Over the past few years, I have restored over 100 HK tube amps and receivers and sold many of them on EBay.
See feedback on my amps and receivers at the end of listing.
This is a very nice Harman Kardon A500 tube integrated amplifier, serial number 4163248.
See my other listed HK tube units listed on eBay.
This is an HK A500
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 receivers—and learned all that I can about these specific units.
I never put power to these amps without first replacing the power supply electrolytic and paper/oil coupling capacitors.
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. Some people believe that 'reforming' capacitors (bring them up to voltage with a variac over a few days) will provide safe operation, but I would rather use new capacitors even though that is a much more expensive and labor intensive route. Interesting enough, most the other components (tubes, transformers, wiring, most resistors, coils, etc.) do not generally fail with age. Switches and potentiometers (volume, tone, balance, etc.) do become noisy with age, but usually can be restored with proper use of quality cleaning (DeOxit) solutions.
I believe it should be the intent of restoration to bring the amp back to the quality and sound of the original unit as originally designed by the HK engineers and I have selected the components to match the original design with one exception. There have been improvements in rectifying diodes since these units were first built, and that's one area where I provide an upgrade. New diodes, with fast turnoff /soft recovery are now available and because of their characteristics, provide a cleaner rectifying operation than the original diodes—fear not, the ‘tube sound’ is not diminished in any way with these diodes—only a cleaner power system.
Proper restoration of the A500’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 circuits consisting of fixed resistors and potentiometers. Before I undertook the A500 restorations, 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-(capacitors are my typical A500 set, may vary slightly in appearance). 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, (using premium Sprague/Vishay 716 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. The four 7355 output tubes are performance matched GE, all circa 1962.
Appearance condition: The condition is excellent with some very minor issues. The faceplate is nearly imaculate, a small issue is a very light vertical scratch on the left edge of the faceplate, all lettering on the faceplate and chassis is crisp and clear. Except as noted, there are almost no indications of wear on the faceplate or chassis. (See pictures-note: lighting is difficult, the amp 'color' is closer to the close up shots of the faceplate--more nickel than gold). The knobs are all correct (original) and have been restored. Overall, this is one of the cleanest A500's I've seen.
As mentioned, the A500 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 check 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. (See 4th from last pictture).
Work performed on this A500 consisted of:
- Replaced all of the coupling and electrolytic capacitors--not because they have failed, but to increase reliability and bring the unit back into specifications. (total of 24 capacitors). Capacitor failures can ruin your day (and your equipment).
- Replaced the power supply rectifying diodes with modern diodes that perform the identical function, but with less noise.
- Tested all the tubes on my B&K 707 tube tester and replaced all tubes that did not test strong.
- Cleaned all switches, controls and tube sockets with Deoxit cleaner--D5 for tube sockets, switches and contacts, Fader F5 for the potentiometers.
- Verified all controls, B+ voltages and operations.
- Replaced the bias control pots and resistors.
- Added bias balance set test points and provided a meter to set the bias balance.
- Ran amp for a minimum of 8 hours after restoration--with no issues.
If you are reading this, you probably are familiar with the ‘tube sound’. It’s just mellow, and clear and wonderful (my opinion).
I am a retired electrical engineer and restore these as a hobby--there is little profit to be made doing this, but I enjoy this project, and gain satisfaction in knowing that I am increasing reliability of these 40+ year old amplifiers and making them available to a new generation of tube folks. The HK tube amps were (and are) highly respected units from the 'golden age' of tube systems. Probably says something for HK in that they are one of the very few hi-fi manufacturers from the 60's that are still in business.
The main specs of the A500 are:
IHFM music output power—25 watts per channel. These tube amps really like high efficiency speakers, many folks use Klipsch speakers with efficiencies in the 93-98 db range, I personally like the Electrovoice TRX12B's. How much power you need also depends on your room size and listening style.
Frequency response--+/- .5 db 12-35,000 cps at normal listening levels.
Output impedance—4, 8 and 16 ohm
Stereo inputs—low level—2.5 mv. And 4.0 mv. For magnetic phono cartridges and tape heads (from tape recorders).
Stereo inputs—high level –200 mv—this is suitable input for tuners, CD decks, and most mp3 players.
Third channel output with volume control (called ambience) —to feed a center channel amp, reverberation unit (remember those?) or powered subwoofer.
Stereo tape outputs—to feed a tape recorder.
Headphone jack--does not disconnect power to the speakers when in use.
Separate Bass and Treble controls for each channel—more knobs to turn.
Now—my lecture. This is not your son’s amplifier. This is a tube unit, and as such, has voltages inside the chassis that can be lethal—350+ volts. Tubes and transformers get hot and while the unit is rated for a 100% duty cycle, I suggest turning it off when not in use.
My goal was to make this amplifier as safe and reliable as I know how to without losing the wonderful ‘tube sound’. I believe I have accomplished this. I have a copy of the operator’s manual, which includes setup, operation and the wiring schematic that I will email to the successful bidder.
