Scully 280 tech?

[soundguy]

My favorite peeps:

I finally finished a project that has been haunting for the last few weeks, hunkered down to run safety dubs on 11 reels of tape about 48 hours before Im scheduled to leave, turn on the scully 280 I have here, did the playback cal, fine, tried to do the rec cal (WTF are all these trimmer pots for...) seemed ok, listened to the deck and its fully ******. Im pretty sure the problem is in the record amplifier, but heres whats happening.

when I start the machine from a stop, in record, I have oscillating in both channels that starts off pretty low, definitely well below 1K and then gradually increases in frequency over time, after about 4 minutes of rolling, the sound goes away. If anyone knows the sound of oscillator sync on an EMS VCS3 or a moog prodigy, it sounds identical to that. Its a very cool sound, but I cant run my safety dubs with a ****** up deck. Ive already kinda thrown my hands in the air and am guessing Im not gonna fix this, but any suggestions on what may be going on? Germanium transistors in the electronics, Ive had the thing on for about three hours before screwing with it so I dont think its a heat stabalization issue.

how do you do the record cal on this deck? Boo to the scully engineers.

dave

 

[Mark Burnley]

Bo Hansen has got some of the audio schem on his noticeboard:

Scully 280 Audio Schem

Some kind of weird heterodyne fault from the bias oscillators?

:?

Mark

 

[soundguy]

the whole machine was recapped a few years back, but Im not doubting that a cap could be the cause. What bugs me is that its effecting both the audio channels which leads me to think that its originating somewhere else in the machine. Maybe its in the bias trap, I dont know, I dont know if my ampex 440 troubleshooting even applies to this thing, this is a very different deck. I dont think Im going to pursue this now, Ill deal with it when I get back, but am of course curious. Sound like a bias circuit problem to anyone else? Leaking bias modulating the audio band?

dave

 

[jrmintz]

Dave - check your email. I have some spare cards if you need to borrow them.

 

[rlaury]

HEY! HEY! check the roller between the heads and on the input and output of the head stack. The bearings sometimes chatter if the machine hasn't been used for a while. The chatter (squeal) will transfer to tape just like an oscillation internal to the machine. If the room is really, quite and the monitors off, you can actually hear it. This happend to me once with a 280B. Oops! I think I just told my age.

 

[soundguy]

I'll check that out. this sounds like an electronics thing though, sounds totally like a vcs3...

It only does it monitoring playback in record, monitoring record its clean. I wonder if the record monitor is monitoring the record head or if its just an input monitor. Boo.

dave

 

[hitchhiker]

hi Dave ,

I have a Scully 280 8trk. I have some good directions from the tech
who kept in various studios around Vancouver. He owned the machine for 20 years. He told me that I wouldn't have to re-do it very often because the machine stays in very well. I can try to walk you though the notes he put in my manual but I have to admit I've never tried the set up yet.

Lance

 

[soundguy]

hey lance-

could you photocopy the alignment pages?

seth, thanks for the offer! Im gonna leave this be for the time being...

dave

 

[hitchhiker]

ya sure. I think they are in a binder. My scanner is not too good so that would be the best .

Lance

 

[soundguy]

while recording, I get the oscillation when monitoring the playback. When I monitor record, its clean, I dont know however if the record monitor is simply an input monitor or if it is the record head monitor, the input monitor is clean... The tapes playback with the sound and I think its being recorded but I havent put it on a different tape deck to check.

dave

 

[soundguy]

I'll go over those when I get back.

nothing happen when I hit the linear test button, whats it supposed to do?

the linear pot crackles when I turn it... haha

dave