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Bender Comments Page

These are Reel to Reel Questions, Answers, and comments, things I've posted on several discussion groups, some when people write and ask me questions.


Comment #50

Subject: Reel to Reel Head Question

Date: Wed, 21 Apr 2004 19:11:02 -0700

From: Jim Ellis

Dear Steven:

I recently read a post of yours on regarding tape heads, and I was extremely impressed with your degree of knowledgability on the subject. Would it be fair for me to summarize your argument by saying simply that the GX heads are superb, and last forever, and that all others basically suck?

I wanted to question your assertions that other Ferrite head designs are so vastly inferior to the GX heads. You said that the other designs head gaps would chip over time, and widen. Obviously, if you are correct about this, then this would be a very bad thing. However, I simply fail to understand why you think that if other Ferrite designs are subject to this problem, why Akai's are not.

I fully realize that the Akai's are partially made of glass. From what I can tell, by looking at the heads of my GX 747, it seems as if glass is being used to sandwich the electromagnets for each channel inside the heads into position, rather than using a substance like plastic for this purpose.

But, I fail to see why this construction would make the heads any more immune to the gap "chipping" effect on the ferrite portion that you wrote about, than are other very high quality ferrite heads, like the Sony F&F heads.

One statement that you made that I noticed did not fit with my experience. You claimed that the High-End Sony's rejected the ferrite designs, and that only the lower-end, and older designs used the ferrite heads. I am familiar with the majority of the Sony R-R line, and the VERY best decks that Sony made (with only one exception, the 788-4) all had the F&F Heads.

The 788-4 only lacked them because it was a 4 channel design, and Sony never made any 4 channel F&F heads. Of note, Sony's very best Decks the ever made: the 755, 756-2, 758, 765, 766-2, and the 880-2, all had the Ferrite and Ferrite Heads, as well as numerous other Sony Models.

Your statement was correct about Teac, who did reject the Ferrite designs in the 80s, after using them for a while during the 70s. I had always thought that they rejected the ferrite designs to the higher permeability, and slight magnetic superiority of some other materials, not do to the chipping issue, but I could be wrong about this.

Anyway, I sincerely hope that this email is not coming across as hostile: it is in no way intended to read that way. I actually have quite a bit of respect for you after reading your very knowledgeable posting. I simply want to understand your point of view better on this subject. Specifically, why do you believe that the glass inside the Akai heads would make them so immune to the gap chipping that other Ferrite designs are supposedly so subject to?

And, do you really believe the Sony F&F heads are so much more fragile than the GX heads? I had always thought of these two heads designs as being about equally fantastic.

Thanks for your help!


********** And Bender Sez: **********

Hi Jim,

I hope I'm up to the task of answering them...

Yes, many high end Sony sets did used the F&F Heads, and it is truly difficult to know why any manufacturer did anything at all, some 20 or 30 years in the past, I'm guessing different design teams came up with differing sequences of mechanical, electrical, and conceptual designs, depending who was on a particular design team. And in some cases, there may have been a choice of "A" or "B" type heads, and someone just chose one.

Next, the chipping effect on ferrite tape heads seems to be related to wear, with ferrite on the surface, the wear effect is minimal due to the hardness factor of said material. The problem of chunks of ferrite chipping off from the gap probably relates to bound oxide chunks, on a microscopic scale, hitting the gap edge a few billion times as the tape travels past. Over time, this failure mode was found to exist and so Ferrite heads don't quite last forever.

I guess depending on the level of Calendering of the tape surface, this can influence the ferrite tape head's life. That also goes for the Akai GX heads, where the typical erase heads appear to be of a normal ferrite construction, and these do tend to show wear first. The top of the ferrite mirror-like surface turns a lighter shade of gray, and looks rough when wear is present. So even ferrite surfaces do wear away, eventually.

The GX Record and Play types tend to show some central point of contact wear by some point. I've seen many and it is the construction of those which not only places the "pretty much" friction-free glass or crystal-ferrite inside the head, but also on the surface layered in front of the ferrite pole piece surfaces.

If this patented glass covering layer wasn't present, then the ferrite poles would be exposed to the tape, and subject to wear and tear and edge-gap scatter or chipping just like the Sony F&F / Teac ferrite heads. I guess if they wanted to pay huge sums of money to Akai... Sony and Teac could have had this too.

However, as much as the glass coverage prevents edge-gap scatter damage, it does appear to be a very thin layer of glass on the later GX heads. I've seen many instances where under magnification the glass clearly shows the pock marks of worn or chipped areas within the mirror-smooth glass surface. So it too can get worn away, in some respect, it begins to look like the surface of the moon, with craters and such.

