Ampex AG-440 alignment issue?

[scott9873]

Hello,
I don’t know if this is the right place to ask a question about a tape recorder, but my Ampex AG-440 is performing beautifully after I’ve done a calibration and restoration - well, there is a small problem I guess? When I play my MRL tape, the 10kHz tones fluctuate quite a lot in levels, and sometimes the channels drop by around 5dB for periods of a couple seconds, then it returns back to 0dB. Is this normal? Is my tape tension set incorrectly? Heads need to be relapped?
Thanks

 

[EERecordist]

I need to do some work on my Otari, transfer some tapes and sell it, so it is a topic I follow. Is your alignment tape worn? When was the last time that tape on that deck, or that tape on another deck performed as expected? How does music sound, pre-recorded and off the tape monitor?

I would guess if you restored you restored the rubber pinch roller, but that would be short variations, not long. Usually head wear is evaluated by visual inspection. Several seconds could be the playback electronics, maybe monitor the power supply in real time to start as it is happening. There could also be intermittently faulty capacitors in the signal chain if you did not replace all the capacitors.

The expert is Curt reeltoreeltech.com in BC Canada, but I'm not sure how much troubleshooting information he gives over private messages. He does have a list of tape techs on his website because he can't handle all the work he is getting. There may be other reel to reel troubleshooting discussion groups beyond ASR. If you don't have the maintenance manual, finding one would be a good start.

Tell us how it works out.

BTW Curt Palme of Reel to Reel Tech has an active FB group on his restoration, repair and sales of vintage tape decks which may be of interest to ATR readers. I'd love to buy a famous Ampex ATR100 from him, but I have no use. Best transport ever made and a joy to work on back in the day when editing tape. He buys low, but given an hourly rate, has very economical prices for the restored tape machines.

 

[Palmer]

Hi, congrats - nice machine. Absent any issues in the electronics for a moment - you'd have that problem when you play back any other material than the MRL...
So if any of your tapes play back fine, it's the MRL - heads and tape guide issues would raise their ugly heads on other tapes, too - pun intended. Same for electronics of course.

You could always get a 10kHz out of, say your computer or phone - and record that and listen off of the playback head while recording, after that if you can, from the record head, on SelRep - though I'm not sure if that's possible on the AG-440...

 

[scott9873]

Thank you so much for your help! Perhaps my MRL tape is worn, but it doesn’t make sense because I bought it maybe a year ago and always cleaned and demagnetized the machine before playing it. The tape itself looks brand new, no marks at all. I’ve bought a new pinch roller for it, and the tape doesn’t slide up and down on the head. I think the electronics might be the suspect here.. I think I wanna try connecting the heads directly to a oscilloscope and seeing if those oscillations appear on there.
I do have other good material that plays back beautifully, but these oscillations in HF level could happen even on those tapes without me noticing, perhaps?

 

[Palmer]

Thank you so much for your help! Perhaps my MRL tape is worn, but it doesn’t make sense because I bought it maybe a year ago and always cleaned and demagnetized the machine before playing it. The tape itself looks brand new, no marks at all. I’ve bought a new pinch roller for it, and the tape doesn’t slide up and down on the head. I think the electronics might be the suspect here.. I think I wanna try connecting the heads directly to a oscilloscope and seeing if those oscillations appear on there.
I do have other good material that plays back beautifully, but these oscillations in HF level could happen even on those tapes without me noticing, perhaps?

Doesen't have to be worn, I do remember drop outs on the MRL, from days long ago. Unless you have receding hearing, I am sure it would make itself heard when playing back other tapes, as high as 10K is - drop outs for a couple of seconds would become audible. You could always have a marker in your hand, and see if these drop outs on the MRL are at the same spots... That would prove it's the MRL.

 

[scott9873]

Well, the electronics/preamps are fine and pass clean audio up to 22kHz and beyond (connecting my phone to the repro head socket).. so I think the headblock just needs a relap. This unit is very old and has recorded tons of tapes so it makes sense.. I will try to contact a relapping service.

 

[pollock0424]

You'll probably get more help on the tapeheads. Many techs there are actively taking clients.

 

[scott9873]

I’ve been quite busy lately and only now I think I’ve figured out the situation after playing with my equipment.
Here’s the conclusion: My stereo AG-440 desperately needs a relap, and my test tape is now magnetically degraded. I don’t know how, but it happened for sure since the levels fluctuate slowly when played back on my mono full track AG-440, and that unit is in absolute perfect condition and makes steady recordings.

 

[scott9873]

The stereo heads are quite unique and it’s hard for me to determine the wear on them..

 

[pollock0424]

Yes, you need a magnification of 100x to see what's actually going on. If you're dealing with cassette tape heads, tolerances for track registration and height are in the range of ~0.1mm and in a few arc minutes for azimuth(no wonder cassettes sounded lousy to most people because most people are not engineers) . If you do not have proper guages, calibration tapes then leaving the heads alone is a good idea. I'm trying to learn how to lap heads using throw away samples. It requires patience, planning, and all guages and measurement gear. Here is a head that I'm working now..

Openreel heads are a lot easier to lap but again you'd need all the gear. A gentleman who has extensive knowledge in magnetic media has been guiding me so far.
This is my lapping rig starting at 9micro and ending at 0.3micro.