AKAI M8 recapping

[RoyceVM]

Hi, I like to do full recapping (all electrolytic caps and any other ones that are necessary)) on my M8 and like to know the capacitor list with electrolyte types and film capacitors need to get replaced. The schematics don't show a good pic with the capacitor values.

The film capacitors should be fine right and so also the mica types, right?

The following is a list I got from audiokarma
https://audiokarma.org/forums/index....needed.360104/


C-ET25-50 Capacitor - Axial Lead Electrolytic, 25 ?F @ 50V x 8

C-MKP1-400 Capacitor - Audiophiler MKP Audio, 1 ?F @ 400V x 2 (what type is it?)

C-PD01-400 Capacitor - Polypropylene Film, .01 ?F @ 400V x 8

C-PD022-400 Capacitor - Polypropylene Film, .022 ?F @ 400 V x 4

C-SM390 Capacitor - Silver Mica, 390 pF @ 500 V x 2



33uf 450v Axial x 6

100uf 450v Radial x 2

I want to make sure I am ordering the correct ones. What are the ones I need to order from the above list?

[RoyceVM]

I found this list from the Service Manual

[Welsh Anorak]

Ah - the thorny issue of 'recapping'.

Most forum members, myself included, advise against recapping for the sake of it. I stress this is my opinion - others may (and probably will) disagree.

Three reasons.

One is that many vintage products, your machine included, have very good capacitors fitted originally and most will have a good few years ahead of them.

Two is that, despite what many forums say, there won't be much benefit to replacing them with 'audio grade' and so on, simply because the machine was designed with what was available at the time to give best results with the small internal speakers.

Three is that we have 'seen' many instances of people recapping a machine that was working and then it doesn't as they've made an error or caused an additional problem.

That's not to say at the age of the M8 all will be fine. Have a look at those in the HT line and the output stage input coupling capacitors. However I very much doubt any noticeable improvement will come by replacing other ones in the audio path. As you say, best to leave the non-electrolytics alone.

When you do replace components on a working machine do it one at a time, checking your work as you go to make sure it still works. We've all made mistakes!

Your machine, though one I like, did not have the greatest amplifiers and speakers. They are fine for a portable (!) all-in-one machine but to get the best from it you'd need to connect it to a hi-fi system where it can show off properly.

Rather than spend lots on expensive capacitors, I'd suggest you invest in an ESR/capacitance meter. These are available from China as component testers for very little money and are surprisingly accurate. With one of these you can test a capacitor and then decide if it merits replacement.

This isn't meant as a criticism, just some friendly advice.

[RoyceVM]

Great Advice! Much appreciated! Thanks so much!

I do have many other reel to reels like AKAI GX 747, 635D, 4000, 640, several TEACS and so on but thought this might die if I don't recap it.

M8 is all working fine and in like new cosmetic condition, and I was also a bit hesitant on recapping or not! I oiled and removed old grease and lubricated it.

[Analogue man]

I agree completely with Glyn, I never needed to recap my M8 right up to the point that I sold it. I have never needed to recap fully any vintage device although if the machine has been left unpowered for some years then the smoothing/reservoir caps could be dodgy but if regularly used then they should be fine. This is one of the finest sounding domestic decks of it's era (and better than some later machines too).

[Uncle Bulgaria]

Another seconding of Glyn's advice. 'Recapping' is a fashion common in the US that is based on misinterpretation of certain practices that were beneficial to a particular individual case. If you imagine a house, it's rather like considering one of the carpets is dirty, and then replacing all the windows and the roof just in case. You can imagine the possibilities for extra damage that would raise! Instead, when the device breaks, diagnose the fault and replace the faulty component, otherwise you risk fixing it until it breaks, or introducing other faults.

Also, don't worry about 'audio grade' capacitors. In electrical terms, the audio band is extremely easy to work with and very low frequency compared with many industrial applications capacitors are used where differences actually matter.

Any differences between a £10 beeswax and ambrosia capacitor made by monks and a 10p standard component would be, at best, completely inaudible. At worst, the boutique component may introduce distortion.

[knobtwiddler]

There are certain 'rogue' brands of electrolytic cap that ought to be replaced on sight, such as 70s / 80s Frako brand (gold coloured can - common in Revox and Studer). However, some of the Japanese brands can keep on going for many decades, even in a hot environment. In the case of a power amp that I have, the caps outlived a whole bunch of the resistors (they were fusible resistors, but once replaced, I could see no fault elsewhere in amp. There was no charring on them or reason to suggest they'd blown to protect anything).

As documented here when I changed the Rs in the 1978 power amp, because I have a Hakko FR300, I decided to change the non-reservoir electrolytics, as I was replacing resistors right next to them and had stock on the shelf. It added only a few minutes to the job and considering that the amp runs well into Class A, i.e. runs hot all the time, even having double shielding on the heatsinks to prevent exposed metalwork being near any external faces. Once I'd changed all of the caps, every single one tested within tolerance for capacitance and ESR.... Even the worst one on the link above measured within 20%.

