Hey guys, alot of good reading on this forum.
If you would help me date my amp I'd be greatful.
/Matt
OR120M, help me date this thing.
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Re: OR120M, help me date this thing.
Looks like 1978: http://web.archive.org/web/200806291318 ... eline.html" onclick="window.open(this.href);return false;
Sooner
AD1512 Serial No. 001
AD1512 Serial No. 001
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Re: OR120M, help me date this thing.
Indeed it does, thanks for that.
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Re: OR120M, help me date this thing.
There may well be a date tag inside attached to the board. My OR120M, ser. no. 015637, is stamped 10th Aug. 1978.
If you do remove the chassis to check for a tag DON'T touch anything on the circuit board!!! There may be very high (lethal!!!) voltages stored in the big capacitors long after powering the amp down. Maybe best just to have your tech check this the next time he has the amp open eg for biasing up new power valves. Indeed pretty much certainly a '78 though.
Andy.
If you do remove the chassis to check for a tag DON'T touch anything on the circuit board!!! There may be very high (lethal!!!) voltages stored in the big capacitors long after powering the amp down. Maybe best just to have your tech check this the next time he has the amp open eg for biasing up new power valves. Indeed pretty much certainly a '78 though.
Andy.
aNDyH.
Ever tried to outstare a mirror?
In the bathtub of history the truth is harder to hold than the soap, and much more difficult to find!
Ever tried to outstare a mirror?
In the bathtub of history the truth is harder to hold than the soap, and much more difficult to find!
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Re: OR120M, help me date this thing.
Interesting, will have a look.a.hun wrote:There may well be a date tag inside attached to the board. My OR120M, ser. no. 015637, is stamped 10th Aug. 1978.
If you do remove the chassis to check for a tag DON'T touch anything on the circuit board!!! There may be very high (lethal!!!) voltages stored in the big capacitors long after powering the amp down. Maybe best just to have your tech check this the next time he has the amp open eg for biasing up new power valves. Indeed pretty much certainly a '78 though.
Andy.
Is the bias fixed on these things or will I have to get it rebiased after replacing tubes?
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Re: OR120M, help me date this thing.
Both!Mattias666 wrote: Is the bias fixed on these things or will I have to get it rebiased after replacing tubes?
'Fixed' biasing is a slightly misleading term. It doesn't mean that it can't be adjusted, only that once it is adjusted it stays at the set level. So yes you do have to have the bias checked for new power valve sets. Make sure you get good strong valves too or the OR120 will trash them in no time. You'll be good with things like JJ or 'Winged C' brand SED Svetlanas. Most other modern ones won't last long at all though as the amp voltages / currents are unusually high.
The other type of amp biasing - 'cathode' biasing - is only found on some lower powered amps (up to about 30W output power). This type of circuitry gives a range of 'self adjust' shifting the bias current both for different valves and for different levels of signal. So while the range can also be adjusted by a tech it doesn't stay fixed at any one level.
Only power valves need bias checks BTW. Preamp valves can just be replaced with no such worries.
Andy.
aNDyH.
Ever tried to outstare a mirror?
In the bathtub of history the truth is harder to hold than the soap, and much more difficult to find!
Ever tried to outstare a mirror?
In the bathtub of history the truth is harder to hold than the soap, and much more difficult to find!
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Re: OR120M, help me date this thing.
Thanks for the info!
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