While this doesn't affect the physical parameters of the ferrite of the underlying gap, eventually with enough wear, I suppose it would. I don't know if the original GX warrantee of 150,000 hours was based on actual 3.75 / 7.5 ips tests, or from simulated tests running tape across the heads - at accelerated high speeds. Don't know if they are in general truly accurate.

Seems to me... earlier GX heads had both a thicker and wider surface of the glass covering and tended to remain unworn longer, while the later GX Record heads seem to have like an extended forward "plate" of GX glass, while the Play heads which seem to be full surface covered in glass. I don't really know why the different construction, it might be a cost thing in terms of construction... for better, or worse...

As for the higher permeability, and slight magnetic superiority of some other head pole making magnetic materials ( such as Permalloy ) well, that I suspect goes to trade-offs, and costs. And yes, I think that soft permalloy heads as are present on many decks do indeed simply have a better "sonic" than any form of Ferrite, which includes the Sony F&F and Akai GX heads.

I can not explain it in any other terms, but playing a tape on any GX Akai, a GX-365D, GX-267D, GX-400D, GX-747, or even a PRO-1000 seems to be perfect, until you then quickly switch the tape onto something like a Sansui SD-7000, or a Pioneer RT-909 with permalloy heads. Now, suddenly the same tape appears to have more dynamic range, more musicality, gives a sonic one step closer to the original than on the ferrite based machines.

I design power amplifiers, and I have my own designs units which I strongly believe are more sonically neutral and more transparent than anything else on the market, exccept for a few mega-mega-buck and exotic high-end tube amps. And just maybe it does take this "extra level" of "sonic transparency" within the audio chain to be readily able to then discern these differences between the ferrite type and the permalloy type tape heads.

Certainly the SD-7000 doesn't have lower wow and flutter or better distortion than than a GX-400D, or PRO-1000. Maybe the RT-909 does, but then its loaded with plenty of late 1970's level IC's in the audio path, which can't possibly make it sound better... so its' gotta be the heads, right ?

Of course, the transistors / IC's used, and the coupling caps used in the audio sections, as well as the decoupling between channels within the power supply, would all have an added effect here; along with the amount of available headroom present in the playback electronics. Also the topology and complexity of the electronics the signal is being passed through ( the level of complexity tends to be about the same in these types of consumer decks, but not always ).

So in the end, it can be extremely difficult to isolate this effect and truly say that it is the heads alone which are causing this effect... but well, that's MY guess.

I was going to one day mount a set of later Akai GX Heads into a Sansui SD-7000 with worn heads, and try and run a bunch of listening tests, as it would be a really great project... I just never had the months of time and inclination to do it.

I hope that sufficiently answers the important points in your questions!

Steven L. Bender, Designer of Vintage Audio Equipment

Comment #51

Subject: Spare Part for AKAI GX77

Date: Sat, 24 Apr 2004 20:44:18 -0700 (PDT)

Brian Long wrote:

Help!, I inadvertently grabbed both reels as it was loading and have broken a tooth off the small planetary gear (white 'nylon' appx. 1/2" diam) which rotates around to 12 o'clock position to move counter roller to top of travel.

Any clues where to order one?

Thanks and regards.

Brian Long.

********** And Bender Sez: **********

Hi Brian -

I'd be very surprised if you could come up with that part from any source. The GX-77 was Akai's worst horror, as it was most prone to mechanical break downs... and as such, Akai ( the Akai that existed 20 years ago ) had many parts revisions, and back then those replacement "upgrades" when the sets broke were available for a few years, but those parts went out of production almost 15 years ago. You might have stood a small chance of finding a GX-77 part 15 years ago...

but today... You'd have to buy a working GX-77 and yank it out of there, that is, if you could find one that works.

Your set likely has become a door stop.


Steven L. Bender, Designer of Vintage Audio Equipment

Comment #52

Subject: Re: Akai GX-266D

Date: Sat, 24 Apr 2004 21:13:12 -0700 (PDT)

robert duchane wrote:

Ok, I just bought a Akai GX-266D Deck that will not play. Motors operate normally but the pinch roller will not engage. As I am not too familiar with this chassis I thought I would post before going to far and getting lost. lol Any help would be appreciated.

