Thisis a very nice Harman Kardon A500 tube integrated amplifier, serial number 4986368.

NOTE: Revision, I found a nicer set of knobs, first two pictures updated.

Over the pastfew years, I have restoredover100 HK tube amps and receivers and sold most of them on . See response on my amps and receivers at the end of listing.

See my other listed HK tube amps and receivers now listed on . I also will be listing a tube cage for this amp in a separate listing.

This isan HK A500integrated 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 HKamps 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 coulping 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 andlabor 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.) may become noisy, 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 inrectifying diodessince these units were first built, and that\'sone 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.

Properrestorationof the A500’s is 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 thecoupling and electrolytic capacitors and potentiometer replacement. On this unit in addition to the premium Sprague/Vishay 716 series orange drops, I installed Russian K40 PIO\'s (paper-in-oil) for coupling to the output tubes-K40\'s are prized caps by tube folks). 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 myB&K 707tube tester—and replacedany that were marginal.The four output tubes are a matched GE set, all dated coded April, 1964..

Appearance condition: Thecondition isexcellent with some very minor issues.The faceplate is nearly immaculate,an issue is a very light vertical scratch on the left edge of thefaceplate, all lettering on thefaceplate and chassis is crisp and clear, chassis exceptionally clean. Except as noted, there are almost no indications of wear on the faceplate or chassis. (See pictures). The knobs are all correct (original). This is one of the very cleanest A500\'s I\'ve had.

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 picture).

Work performed on this A500 consisted of:

• Replaced all of thecoupling and electrolytic capacitors--not because they have failed, butto increase reliability and bring the unit back into specifications. (total of 24 capacitors). Capacitor failures can ruin your day (and your equipment).
• Replaced thepower supply rectifying diodes withmodern 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+ voltagesand 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 of8 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 50+ year old amplifiers and making them available to a new generation of tube folks.The HKtube 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 93-95 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 andwhile the unit is rated for a 100% duty cycle, I suggest turningit 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 buyer.

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, Ioffer both USPS andFedEx shipping, check both for cost.I do prefer FedEx, seems to be a better choice.

For international shipping, I ship to all countries covered by the Global Shipping Program. If your country is not listed, contact me, maybe we can work something out.

If there is an issue, I will work with you--check my response, I am honest.

Happy Listening!

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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!

Harman Kardon A500 integratedtube amplifier, refurbed to original 25 WPC, nice! (#231103795100) ExtremelySatisfied Exactly as described. Bought before AAAA++++ Seller

Refurbed Harman Kardon A230stereo integrated tube amplifier, 6BQ5/EL84, 15WPC (#231101498741) Perfectpackage, quick shipping, accurate description, excelent communication++

Harman Kardon A300 integratedtube amplifier, refurbed to orig., K40-9 PIO caps (#231113685092) A+. The packaging, communication andof course the A300... just awesome. A+A+A+

Harman Kardon A30K (A300)integrated tube amplifier, refurbed, K40-9 PIO caps (#231123278867) Amazingamp! Packaged well, sent out in a timely way! A great seller!!!!!!

Harman Kardon A300 integratedtube amplifier, refurbed to orig., K40-9 PIO caps (#231127557692) A+++++ excellent communications &great shipping/pkging. Great restore on unit!

Harman Kardon A300 integratedtube amplifier, refurbed to orig., K40-9 PIO caps (#231117161141) Thegreat seller! Very responsible! Excellent packing!!! Extremely recommended! Note: Sent to the Russian Federation.

Harman Kardon A300 refurbedintegrated tube amplifier, K40-9 PIO caps, beauty! (#231129361216) Couldn\'thave been a better experiance.

(2) Harman Kardon refurbed tubeA10 amplifiers, pair for stereo, 6BQ5 / EL84 (#331108899546) Highlyrecommend this seller.

Harman Kardon FA3000X tubereceiver, HK A300 amplifier circuit 15WPC 6V6 7408s (#331115414080) ******6 Stars!!! Best communication! Best shipping on complex item! Excellent

Harman Kardon refurbed FA10 tubemono receiver, 6BQ5 / EL84 10 watt,nice unit HK (#331121436673) Best experience I\'ve had on .Excellent service and knowledge

Harman Kardon refurbed tube A10amp & FA10 receiver pair for stereo, 6BQ5 / EL84 (#231150623416) Unbelievabledetail,care,support!! Best seller on ...best on the planet!!!!!

Harman Kardon A224 integratedstereo tube amplifier, refurbed nice vintage amp (#231159509912) 6 starsif I could! Could not be happier - I love, love love this amp!

Harman Kardon A300 refurbedintegrated tube amplifier very nice! (#331115102141) Great transaction.Packaging and followup assistance was beyond expectation.

Harman Kardon recapped F10 monotube tuner, matches HK A10 series amplifier (#231161867801) Top notchseller and very pleased with the item. Thanks!

Harman Kardon recapped F10 monotube tuner, matches HK A10 series amplifier (#231154397752) goodpacking, fast shipping, good communication and a very nice product

Harman Kardon A300 refurbedintegrated tube amplifier, Russian K40-9 PIO caps (#231166554536) Arrivedpromptly, very well packed. I already am enjoying the sound!

Happy listening!!