GX glass head dilemma.

markn2wae

markn2wae

Mark T N2WAE
I just got a AKAI GX630D-SS RR machine and am in the process of repairing it and found that the playback head has one track that seems to have a wide gap as the high frequencies seem to be rolling off badly as compared to a working track, let me explain.

To test playback independently of record, I recorded a stereo track of pink noise on L & R on a standard 2 CH. RR that is known to be working properly and verified I was getting nearly flat response up to 16K at 7.5 IPS at -20 on the meters.

Playing this tape on the AKAI machine, the right channel showed nearly a flat response, the left channel was BADLY rolled off, starting at 2K and falling fast.

To check if the electronics or the head was at fault, I temp. swapped the cables going to the head's L and R channels and tested again, the problem swapped sides, I even put in a new piece of signal coax cable to test, not an issue.

I removed the head from the machine and even with modest magnification, you could see a widened gap in the pole pieces of track 1 (L ch.), I suppose now I need new (4 track) head, are these expensive and available?

What is REALLY driving me nuts is the fact that many used tape machines are worn to some degree (unless you are lucky) and I thought by having a machine with longer life glass heads, I would be lucky to have heads that would have minimum ware on them.

How can a glass head get worn to the point to widen a gap and NOT show a groove\wavy-ness common to "normal" heads, this is all a new experience for me, and if this machine is not worth restoring because of "un-obtainubum" I would like some feedback please.

Mark T.
 

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Akai's 600 series reels are known for bad transistors. Might want to look there before doing anything else too drastic.
 
Sorry, but I don't get what "transistors" would cause a loss on a playback channel. I've heard of other problems with IC and transistors.
 
garww said:
Sorry, but I don't get what "transistors" would cause a loss on a playback channel. I've heard of other problems with IC and transistors.
Click to expand...

AKai did use a transistor 2sc458bl , that is prone to cause allmost anykind of strange problems .....

but - having seen the pic of the head, and read that swapping leads from the head, moved the error to the other channel - i'm afraid that head is shot

..... not the first Akai head to be replaced :yes:
 
jan_stevns said:
AKai did use a transistor 2sc458bl , that is prone to cause allmost anykind of strange problems .....

but - having seen the pic of the head, and read that swapping leads from the head, moved the error to the other channel - i'm afraid that head is shot

..... not the first Akai head to be replaced :yes:
Click to expand...

+1 on the transistors,I just replaced about a dozen on a GXC-635D I had, Not hard, just tedious as some are awkward to get to. But my problem was distorted sound, so even after you get the head squared away, this issue could come up.

The good news is the replacement transistors are like $0.20 each, so if you can handle a soldering iron, it's about a 2 hour job.
 
Kinda hard to believe though that only one head was shot. It takes ALOT of wear to kill a GX head. How do the others in the stack look? If all are showing their age, all you can do is hunt down a parts deck and take it's heads. I don't think a GX head can be relapped. No head can be relapped if it's gap is opening up.
 
Numistrek09 said:
Kinda hard to believe though that only one head was shot. It takes ALOT of wear to kill a GX head. How do the others in the stack look? If all are showing their age, all you can do is hunt down a parts deck and take it's heads. I don't think a GX head can be relapped. No head can be relapped if it's gap is opening up.
Click to expand...

It's not your everyday dish - but it do happen - GX heads can develop a crack, (same goes for ferrite) wayand then things go wrong very fast - as you correctly say, GX heads can't be relapped.

This is among the worst heads i've ever seen - i wonder how the others are looking
 
Same electronics, different head, problem swapped.

Numistrek09 said:
Akai's 600 series reels are known for bad transistors. Might want to look there before doing anything else too drastic.
Click to expand...

Using the "good electronics" connected to the "bad" head channel showed the problem.

Mark T.
 
Thanks for all the feedback and help.

Thanks for all the great feedback\info!:tresbon:

I agree that the playback head is shot, and will keep my eyes open for replacements, this project will be put on "hold" until I get parts ('Karma' may not put all of the pieces in our hands at once, but being a patient person, this is not a problem).:D

Mark T.:music:
 
Seems to me that, given the supposedly indestructible nature of the GX heads, the deck you have *is* the parts unit. You need to find another deck to put parts into... from the one you have now.
 
I don't know if it is possible to have a GX head relapped or not. If it is, that is probably your only option, other than attempting to shoe-horn a new Teac head inside of there. GX heads in general are extremely difficult to find. A 4-track GX head, well that is unobtainium, except from a parts machine, and Akai didn't make too many 4-track models.

I know that some places like JRF can definitely relap ferrite heads. So I would contact them, and send them your head for evaluation.
 
Way back in 1974, I began to see bad glass Akai heads. Back then, they had "lifetime" warranties, but Akai did not honor those warranties unless the set was brought to their authorized service facility, and here in San Diego the ASF had been told to "hold down" the number of head replacements.

Micro-examination of the heads in 1974 and later revealed that the gap area was corrupted. My conclusion at the time was that the glass heads were extremely brittle -- far more brittle than a hard-permalloy head. The large temperature changes in the gap area caused by running the tape would cause expansion and contraction of the glass and the ferrite core. These had different coefficients of expansion/contraction. Internal stress gradients were generated. After a time, micro-structural defects would develop, and these would grow into crumbling gap areas.

There was no cure then other than replacement of the heads, and there is no cure now. I believe the Akai engineers miscalculated as far as their assumptions of the longevity of these heads.

Fred
repairing audio since 1972
 
Bummer!

Party pooper! (Just kidding!) :D

You are a wealth of information on these heads, my learning curve is going almost vertical!:scratch2:

I guess you can't win, make a head of "normal" materials and it will ware out relatively fast, make one of "exotic" materials, and you get more life out of it but now have unexpected\unforeseen problems.:sigh:

I'll just store it away, it is not the first time I kept something and got parts at a later time, often when not expecting them!:thmbsp:

Mark T.:music:
 
Fred Longworth said:
Way back in 1974, I began to see bad glass Akai heads. Back then, they had "lifetime" warranties, but Akai did not honor those warranties unless the set was brought to their authorized service facility, and here in San Diego the ASF had been told to "hold down" the number of head replacements.

Micro-examination of the heads in 1974 and later revealed that the gap area was corrupted. My conclusion at the time was that the glass heads were extremely brittle -- far more brittle than a hard-permalloy head. The large temperature changes in the gap area caused by running the tape would cause expansion and contraction of the glass and the ferrite core. These had different coefficients of expansion/contraction. Internal stress gradients were generated. After a time, micro-structural defects would develop, and these would grow into crumbling gap areas.

There was no cure then other than replacement of the heads, and there is no cure now. I believe the Akai engineers miscalculated as far as their assumptions of the longevity of these heads.

Fred
repairing audio since 1972
Click to expand...

I'm not arguing against you, but there are a lot of fully functioning Akai GX decks still out there.
 
Is this brittleness why TEAC didn't offer glass heads on the X series? I know adds said Permalloy heads sound better, but maybe this had some bearing on it.
 
can't say why they didn't - but a cause could be that Ferrite or glass heads often have linearity problems in the low frequencies - that combined with DBX ain't good - permalloy and sendust heads are more linear - DBX would double linearity problems

... then again - some AKAI's with GX heads have DBX ... well ....
 
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