Studer A807 Erase/Bias Transformer

C

carlosraj

New member
Hi

I am looking for a pair of Erase Transformer(1.022.271.00) and Bias Transformer(1.022.272.00) for my Studer A807. Can someone let me know where can I purchase new or used parts for Studer A807.

Thanks
 
Ebay. There's a guy there who regularly sells channel cards. But are you sure this is the problem? I'd be a bit surprised if it was the bias oscillator given your earlier thread.
 
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jpmorris said:
Ebay. There's a guy there who regularly sells channel cards. But are you sure this is the problem? I'd be a bit surprised if it was the bias oscillator given your earlier threat.
Click to expand...

+1 Very rare that "audio" transformers fail and the chances that TWO would fail at the same time are astronomical! Oscillators require a certain minimum gain to start. That gain can be too low for several reasons,
1) capacitors, both electrolytic, emitter bypass e.g. and foil, tuning. More likely the former.
2) Lowered supply rails. Age can cause V set pots and even active devices to change very slightly, 0.5V could be the difference between an osc' kicking off or not.
3) bad joints/plugs and crimped cables going slightly high resistance.

Do you have a schematic? If not stop and bloody get one! THEN post the relevant parts here!

Dave.
 
ecc83 said:
+1 Very rare that "audio" transformers fail and the chances that TWO would fail at the same time are astronomical! Oscillators require a certain minimum gain to start. That gain can be too low for several reasons,
1) capacitors, both electrolytic, emitter bypass e.g. and foil, tuning. More likely the former.
2) Lowered supply rails. Age can cause V set pots and even active devices to change very slightly, 0.5V could be the difference between an osc' kicking off or not.
3) bad joints/plugs and crimped cables going slightly high resistance.

Do you have a schematic? If not stop and bloody get one! THEN post the relevant parts here!

Dave.
Click to expand...



Yes, I think it's not the audio transformers. If I insert any of the 2 audio cards into the second slot (right channel) on the "audio control board", both the boards erase fine. Now if I insert any of the 2 audio cards into the first slot (left channel), both are not erasing. I have changed all the ICs on the "audio control board", but no difference. Can the problem be in the main "command board" which sends all the control signals to the "audio control" board. Please assist.

Thanks
 
First, let's be absolutely clear: Is the erase head a 2-channel erase head with two visible elements, or the full-track one which has a single vertical strip? The A807 comes in multiple configurations. For a full-track erase head, one of the two cards will be responsible for erasing both channels.

EDIT: Also, unless I'm grossly mistaken in my reading of the schematics, the erase head is connected directly to the audio cards via J4, which is the connector on the top of the card, under the metal shield. (This connector also connects the record head too, I believe). I don't think the audio control board has anything to do with erasure, I think it's just the preamps for line input and output.
 
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carlosraj said:
Yes, I think it's not the audio transformers. If I insert any of the 2 audio cards into the second slot (right channel) on the "audio control board", both the boards erase fine. Now if I insert any of the 2 audio cards into the first slot (left channel), both are not erasing. I have changed all the ICs on the "audio control board", but no difference. Can the problem be in the main "command board" which sends all the control signals to the "audio control" board. Please assist.

Thanks
Click to expand...

I put audio transformer in " " because I include bias frequency transformers in that group. They are similarly very unlikely to fail.

In the absence of any schematics or pictures of the devices I am working in the dark and I don't think it is up to me to go hunting the Web for that information?

Dave.
 
jpmorris said:
First, let's be absolutely clear: Is the erase head a 2-channel erase head with two visible elements, or the full-track one which has a single vertical strip? The A807 comes in multiple configurations. For a full-track erase head, one of the two cards will be responsible for erasing both channels.

EDIT: Also, unless I'm grossly mistaken in my reading of the schematics, the erase head is connected directly to the audio cards via J4, which is the connector on the top of the card, under the metal shield. (This connector also connects the record head too, I believe). I don't think the audio control board has anything to do with erasure, I think it's just the preamps for line input and output.
Click to expand...


I think it is a 2 channel erase head, it has 4 wires, 2 for each channel. Each J4 carries the the connections to the erase and record head for each channel individually. Each audio card has an individual erase transformer and bias transformer. I guess the signals to the erase and record head are also individual for each channel. What do you think.

Thanks
 
carlosraj said:
I think it is a 2 channel erase head, it has 4 wires, 2 for each channel. Each J4 carries the the connections to the erase and record head for each channel individually. Each audio card has an individual erase transformer and bias transformer. I guess the signals to the erase and record head are also individual for each channel. What do you think.
Thanks
Click to expand...

Did you try adjusting R139 in case the erase level pot has gone scratchy? Otherwise, if it were me I would be tempted to start replacing the electrolytics and see if that makes any difference. Another option is to get a spare channel card off ebay and see what that does - if the problem goes away on that channel we'll know there's an issue with your cards (again, the capacitors are the usual suspects). If the problem stays the same, we know it's elsewhere in the system.
 
jpmorris said:
Did you try adjusting R139 in case the erase level pot has gone scratchy? Otherwise, if it were me I would be tempted to start replacing the electrolytics and see if that makes any difference. Another option is to get a spare channel card off ebay and see what that does - if the problem goes away on that channel we'll know there's an issue with your cards (again, the capacitors are the usual suspects). If the problem stays the same, we know it's elsewhere in the system.
Click to expand...

Oooo! Where did you get "R139" from? Do you have a map?

Dave.
 
jpmorris said:
Did you try adjusting R139 in case the erase level pot has gone scratchy? Otherwise, if it were me I would be tempted to start replacing the electrolytics and see if that makes any difference. Another option is to get a spare channel card off ebay and see what that does - if the problem goes away on that channel we'll know there's an issue with your cards (again, the capacitors are the usual suspects). If the problem stays the same, we know it's elsewhere in the system.
Click to expand...


OK, I will try adjusting R139.

Thanks
 
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