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- Thread starter brad225
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For what appears to be a happy ending, almost finished.
My EE friend was able to acquire a full set of schematics and parts list for my 610t amps. Along with those he has the upgrade schematic and parts list for the change to KT120 from 6550 tubes.
He has gone through the amps and replaced 220+ original resistors with non inductive resistors. Every Capacitor has been replaced with better quality and all of the relays changed. This covers all of the high and low voltage power supply. A number of other things to make them better than new.
Next will be the tube upgrade.
I'm looking forward to listening to them for years.
My EE friend was able to acquire a full set of schematics and parts list for my 610t amps. Along with those he has the upgrade schematic and parts list for the change to KT120 from 6550 tubes.
He has gone through the amps and replaced 220+ original resistors with non inductive resistors. Every Capacitor has been replaced with better quality and all of the relays changed. This covers all of the high and low voltage power supply. A number of other things to make them better than new.
Next will be the tube upgrade.
I'm looking forward to listening to them for years.
Well, that was an over optimistic comment starting that last post.
The amps returned to my listening room on March 12 and even with no break-in time are amazing.
The almost finished, comment, turned into nearly 3 months of trouble shooting an issue in one amp. The are 2 adjustable resistors that take a specific low voltage on each side of the bias circuit and adjust it to "0". This would not work on one amp.
My friend pulled dozens of parts back out and re-tested and tested traces. Many questions were ask of ARC things they knew about this problem.
After many weeks we received an email saying. An engineer that had been there when the 610t was in production remembered that at one point they ran out of resistors and changed the design of the circuit to accommodate parts they had in stock. This was only until the proper parts were back in stock. The thing that was not done was to include any information on the schematic mentioning a change.
ARC offered to send us the proper parts at no charge and we were happy that everything was coming to an end.
Unfortunately the new parts helped with the voltage but didn't solve the problem.
My EE friend then knowing this was the problem started calculating and through some trial and error created a series of resistors to achieve the
+ and - voltage within specs, that each adjustable resistor needed to work properly for the biasing circuit.
I will say that ARC was very helpful and gave us what they could from 15+ years ago when the amps were built.
It does seem a bit odd that the original owner was sent 2 amps with different designs and no real record of the change.
I can only thank my EE friend Phil for sticking to the extra 2+ months he spend trying to find this issue repairing it. The good news of it taking so long and different parts being removed and tested before replacement is he found no less than 6 ground loops that were removed.
Now I need to find time to start listening to music again. Who ever said that being retired gave you lots of free time was clearly, wrong.
The amps returned to my listening room on March 12 and even with no break-in time are amazing.
The almost finished, comment, turned into nearly 3 months of trouble shooting an issue in one amp. The are 2 adjustable resistors that take a specific low voltage on each side of the bias circuit and adjust it to "0". This would not work on one amp.
My friend pulled dozens of parts back out and re-tested and tested traces. Many questions were ask of ARC things they knew about this problem.
After many weeks we received an email saying. An engineer that had been there when the 610t was in production remembered that at one point they ran out of resistors and changed the design of the circuit to accommodate parts they had in stock. This was only until the proper parts were back in stock. The thing that was not done was to include any information on the schematic mentioning a change.
ARC offered to send us the proper parts at no charge and we were happy that everything was coming to an end.
Unfortunately the new parts helped with the voltage but didn't solve the problem.
My EE friend then knowing this was the problem started calculating and through some trial and error created a series of resistors to achieve the
+ and - voltage within specs, that each adjustable resistor needed to work properly for the biasing circuit.
I will say that ARC was very helpful and gave us what they could from 15+ years ago when the amps were built.
It does seem a bit odd that the original owner was sent 2 amps with different designs and no real record of the change.
I can only thank my EE friend Phil for sticking to the extra 2+ months he spend trying to find this issue repairing it. The good news of it taking so long and different parts being removed and tested before replacement is he found no less than 6 ground loops that were removed.
Now I need to find time to start listening to music again. Who ever said that being retired gave you lots of free time was clearly, wrong.
One thing I forgot is the temp difference.
After 1 1/2 hours listening on Sunday I walked up to the amps and you could put your hand on 5 KT120 tubes actually touching them for a moment.
With the 6550 you could get your hand to within 3" and it was hotter than the KT120's. We tried listening to music with the thermostat set for 6550 listening and had to turn it up to a warmer setting as we were both to cold to sit longer.
Hard to believe the KT120's won't have a longer life than 2000 hours.
After 1 1/2 hours listening on Sunday I walked up to the amps and you could put your hand on 5 KT120 tubes actually touching them for a moment.
With the 6550 you could get your hand to within 3" and it was hotter than the KT120's. We tried listening to music with the thermostat set for 6550 listening and had to turn it up to a warmer setting as we were both to cold to sit longer.
Hard to believe the KT120's won't have a longer life than 2000 hours.
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