A Collins 30S-1 Amplifier

I recently acquired a vintage Collins 30S-1 console type HF amplifier. I've been considering one for quite some time, but due to it's 160 pound shipping weight, that made purchasing one outside of my area prohibitive. Fortunately, a few weeks ago, one was listed for sale near my home. Therefore, I decided to purchase that amplifier while I had the opportunity.

Several of my ham radio friends own a Collins 30S-1, and are very pleased with them. The 30S-1, I purchased is in good operating condition.  Cosmetically, the amplifier is in good condition for it's age. It's been updated with new capacitors, diodes, and a Peter Dahl filament transformer.  However, there are a few issues that require attention before I place the amplifier into the operating position.

The first issue, the front panel has two push switches, OFF and ON, and an indicator light for ready to operate condition. However, the off switch has been replaced with a generic switch.  It works, but I would prefer to have a switch or a set of switches that are closer in appearance to the original.  The original switches are no longer available, but there are similar switches available from Newark Electronics, manufactured by EAO.  I found the following information on the website of Al Waschka.

Newark #             EAO #                                                         Description 
50F8257         31.121.025                     Series 31 Rectangular Switch, Snap Action, Momentary 
50F8263         31.040.005                     Series 31 Rectangular Indicator 
50F8264         31.901.2                         Series 31 Rectangular Lens, Red 
NS/Order        31.901.0                         Series 31 Rectangular Lens, Black 
NS/Order        31.963.1                         Bulb, 14V 
50F8269         02.905                            Lens Removal Tool 
50F8270         02.906                            Lamp Removal Tool 
50F8273         01.927                            Series 31 Rectangular Protection Guard


The second issue is more critical.  Mr. Warren Brune, designed the amplifier for Collins in the late 1950's. To protect the 4CX-1000 tetrode tube from over heating. A mechanical method was utilized using a normally closed, heated bi-metal sensor, that is connected in series with the interlock circuit.  A 250 volt/2 watt 500 ohm potentiometer is used in series with the 120 Volt supply for the heating circuit, to vary the temperature of the sensor, thus setting the activation threshold for when the sensor will open to protect the tube.

When I purchased the amplifier, the seller indicated the previous owner had deactivated the tube protection circuit, because one lead on the temperature potentiometer was arcing the 120 Volt AC supply to ground.  I plan to replace the potentiometer.  I was amazed to find the same part with the exact same part number was still available.

The final issue (I hope), the three minute HV timer has been deactivated as well, more than likely a quick fix, perhaps after the timer tube failed.  I may build a simple solid state equivalent to interrupt any depression of the HV ON switch for three minutes.

Hopefully, I'll have the repairs completed soon and can give it a through shakedown.

73'