I recently picked up this amplifier, it was very, very dusty, and it seems to have had several electrolytic's on the main filter board replaced after a probable catastrophic failure. The caps are BLU-SEAL and have the original cardboard tubing on 4 of the 6, however 2 of them seem to have had newer and shorter caps inserted into the tubes. This is the ONLY section of the amplifier that appears to have been modified or upgraded as far as I can tell, all the remaining solder joints still have the red glyptol inspection varnish in tact leading me to this conclusion. From information I have collected I believe Collins produced around 17,000 of these amps during the 20 years it was in production starting April 1961, which would be an average of 70/month. I have found three components in the amp that have 1961 manufacture dates, the latest being two of the 811 tubes that have a manufacture date of week 26-1961. So, the earliest this unit could have been built would probably be July 1961 (I was just 10 at that time). Presuming that serial numbers for the 30L-1 started at 11000 that would make this unit #487, and at 70/month puts the probable manufacture date at around Oct/Nov 1961. As Collins did not publish serial numbers and correlating years for those s/#'s this is purely conjecture on my part. Now to my question for the Collins aficionados and restorers. I would like to complete a restoration on this unit but do not want to destroy it's collectible status with upgrades and modifications, so I would like some advice please. How far do I go with the restoration process? I intend to rebuild the filter board as it does have what appears to be some non-original resistors, however, I am leaning toward a Harbach PM-300 in order to safely bring the unit back online. I will leave the original diode board in place, but disconnected, keeping the refurbished filter board in case the next owner prefers to replace the PM-300 and return the amplifier to it's original condition. I would really appreciate some input and guidance on how far to go with the restoration on this early 30L-1. Thanks for taking the time to read this and I look forward to any guidance offered. Greg.