With proper components and internal wiring upgraded it gives excellent sound

I’ve owned the AI 500 for ten years. I bought it first-hand in 1989. The amp is very good stock standard: its mains and output transformers, as well as some crucial passive components are of very good quality. Manufacturers managed to achieve a competitive price saving money above all on the quality of the tubes, on the input rotary switches and on the carbon pots used for volume and balance controls, more suited to cheap consumer goods than to high-quality audio equipment.
After a few months from purchase I experienced the same kind of problem reported by audio enthusiast Tungsak in his review dated 11/13/97. The trouble he reported with fire was probably caused by the general poor quality of the valves the amp was equipped with - the EL 34s in particular, whose plate tended to overheat with the consequent burning of both the plate itself and the cathode resistor. Replacing both the original EL34s with selected matching pairs from Golden Dragon (as in my case), and of course the original cathode resistors with good quality ones (Resista), has eliminated the problem (I haven’t experienced it for more than five years since then).

Indeed, the amp benefits greatly from tweaking. Given the poor quality of the valves - in my amp, for example, phase splitting was obtained through a couple of PCC88s (cheap TV tubes) instead of the far better and more expensive 6922s - a complete revalving of the amp is a “must”. Besides, I’ve tried different tweaks, which can be summarized into two main options: a “basic” and an “extreme” one.
BASIC (costing about US $ 70 in passive components):
1. Replace the EL 34 cathode resistors with Resista type and remove the poor electrolytic capacitors connected in
parallel to these resistors, whose function is to partially decouple them and, consequently, to “soften” clipping at high volume levels. The tweak will help reduce sound grain. Clipping will be sharper, but you won’t face the problem at
all with sensitive speakers. If you don’t want to remove these capacitors, replace them with high grade audio types such as Elna Cerafine or Nichicon Muse.
2. Remove the two input 0.22mF/400V ERO MKT 1813 capacitors. Their only function is to protect the circuit from possible residual AC (EU requirements?): signal will be cleaner.
3. The two generic 100mF/50V cathode electrolytic capacitors in the drive stage should be replaced with Elna Cerafine or Nichicon Muse types. You should extend the tweak to the phono stage, if you use it often.
4. Decoupling capacitors: the generic 33mF/350V capacitors decoupling the drive and final stages should be replaced with compact radial or snap-in 105°C low ESR types.
5. Input selectors: they are quite poor and should be replaced with better types (silver contacts), ensuring great precision for long periods;
6. Volume control: the original potentiometer is of poor quality: a standard ALPS will guarantee a long life with no “scratches”.
EXTREME (add further US $ 120):
7. Power supply: replace the generic bridge rectifiers with IR Hexfred HFA08TA60C (anode voltage) and Schottky
SB 340 soft recovery diodes (driving and phono stage filaments);
8. Coupling capacitors: the AI 500 is equipped with very good ERO MKT 1813 capacitors, among the best sounding in the polyester series. Yet, their replacement with Jensen paper in oil capacitors (aluminium foil)
will allow a significant improvement in detail, depth and imaging. The considerable dimensions of paper in oil capacitors make replacement complicated, as it implies a new design in the printed circuit of the stage.
9. Replace Beyschlag metal film anodic resistors with 2W matching pairs Allen Bradley carbon film resistors.
Tweak 8 is quite demanding, since it implies a new design in the printed circuit of the final and drive stages which, in turn, will allow the use of the AB resistors, bigger than the Beyschlag. Yet, in combination with the other tweaks, it will allow a great improvement in the general performance of the amp. The sound I have obtained is really gratifying. It is larger in the three dimensions, closer to that of monotriode amplifiers: power seems to go far beyond the 25 Watts declared, probably because of the illusion created by a sound which seems to be “big” without being massively loud. Mids are revealing, high frequencies airy and silky, drums acquire in depth and realism. That slight haze, especially in the upper mid and in the higher frequencies, which prevented me from listening with full precision before the tweak, seems to have disappeared: imaging is solid and close to real, vocals lifelike and involving, impact and dynamics surprising for a valve amplifier. With about 200 US $ added to the amp price and a bit of my spare time I have managed to obtain an amp whose sound can rival with that of amps costing the triple. Give it a try, bearing in mind that tweaking tube amps requires care: anode tension is almost 400V in the AI 500, so do not proceed in any case if it is the first time you use a solder!

25W

no

Ineed audio inovation series 500 manual!!!!!!!

