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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 30th Jul 2023, 8:35 pm   #1
bigfathairyvika
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Default Akai 4000DS head condition.

Hi All,

Just had a friend drop round an Akai 4000DS reel to reel deck he was given.
Looks clean inside and out.
Have no idea if it actually works OK as haven't any tape or reels.
It definitely needs a hum sorting and a set of belts.
I read that if the heads are U/S then it is junk as replacement would probably cost a small fortune.

Is the only way of checking the heads - playing a tape?
Picture of playback and record heads attached.

Mark
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Old 30th Jul 2023, 11:42 pm   #2
Ted Kendall
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Default Re: Akai 4000DS head condition.

There appear to be shallow wear tracks on the heads, but they seem to have plenty of meat left. I'd give them a try.
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Old 30th Jul 2023, 11:44 pm   #3
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Default Re: Akai 4000DS head condition.

Difficult to tell from the photo but they do not look bad to me (but I am not an expert on heads).

Akai heads generally have a good reputation, although the 4000 series heads are not as good as the later Akai GX series machines that have Glass & Crystal (X'tal) heads that are known for longer life/less wear.

Unless the machine has had very heavy usage it is unlikely the heads are U/S, it is possible for heads occassionally to go open circuit, then they would be no good but rare I would say for Akai heads.

The heads should be given a thorough clean and tested with a tape. The capstan drive belt unless broken should be functional and the tape counter belt if broken is not important at this stage.

David
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Old 30th Jul 2023, 11:56 pm   #4
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Default Re: Akai 4000DS head condition.

There are two known weak spots in these machines.

1) the two big levers for tape movement control have large cams inside the unit. The cams are diecast zinc alloy (Think matchbox toys!) and the metal degrades and goes crumbly.

2)The DS version has hybrid amplifier units in the record and replay paths which have been known to fail.

I used a DS for seven years and used it very heavily, but I used good quality TDK tape and the heads were fine. I did wear out and replace the bush bearings which carry the spool shafts which gives you an idea of the amount of use mine got.

Glass/Crystal/ferrite heads are actually a little noisier than the basic metal types, they can also limit flux densities that can be recorded, so Akai's metal heads aren't much cause for worry.

I bought a Revox when I sold the Akai.... and I have had to replace the heads in the Revox

David
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Old 31st Jul 2023, 1:49 am   #5
TIMTAPE
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Default Re: Akai 4000DS head condition.

It's hard to estimate the remaining head life. The true amount of wear only becomes visible after it's worn out.

In the diagram courtesy of John French of JRF Magnetic Sciences the yellow section circled in red is the gap area. Once the wear goes down into the V shaped area, the gap has started to open out and the head is effectively gone.

A new head might have 1mm of "meat" (labelled depth of gap or tip depth on the diagram) so a 1mm wear groove caused by tape abrasion is a significant amount of wear, but not all heads have the same amount of metal in the first place.

Another way to estimate wear is to measure head inductance compared to the measured inductance of a brand new head, and a just worn out one - if we happen to have those figures on hand...
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Old 31st Jul 2023, 9:17 am   #6
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Default Re: Akai 4000DS head condition.

Quote:
Originally Posted by Radio Wrangler View Post

The DS version has hybrid amplifier units in the record and replay paths which have been known to fail.

David
If the 4000DS is the Mk. II version then it does not have the Sanyo LD-3141 I.C.s that can fail.

David
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Old 31st Jul 2023, 9:26 am   #7
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Default Re: Akai 4000DS head condition.

The DS Service manual gives head Impedance values (at 1kHz for Record/Playback heads & 100kHz for Erase head) plus DC resistances also listed for the Mk. II heads but does not state Inductance values for any of the heads.

David
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Old 31st Jul 2023, 10:13 am   #8
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Default Re: Akai 4000DS head condition.

Have a closer look at the wear pattern. Your (phone?) picture makes it difficult to assess, but to me it looks rather asymmetric (as if the zenith is way off), which could be a nuisance.

There are three issues with the heads on consumer 1/4-track machines (two interleaved in each direction):

1. they tend to be slow speed (7 1/2 and 3 3/4 IPS), meaning the replay head gap has to be extremely small (relatively) in order that its turnover frequency is high enough to give the desired bandwidth. It's not so critical for the record head (recording happens as the tape exits the field; replay is driven by the flux between the pole-pieces). To get the necessary small gap, the replay heads do have a significant bevel on the rear of each polepiece, so, as others have said, they can degrade dramatically once they start to wear. BUT... Akai used the hardest material practically available (admittedly at the expense of output), so, as long as the tension has been kept within spec. and the machine relatively lightly used (after all it's around 50 years old now) they should still work.

2. The inter-track gap means replay azimuth is super-critical. Not only does it affect HF performance when it's off-azimuth, but you also get an exaggerated phase shift (half-track machines do this too, obviously, but usually operate at faster speeds, so it's less significant).

3. On the heads, polepieces and the inter-track filler material wear at different rates, and because of the track layout it's quite asymmetric. If things aren't kept clean and well aligned, nasty contact area shapes across the head can develop. There's little you can do about this on Akai heads, as re-profiling isn't really an option because of the material used, and anyway you need specialised kit to do it.

4. Related to (3), in those circumstances, you'll probably see an increase in crosstalk between the interleaved tracks.

I had the immediate predecessor of that machine, the 4000D. I remember the tape tension was really tricky to sort out, as it really came down to felt friction pads on the feed spool shaft (a sort of slipping clutch). But then I was in my early teens at the time... I didn't mess with the head stack, beyond cleaning and demagnetising (probably far too often!).

