Alpage AL-300 HF loss

HazzeB

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#1
Hi all, new member from Sweden here, been reading a lot in the forum and posting now for first time, needing advice regarding an Alpage AL-300 cassette deck.
Many years back I bought this new, had it for a year or two then sold it to a friend. A few months ago I meet him and asked if he still had it, and yes he had it put away in the garage many years ago. He asked me if I wanted it, I said yes and he gave it to me for a nice bottle of whiskey in exchange.

Well, the deck was rater dirty from being stored in the garage whitout a box for a long time so I took it apart. Cleaned the entire deck, changed belts, idler tires and pinch rollers, lubed/oiled moving parts.Cleaned the tape head with aceton and polished with autosol, cleaned again with IPA.

Everything works fine, wow and flutter is ok.

When checking the playback frequency responese, the the response is falling from 1 KHz, reaching a minimum at -6dB around 10-12 KHz and then rising again towards 18KHz (se graph). Test was done using the tape from HPR, azimuth was adjusted (with analog oscilloscope) to match the response tape.
AL-300 IEC curve 240407.jpg

A -6dB high frequency loss does not look so good, so did another test with a flux loop to see if the loss was due to the playback eq or elsewhere. As it looks to me the flux loop curve nearly exactly follows the table from the Ampex flux loop paper, so if the flux loop curve looks right the playback response should be more or less a flat if the tape head is in good condition? If so, the HF loss much be due to the tape head?
al-300 flux loop chrome.jpg

Flux loop table.jpg

Found a graph of the AL-300 playback response on LAB2104 Research Labratory homepage showing a -4dB loss at 10 KHz. Not as much loss as my deck but indicating that the loss could be expected.

lab2104 al-300.jpg

After calibrating and doing a frequency sweep, I have no problem getting a flat record/playback response up to 20 KHz with low distortion and minimal channel imbalance. Used tapes was TDK SA (Chrome) and TDK D (Normal), both resulting in frequency response above 20 KHz.

This makes me a little confused rising some questions.
1. Is the IEC tape playback HF loss normal for this type of tape head/cassette deck?
2. Can the HF loss be due to wear of the head? As I understand, being a Ferrite head it sholud not be as sensitive to wear as other heads with softer alloys?
3. Have read some about Ferrite heads being sensetive to corrosion widening the gap, knowing that the deck has been stored in a garage (not in a box) for shurley more than ten years, exposed to humidity and temperature changes, could this have affected the head?
4. If cause is 2 or 3 above, could a relap of the tape head fix the HF loss?

The tape head is ALPS (41139, U02,A01F) as I read in the forums highly regarded. Picture of head below, not enough magnification to show if wear or not but maybe the general condition of the head.

ALPS.jpg

Any advice or thoughts would be most welcome.
 

HazzeB

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#4
Hi and thank you Marco, much appreciated!

Yes, I have the service manual, same version as attached. My deck is low serial so the manual doesn't 100% match my deck layout-wise, but circuit-wise close enough.

I have checked the head aligment height, tilt and azimuth with m-300 gauge and the test cassettes from HPR for head hight and azimuth and it all checks out fine. No possibillity to adjust the playback eq just procedure for the recording side, which I followed with good result.
Recording/playback on this deck measures very good and sounds great. I could just let it be and use it as it is with no problem but the compability with other deck would not be so good.

I thought that maybe the frequency response tape from HPR would not being accurate but I cross-checked with the other test tapes for azimuth and dolby level, the relative dB levels match up just as they should so propably not any wrong with the frequency response tape.

I did a test modifying the feedback part in the eq amp, placing a resistor and capacitor parallel to R409, with this done I had a +-1 dB frequency response upp to 18 KHz. This looks fine but I feels like just taking care of the symptoms and not the root cause.

eq amp.jpg

Best thing would be if I hade a playback frequency response from an other AL-300 to compare with, then it would be clear if my deck is working as it should or not. I'm keeping my eyes open for a second unit, always good to have a backup. :)

Hans
 
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HazzeB

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#6
Thank you 20tajk7!
Great thread and absolute perfect with the clever modification of the oscialltor circuit! :D
I have noticed the 10 KHz peak always present, very annoying, will be nice to get rid of it.
I have replaced all elcos and tantal capacitors, that cured some low frequency noise from the power supply. Will take a look at the muting transistors also, thanks for the tip!
I see that you've refurbished a lot of AL-300's, out of all of these, have any of them had problems with head wear? If not I can propably put my worries about that to rest.
 

HazzeB

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#8
Been busy with work and the garden for a while now, so haven't had time for important things, such as hifi equipment, but next weekend the wife is away, which frees up time for this.:D I've read through 20tajk7's thread carefully and think I may give the tape path another look. W&F is a bit high and all though gone through the alignement several times, I can't manage to make the PB treble response any better. As Jim stated, the head looks fine and maybe the problem lies elsewhere. I don't have equipment to measure torque, but could it be that back tension is on the low side and affects both w&f and the contact with the head? There is nothing in the service manual about how it is adjusted but I think it is done with the plastic screws that the back of the flywheels rest against? When I had the transport apart, I lubricated these with silicone grease, maybe that wasn't a good idea? When I feel the capstan shafts, at least the right one, it has some play in the longitudinal direction, maybe a mm, for the left one I can't feel any movement. The play in the right should affect w&f, right?
 