So, the moral of the story (in keeping with previous posts) is that in some Japanese-made gear from the 70s and 80s, the electro caps are some of the most reliable parts!

NB - I realise that the M8 is from the 60s, but the caps may well be fine.

[TIMTAPE]

The M8 is an early 1960's all valve machine which means high voltage, lower capacitance caps. Not sure how or if that changes things here.

[RoyceVM]

Today when I turned on M8 and after playing for 5 minutes I heard cracking noises and it stopped after 30 sec. This happens once in a while. The pots are all cleaned, and it is not from the pots. I suspect it is from dried electrolytic caps. So, I will try replacing all electrolytic caps.

[Uncle Bulgaria]

Such a problem could be from a number of reasons. A capacitor could be at fault, but equally a corroded connection or dry solder joint could be to blame. Such intermittent faults are very frustrating.

However, an assumption followed by a blanket action of replacing all the capacitors could easily lead to more problems that are more difficult to diagnose, since you would have made many changes that could disguise the real fault.

I can only say that I would follow any diagnostic procedures in the service manual, particularly with regard to any DC voltages specified. Significant differences here would suggest a leaky capacitor passing DC. The circuit is logical, so a step-by-step diagnosis and the replacement of a faulty component, especially if like me you're inexperienced, is always a better idea than a scattergun approach.

It may be that one of our resident Akai experts will be able to tell you that this fault is common and from a known cause, with a suitable solution for you.

[Welsh Anorak]

As the M8 has two similar amplifiers, you should be able to tell where it's coming from by seeing if it's one speaker only or both, or actually a noise from the machine.

My money would be on a loose valve or dirt on the record-play switch. Remove each valve in turn, clean the pins with some fine wet-and-dry paper and re-insert. Clean the other switches with switch cleaner and see how you get on.

Take it slowly and don't rush in - although it COULD be a capacitor causing this there are many more things that are more likely.

[Analogue man]

Again I agree with Glyn, much more likely to be poor connections to the valves and the amplifiers on this deck unplug from the chassis this is also possible but mine suffered from dirty switch contacts so before you change any capacitors do go through all other possibilities, it may be a little time consuming but worth the effort.

[RoyceVM]

Thank you, UB, Glen and Graham!
I will clean the valve pins and holder, spray Deoxit on the pin holders, check the valve seating, then clean the record switch again and see how it goes. The two record switches I cleaned it well with Deoxit FaderLube5. So there is a good chance it is from the valve seating or bad solder, connection from the pins.
Royce

[Radio Wrangler]

You have to be exactly right in your choice of new components.
You have to be good at finding a source to buy from which doesn't send you fakes.
Your standards of workmanship have to be excellent. No dry joints, no solder splashes.
You need to take care over static electric damage to components you may not be changing but are connected to places you are touching.

Because most things contain an awful lot of capacitors, you have to be very good indeed at ALL of the above or you will probably introduce more new faults than the thing had in the first place.

If you're taking the 'just change them all' route as a way of avoiding the need for diagnostic skills. then be aware that for a lot of people it has proven to work the other way.

If you replace only one part at a time and test the set each time, then finding any problem you introduced is made a lot easier, but the labour savings you likely expected from just doing the lot went out the window.

Don't take this as criticism, it's just that the statistics get loaded against you quite badly by the quantities involved. We all make mistakes, but the statistics with so many variables make the crossover point where the probabilities become favourable quite a distance from where you instinctively assume it to be.

Sometimes, changing the lot is the best approach. It's just that recognising when takes some work and some experience.

David

[RoyceVM]

Thanks David! Great advice!
I will replace the caps one at a time making sure about the right polarity. I have fully recapped many tube radios, reel to reels, decks and boomboxes in my collection. German SABA 125 and SABA 300 plus several Philips high end tube radio's full recapping gave me some good experience. I am no expert and there is a lot to learn over time. Always on the learning curve! There is a lot to learn.

[RoyceVM]

While cleaning the tube pins and all on the right channel, the tube holder slipped off from my hand and broke V5 (6X4??) tube.
Big mistake! I should have uses hook to pull the wire spring holder out and then remove the tube.

It is NEC 48 and I believe it is V5 (I have the HiFi Engine manual that is so blurred! I can barely see the pics.

Now looking for a replacement.

[RoyceVM]

I believe V5 is 6X4 tube.

It says NEC 48

[RoyceVM]

Yes, 6X4 that I could read it on the left channel tube and ordered one.

[DMcMahon]

The schematic clearly shows that the V5 fullwave rectifier is a 6X4.

I presume NEC is the manufacturer, do not know what 48 signifies, do not think it is part of a valve type designation.

David

[RoyceVM]

Thanks David!

Yes, schematics shows it clearly.

I already ordered 6X4.