Frequently Asked Questions Will these lamps work in the L4 or L4B amplifiers? Yes, the lamps work fine in the L4 series amplifiers.  Each amplifier requires two of the MOD-4LINEPTO lamps.  Installation does require a bit of work and I include the information in the next paragraph that was kindly provided by Stew K3ND. "Installation did require the entry holes to be reamed out slightly.  I first removed the top and bottom case and then the tubes and chimneys. There is no way to ream out the mounting holes without removing the outer front panel. To do this, you remove all the knobs, unsolder the wires (4) to the two indicator lamps, and the front panel comes right off by removing the six mounting screws. I then used a tapered reamer from the front side to open up both holes a bit. I just reversed the process to put everything back together. As I recall, it took me a little over an hour to do the whole job." Why are there different lamps for the T-4XC and RV-4 Models? Drake designed some of their equipment to run the lamps directly across a 12.6VAC source or in series with a small valued current limiting resistor.  All other 4-line units operate across 6.3VAC or have series connected lamps across the 12.6VAC source.  For the directly connected 12.6VAC units it requires a larger current limiting resistance be built into each lamp base.  That is why I have special lamps specifically listed for these models. Warranty D.A. Buska Engineers LLC products are guaranteed to be free from defects in material and/or workmanship and to perform as advertised when properly installed, used, and maintained in accordance with published instructions. Failure to adhere to and/or comply with operation manual instructions will void all associated warranty obligations. Should any part(s) prove defective within thirty days from date of purchase, it(they) will be replaced without charge provided the defective part(s) is returned with transportation charges prepaid.     Return