rotovator
Cassette deck fanatic
[This post discusses some tapedeck's head problems and DIY tests. It is probably not interesting to those not skilled or experienced in repairing vintage decks, and it's quite long]
I've been repairing my old aged Pioneer CT-F1250. When I bought it, it was probably the
most used and dusty deck I've ever seen. From outside, it looked quite correct. once open
the internals were covered in dust.
The deck was mechanically ill and electronically totally out of specs. Motor had no torque,
it couldn't rewind or ff with energy. Play position could't go for more than 20 seconds
Recording was totally impossible. Calibration procedure was pure fantasy. And playback
sound was dull and without highs.
I changed belts, tyres, cleaned the motor internals twice, replaced pinch roller tyres
cleaned many pulleys, azimuth adj. demag (several times with two devices), etc.
I tried to recalibrate the recording circuit and made recording possible, though with
low quality.
The only thing left was to get a decent playback response.
Upon close visual inspection, the heads looked fine. I used a magnifying glass and proper
illumination to check for any crack on the surface. I think those heads have a crystal
layer and are quite resistan to wear. The surface looked perfectly shaped, elyptical
without cracks or flat areas. I've run across several weared heads and can
tell the diference from a unweared one..
I checked all the things that I can think of, even the pots on the playback eq circuit.
So, at this point I had planned to either replace caps in the playback circuitery or
to test the circuitery from sources other than the mounted heads. I highly suspected
that the heads or playback circuit was bad.
One worrying symptom happened when recording and monitoring the response (tape position),
I could hear the highs from the original music played together with
the music readed off the tape. I think that the magnetic flux emitted by the
record head reaches the playback head and induces a response. I recorded withouth
any tape while the tape/source switch was set to tape and I could clearly listen
to that very high equalized signal I was sending to the record heads. Sometimes this
may happen, but this time was like I never heard before. To further experiment, I
placed a steel screwdriver over the head at a very close distance and it seems that
the magnetic flux from the record head was driven to the playback signal much more. the
level was loud and the sound was even more linearly equalized as if there was a real
tape passing by the heads.
To get more data I did the following test which can be interesting to other people willing
to repair their decks with similar problems. I took a Pioneer CT-F600, an old aged deck, I fixed it
from some of the problems it had. I put a new head because old was visually weared and didn't
play fine. The new head played much better .
I made a pair of shielded cables with alligator clips ((signal + ground) x 2) on
its ends to connect the output of the heads (input of the amplifier circuit) of
one CTF600 deck to the same point in the CT-F1250 (input of the amplifier circuit).
this is: both decks shared both heads. It is like if one deck used the heads of the other deck
Besides, I connected the line output of the small CTF600 deck to the record rca input of
the CT-F1250. And the output of the big CT-F1250 to the amplifier.
This way I could:
Play a tape in the small CT-F600 with new heads use the head amplifier
section of any deck and compare them by swaping tape/source in the
CT-F1250. I could also adjust playback levels ( recording level) to my
needs.
Or I could do just the same but with the cassette inserted in the
CT-F1250.
During any test only one of the two decks had a cassette in it, the other was playing empty.
Results:
The tape, when played with the new head of the CT-F600 sounded crisp and clear
on both decks. CT-F1250 seemed to amplify better; but, probably due different
equalization, lacked some bass. So I calibrated the playback equalization (only
possible in the CT-F1250 AFAIK) and both decks showed similar playback
response.
When the tape was played with the heads of the CT-F1250 (on either of the two decks
amplifying the heads signal) the sound was dull, without heighs
on any of the two decks (azimuthed ok). This time, the CT-F1250 was also better, but
the sound was so bad that it was unimportan to think about it.
The test showed that I couldn't get any acceptable sound quality from the CT-F1250's head.
While other head did sound much better.
conclusion so far: The venerable crystal head is damaged or degradated somehow.
I think The test made leaves no doubt.
I need new heads for my beast, and I highly suspect they are unobtanium.
I've been repairing my old aged Pioneer CT-F1250. When I bought it, it was probably the
most used and dusty deck I've ever seen. From outside, it looked quite correct. once open
the internals were covered in dust.
The deck was mechanically ill and electronically totally out of specs. Motor had no torque,
it couldn't rewind or ff with energy. Play position could't go for more than 20 seconds
Recording was totally impossible. Calibration procedure was pure fantasy. And playback
sound was dull and without highs.
I changed belts, tyres, cleaned the motor internals twice, replaced pinch roller tyres
cleaned many pulleys, azimuth adj. demag (several times with two devices), etc.
I tried to recalibrate the recording circuit and made recording possible, though with
low quality.
The only thing left was to get a decent playback response.
Upon close visual inspection, the heads looked fine. I used a magnifying glass and proper
illumination to check for any crack on the surface. I think those heads have a crystal
layer and are quite resistan to wear. The surface looked perfectly shaped, elyptical
without cracks or flat areas. I've run across several weared heads and can
tell the diference from a unweared one..
I checked all the things that I can think of, even the pots on the playback eq circuit.
So, at this point I had planned to either replace caps in the playback circuitery or
to test the circuitery from sources other than the mounted heads. I highly suspected
that the heads or playback circuit was bad.
One worrying symptom happened when recording and monitoring the response (tape position),
I could hear the highs from the original music played together with
the music readed off the tape. I think that the magnetic flux emitted by the
record head reaches the playback head and induces a response. I recorded withouth
any tape while the tape/source switch was set to tape and I could clearly listen
to that very high equalized signal I was sending to the record heads. Sometimes this
may happen, but this time was like I never heard before. To further experiment, I
placed a steel screwdriver over the head at a very close distance and it seems that
the magnetic flux from the record head was driven to the playback signal much more. the
level was loud and the sound was even more linearly equalized as if there was a real
tape passing by the heads.
To get more data I did the following test which can be interesting to other people willing
to repair their decks with similar problems. I took a Pioneer CT-F600, an old aged deck, I fixed it
from some of the problems it had. I put a new head because old was visually weared and didn't
play fine. The new head played much better .
I made a pair of shielded cables with alligator clips ((signal + ground) x 2) on
its ends to connect the output of the heads (input of the amplifier circuit) of
one CTF600 deck to the same point in the CT-F1250 (input of the amplifier circuit).
this is: both decks shared both heads. It is like if one deck used the heads of the other deck
Besides, I connected the line output of the small CTF600 deck to the record rca input of
the CT-F1250. And the output of the big CT-F1250 to the amplifier.
This way I could:
Play a tape in the small CT-F600 with new heads use the head amplifier
section of any deck and compare them by swaping tape/source in the
CT-F1250. I could also adjust playback levels ( recording level) to my
needs.
Or I could do just the same but with the cassette inserted in the
CT-F1250.
During any test only one of the two decks had a cassette in it, the other was playing empty.
Results:
The tape, when played with the new head of the CT-F600 sounded crisp and clear
on both decks. CT-F1250 seemed to amplify better; but, probably due different
equalization, lacked some bass. So I calibrated the playback equalization (only
possible in the CT-F1250 AFAIK) and both decks showed similar playback
response.
When the tape was played with the heads of the CT-F1250 (on either of the two decks
amplifying the heads signal) the sound was dull, without heighs
on any of the two decks (azimuthed ok). This time, the CT-F1250 was also better, but
the sound was so bad that it was unimportan to think about it.
The test showed that I couldn't get any acceptable sound quality from the CT-F1250's head.
While other head did sound much better.
conclusion so far: The venerable crystal head is damaged or degradated somehow.
I think The test made leaves no doubt.
I need new heads for my beast, and I highly suspect they are unobtanium.
