 is a more rugged version of the 6V6, which are highly prized in tube amplifiers. For tube rollers, the 6V6 is a direct replacement for the 7408.

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I have verified all the operations. The controls and switches all function as designed. All the inputs are operational. I have run this unit 8 hours without any issues after the refurbishing. This unit has a very nice appearance, the faceplate is excellent for it’s age, the issue is a scratch on the upper LH corner, see pic. The vertical lines on the faceplate are from the lighting. This is one of the best A30K’s that I’ve had. The knobs also are in very good condition. Chassis has a few stains, chassis lettering is sharp and legible–see pictures. As a stereo integrated amplifier, there are inputs for lo level (magnetic) phono or tape head, hi level (ceramic) phono, tuner and auxiliary inputs. The controls are: Source Selector, Loudness (Volume), Bass, Treble, Balance, and Blend. Switches are provided for power, rumble filter, contour, equalization and stereo reverse

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Harman Kardon | A50K | A500 Tube Amp | SOLD

Harman Kardon | A50K A500 Integrated Tube Amp
Harman Kardon | A50K A500 Integrated Tube Amp
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Seller assumes all responsibility for this listing.
Item location: Italy | Ships to: Worldwide
This listing has ended.

Harman Kardon A50K tube integrated amplifier, the kit version of the A500 amplifier, serial number 6001200. To see one of my recently sold restored A500’s copy and paste 330734051861 into the eBay search box. This is an HK A50K integrated stereo amplifier from the golden age of tube amps. I had an HK A300 in college many years ago and was always impressed with its sound. So–as much for a hobby as anything, I researched these ‘Award Series’ amps with the intent of updating them to make them safe and reliable. I have been very focused in my efforts—I am not a generalist, but have concentrated on the tube type HK amps and reveivers—and learned all that I can about these specific units. The ‘restoration’ of these (and any other 40 year old tube radio, tuner amp, etc.) per the experts includes replacing the electrolytic and signal coupling capacitors. These specific capacitors do not age well, and it’s generally agreed that ‘recapping’ is an essential requirement if you want to keep a tube unit reliable and safe.

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Proper restoration of the A50K’s is pretty extensive. There are a total of 24 electrolytic and coupling capacitors to be replaced. In addition, the A500 has adjustable output tube bias balance circuits consisting of fixed resistors and potentiometers. Before I undertook the A50K restoration, I reviewed my plans with the ‘recognized HK expert’. He indicated that these pots and resistors should be replaced as part of the restoration—they are too critical to take chance on possible future failure. The last three pictures show the ‘before’ and ‘after’ of the coupling and electrolytic capacitors and potentiometer replacement. The bottom cover was removed for these pictures. After recapping, I have verified all the B+ voltages to be within original specifications.

In addition to replacing the electrolytic and coupling capacitors, I have tested all the tubes on my B&K 707 tube tester—and replaced any that were marginal. The four 7355 output tubes are matched RCA’s, all dating from 1961.

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Appearance condition: The condition is good, with some minor issues. The faceplate is in pretty good condition, a few scratches, and one noticeable mark on the lower RH corner–see pics. The chassis is very nice, the faceplate lettering is decent, light in a few places, the chassis lettering excellent, the chassis itself excellent–clean, nice and shiny. The knobs are in very good condition. All-in-all a very nice appearance for the age of the amp.

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As mentioned, the A50K has a bias balance feature for the output tubes. When properly set, each output tube carries the same amount of load. Some tube amps have built in meters to set the bias balance—not present on the A500’s –so the procedure has been either to use a intermodulation distortion analyzer (not at all common) or to measure inside the unit with the bottom cover off—I don’t like doing that with that much high voltage nearby. So, I ran the points to test jacks on the chassis to allow setting the bias balance with the unit buttoned up. The potential on the test points is safe–less than +/-10 volts. Since not everyone has a multimeter, I am including a proper digital meter and instructions on how to set the bias balance–very easy to do. This should be done whenever the output tubes are changed, or every 100 hours or so of operation.


Rare Coronet Tube Receiver by Harman Kardon Restored

$975.00
End Date: Sunday Jun-25-2017 8:57:42 PDT
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Classic Harman Kardon Citation II Tube Amp serviced gold inputs/outputs NICE

$2,399.99
End Date: Friday Jun-23-2017 8:30:17 PDT
Buy It Now for only: $2,399.99
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Harman Kardon Citation II Vacuum Tube Power Amplifier (Modified for EL34 tubes)

$2,700.00
End Date: Tuesday Jun-20-2017 9:39:22 PDT
Buy It Now for only: $2,700.00
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Harman Kardon Citation II Vacuum Tube Power Amplifier Serviced 100% Original

$2,500.00
End Date: Wednesday Jun-14-2017 11:29:59 PDT
Buy It Now for only: $2,500.00
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Harman Kardon | A224 | Stereo Tube Amp | SOLD

Harman Kardon A224 | stereo tube amp
Harman Kardon A224 | stereo tube amp
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Seller assumes all responsibility for this listing.
Item location: Italy | Ships to: Worldwide
Best offer accepted

 

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Harman Kardon refurbished tube type A224 integrated amplifier, serial number 2904939. The A224 is one of the nicest EL84 tube amps of that era (about 1959). This amp appearance is excellent, the faceplate looks great, I see very minor mars and scratches, one ding on the lower LH corner, see pic. , the knobs are excellent, all the lettering is legible and distinct–see the pictures. The cover has been repainted, and looks very nice. Now, when the cover is removed, you will see that this has a copper flashed chassis, and generally is impossible to clean, so best to keep it covered. The amp size is compact, about the size of a turntable, see pic.,

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The A224, as a tube unit has a sound unlike solid state units. These were (and are) highly regarded amplifiers, and have that highly desired ‘tube sound’. Interesting that HK is one of the very few hi-fi companies of the 1960’s to still be in business. As a stereo integrated amplifier, there are inputs for lo level (magnetic) phono or tape head, hi level (ceramic) phono, tuner and auxiliary inputs. The controls are: Source Selector, Mode, Loudness (Volume), Bass, Treble (with power switch), Balance, and Blend. Switches are provided for rumble filter, contour, and speaker selection. I will provide the winning bidder the A224 operator’s manual, which includes setup, operation and the wiring schematic.

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It is strongly recommended (Google ‘recapping radios’) that the electrolytic and paper or molded (original disc mica type are OK) coupling capacitors be replaced in old tube units. Some people say it’s OK just to ‘reform’ the power supply caps. (bring them up very slowly over a couple of days on a variac). While this is a much simpler and less costly alternative, I’m not convinced that it is a good as replacing dried out caps with new current fresh stock.

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See the last two pictures, ‘before’ and ‘after’ recapping. After restoration I also verified the B+ voltages and critical components are to specification. This restoration does not modify the wonderful ‘tube sound’–no real modifications, but rather put back the way the HK engineers designed it, only make the unit safer and more reliable.

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