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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 #40

Subject: Akai GX-255D

DATE: Sat, 31 Jan 2004 19:31:46 -0800 (PST)

From: Jimbo

I'm also interested in possibly purchasing an Akai GX-255D. What interests me about this machine is that it's direct drive and that it's newer and I think Akai may have gotten over some of its glitches about the time this model was made. Could anyone let me know what they think of this machine and if there are anything that I should look out for.



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

Well Jim -

The later GX-255 and GX-266II, are now among Akai's most problematic sets, usually the failures seen are more extensive and tend to show up 15 to 20 years after manufacture...

Seems the GX-635D are also subject to some of the same failures, and I would guess it affects more Akai models too, that date from a 1978-79-80 time frame.


Steven L. Bender, Designer of Vintage Audio Equipment

Comment #41

Subject: EE Position Tapes

Sun, 1 Feb 2004 23:01:10 -0800 (PST)

Conrad wrote:


What happens if I use EE tapes on a non EE machine like the RT-909?

Will it record ok but not be able to erase them? I hear EE tapes are like the METAL tapes on cassette decks.

Anyone know?

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

- First, the recording will have a rising high end, severely skewed towards the treble, and the level will be about 10dB lower than say using a Maxell UD or UD-XLI tape.

- It will record but play levels may be unusually low and it will seem like the treble control had been totally cranked up.

- No, you will not be able to erase them, and most bulk erasers won't be able to erase them either!

- The EE tapes reportedly are also somewhat more abrasive than normal iron oxide tapes or "enhanced" iron oxide tapes, then, considering that Pioneer adjusted the tape tension to be about 50% higher on the RT-909 than on most other sets, the heads in the RT-909 only last 1,500 hours in the first place; compared to the expected 2,000 hours for normal Permalloy ( non-ferrite type ) heads on other decks before deterioration is noticeable.

That might have been OK in 1985 when the sets were new and getting replacement heads and parts were no problem... Of course, the proper heads are no longer available 20 years later. EE tape on the RT-909 would further increase head wear, and reduce head life even further. If its not enought that Pioneer and certain online parts places who now try to pawn off the RT-707 heads to unsuspecting techies at exhorbitant prices, well they simply aren't made the same...

Other stupid things were present in that sets' design too.


Steven L. Bender, Designer of Vintage Audio Equipment

Comment #42

Subject: Akai GX-365D

Date: Sat, 31 Jan 2004 19:21:17 -0800 (PST

Jimbo wrote:

I purchased an Akai GX-365D from Ebay a couple of years ago and it worked fine for quite awhile actually. Most recently I noticed 2 things. First the playback in reverse seems to be mostly on one side. The sound I mean. It seems to be low on the right side and normal on the left.

Also when I hit the reverse button it takes a couple of seconds to engage and the left side didn't turn. It almost spun the tape off the take-up reel. I had to sort of help it by hand to get it to engage. What could be causing this? Is there some part or parts that need to be replaced, like a belt or something?



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

Hi again Jim,

These 2 failures low left channel; recalcitrant left reel when in Reverse Play... may be inter-related ( or maybe not... ). The GX-365D dates from around 1969/70, and was the first "GX" set, so its now almost 35 years old.

Among the problems that exist, they could be caused by decades of Air Pollution effects may have caused excessive friction in the left motor. The result would be lower torque, or tape tension - much lower than previously.

The lowered motor torque could cause the tape to lose contavct with the head just enough to skew or effect the left channel first. First, keep the tape path clean, and the problem still may exist with lowered tension or torque.

The main belt is only for the capstan flywheel, in this 3 motor machine, the left and right reel tables are directly powered by the reel motors which have no belts for that.

Problems with the relays from arcing of contacts could cause lower than normal voltages, which could also reduce motor torque. That set has 13 rather proprietary power relays, I doubt that suitable replacement relays are available, if they are, I haven't found them...

There are also large power resistors ( huge green resistor things ) that give off heat, in lowering the voltages; they have if I recall properly several adjustable takeoff tabs which direct different voltages to the reel motors depending on the function chosen. So over time, these voltage adjustments also might become loose or "off" causing improper voltages to appear across the motors, and again, low torque.

Or the tape path could be clogged with oxide debris. This causes excessive friction and will also cause the same symptoms. I don't repair the GX-365D, due to the unavailability of the many power relays, but I do know that dirt and excessive friction were definately the problem of slow speed on MY OWN GX-365D when it first arrived here. After a total tape path cleaning, it has been working OK ever since.

I can supply the GX-365D Service Manual, which would be of help in diagnosing and fixing the problem if it is adjustments or any failure other than debris in the tape path.


Steven L. Bender, Designer of Vintage Audio Equipment

Comment #43

Subject: Bias

Date: Wed, 4 Feb 2004 04:00:57 -0800 (PST)

harald wrote:

Hello everybody,

How do you check and fix your bias setting to several tapes? Is it enough if you run a frequency sweep (20-20.000 hz) from a test cd through and it's ok when you see the vu meter fixed at the same position? I'm not sure. I would like to know how you set bias really well (don't always trust my ears)

Thanks in advance for the advice

Best regards,

Harald Roelofs

Amsterdam, The Netherlands

David wrote:

1) When bias is too low, distortion will be increased, and frequency response will rise in the treble. When bias is too high, high frequency response will be greatly reduced. The ideal bias is dependent on the specific tape formulation used.

