You should not leave this amp powered up at all times for several reasons. If the amp is in original stock condition, there are some very well aged parts inside this amp that might be in less than top notch shape. You risk damaging the amp and your speakers by leaving it on at all times and most especially if you are not in the space to monitor any malfunctions. If the amp has been refurbished and given a good condition report, then you should make your decision about on time based on tube consumption. Most tube amps will idle very hot which will use up the limited lifespan of your tubes while doing nothing other than heating your room. You will find yourself buying output tubes every 6-12 months at about $100 per set, not to mention listening to the amp with deteriorating tubes for most of their life.

After you've listened to the amp for several weeks you'll have an idea how much time it requires to come up to listenable sound quality. The amp needs to bring all of its components up to proper operating temperature and this takes at least twenty minutes for most tube amps as the iron cores of the transformers are slow to change. If you listen for several hours at a time, you'll probably notice the amp does continue to get slightly better over that entire time as the components reach thermal stability.

You can try your speakers on the various output taps to find which set of taps provide the best sound quality with your speakers. If your speakers are rated at a nominal eight ohms, try the four and the sixteen Ohm taps to see if there is an improvement. It is not uncommon when pairing today's speakers with vintage electronics to find a lower or higher impedance tap provides the best sound quality due to the wandering impedance curve of most modern speakers.

Never do anything to the amp when it is powered up. Make any connections or tube changes with the amp powered down. Most importantly never run a transformer coupled tube amp without a load, either speakers or a proper load resistor must always be in place when the amp is powered up.

Do not poke around in this amplifier unless you are certain you know where not to stick your hands, which is almost anywhere inside a tube amp. The voltages inside this amp are in the 350-650 volt range, more than enough to kill you. And these voltages are present even after the amplifier has been powered down for 24 hours. Either learn how to work on a tube amp or have someone who is trained to work with tubes do your repairs and refurbishing.

If this amp has been in storgae, you should not be plugging it into a 120Volt outlet and slamming it with full voltage by flipping the "power" switch. Vintage electronics need to be brought up to operating voltage while connected to a Variac and the current draw should be monitored while the amp comes up to full power. If this amp has ben in storage for any number of years, you will probably have capacitors that require service. If you begin to hear a solid 60Hz hum from the amplifier, caps are going out. If you haven't already, I would begin searching for a repair technician who is experienced with tubes. Better to have someone lined up when you need them that to go searching once a problem has occurred. If the amp hasn't been serviced lately, that would be a good idea at this time before you start running the amp on a constant basis.

If you do not know how to set the bias on this amp, have someone show you how to set the amp up for proper operation.

Tubes have a use life. Leaving it on all the time could be expensive. That said, I bought a basic Jolida 202 integrated amp in 1996 and just traded it last week. It used 4 EL34's as drivers and I was still using the original tubes when I traded it. I bought a PrimaLuna integrated amp with KT88's and had one die after 7 months. I can recommend one wait perhaps a couple of minutes before you try playing the unit but half an hour is way beyond my experience. I would also try to figure how to properly bias the tubes in your unit and then insure they are all pretty much the same.

I know nothing of a Variac and have no opinion. I do like power conditioners and can recommend a basic one like a Monster unit at a resaonable price.

Here is a source for used power products

http://www.thecableco.com/prodListing.php?cat=2

If you want new (and in this area I do) try PS audio

http://www.psaudio.com/power.asp

I like their power cords. If you are really on a tight budget, try APC, a computer protection brand that works OK for audio in most circumstances.

No, you do not need to buy a Variac. It is used to slowly increase the available voltage and current to a load, in this case that would be your amplifier. If your amp has been serviced and refurbished recently, there probably isn't a need for such a device. However, a unit that has ben in storage for several years will typically have power supply caps that have dried out. Hitting these with 120VAC can lead to their quick demise. The amp will operate without problems for a few days/weeks and then you'll hear the hum caused by bad caps. Bringing the unit up to full power by way of a Variac and monitoring the current draw while the power increases ensures that amplifier doesn't have potential or serious problems and is likely to be safe when you attach a pair of loudspeakers. Any shop should be able to perform the basic service of checking current draw on the amp, the question would be whether they want to get tied to a unit that old about which they know nothing.

If you've been using this amp without checking it out first or any assurance of its condition, the best you can do now is go ahead and run the amp and hope for the best while preparing for the worst should that occur.

You should decide on a power conditioner according to your situation and location. If you live in an area prone to electrical storms or power failures, then a surge protector would be a good investment. Panamax builds good units and there are advertisers in Stereophile you might also consider.

I was never a fan of the Dahlquist line but you should decide for yourself what you prefer. Since the introduction of the Dahlquist speakers, loudspeaker technology has improved by considerable margins. IMO there are only a handful of speakers from that time period that would still be competitive with today's budget speakers. Listen to a few selections at a respectable dealer's showroom before springing for used speakers.

Quote:
I can recommend one wait perhaps a couple of minutes before you try playing the unit but half an hour is way beyond my experience.

