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Akai GX-635D

Stereo Tape Recorder (1979-80)

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Akai GX-635D


Track system: auto reverse, 4-track, 2-channel, stereo/monaural system

Heads: 2 x GX record, 2 x GX playback, 2 x erase

Motor: 2 x reel drive, 1 x capstan

Reel size: up to 10.5 inch reel

Tape speeds: 3 34  7 12 ips

Wow and flutter: 0.04% (7 12 ips)

Frequency response: 30Hz to 27kHz (7 12 ips)

Signal to Noise Ratio: 62dB

Total harmonic distortion: 0.5%

Crosstalk: 40dB

Input: 70mV (line), 2mV (DIN), 0.25mV (mic)

Output: 0.775V (line), 0.3V (DIN)

Dimensions: 440 x 483 x 256mm

Weight: 21kg

Accessories: connection cords, reel hub adaptors, empty reel


schematics   English -

instruction/owners manual   English Deutsch Francais -

service manual   English - Ivy Caudieus

instruction/owners manual (alt scan)  English Deutsch Francais - len davis

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Reviewed Mar 05th, 2014 by ecl

From by point of view this is the best AKAI GX reel-to-reel [for consumers], even that GX-747 has 25Hz to 33kHz (7 1⁄2 ips) and BIAS adjustment. Most people hear around 20Khz, and they begin to age at 15kHz, the GX-747 important corrections ton. Aesthetically GX-635 is 2 times more beautiful: metal, metal and metal again.



re: GX-635D

My Akai GX-635D was working fine until it lost speed control. I can't control the speed in which it plays. It's too fast. Any recommendations?

re: GX-635D

Open the rear and check the main capstan belt. Is it riding on the motor pulley flange instead of riding in the pulley's center?

re: GX-635D

This model does not use a belt drive. The capstan is a direct drive. Thank you.

re: GX-635D

I have just delved into my 635D to repair the right channel, which was dead. I replace TR9b and TR10b 1st and that was it. The channel worked. Then I noticed the other REC inputs and things were not right so I replaced many more of those 458 transistors. I wanted tell others that I noticed that even though the schematic claims that some were other #'s, every one of the ones I pulled out were all 458's, contrary to the schematic. So, I replaced with modern 458s. Seems good. Now my recording is not at the same level as the input. So, I will rebalance or replace more transistors in another stage that I have not interpreted on the schematic yet. Love this unit. Hope to restore and sell this one.

re: GX-635D

Wow! What A Resource! Having just inherited a GX-635D, I am eager to see if it works correctly, my first job will be to locate and obtain the correct power cord! The downside is, whilst I appreciate it for what it is, an absolutely stunning audio sculpture, in no way will I ever appreciate it's abilities, so I am simply looking to return it to full working order prior to finding it the new home it really deserves.

Problems with my GX-635D

My GX635D worked properly until about 2010.
From that time, when playing or recording, it happens that the machine slows suddenly, and slows again and finally stops.
It works normally after turning the machine off or playing with Play-Ffw-Rev-ReversePlay buttons.
Sometimes it takes a longer time to work again normally.
Does someone know how to repair it ? Condensators,

re: GX-635D

Just purchased a very nice clean working example, one family owner from new, and with original Akai reels and NAB adaptors, plus a load of tapes. This is such a nice machine, and I will be giving it a full service, then adding custom sides. This site is invaluable for manuals, thanks for the effort! Thank goodness I kept my original servicing Philips Dual Beam 'scope and Gould signal generator!

re: GX-635D

When you open it up and look at the transistors on the bottom PCB, I would be interested to hear whether the Mic Amp transistors have clean silver leads - or are they (like mine) powdery black with the occasional tinge of yellow as they go into the PCB. Particularly prone to corrosion are the 2SC458's which are TR1, TR2 and TR3 in the Left and Right Mic Input Channels. Mine is on the bench right now, stripped down in such a manner as I can hinge that PCB to examine and get at either component side or solder side. I am waiting for someone to explain to me just what constitutes transistor 'corrosion' in the GX-635D. Hope yours is OK! I bought mine new in 1983.
Michael (UK)

AKAI GX 635D (Auto Reverse)

I got this deck for a really nice price, and it's very clean. Plays and records in both directions, but it does not auto reverse. I've place the sensing tape at the begining and end of the tape and switched it to continuous play, but it does not reverse.
Any suggestions?