Thanks Bob

Frank Oomen responded:

Bob, I just read on the schematic the pinch roller solenoid is activated by the "play" relay and is powered by a bridge rectifier. There's also a diode soldered across the connections of the solenoid. So you're dealing with a bad bridge rectifier, a stuck (or dead) relay

or maybe the diode across the solenoid has blown. I have a GX-266D too and I think it's not a difficult fix. If you need to have the repair manual and/or the schematic for yourself or for your repair-person let me know. I have the original operator's and service manual for the GX-266D/267D and I could have it reprinted for you.

Good luck,


Robert DuChane replied:

Thanks for the info frank. As I was following the board I happened to find an open trace between loc# 24 (common for both pinch solonoid and record switch solonoid) and #25 (goes to capacitor). Cap didn't appear swelled so I wired a jumper between the two point and solonoids work but now when it engages the reel tables don't move.

This is getting frustrating. If I didn't like Akai's so much I would probably give up now......but. Anyway if you have any info on what triggers the reel motors please let me know, keeping in mind that they do work properly in fast forward and rew. Thanx again

********** And Bender Sez: **********

Hi Bob -

The GX-266D is usually a very reliable set. It has 3 motors and six heads and records play in both directions. Its operational control is done using discrete transistors, and such complicated operations are controlled by over a dozen transistors, and three four-pole power relays.

You might be seeing a transistor failure, a relay problem, or a power supply problem.

You will need the schematic to trace down such problems or the service manual. I have the transistors, replacement gold plated contacts drop-in replacement power relays, the schematics, and/or service manual available to assist you.

Sometimes, if the GX-266D has been dropped "on its face" the reel tables get jammed inward onto the reel motors and won't move when reels are on it. To check for this, tie the two L & R tension arms to the middle or end of their travel using a rubber band and check for motor and reel table operation without any tape or reels. If it works under that condition, and the motors appear to have the proper torque, then the reel tables need to be physically reset so they clear the the front panel, and maintain a proper azimuth with the tape path so tape doesn't bind, and winds in the center of the reel. This is also shown in the service manual.


Steven L. Bender, Designer of Vintage Audio Equipment

Comment #53

Subject: Akai GX-265D

Date: Sat, 24 Apr 2004 21:00:07 -0700 (PDT)

Janice wrote:

I need the record playback head for an Akai GX 265.

********** And Bender Sez: **********

There is no record/playback head on that set. There are two combo Erase/Record Heads and two Play Heads.

Have you measured the resistances across these heads with a low current, low voltage, ohm meter to verify they are bad or open ?

I'd tend to think its something else, almost anything else, as I've only seen 2 bad Akai heads out of hundreds of Akai RTR sets...

If you're sure that's the problem, I do have both the GX-265D Play Heads and Combo Erase/Record Heads available.


Steven L. Bender, Designer of Vintage Audio Equipment

Comment #54

Subject: Akai GX-630D Service Manual - Technical Questions

Date: Mon, 12 Apr 2004 12:15:25 -0700 (PDT)

From: Harald

Hello everybody,

The service manual of my Akai GX-630d says two things I don't really understand. It says for instance bias leak, better then -30 db. What does that mean? And another thing is: High frequency deviation: within 3db, at playback of an 8,000 hz 3-3/4 ips pre-recorded tape at 7-1/2 ips. The last sentence puzzles me even more. Do they mean you get 3 db more high frequency today than tomorrow? Or between channels? And playing a low speed tape at high speed is apparently necessary to get this result? strange...

If anyone can explain, that would be great Thank you, Harald

********** And Bender Sez: **********

Hi Harold,

Bias Leak is the high frequency (usually ~100 Khz.) signal that allows recordings to be put on tape with a minimum of distortion. In the absence of Bias, the distortion would be quite horrendous, as the magnetic particles that make up audio tape don't readily accept audio frequencies by themselves.

You may also note that the GX-630DB has a much better cited number of -50dB for Bias Leak, this is due to the added filtering incorporated into the dolby circuits in the GX-630DB. In all Tape decks this bias signal isn't completely filtered out down to zero.

As a result, some does still leak into the output circuitry; while this usually is not a problem, it is in the case of the added-on Dolby B circuits which are present in the GX-630DB, or any tape decl which has Dolby B circuitry. So this bias leakage would likely trip the dolby B circuits into bad overload, so Akai added this spec to define that its 20dB "better" in the unit which has the Dolby circuits.

The High Frequency Deviation spec is a bit of an odd term, it usually does not appear in service manuals. Again I'm pretty sure it relates only to the unit with the Dolby B Circuits, even though it does not say so... Again, I'm not quite sure what the relevance of that spec is, except possibly to prove the addition of the dolby circuits doesn't change the high frequency response more than 3dB.


Steven L. Bender, Designer of Vintage Audio Equipment

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