2) Many professionals use the following approach, often called "overbiasing" It provides a good compromise between minimizing distortion and maximizing high frequency response.

3) First of all, the heads should already have been properly aligned physically, and playback EQ adjusted for flat response, by using a standard alignment/test tape in good condition.

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

These three items are very much correct.

In addition to counter the effect of past head wear, or lack of proper factory alignment, the Record Head Azimuth should be very slightly "tweaked" until the phase response is exactly the same between the channels assuming a 2 channel set. This method I've described previously using a "Null Adapter" in answer to a prior question.

David wrote:

Next, using a tone generator and the type of tape for which you are setting up the machine (best results will then be found when you consistently use the same tape formulation) record a high frequency tone between 10kHz and 15 kHz at about a -20 dBU level (to avoid effects of tape saturation).

Adjust bias to achieve maximum level. Then continue to increase the bias current until the output of the high frequency tone drops by 2 or 3 dB.

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

The main problem with this is almost ALL sets that are not profesioinal STUDERS will have changes in frequency response with respect to recording level. Using the -20 dB method basically means you can get great recording as long as the VU meters are barely moving, but once the recording level is higher than -20dB the frequency response drops off precipitously!

How many people do you know who want to waste the additional 25dB of headroom possible with better tapes ( and also lose 25dB of signal to noise ratio ) by recording way down at -20 dB ?????

Most people want to see those VU meters move! Most vintage recordings, when I buy used tapes, of Vinyl, FM radio, or concerts - I find people have recordings that pin the VU meters at times, and tend to do a long term average close to -3dB or 0 dB while recording. Hitting 0 dB or even going into the red, the resulting recording will then have severely limited high frequency response or much distortion if using the -20dB method.

I use a -3dB recording level on the VU meters, when adjusting high quality 3 head RTR sets, and using better Low Noise / High Output type tapes, such as: Basf LPR-35; LP-35 LH Super; or LP-35LH Studio; Fuji FB-151; Maxell UD; UD XLI; TDK Audua; LX; GX; Sony SLH; ULH; Scotch Classic; 207, and similar etc.

In most cases -3dB is close to the center of the meter scale, where the meter is the most accurate, also, changes can be more readily seen at that level, such as 1/2 dB is easily descernable. Can you tell 1/2 dB when using -20 dB I think not! You would be luck to guess at a 5 dB change. In this way, I have obtained a record/playback frequency response of about +/- 1dB. or +/- 2dB. from 50 to 20,000 at 7 1/2 ips on better machines.

Head Fringing effects can make for some rather devilish variations down below 100 Hz. on some sets, so expect variations down there between 35 and 75Hz. - its normal. And many sets do roll-off below 40 Hz. so -9 dB or -10 dB down at 20 Hz., is pretty typical.

So really! don't expect 20hz.-20Khz. +/-1 dB on your non-Studer machine. I adjust the bias level so that high end is flat or then -1 or -2 dB but using a -3dB recording level, which more closely approximates what better tapes made in the 1970's, 80's, and 90's could do. In doing so I GAIN about 20 to 25 dB of signal to noise over the -20 dB method.

David wrote:

Continuing to record, now adjust the record equalization to achieve flat record-play response.

The procedure must be repeated for each speed and each channel, assuming that the machine has independent controls. (Most true professional machines will -- some consumer machines have adjustments only for one speed, requiring that you adjust for that speed and just live with the results at other speeds.

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

Bad Idea!!! If this is now done, the tape is now non-standard and won't playback properly flat on ANY other machine... Adjusting the Record Eq. you also might be causing an increase in distortion, intermodulations, and other saturation problems.


Steven L. Bender, Designer of Vintage Audio Equipment

Comment #44

Subject: GX-270D

Date: Thu, 5 Feb 2004 14:25:56 -0800 (PST)

Dan Cebalo wrote:

Hello, Is it possible to use reel to reel with voltage converter?

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

I'm always against this, as voltage potentials might exist between the ground on this set and the interconnected amplifiers, you could touch something and get seriously zapped or dead!

Today someone mentioned feeling a slight tingle sensation when touching the panel of a powered-up set, one that is working on proper voltages, and so he was concerned... well he has voltage leakage... and such problems are fairly common in complicated sets some 20 or 30 years later; if someone tried to run such a set on a 220 Volt converter, then someone will get injured!

> Wouldn't that affect the motor speed?

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

On many sets the cycles being different, it would affect the motor speed. On some the transformers would overheat running on 50 Hz.

> I'm currently looking to buy an unit that can only work on 120V 60Hz. Is it possible to use it with converter in Europe (220v 50Hz)?

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

Dumb idea, AS PER above reasons.

> Also, what is the function of output volume control, since reel to reel unit is to be hooked up to an amplifier anyway?

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

Often one wants to match input levels among various inputs, so when switching, between them, one doesn't get blasted / blow out the speakers, etc.


Steven L. Bender, Designer of Vintage Audio Equipment

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Last Update - February 13th, 2004 4:45 PM.

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