Akai M8 Restoration

M8 Left Channel

As promised we move on to the inner workings of this single motor transport deck and tube amplifiers.

Note that we have also details on this marvellous amplifier and deck on our sister website’s pages:  Analog Ian

Restoring an Akai M8

This tape recorder came onto market about 1965 sometime (HiFi Engine lists this as 1963). It was preceded by the M7 and then afterwards, the transistorised M9.  Both these models also proved to be very popular. Enthusiasts veer towards the tube amplified version, discarding the deck.  If the deck is still in good condition I would not advise this as much of the parts can still be purchased through eBay albeit at astronomical prices or if you are fortunate enough, repair machined locally.

I purchased two of these units over the last two months. The first unit was not in bad condition, the amplifiers still worked but the head switching mechanism (mechanical) was missing. The pinch roller shows capstan burn. Capstan/flywheel belt is loose. Counter belt also loose but has enough tension. A catch was missing from the lid as well as not having the metal rear cover.

The second unit was the conundrum. The photos on Gumtree did not do it justice. When received I found it to be in many ways better than the first deck although I was going to use this for spares to get deck number one running.  Both M8s cost about 200 U$ which I felt was pretty much realistic for what I was getting.  Paying more for these recorders may leave one frustrated if there is an issue with a tube, mechanical cam etc. Although everyone sells these as being in excellent working order guaranteed there’s going to be a hiccup – if not hidden in a sea of lies maybe through shipping damage. Tubes do not travel well. This deck also had a dodgy pinch roller (dried and cracked). The heads still looked very good though.

For those buying these recorders for the tube preamp and class A single Pentodes must note that these amplifiers run off 110V and not 220 or 240V. There is an auto transformer mounted in the case which supplies the correct voltage to these amplifiers – so you will need another 2:1 step down transformer for mono block usage. These amplifiers have their own 110V (primary) isolation transformers.

Both recorders had major pinch roller slippage (as received). Back tension also felt very high. The metal cams used in the FF/REW which everyone complains about was still intact and in great condition. Cleaning and de-greasing required. Start capacitors for motors seemed to still be good, both decks had very strong motors and FF/REW pull was like new. I don’t have test tapes – this is next on the agenda but right now we are aiming to restore only one M8 and do the other one later.

At this stage I must mention that although both these machines are over 50 years old the transport mechanisms were still in very good condition (bar the rubber).  There’s a few words of caution which must be heeded when working on any vintage circuits (actually all goods running from mains power):

  • The supply rails to tube amplifiers are lethal. We are not talking about starved anode supplies but the real M’Coy.
  • Discharge all capacitors after powering up and switching off.
  • Always remove the mains plug from the outlet.
  • When working live make sure you follow the one hand rule. (keep one hand behind your back if need be).

Electrolytic Capacitors

Electrolyte dries out of older cans and these caps need to be replaced. Enthusiasts call applying a low current source at the working voltage of the capacitor reforming. In many cases electrolytics should be replaced with new units. Sometimes we can get our hands on NOS (New Old Stock) cans and because we want to keep the equipment vintage we stick to these. It’s not always the best solution. Electrolytics can blow up entirely or blow smoke and flame through the vent, not a pleasant sight, neither smell. Electrolyte is conductive and will damage other circuitry – it’s just not worth it. (a certain Chinese brand of computer power supply was notorious for catching fire so be careful of the quality of these electrolytics – and this is not to say that all manufacturers in China make shoddy products, some are excellent).

If you can, power up through a variac or have a current limiting solution like a light bulb, possibly a 60W for high voltage and a regulated supply for low voltage reforming.

Mains Transformer

The mains transformer in the Akai M8 is not an isolation transformer but an auto variety. This is a multi-tapped transformer. A while back a reader asked how to connect this to his amplifiers because the wire colouring did not match that of the diagram. The rule of thumb here would be to have an accurate resistance meter do the work for you. The highest reading between the windings on resistance check should be the 220V leg. Midpoint would be 110V. A variac or lightbulb in series is the best way to check after you have done the resistance checks to prevent the transformer from burning out. If the voltage is too high the transformer will start sizzling – they can be resilient beasts but always be very quick on the switch. Never apply power to a transformer if you aren’t sure of the winding configuration with a load applied.

Before powering up

Always clean the insides. A spider or roach resting across the terminals of a high voltage source may catch fire putting an end to your project. Smell, look and feel.  Something that doesn’t smell right is not alright. The previous owner may have cooked the mains transformer, a capacitor may have leaked, a resistor may be burnt.

Make sure the voltage setting is correct. Especially if you live in a 220V country.

Next up, some circuitry to look at:

M8 Left Channel
Akai M8 Left channel with bias oscillator

Next Page:  The circuits

The Revival of the Akai M8

Akai M8

The Akai M8 Crossfield Head Recorder

Dedication

Those who were around in the 1960s will remember the furor caused when this machine came to market. I dedicate this article to my late father Chris whom had one.

