Collins 30L-1 Amplifier
Worker Bill Schaal – K2YGF
Photos Kevin Shannon – WA2ISC
Amateur radio equipment, like any other electronic equipment, needs occasional repair. Even the vaunted Collins equipment is not exempt from the immutable laws of physics. When this eventuality does occur, it often involves partial disassembly of the equipment. Owing to the myriad mechanical wizardry of Arthur Collins’ engineers, it is helpful to have advice and moral support from one who has previously done the same repair. Experience is the best teacher, and disassembly of Collins equipment often leads to the necessity to get it partially apart before understanding how the next section is to be removed.
I recently have been having problems with low and unstable output from my 30L-1. After searching the schematic for possible trouble spots, I came to suspect a problem in one section of the multi-section band switch. Figure 1 shows the 30L-1 with the covers off. Getting that band switch out is no intuitive task!
First, remove all cables and power from the unit. Also, remove the amplifier from its cabinet (4 feet and 1 positioning screw on the bottom, and 2 panel screws on the top front). Remove the top cover over the finals, and the bottom cover. Then remove the back cover.
After removing both top and bottom covers, remove the 811As and carefully set aside.
Set the band switch at 80 meters, and index the wafer position for re-assembly. Also, place both the tuning and loading capacitors to fully meshed. This will help prevent any bending of the rotor plates during subsequent operations. A piece of masking tape across the plates will further prevent damage. Next, remove the loading capacitor connections to the switch, as shown in figure 2. Be very careful in removing these connections. The wires are quite stiff, and you don’t want to risk damaging or breaking the capacitor’s lugs. Also, watch out for the choke across the first 2 sections of the loading capacitor.
Remove the screw that holds the coil to the coupling capacitor. Then remove the screws holding the switch linkage. These are, in typical Collins fashion, Bristol screws, and they are set with Glyptol. It will take some effort to break them loose. Be careful here, or you could strip out the screw heads. Bristol set screws are not that easy to come by, unless your junk box is bigger than mine. We lucked out, as one of these screws was not tightened (I assume from the factory) so our task was lessened. See figure 3 for locations
Once these screws are removed, put them in a little lacquer thinner to dissolve the Glyptol. You will find several locations where this fine GE glue product was used. While great stuff, it does make it difficult to remove these screws. I used a tap (4-40) to clean any Glyptol from the tapped holes.
Remove the band switch knob, and the associated panel fixing nut. Then remove the 2 screws holding the entire switch assembly to the chassis. Finally, loosen the 2 Bristol set screws at the back switch section coupling, slide it back, and remove the coupling shaft, as shown in figure 4. This is the time that you should verify that the switch sections on the rear wafer are indexed! The switch linkage is a part of this assembly, so just thread it through the remaining components and remove.
Carefully remove the entire assembly, which consists of all but the rear switch wafers, plus the 2 tuning coils. As a bonus, this then opens up access to another problem component, the main power switch. See figure 5.
Clean the switch c ontacts, as well as the coils. After 30 years, quite a bit of dirt will have built up. Since these components are all silver plated, I used Tarnex silver cleaner with great success. Wash the Tarnex off with water, as it is an etchant. Finish off the cleaning with a burnishing tool (not a file!). Before and after are shown in figure 6.
Lubricate all bushings I used DE-OX-ID, another great product! Then re-install the switch/coil assembly into place, and loosely install the 2 bracket mounting screws. Also loosely replace the front panel switch bushing and nut. Align the front and rear switch sections (you did index them, right?) and install the coupling shaft and tighten the set screws. Also, re-tighten the switch linkage coupling hardware.
Re-solder the connections to the loading capacitor, and re-bolt the coil to the RF bus. Install the final tubes and replace the plate caps. Replace back, top, and bottom covers. Finally, re-install the unit into the cabinet, re-connect cabling and fire it up!