So, if you are into tubes, or just starting, here is an amplifier that is ready to go right out of the box.
As with essentially all vintage electronics, as this amp is about 50 years old, there is no continuing warranty or returns-but it is guaranteed to be non-DOA.
Amplifier will be carefully packed--I have shipped these amps safely domestically and to many countries successfully. Insurance is required and included in the shipping price. These are heavy units—shipping weight is 37 lbs. Local pickup is welcome. For Domestic shipping, I offer both USPS and FedEx shipping, check both for cost. I do prefer FedEx, seems to be a better choice.
For international shipping, I ship either Priority Mail International or Express Mail International, insurance required, depends on your country, (size and weight limits and insurance availability varies by country), contact me for shipping costs to your country, might be different than calculator indicates. Also, for overeseas customers, I warranty that the amp is in proper working condition when I pack it, International shipping costs preclude returns for any reason. If the amp is damaged in shipping, I will provide claim information for the buyer to pursue with the shipping company.
If there is an issue, I will work with you--check my feedback, I am honest.
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Harman Kardon refurbed PC200 integrated mono tube amplifier 6V6 circa 1956 (01) (#230722704207) Fine old tube amp, well packed, prompt shipping, very helpful seller.
Harman Kardon A300 refurbed to original, integrated tube amplifier 7408 tubes 28 (#230730395558) Very nice seller. Efficient shipping. Item performs great! A++++++ ^^ (Note: Sent to Hong Kong)
Harman Kardon tube refurbed A10 amp & FA10 receiver pair for stereo, 6BQ6/EL84 (#230734182766) I hate that I have to take this stuff apart, I'm not a techie Comment: Most tube amp sellers ship with the tubes not installed, pretty straightforward and easy to install the tubes—instructions included.
Refurbed Harman Kardon FA3000X vintage tube receiver A300 amp15WPC FM MPX nice (#230625885892) Excellent transaction, item exactly as described, very helpful seller too
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Harman Kardon tube refurbed A10 amp & FA10 receiver pair for stereo, 6BQ5 / EL84 (#230728302474) Flawless transaction, couldn't be happier, currently enjoying sonic bliss-Bravo!
Harman Kardon refurbed A224 integrated stereo tube amplifier EL84/6BQ5 beauty! (#330684623823) What can i say...Camaroguy is simply a true gentleman!!! Can buy eyes closed. (Note: Sent to Cambodia)
Harman Kardon tube refurbed A10 amp & FA10 receiver pair for stereo, 6BQ5 / EL84 (#330698463548) thanks for your help. A+ (Note: provided follow-up info. on hookup and operation of units)
Harman Kardon A300 refurbed to orig integrated tube amplifier 7408 tubes beauty! (#230782913856) Very generous with info/details about item. Packaging went "one step beyond." A+
Refurbed Harman Kardon TA3000X tube receiver, A300 amplifier circuit 15WPC 7408s (#230791745437) Plays well, good communication....fine Ebayer Also email: …Sounds really good... It was absolutely the best packing job I've ever seen. It was true care.
Harman Kardon A500 Integrated Tube Amplifier, Refurbed to orig. specs 25WPC (#330734051861) Absolutely the best amp I've ever owned. Expertly refurbished and shipped.
Harman Kardon A500 Integrated Tube Amplifier, Refurbed to orig specs 25WPC beaut (#330742827034) A+++++++++++++++++++++++++++++
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Harman Kardon A300 refurbed to orig., integrated tube amplifier 7408/6V6 beauty! (#330724342234) SUPER item, GREAT SELLER TO DEAL WITH -now just have to set this baby up! Thanks
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Harman Kardon A30K (A300) integrated tube amplifier, refurbed to orig., nice (#230942903430) Packaged very well and fast shipping, pleasure to do business with
Harman Kardon A300 integrated tube amplifier, refurbed to original, nice unit (#330896129005) I have never received anything that was packed this good. Excellent Seller!!!
Harman Kardon A300 refurbed integrated tube amplifier, K40Y-9 PIO caps, nice amp (#330901386193) Packed very good,sounds great and works like a champ, my first tube amp.TY
Harman Kardon refurbed A224 integrated stereo tube amplifier EL84/6BQ5 beauty (#330901581618) Very good communication, helpful and honest seller. Recommended.
Harman Kardon A300 refurbed integrated tube amplifier, nice amp. (#230980302576) A+++++ everything was as described phenomenal customer service
Harman Kardon refurbed A230, 15WPC, EL84/6BQ5 integrated stereo tube amplifier (#230991580545) Thank you. Perfect. Fast. Great communication.
Harman Kardon refurbed Prelude PC200 integrated mono tube amplifier 6V6 outputs (#231003877976) Carefully wrapped and boxed. Packaged so well it could have been air dropped.
Harman Kardon A30K (A300) refurbed integrated tube amplifier, 7408 (6V6), nice (#231013537159) Amp is great! Just as described, very good communication, Recommended!