Akai M8
Akai M-8 – Vintage pre-1970

The Akai M8 was not the best machine out there, neither was it supposed to be at the price point it was released. It certainly wasn’t cheap but more to the point, those that had the test tape will remember that it’s fame was not around the tape quality at 15 i.p.s. but rather 1 7/8 i.p.s. and the Cross Field Head, licenced by Tandberg. Many audio enthusiasts unfairly compare this machine to professional machines at the time which came out with three motors.  The point here is that a machine with one motor is often more difficult to design compared to one with three motors. These motors can be very expensive and in order to mass produce at an affordable price point there was usually quite a bit of sophisticated engineering involved. (a case in point is that many enthusiasts in the 50s and 60s used to design and build their own mechanisms – often with three motors. Solenoid and switch control is easier to design (and build) than manufacturing cams, linkages and gears).

Revival

The M8 has made its appearance again over the last 5 years, not for it’s marvellous deck but for it’s audio amplifiers. I recently purchased one and will be restoring the deck and the audio section. A good price is usually around 100 dollars for a working unit. I paid about 65 dollars for mine. I do not know whether the amplifiers work because I should run them up through a variac first (which I don’t have) but the deck does need some maintenance. Strangely enough the pinch roller is not in bad nick although the belts will need replacing. This unit must have been kept in storage for some time gauging by a look at the casing.

Wow and flutter, hum and noise and cross talk may not have been perfect but I do recall on the new machine recordings of piano playing were usually exceptional – I recall this because I was ten at the time. When my hearing was still intact. A ten year old doesn’t know what wow and flutter may mean but will certainly complain if it was audible.  The other thing, at 15 ips these machines were very capable. Most RTR of the time were only 3 3/4 ips and looked their age. The M8 in comparison looked like a space ship. No, it’s not a Zoom H6 but in capable hands and with good quality tape some pretty damn near professional recordings could be had.

Restoration

This deck will be restored because I do believe the transport mechanism is not in bad shape (which we will come to later). Quite often on the forums we have the vintage collectors pleading for owners not to cannibalise or modify these decks for the amplifiers but personally speaking if the deck is in bad shape it may just not have any value to the owner in any event. Many of the students of tube technology have absolutely no interest in the deck – only the sound of the amplifier.  My recollection is that the amplifier quality was not bad,  a fairly flat response and the reproduction of vinyl was crisp. This was also in the 70s when transistorised amplifiers were making their mark. Not knowing much about audio quality I do recall the solid state amplifiers as being powerful and crystal clear, the tube amplifiers were just lost in all that power and “perfect” imaging of the program source.

I do not believe that tube amplifiers are better than SS. I do believe that they sound different and depending on their use tubes can be superior. I do not believe that tubes should be used for home theater and in my own experience if one needs a tube microphone preamplifier it should be all tube. Power amplifiers are cheaper in SS format and we shouldn’t be clipping them in any event unless that’s the desired sound required. Tubes are remarkably resilient and for those that now claim they have a lifespan of two years then I wonder how CRT manufacturers got away with for so many years. My personal favourite is Mullard. Tube biasing is a personal cringe I have. We have so many different types of biasing now available today one must wonder if the engineers of yesteryear were just plain stupid. No, it’s all marketing hype. I have worked on transmitters delivering thousands of Watts to the load and the only advantage we have in modern times is that the critical safety circuits have all gone the SS route. Because it’s cheaper and more compact.

The EL84 output stage of the M8 is nothing unique. The design was very popular and of course the EL84 was definitely one of our more popular tubes. In the USA we have other permutations and audio engineers had their own preferences, often very valid. Compare USA and Brit guitar amplifiers for instance. The more popular “Hi-Fi amp” was the push pull version of the EL84 amplifier. In the 70s I rarely came across any tube amplifier reproducing more than 15W and the El34 was seen as an extravagance – quasi-complimentary and complementary transistorised amplifiers were becoming popular, didn’t smell as much and were way more efficient. I mention “smell” here because anyone not familiar with tube equipment will think there’s something wrong when first powering up their vintage piece of equipment.

Something to remember:

Tube amplifiers use in most cases dangerous voltages on their anodes (or plates) and screen grids. The supply rails can be anything above 250V DC and in high powers 750V or more. This will cause serious burns and God forbid, your early demise if you are not careful. Ensure the equipment is switched off and unplugged. Discharge all smoothing capacitors either across their terminals (better) or across ground and + rail.  Do not use your multimeter probe to short out the capacitors if you value the probe. Tube circuits use high impedance and it’s not advisable to “probe” around on the control grid circuits unless your meter has a very high input impedance.

This Akai deck is often compared to decks costing very much more.  Indeed the M8 does not have a boastful spec compared to modern equipment but then again neither does Tandberg, Teac and Revox/Studer. The Akai GX series were funky looking and the quality on spec often superior to the older tube amplifiers and single motor decks. They can be obtained off eBay for fairly realistic prices. Magnetic material (composites) used on tape for recording and the biasing also plays a remarkable role in the end product.

Interesting article here:  The Roberts Akai relationship at the museum of magnetic sound recording. (we include this because there has been a large amount of nonsense written about these two brands in the forums).

Part Two – the restoration process

Tape Recorder bias