I don't know the Jolida line well enough to be certain of how they operate. However, most modern tube gear has a "Standby" function that keeps the idle temps stable by way of a trickle current and this allows for better overall performance and longer tube life. Also, if the Jolida has a soft start circuit, this will extend tube life by slowly bringing the amplifier up to full power slowly rather than slamming the tubes with 120VAC. The older HK amp won't have either function and tube life will typically be shortened compared to a modern tube amplifier. The "Standby" function also keeps the unit at a more consistent internal temperature and such an amplifier should sound better after a shorter period of time than a vintage tube unit which must come from dead cold to close to full temp before it starts to sound good. I find my tube pre amp, even with a "standby" mode, requires about twenty minutes before it evens out and the balance between channels is set. If I power down my vintage Mac tubed power amplifiers for any length of time, I will hear a slow but consistent improvement over the first thirty minutes and then a gradual improvement in sound quality over the first two days as the transformers settle in. However, the McIntosh amps idle at a very conservative temperature and I can place my hand on the transformers of the amp when it is at idle. Not many vintage amplifiers would allow this and you would come back with a burnt hand with most vintage amplifiers.

Thanks...that is how my PrimaLuna amp works, a slower powerup, but that still only takes a couple of minutes. The thing sounds good in under 5 minutes but it is a very new design.

No, you still don't need a Variac. It's purpose is more for test bench operation than day to day use. Your amplifier will sound better run either directly from the AC outlet or from a power line conditioner. If you search the internet you can find "soft start" modifications for tube amps of the same vintage as your HK. Possibly the shop in Denver that took care of your amp can suggest such a modification or perform such on your amp. Otherwise, just run the amp as it was intended. Tubes wear out and you'll have to accept that sooner or later you'll need new tubes.

Quote:
Will a power conditioner provide a minimal amount of power to the amp ...

I'm not sure what you're asking here. A power conditioner does not provide power, it merely smooths the incoming AC voltage to minimize the surges and noise found on most AC lines. Do some reading on line conditioners and determine what you feel is necessary for your installation. If your location is not bothered by storms or power surges/outages, then you can very likely get away without a line conditioner. Most items such as the Panamax are sold with a return policy which affords you the opportunity to try before you buy.

I would avoid the strip type surge protectors as they do not respond fast enough to secondary surges to actually protect your equipment in a storm. Cheapo strip devices will prove detrimental to your sound quality.

Buy as good a product as you can afford but, if you do so, make certain it is a unit you really believe you can live with for long periods. Technology changes over time and what you buy today might be outdated in a short while. Spend wisely rather than spending often.

http://hktubeaudio.homestead.com/files/tubecode.html

http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm

http://www.lh-electric.4t.com/tutorials.htm

http://www.symphonysound.com/articles/tubefriendly.html

http://www.worldtubeaudio.com/

http://www.vintage-electronics.cc/index.html

http://www.tubedepot.com/whisbipo.html

spencerlholbert wrote:

An update about your feedback and the Harman Kardon amp: The amp tubes have been recently biased and "tuned-up" by professionals in Denver. Everything seems to be in as good of shape as possible for the amp's age. I know there is a lot of talk about tubes burning out, but this amp is all original besides maybe a few capacitors. I think that it is one hell of an amp to be even running the original tubes after 43 years. Also, the amp runs ETREMELY cool, that is probably why the tubes have lasted so long. I could literally touch the tubes after they have been running for an hour (I do not want to because I do not want to get oils and what not on them). What I have found out about the construction of this amp is that it runs the tubes at 360v and 25 watts, but the tubes are rated at 500v and 50 watts. That is probably the reason it runs so cool and the tubes have lasted over four decades. I can show you pictures of it if you want, or you can view a refurbished model at (http://www.wardsweb.org/audio/HK.html). Yet I still have some questions...

About the variac and/or similar devices: Seeing how my amp does not have a standby, and that I plan to stick with older vintage amps (more nostalgia, in my opinion) should I invest in one? Would a more expensive power conditioner from panamax or another company do basically the same thing? I would prefer to spend $400 on something that will last a long time and will provide multiple solutions than to buy several individual devices. I know this is not "audio purist," but I do not have a lot of space and I will have to move all of this stuff in December 2009.

Will a power conditioner provide a minimal amount of power to the amp (provided I spend the money) or is a variac the only solution? I would like to baby the original tubes for as long as possible, so whatever would be best, not only for this amp, but also for all of my future upgrades. I would rather spend $600 on a device that will meet all of my needs for the next ten, twenty years, especially something like a power conditioner. I would rather bite the bullet once and spend my money on the other components for now on. Is that flawed logic?

One last thing: If I will need to buy something to ease my amp into it's full power level no matter what, and a power conditioner could not perform this task, could I be a bit cheaper and buy the "power-strip" conditioners instead of the component versions? Again, if something like that will not meet all of my needs currently, I do not want to pay $125 for it when I could spend a bit more and get a much better unit.

Sorry I wrote so long, and thank you so much for all of your help! I am just a 22 year old beginner! I have been in that evil world of solid-state for the past 14 years.

I bough my A500 new in 1963 or so, and just used it daily until 1979. I never replaced the power tubes, and they tested fine after many years of service. They are not highly stressed in that circuit unless you have raised the high-voltage on the plates.

I operate ALL of my audio and video gear from a APC battery backup UPS unit, and it can protect gear very well from the power company's surges and outages; I recommend spending $250 or so on one of them to keep everything running during various events that can damage mechanisms and integrated circuits.