J!m

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#9
On the Sony D5, there is a felt washer soaked in oil on the capstan shaft. Well, 50 years ago there was…

No luck finding one but I found a replacement in the form of oil impregnated plastic.

Anyway, the point is that the capstan shaft can slide in and out ~.060” when that washer has turned to dust. This seriously destroyed any hope of having acceptable W&F.

With the new washer and proper end float set, along with all the usual fixes, my D5 performs better than new specifications.

Food for thought…
 

20tajk7

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You never have too much tapedecks ^^
#10
High w&f is usually due to a bad belt.
Too high back tension will also increase the w&f, too low back tension will affect the tape to head contact and can also damage the tape.
The supply reel table has a felt clutch for back tension, I can't remember if it's adjustable, 'll check on my notes.
Lubricating the back of the flywheels with silicone grease is good but the flywheels bearings should also be lubricated with thin oil for sintered bearings.
The capstans should have a little longitudinal play, usually 0.1 to 0.2mm, too low play will increase w&f due to friction, too high play will cause tape skewing which affects frequency response.
 

HazzeB

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#12
As always, the devil is in the details, thank you for pointing me in the right direction!
I lubricated the flywheel bearings with 5/30 synthetic oil, at least I think so, I remember I hesitated between that or Isoflex PDP65 which I also have on the shelf.
 

mr_rye89

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#13
On the Sony D5, there is a felt washer soaked in oil on the capstan shaft. Well, 50 years ago there was…

No luck finding one but I found a replacement in the form of oil impregnated plastic.

Anyway, the point is that the capstan shaft can slide in and out ~.060” when that washer has turned to dust. This seriously destroyed any hope of having acceptable W&F.

With the new washer and proper end float set, along with all the usual fixes, my D5 performs better than new specifications.

Food for thought…
Hmmm I'll have to see how my D3 is set up, it's based on the WM-2/DDx walkmans so it's different for sure. I might be able to get it's w&f even better
 

HazzeB

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#14
I checked the longitudinal play for the capstans, the left had major play, 1.2 mm, adjusted it to 0.2 the right one was about 0.2, left it as is. This made the tape travel across the head more stable, had some wandering sideways sometimes before, did not better the w&f though, which is still pending from 0.06 to 1.1 (DIN, wfgui), speed fluctuations is less than 0.5%.
Made two observations, one is that the capstan belt jumps sideways brifely when capstan motor starts and then returns to the center. Maybe a sign that the belt is to short or not elastic enough, seeking the shortest path? The second thing I noticed is that the idler tire on the take up side is not abslolutely round. I guess in the end everything adds up, affecting the w&f.

I have ordered a set of new idler tires, ordered by size after measuring the old ones, and a new capstan belt 245x4.0x0.5., will see if that helps. Also have a used capstan belt for a Denon dr-22m that measures 244x0.5x0.4, it's in good shape so I will try this to if it does not work with the new belt.

Checked the alignement again, set the hight and tilt with the gauge, fine adjusted the height with the 1 kHz test cassette and adjusted the azimuth. Returned to the gauge double checking the tilt after this, which was ok. All cassettes used are from the 6 cassette HPR calibarion set.
When looking at the azimuth the phase is pretty stable, only some small occasional jump left and right. What disturbes me is the levels, they are equal but not up to level (-10dB), but nearly -14 dB, 4 dB missing.
When checking the playback frequency response, adjusting the azimuth for this cassette first, the high frequency roll off is slightly worse missing nearly 6 dB at 10 kHz and then rising towards 18 kHz.
The levels are also fluctuating at high frequencies, -+ 1 dB.
Back to my initial worries, could this be sign of head wear?
I guess the only way to determine that for sure, is by removing the head from the deck and examine with proper magnification.

Another strange thing, high frequency response gets better toward the end of the test tapes, both the azimuth, and pb frequency response tape, level at 10 kHz is almost 1.5 dB higher. Not shure what to think about that, maybe the take up torque inceases towards the end of the tape as the cassette reel increases in size when the tape adds upp on that reel?
 

HazzeB

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#15
Some updates, got new idler tires, changed the present ones for these, they new ones fit perfect, reassembled the transport and tested w&f... No change, but the transport got more quiet and ff/rw works very smooth now.
Ok, took the transport apart again, cleaned the capstans and bearings again, put a drop of oil in the capstan motor front bearing, changed belt to the old Denon dr-22m belt (244x0.5x0.4). Reassembled the transport, well the w&f now residues around 0.05 (DIN, wfgui) and deviation is less than 0.1%, more than happy with this!

Encuraged from this succes I once more went over the alignement. Come to thinking that I had not given much attention to the tapeguide by the left pichroller, just set it at the same hight as before I removed it to change the pinchroller.
This time I set the hight and tilt for the tape head with the m-300 gauge and did a rough azimuth adjust. Loaded a c-120 tape with some of the shell removed for free sight to the tapehead and adjusted the left tapeguide for no curl at the tapehead, then loaded tape for head hight and adjusted again the left tape guide for equal level. Azimuth adjustment after that, checked again with the c-120 tape and so on for quite a while. Well after some time all matched up, levels equal, azimuth spot on and no tape curl.

Azimuth.jpg

Checking the playback frequency response things was much better, 50-10 kHz +-1 dB and then rising +3dB towards 18 kHz, channel balance almost perfect!

AL-300 IEC curve 240516.jpg

Also took care of the 10kHz playback noise, thank you 20tajk7!

Mods.jpg

Next will be adjusting the playback section.
 
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