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maicthosh 270

fantastic sound, great looks

For three years this sweet amp is processing my music. Even with my medium sensitive (86 db) Vifa speakers the sound is warm, enthousiastic and never tiresome. Recently I changed my old EL34's for new ones from ValveArt and the sound is even more impressive. Ella's beautiful voice is even more clearer and warmer. My AI500 is De Jong Systems upgraded with better parts.
For the money (aspecially when purchased second hand) you can't get a better sounding amp.
It deserves al the stars it can get

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Quad 66, Sphinx Project 10

Typical valve strengths of midrange tranparency.

Soggy bass even with Snell model E and J speakers
that are supposed to be suited to this amp.Pretty mediocre
at dynamics. Only suited to vocal and small scale music.

An old valve amp design with too many weak spots
to be recommended, even used. Audion silver night
is far superior in every area of performance, although
the price difference for a used one is not huge. I simply
feel that even if the midrange is far superior to
many cheap transistor amps I cannot really recommend
this amplifier. Even a pair of old Quad II s sound
superior.

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Hiraga class A, Audion silver night 300B

Sound, Look

none

I had this amp 8 years ago and the unit I have right now was purchased as a second hand over the internet from Border Patrol.

My first unit had a beautiful sound and it was driving B&W801 speakers. It had some limits in power but still the sound was huge, warm and yet detailed.

The second unit come with 5881's as output tubes and some no-name ECC88 and ECC83. I must admit that after first listening I was really disappointed. I remember from previous unit that this amp could sound heaps better, so I start to experiment with different NOS tubes. After changing a few different brands I end up with two E88CC SIEMENS, three 12AX7 TELEFUNKEN and four 6L6GC SVETLANA for output stage.

The sound of AI 500 with this tubes is the best I ever heard. The bass is very tight, strong with a lot of punch. The mids are beautiful, very realistic and detailed and the highs are clean, extended but with no harsh at all. Soundstage is wide and deep....

I will highly recommend this amp and I think that as a second hand buy it is a really great value for the money.

My gear:

Audio Innovations 500
Audio Note AN/J speakers
Audio Note AN V silver interconnects
Audio Note AN L speaker cable

PS. Sorry for any mistakes in English....it is not my native language...

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Audio Innovations 800MkII

I bought this amp second hand about two months ago from a local dealer. So far I've found it to be very easy to live with possesing a smooth, warm and rich sound. The source to the amp is a Teac CD player with an Audio Alchemy Dac in the Box offboard D to A. The amp feeds B&W CDM 2se speakers. Prior to this I owned an Adcom pre/power combination that was very powerfull but a little cold and uninvolving. All in all I think the 500 is a gorgeous amp but it could sometimes do with a bit more clout. Worth the money and four stars.

I've listened to a lot of the Audio Innovations amps - the 500, the 700 and what I currently own - the 800 Anniversary power with P2/L2 preamps.All AI amps are well-built - unlike much low-priced valve gear - and well-designed (ditto).
But all of them can be transformed with an outboard power supply from Border Patrol - they're designed by a guy who had a lot to do with AI when they were in operation, and can service all AI kit. (Not much good for you lot in the USA, I know, but occasionally us Brits get something you Americans don't).
Audio Innovations amplification is solid, powerful (despite its rating) and doesn't have the foibles a lot of fragile valve gear is infamous for.
Look out for any second-hand and don't buy it - send it back to the UK and we'll buy it!

THIS IS A 50 WATT PURE CLASS A PENTODE TUBE AMPLIFIER, WHICH IS VERY PLEASING TO THE EYE AND EVEN MORE TO THE EAR. SENSITIVE SPEAKERS A MUST!

I'm a proud owner of a Audio Innovations 500. When I wanted to buy this amp, I first talked to the designer of this amplifier which version was best to buy. The best sounding one is the one with the 4, 8 and 16 ohm output transformer. This amp is the best one I've ever heard for it's prize. I'ts a pitty that the company doesn't exist anymore. For all the dutch owners, if you still want to upgrade you're amp, or give it a good check, call De Jong Systems Tel: 0493- 312604

I purchased one of them secondhanded and I must admit that the sound already made me cry out loud in the shop. It was soooo smooth like nothing else. It even looks very good.Even though you can't comapre it to a manley tube amplifier, I think this little wonder comes very close to being perfect!!!
It deserves 5 stars!!!