#COLLINS 51S 1 RECEIVER MANUAL#
#COLLINS 51S 1 RECEIVER SERIES#

My 51S-1 has the standard IF transformer configuration instead of the mechanical filter and this is what you will find in the majority of 51S-1 receivers for sale, it provides good selectivity for broadcast AM with decent audio quality and better fidelity than the mechanical filter.

#COLLINS 51S 1 RECEIVER MANUAL#

The change procedure is in Collins SB2 revised for the 51S-1 receiver, you can find the service bulletins along with the manual for the 51S-1 here. With the modification, those are removed and a mechanical filter is installed in their place. In a stock 51S-1, transformers T14 and T15 are directly to the right of the cover over FL2,3,4 when looking from the front of the chassis to the back. A missing filter cover can be replaced but this is a fairly high priced receiver so it isn't usual for them to be parted out unless there are serious issues so shop with care. I would stay away from any 51S1 that has had the filters removed because it likely has more issues. The PTO should also be lubricated to retain the light tuning feel and protect the mechanism, this isn't difficult.

#COLLINS 51S 1 RECEIVER SERIES#

I don't know of any common failure points with the 51S1 although for safety it wouldn't hurt to put a large value capacitor in series with C125 to protect the mechanical filters just as is done with the Collins R-390A. The 51S1 readout assembly makes a clicking sound as you tune which you will either love or hate.

I really like the 51S1 with its smooth tuning feel and mechanical digital readout. Note that although the 51S1 has 'S line' styling, electronically it is more of an evolution of the A line series and it uses a 500 khz. For broadcast listening, the stock filter is fine. bandwidth -6db and a much better shape factor. Collins made a mechanical filter kit to replace this AM filter with a resulting 6 Khz. Stock AM was a pair of IF transformers that provided a nominal 5 Khz -6db bandwidth but with a very poor shape factor. