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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 #35

From: "koko98584"

Subject: Hi

Date: Wed, 14 Jan 2004 12:57:04 -0800

Where can I find a volume control for my Akai reel to reel tape deck.

Do you think I can maybe spray it or something---It's getting real scratchy. model # 4000DS

thank you

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

Hi -

Do you mean the input mic/line controls or the output / headphone control ? Yeah, they aren't sealed from the air and then wear, and dust, and fungus growth over a few decades sometimes makes them pretty scratchy. Most sets are like that after 20 years. Spraying can sometimes help, but usually ruins the pot several months later, then you're simply out of luck, unless you can replace it.

I have some very similar replacement controls that work in the higher-end Akai sets, but most likely if its the dual knob controls, I'd have to pull one off another set, and it could be scratchy too, or could soon become so. Also, if you have the original 4000DS it could be something else.

The 4000DS input level controls are just before an LD-3141 IC, and this could be impending that the IC is going bad. Also the Playback level control is inside on the circuit board, in the feedback path of an LD-3141 IC. This IC is known to go bad in large quantities, and is problematic to find good NOS or used ones. There are 4 of those IC's inside the 4000DS, so the set could go inoperative at any time from any of those 4 IC's.

This IC was replaced with discrete transistors in the 4000DS MKI and MKII, probably due to the large number of failures seen in the first few years after the original 4000DS sets were sold. Today, typical price for that IC is around $30. for each IC. So if you have the original 4000DS, now, 20+ years later... I'd recommend not spending any money on it.

I'd say buy yourself a later version - the 4000DS MKII, or a GX-4000D, or upgrade to one of the higher-end 3 Motor Akai sets... like a GX-230D, GX-255, GX-266D, GX-267D, or even a GX-6xx series set, like a GX-600D, GX-630D, GX-630DB, GX-620, GX-625, or GX-635D. These days they only cost a fraction of what they went for new. Might even cost less than the cost of parts and labor to make repairs to your set.


Steven L. Bender, Designer of Vintage Audio Equipment

Comment #36

Subject: WOW

Date: Fri, 16 Jan 2004 15:13:00-0800

From: Master Wizard Henry

Master Wizard Henry wrote:

Hi glad you are here injoyed looking over your site.

I have a 1800D SS I beleve it may need belts as it gets real slow sometimes in a rewind.

Do you know where to get any parts or any kind of help?

The Reel to Reel works great other than that.

I have some great stuff on Reels and like using it in the computer room

I get a lot of coments about it.

Thanks for any help.



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

Hi Henry,

First - Make sure you keep the tape guides clean, any debris that falls off the tape can increase the friction making the wind slow.

Second - It might also be the motor run cap, it can start to go bad after like 15 or 20 years and the set is almost 35 years of age by now...

Third - There are lots of switches and few relays in that set, two white power connectors 4 pins P1, P4, and one 6 pin P3 should be checked, pulled apart and put back to gether several times to insure good contact and low resistance between pin and jack after 35 years... as poor contact can cause loss of voltage resulting in motor problems too.

Yet another problem that could crop up - is the LD-3141 IC's which are used in the playback circuit section can become defective. High rates of LD-3141 failure have been seen, mostly they often become very hissy, compared with other channels, so you might find one channel totally hissy at some point and passing no audio signal thru.

Or you might find one or more channels becomes more hissy than the other channels, a good test for this is playing back a known tone test tape like a Dolby level tape, and seeing if all 4 VU meters register equally, then playing a never used tape, or tape that has been bulk erased on a large tape eraser, back to a virgin noise level, and seeing if all hiss levels are about equal ( a oscilloscope would be handy for that test ).

The LD-3141 IC is a part long out of production and the one known ECG equivalent substitute part is also long discontinued, so used parts pulled from sets cost around $20. to $25. and are a gamble, as they can go hissy at any point; while NOS unused parts typically are $35. each if you can find them. Many Akai sets used these parts, including the 4000DS, some lower end GX-2xx series sets, and almost all of the Quad 4 channel units, including the GX-630D-ss, and the GX-400D-ss.

My own opinion is - it would make sense to replace all the LD-3141's in either of those very high-end sets, but not worth it in a set that has pre-GX heads and a much lessor resale value.

Since head wear is a concern on any set 25 or 30 or 35 years old, I'd have to say its not worth putting a lot of money into a set with pre-GX heads if those heads are worn. Typical permalloy record and play heads were good for about 2000 hours use before deterioration would start to noticeably affect recording and playback. Divide that 2000 by 35 years of use and head wear can be seen to add up quickly.

Simple inspection of the head surfaces using a 4x, 5x, or 10x loup may in fact show up disappointing head wear results; and replacement since heads for sets this old are highly unlikely to be found, one should take that notice with a grain of salt. The only real possible solution is either find a suitable GX set with more robust heads, or find a similar model set with very low usage and no other faults - also difficult to find ( but not necessarily impossible ).

I do have the 1800-SS/1800-DSS Service Manual available, as well as the Parts Listing Manual as seen on my Manuals page and also I have modern replacements for the Motor Run Cap, a modern replacement won't dry out and fail as the old type ones did. It could also be rubber wheelies, there are only 2 belts in there, one for the counter, one for the capstan flywheel.

So my guess is - Rewinding Slow would not likely be a belt.

The 1800DSS Service Manual is $29. shipped; the 1800DSS Parts Manual is $29. shipped. Both for $54. shipped.

The Motor Run Replacement Cap for operation on 120 Volt/60 Hz. is $18. There is a second motor run cap that only gets switched in for 50 Hz. operation, so if you are using the set on standard 120V/60Hz. only, then you don't ever have to worry about that second cap; only that the 60 Hz. Motor Run Cap is in proper condition; ( Akai actually called it the "Phase Cap" ).

I might also have a suitable belt for the Capstan Flywheel and the Counter belt too. If so, they are $12.50 and $6.00 respectively.

I also may have a replacement power relay for RL-1 is a difficult one to find, the other relay is more even difficult I probably do not have any replacement for it. The 1800-DSS RL-1 part would run $22.

I hope that helps :-).

-Steven L. Bender

Comment #37

Subject: AKAI 635D

Date: Mon, 19 Jan 2004 18:27:57 -0800 (PST)

From: Double-Wide Bob


When playing a reel, it only plays the left channel in either direction (a bit muffled). While monitoring another source, only the right channel plays - and does so clearly. I reversed the leads leaving the head (R to L) on the PCB at the bottom of the deck and still only the left channel plays. I also swapped FWD w/REV leads and again I only heard the left channel - played backwards of course.

Hopefully someone will be able to steer me in the right direction (sans sarcasm see voo play)...otherwise I'll have to go to plan "B" - listing it on Ebay as Mint :-) - I'm kidding!!! Hope to hear from you ace-technicians soon.

Bob Beaudreaux, Stillweed Mobile Homes/Ebay Vintage Stereo Staging Area

Homer, La

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

Hi Bob...

First off, as I stated in my recent speech before The Gotham Audio Club on January 4th. 2004, it seems transistors are not forever; it doesn't really matter if you really believe AT&T Press Releases that three guys developed the transistor over a 2 year period of research, when there was zero prior intelligencia for assuming that purifying Silicon or Germanium and then adding in heavy poisonous metals in controlled amounts would yield a wonderful new substitute for tubes.

Or the contrary theory... that IBM and Bell Labs guys along with the Army Corps of Engineers reverse engineered the contents of the Roswell spacecraft...

Whatever you believe, many Akai Reel to Reel machines, twenty years later... have transistors that will be "stone cold dead" as one of my friends' put it - quite succinctly. Also the coupling caps and bypass caps can fail, along with bridges and sometimes other parts. Rarely is it the heads, but it can happen! So yank all the little black transistors and stuff in replacements, and your Akai could again come to life ( of course, if its the caps too... ).

Hope that helps,


Steven L. Bender, Designer of Vintage Audio Equipment

Comment #38


To: "Steven Bender"

Subject: frequency problem GX-635D

Date: Tue, 20 Jan 2004 17:06:00 +0200

Hello Steven,

Happy new year, and I hope all your wishes come true.

I would like to ask your oppinion about a problem I experience with my GX-635D.

When I playback forward a tape ( recorded on another deck), the left channel sounds very bass and the right channel very treble. I checked the heads but they are in exellent condition and perfecly well adjusted. Even when I record a tape on GX-635D and playback it I hear the same frequency problem that also exists when I play the tape on another deck.

I tryed to readjust the VR2 and VR2b points (Service manual page 31) but the problem still exists. When I playback and record reverse, there is no such problem. I would appreciate if you could help me with this.

Thank You!


P.S: Did you found any 10,5'' empty metal reels for sale?

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

Hi George -

Obviously the problem is in the recording section.

While you didn't say you checked the gaps of the heads at higher than 10x magnification to make sure they are clean and free of debris or physical damage. You also didn't say which speed, or if both speeds are so affected....

Possible adjustment ( after making sure the head gaps are clean and clear ) is not VR2 / VR2b, but adjustment of T2 / T2b at 3.75 and VR7 / VR7b at 7.5 ips. Overall recording levels are adjusted with VR2 / VR2b when the frequency response is proper. Very MINOR adjustments in bias using T2 / T2b should make large changes in frequency response.

First check overall signal levels, by using a Headphone NULL ADAPTER. This can be made using a 1/4" stereo jack to 1/4" stereo plug leaving off the ground, but having the hot wire in both channels connected. Very high quality jacks and plugs should be used to make this NULL Adapter; one can also be made for feeding a signal from the RCA OUTPUT Jacks, but it is much better feeding headphones than an external power amplifier, as the null is much easier to observe using a pair of headphones.

If you have a difficult time with this, I can custom make these NULL ADAPTERS up for you, if you want.

Then, when feeding in a mono signal ( use one wire into a split connector - one RCA jack to two RCA Plugs ) feeding into the GX-635D's inputs. With the NULL ADAPTER on the RCA outputs or headphones ( whichever type you made ) one adjusts input controls to a usable reading on the VU Meters, and then the VR3 / VR3b FWD. and VR4 / VR4b REV. for NO SOUND, that is the point where signal levels in Source are adjusted to be equal.

At this NULL POINT adjust one of the VU Meters adjust controls VR5 or 5b so both VU Meters now read EQUAL levels.

Using pink noise, white noise, or full spectrum noise from an FM interstation hiss ( muting off ) at a recording level of -3dB on the VU Meters allows you to check sonics between Source and Tape quickly, and then adjust VR2/2b to have the levels equal.

Maintaining the NULL ADAPTER in the circuit, check SOURCE to TAPE... you will likely get a swishing sound along with some amount of a noise spectrum, like mid/upper hiss, when on TAPE. If the SOURCE is still a perfect NULL, you may have to adjust the screw (c) for precise tilt of the Record Head, this is to obtain a precise phase response for both channels, which affects the stereo spread and stereo positioning of a stereo image.

Such an adjustment is usually only a fraction, a few degree's of arc may bring a closer NULL on TAPE. In the FORWARD Direction, adjust very minor changes in (c) screw a bit in both directions for best NULL. In REVERSE Direction adjusting the Tilt would be done using screw (c').

Next using -3dB levels ( because it is the center of the VU Meter and differences are easily seen ) expect to hear almost no source to tape differences at 7.5 ips, but some slight dulling of highs at 3.75 using such a high level. Using straight tones, at 12.5Khz. should be flat at 7.5 ips, but there could be a bump, so it might be above reference level by 1 or 2 dB between 12.5Khz and then maybe -2dB when at 20 Khz. A -2dB or -3dB difference isn't bad and will vary with each type of tape used.

Expect more deviation at 3.75 ips, and using a -3dB level, a -5dB in the 12.5Khz., 15Khz., 20Khz. range is doing pretty good.

If the adjustment of (c) screw on the Record Head and also the internal controls does not have the desired affect, then try also a very minor adjustment (f) on the Play Head. If neither helps get you a good NULL, then possibly the Recording Heads or Playback Heads are still dirty; have bad gaps; or are defective, or another defect exists in the Recording Circuits.

Another possibility could be some of the coupling caps or bypass caps in the circuitry are defective and messing with the frequency response.

It is extremely difficult to diagnose and align a deck that is like 5,000 miles away in another part of the world, but the method I have described should get you going to a much closer alignment as was done in the factory.

Yes, I have several 10" metal Empty Reels on their way to me now, they have not arrived yet.


Steven L. Bender, Designer of Vintage Audio Equipment

********** An Addendum: **********

Subject: Problem Solved!

Date: Thu, 22 Jan 2004 01:32:20 +0200

Hi Steven,

I would like to thank you very much for your valuable instructions. It took me several hours but I finally managed to solve the problem. I followed all your instructions and everything went well and as described. (The Null Adapter was an exellent solution).

As far as my ears can tell me, the quality of sound is great. Once again thank you very much for your valuable assistance.

Thank you


Comment #39

Subject: Question about AKAI

Date: Sat, 24 Jan 2004 22:04:25 +0100

From: "Christer Nylander"


Dear Steven L. Bender

Thank you for your good information about AKAI recorders.

I have a question. My friend has one AKAI GX-635D and one AKAI GX-4000-D.

How good are these for recording singing voice? What microphone should I have and where do I get it from? Do I need Preamp or other equipment?

Grateful for answer.

Thanks in advance.

Best regards,

Christer Nylander


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

Hi Christer -

Well, the Akai Reel machines such as the GX-635D and GX-4000D were indeed very good in their day, and do contain microphone level inputs quite usable for a pair of stereo mics to make live recordings. But unfortunately, now 20 to 25 years later, it has been found that most later Akai's such as the GX-635D and GX-4000D contain transistors with a serious defect.

These faulty transistors slowly loose gain over time, and in return become extremely hissy. Every later Akai, made between 1976 and 1984 that I've seen during the past two years has had at least several of these "hissy-fit" transistors, typically, when this happens, between 8 and 16 transistors have to be changed in order to return the set to normal, functional operation.

By listening using headphones, one can often hear these hissy-fit parts failing. They get worse, first becoming hissy, then later not passing audio at all. Having the input controls all turned down, but switching between source and tape, you might find that either channel is hissy and other quiet, or that going from microphone level turned down to turned up causes one channel to be hissy, or maybe to have a Shott Noise, which is like a faint popping sound.

Going from Source to Tape there again one or both channels might be very hissy. This effect is mostly going to affect the signal to noise ratio, and while some background hiss does exist in all tapes and all tape machines, one can over time get to know what is right and what is a faulty indication.

As for microphones, really good powered studio mics can cost well into the thousands of dollars, but many of todays electret microphones are usually quite good and cost in the $20.-$50. each range. Less expensive mics like that, have the 1/4" inch plugs that typically go right into the Akai's front panel.

While an outboard mixer can also be used, 4, 6, or 8 Channels in, and probably 2 Channels out, typically, these are good when using multiple or a whole bunch of microphones, to cover singers and individual pieces in a band.

Usually the better mics use XLR plugs and such mixers have XLR jacks for inputs and outputs so you would have to either buy more expensive mics, or re-wire when you want to do that. One typical thing to determine how much a microphone is capable of going without overload is the power source, mics that take a single AA battery have only so much voltage that they can develop before distortion sets in.

My own Sennheiser Mic's use a 5.6 volt battery, they come from Germany, and date from the mid-1970's and were several hundred dollars back then. Some of these semi-pro type Electret mics do feature interchangeable heads, having Shotgun-Cardiod, Normal type Cardiod, and Omni-directional pickup charactoristics, as well as bass frequency adjustment switch positions.

I also had some Teac ME-80 and ME-120 and TASCAM PE-120, and PE-125 Models were Electret mics that use a 9 Volt battery, they also do a great job, at fairly low cost, they come with mechanical slip-on pop filters, have an attenuation control ( some inside the head ) and bass reduction switches to adjust for the type of situation it was being used in. The same basic mic as the Teac and TASCAM's anodized in black was very popular and available under the Nakamichi name.

Many companies produced One-Point "Stereo" Mics that were a quick and dirty way of getting into Stereo Recording with a minimum hassles. The Sony ECM-99A made by Sony, the RP-3210E from Technics; the AT9400 from Audio-Technica, and Teac MC-210, and probably many others, have two separate mic elements angled somewhat differently inside a rather large "head" attached to one body that terminates in a pair of 1/4 inch plugs.

These tend to be lightweight hand-held types, somewhat low-end but decent in overall quality, they use a single "AA" or a "C" battery. Twenty or so years back these mics were fairly low priced, but they get you stereo recordings with only one microphone body to deal with.

While all of the products I've mentioned are vintage, and about as old as our Reel to Reel Tape Decks and Recorders, most are still probably in pretty good operational condition even from 30 years ago. I'm sure some of these can still be found at prices probably well under $50.

Over the past 5 years I picked up five of those types of microphones pretty cheap on ebay. Search on "microphone" or "stereo microphone" will likely bring up many choices, new and used on ebay.


Steven L. Bender, Designer of Vintage Audio Equipment

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Last Update - February 5th, 2004 9:00 PAM.

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