Akai GX-635 won't record!!!

Hello there!
Anyone does have an idea of why Akai GX-635 will not record although the heads are clean?
Thank you!

akai 635

You must be to replace all transistors 2SC458 with 2sc2240 from record and playback section, also be cleaned long contactor for play and record fwd-rev. This fault is a usually phenomenon in Akai gx 635. Good luck!

re: akai 635

AKAI GX-635D Transistor substitutes
My GX635D is on the bench with all 2SC458 transistors removed from both Left and Right channels in the Pre-amp. (Board: No.TH50001A as shown on the solder side) I have 60 Fairchild KSC1845's to choose from. and have a new PEAK DCA55 meter to help me. These KSC's, though new, show the Hfe readings range from 403 down to 339. The constants: Ic is 2.5mA, Vbe is 0.74v, Ib is 4.66 and Ic is 0.00. Would someone assist me by explaining how to get the best matches for the two channels. Note: The DCA55 gave readings from the removed 2SC458's ranging from Hfe = 75 to 313 - all of which are well below the new Fairchild KSC1845's. Is this the best way to choose from my transistor hoard? Should the TR1(L) be matched to TR1(R), or should all the transistors in each channel be as close as possible to being the same Hfe? Well, there are NO pairs in this of NPN/PNP, all the Transistors virtually 'daisy-chain' until the OP XFMR. I have tested all those new KSC's but, because I am not really acquainted with the proper understanding of the resultant Hfe's am a bit at a loss. The results I get from the KSC's range from 403 down to 339 - but mostly they are around 340-350. The original 2SC458's ranged from 75 & 80 (only two that low) up to 339. Most of them were in the range of 270 or so. When I bought this machine new in 1983 already there had been some transistor changes - notably TR9(L) and TR9(R) where the original specified 2SC458LG (large gain? low gain?) they had put in a pair of can-type Transistors BC109. One of these gave a much higher Hfe than the 458's TR9(L) is 644 but TR9(R) is 240 - which is quite a lot of difference between even those two mini-cans. The only other change I have noticed had been in replacing TR7(R) from a 458 to a 2N2712 with an Hfe of 181. TR7(L) remained a 458 with an Hfe of 263. I don't know whether there is an accompanying change in the resistor/cap values in that area to compensate. I hope all this makes sense! Your comments looked forward to as I shall go no further on this project until I am sure! Thanks. Michael (UK)

Thank You

Appreciate the manual. Scored the machine from an elderly chap who needed to downsize because of local flooding. No audition & he hadn't used it in 10 years. Thanks to the manual, I now know, it works like a charm. I'm doing the happy clam thing.

Thanks again, and thanks to posters (on DiyAudio) who led me here.

's all good

Akai GX635D

Great site ,Thank you for the information .Been in the industry for 55 years ,I used to repair these units for the State government .NSW Australia many years ago ,and now I have been asked to repair one with a distorted left channel when recording so the manual is very important , Thanks again ,Regards george

re: Akai GX635D

Hi George,

the same here, were you successful with changing the transistors?

Best Regards


theartistthen71's picture

Akai gx-635d

Really nice to find literature for older electronics. The only tape that was working
out of 5 so I need this one. I did a lot of recording in the 70s, probably 5 boxes of
r-r tapes. Bought this one at a yard sale for $50.00. Like to find another one.


Akai 635

Thank you

Thanks ! You made my day :-)

Thanks !

You made my day :-)

Vielen Dank!

Vielen Dank!


Appreciate the efforts made to make these manuals available to download for free
Thanks a lot

Thank you!

You are great!

Thank You!!! Best regards

Thank You!!!

Best regards


Great, searched for manual a long time...



Nice timing

Just had a GX635 come in this AM...Used to do 1 to 2 of these a week back in the day...Thanks...


Great service. Thanks. You're unique.

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