If you can try for better pictures of the heads, it would help (not easy, I know). I write the above, as I couldn't see the wear pattern I was expecting, but could see what looked like asymmetry, which is discouraging.

Hoping to be proved wrong...
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Old 31st Jul 2023, 6:41 pm   #9
bigfathairyvika
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Default Re: Akai 4000DS head condition.

OK, many thanks for the information all.

I've taken some better photos and a photo of what appears to be some sort of heat shine tube on the take up spindle. Should it be there ?

All the die-cast bits I can see look good.

Only other thing I noticed is that the motor is spinning all the time even when not driving fwd or rev. Is this normal?

Also , what's a reasonable price to pay for an spool of tape and an empty spool?
Mark
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Old 31st Jul 2023, 8:07 pm   #10
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Default Re: Akai 4000DS head condition.

Heat shine = heat shrink! It took me a moment to figure this out!

It looks like someone has adapted the capstan to play at a higher speed, possibly from 3 3/4" to 7 1/2".

Look for a prerecorded 7" tape (usually running at 7 1/2" IPS) and see if you get the correct speed at playback.

Ps Yes, the capstan should be rotating as soon as you switch the recorder on.
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Old 31st Jul 2023, 8:07 pm   #11
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Default Re: Akai 4000DS head condition.

That wear doesn't look too bad, really. It also looks reasonably symmetrical, and I've seen far worse. There looks to have been a bit of corrosion on them at some point. As long as there's no obvious roughness in the tape path, I'd leave well alone - the tape will polish them, but obviously clean fairly regularly.

I think those machines were intended to use long-play or extended-play tape. Thick, broadcast tape will wear the heads faster and to a different profile (OK, it will take a while!), so I'd look out for consumer-grade tape if you can find some.

I"m fairly certain the capstan running continuously is normal (but I'm trying to remember almost 50 years ago!). It's also a mains-synchronous motor, so speed stability won't be wonderful.

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Old 31st Jul 2023, 8:19 pm   #12
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Default Re: Akai 4000DS head condition.

Yes the 4000 will always spin the capstan motor when powered as long as the tape is threaded (when switched to Automatic shut off) or when switched to "On" with tape threaded or not threaded.

Your take up spindle underside is different to what mine has, mine has a pulley (the same as the tape counter pulley on the Supply spindle) and some clutch components, I am not saying yours is incorrect though. The Service manual does not show the pulley or the clutch components mine has.

David
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Old 31st Jul 2023, 8:43 pm   #13
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Default Re: Akai 4000DS head condition.

Does your machine have the 7.5 ips speed conversion sleeve ?

First photo shows the sleeve fitted on the stowage post above the heads cover for 3 3/4 ips operation.

Second photo shows the sleeve fitted on the capstan shaft for 7.5 ips operation.

David
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Old 31st Jul 2023, 8:52 pm   #14
jamesperrett
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Default Re: Akai 4000DS head condition.

Quote:
Originally Posted by bigfathairyvika View Post
Also , what's a reasonable price to pay for an spool of tape and an empty spool?
Mark
A brand new 7" reel of LPR35 is £36 from Thomann. I'd be careful with used reels. Used BASF and Agfa tapes are usually OK while Maxell is quite sought after because it doesn't seem to have degraded much over the years. It looks like you could find a used reel of Maxell UD35-90 for less than the cost of a new reel of LPR35.

3M Scotch tapes are a bit of a lottery. Some have survived while others have degraded. Avoid Ampex tapes - most of them will have gone sticky by now and those that haven't will probably be going sticky in the next few years.
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Old 31st Jul 2023, 9:20 pm   #15
bigfathairyvika
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Default Re: Akai 4000DS head condition.

Lovely jubbly.
Yes I do have a little sleeve. It is currently on the storage bit above the heads.
Thank you Simon DM for observations of the heads condition.
I will now purchase a tape to test it with.
Oh and heat shrink is what I meant.
It looks like it is there to provide some friction damping.
I would have thought a wool pad and a spring would be the right way. Which is what I've seen on other reel tape systems ( 1/2 inch data).

Mark
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Old 31st Jul 2023, 10:23 pm   #16
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Default Re: Akai 4000DS head condition.

This extract from the 4000D (predecessor to the 4000DS) Service manual shows the Take Up Reel Shaft Assembly looking similar to yours, your "Heat shrink" part being called "Nylon spring" in the 4000D.

David
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Old 31st Jul 2023, 11:26 pm   #17
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Default Re: Akai 4000DS head condition.

Extract from 4000DS Service manual is very similar, the part in question is item 40 on attached extract and is listed as "Vinyl Tube 15".

David
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Old 1st Aug 2023, 2:43 am   #18
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Default Re: Akai 4000DS head condition.

Re head life, this probably doesnt help but it shows what a head can look like when the gap is just starting to fail. The small vertical black line on the right track (red arrow pointing it out) signals the beginning of the end for this head. This is an old Akai head somewhat similar to yours.
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Old 1st Aug 2023, 12:04 pm   #19
DMcMahon
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Default Re: Akai 4000DS head condition.

Checked another of my 4000DS machines this time a Mk. I, Post 12 was a Mk. II

Photo 1 shows my MK. I which looks exactly the same as yours.

Photo 2 shows my Mk. II with pulley.

Photo 3 shows the Mk. II with pulley removed.

David
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Old 2nd Aug 2023, 9:51 pm   #20
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Default Re: Akai 4000DS head condition.

Arr! So it is factory fitted.

One other question is, should the cabinet hum?
It's not loud, or really noticeable to myself, just to the owner. I suppose it's what you get from a motor spinning inside a cabinet.
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