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RT-909 Calibration Question

buffdriver

buffdriver

Active Member
Silly question, but how do you position the RT-909 when calibrating? Playback response is adjusted on the pre-amp board, which requires access from the bottom. Are there any special issues or limitations if I recline the deck onto its back?
 
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Should be fine, as long as the transport is adjusted properly (reel and brake take-up torques, pinch roller pressure, etc.).

Enjoy,
Rich P
 
Thank you, Rich. I finished the recap yesterday, two years after rebuilding the transport with the aid of your fine writeup. I'm looking forward to completing the job with a calibration.

Regards,

Mark
 
The 909 in my main rig will be similar. I brought it up to full steam, sometime back, including brand new heads and rec/play cal. However, I did not recap. I will be doing an experiment soon, where I will recap with boutique audio caps. I have used them for a variety of restorations for others, but this will be the first time I sue them on my own gear.

Don't forget to revisit the transport adjustments before the rec/play cal.

Enjoy,
Rich P
 
My brake tension is measuring low, but the felt looks absolutely fine. I removed the brake bands and washed the felt with dish soap, then carefully dried them. Still only getting around 200g where they should be 350-450. I've got new wool felt, but I'm carefully considering how difficult it will be to attach the new felt properly. The current plan is to use either the same white glue used for speaker refoaming (dries flexible) or contact cement.

I'm very eager to hear how the high-end caps work. I'm a MTF disciple--Nichicon UPW, UKL, or films. No complaints yet.

Many thanks for your generous advice.
 
Be careful that whatever adhesive you use, it does not soak through to the working side of the felt.

I use a fine grit of sandpaper to rough up the brake drums. The tape handling logic is sophisticated, not dropping the brakes until the motor torque has brought the reels to near stop. If the brake torques wind up a bit low, it should not be a big problem. I use brake felt that has pressure-sensitive adhesive on it. My source has recently passed away, so I do not have one at this time.

Enjoy,
Rich P
 
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If you haven't recalibrated the heads before I recommend you take it to a tech. I bought my RT-909 from a AKer that attempted to recalibrate the heads himself. I'll just leave it at that. Luckily,the tech in my area is an expert on the RT-909 and realigned the heads perfectly.
 
Once heads have been used long enough to make even a slight wear groove, they should not be moved. Otherwise the edges of the wear patterns will damage every tape that subsequently passes over them. Heads that have been moved will have to be replaced or relapped.

Enjoy,
Rich P
 
The heads on this unit have very little wear. I know the original owner. I have not moved them or had them lapped, and do not intend to do so until it becomes necessary down the line. I very much appreciate the advice and reminder.
 
I finished the calibration on my RT-909. Didn't touch the heads and the azimuth looked fine when inspected. I used the MRL 21T204 tape and playback was easily adjusted to within 1 dB for all -10dB tones. Record calibration on Maxell XLI was smooth as well. Below is a chart showing frequency response for a 0dB and 10dB sweep 20Hz - 30kHz. There's also a loopback that shows the freq response looped through the deck at -10dB and monitored via source.

I carefully considered Rich's advice on the brakes and decided to leave them alone. Overall, I'm pleased with the restoration. Many thanks to Rich for his excellent writeup, and for providing expert advice!



Pioneer RT-909 Maxell XLI.jpg
 
Please consider that you are calibrated to a tape that is no longer produced. The available tape of that type has been subjected to unknown, inconsistent conditions, tape to tape. Hence your calibration could vary significantly, tape to tape. The best approach is to calibrate your deck to tape being currently produced, then let the calibration be as it is with older tape. That way, your best recordings will be consistent to the best the deck can produce, when using the modern tape that you calibrated to. Nice job on the cal though.

I calibrate to brand new RMG LPR35, which is closest modern equivalent to what the machine was designed to.

Enjoy,
Rich P
 
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I hadn't thought of it that way. I've had good service from the Maxells, but you have a great point about calibrating with something that is more of a known quantity. I will shop around for at least one reel of either LPR35 or Capture 930 to support calibrations.
 
I think that you will find that calibration to LPR35 (brand new reel) will result in quite presentable performance with Maxell or TDK of bygone days. I know I do.

Enjoy,
Rich P
 
Hello:
I working on a RT909 that I will be calibrating soon.
I was looking at the calibration procedure but I don't see how to get the reproduce and record level to be equal when press the "Tape-Source" button when your do a recording. Any idea how to get them to be equal?

Mando..
 
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