Revox A77 Playback Head wear and how it changes the Frequency Response
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- Опубликовано: 5 окт 2018
- I am restoring my Revox A77 and it is now time to change the both record and playback heads. Before doing so, I wanted to capture the current condition of the deck by measuring the frequency response. Hopefully I will make another video after the recapping and head change and compare the results to observe the improvement.
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Very helpful! Many thanks, really informative.
My Crown CX822 (2 track) & CX722 were just installed with NOS Nortronics 'Duracore' Rec/Ply heads. When aligned & cal'ed for LPR-35 tape, they gave a response of +- 1db from 25hz. to 28khz. & -3db down at well over 30khz., [Ref@-10db.] with I.M. distortion of the play-electronics @ a very low 0.05%. Duracore mu-metal is expected to last over ten thousand hours of use. The only drawback is that the bias osc. is cranked up to maximum output in order to properly set it for Standard Quantegy 456 or LPR-35 tape formulations. These long-pole heads load down the rec/erase bias a bit. Anyway, that's the issue with today's semi-pro tape machines. Try & get replacement heads, Especially the Japanese models! Studio decks can still go to JRF for heads...at least for now.
Very informative video - where did you acquire new heads from ? What should somebody expect to pay for new A77 - REC & PLAY heads ? Much thanks !
Nice explanation - I am just in the process of getting a Revox PR99 back to running.
Ex BBC so it has had some use.
Interestingly my heads are also around 4.5mm across - but on playback at present it records and plays back fine.
I found a BBC service document for radio and tv stations etc and it states that when the heads get to 6.3mm is the time they need to be replaced.
I assume they just kept adjusting the Rec and Reproduce amp settings to the point of no return!
You are correct - untill the gap is not widened by lack of metal it will work not much different - only experienced ear could spot that signal has value deminished . Insted of it recording with even little worn heads creates not fully satisfying new recordings Usualy users after some period of using recorder notice that "new" recordings are not as clear as old and it is progressing with hours. That is why producers of tape recorders developed in 70ties technology with separate not wearing bias head X360 . It slowed speed of changes. In my opinion best solution for home users to save heads is to choose as low tape speed as possible if only it doesn't hurt reception
Hey , I have a problem, I want to set bias trap in rec mode and in playback mode. In rec mode I make it settings successfully the bias trap , but… in playback mode the bias trap is unable to set in the Chanel 2 with coil L801. I screwing with the screwdriver the core of coil L801 but no changing in milivolts. In Chanel 1 I make it setting successful (less then 50mv) but in Chanel 2 no modifications. I changed the repr. Ampl. Card with card in Chanel 1 thinking the coil L801 is defect but no changes ! What is the problem??
Nice video. Where you can buy playback head for Revox A77?
I've found it on eBay.de
for at least 100€ I think?
hy i have this machine and i have a problem, the vu meter in play mode not working, only in record mode working, so why?
that's normal on A77- only the dolby version has off-tape metering, or a B77.
if you put the input switches to "i>ii' & "ii>i", then advance the recording level controls to about 7 or so, you'll see the playback signal on the meters. the channels will be reversed though.
I'm sure you made a demagnetizing befor measuring!? What's the name of the program (CLIO?) you are using? Are you measuring the frequency response with white noise? At which speed it was measured? I am curious very much as the video looks after the exchange of the heads. I've the same machine (MK IV, 4 tracks) and the heads are nearly in the same condition as yours. The (in Germany we call it "Kopfspiegel") heads have 4,5 mm. You say the heads are usable till about 5 mm. With tapes of Maxell I can get a frequency response of 16-18 kHz at 19 cm/s.
Please check the follow-up video ruclips.net/video/9TUKhOYlTSE/видео.html
You missed the point that your measurement covered two processes at once - recording and playback. Slop of sopranos in tape recorders is caused not by play head but by wear of recording head - this head is critical for sopranos, shatters band and lowers level of tape magnetization . Your measurement in fact shown that most popular problem with recording head . Replacing them bot in instance you lost possibility to learn it. .But no problem as it was needed too - by replacing play head you also gained more voltage from play head I address only your miselading explanation
Measuring the wear by electronic rule is not realiabe. Important is only the center area where is gap and how deep is gap .Play head untill is not competly worn "to bottom" has its normal frequency charactrisitic - I had such head and it was reading nicely 19 kHz from my old recordings exatly the same as when it was new - only when some layers of metal brake down into it is not usable due to great lack of sipranos. Untill then the only problem is that voltage in whole spectrum falls down and noise/signal is growing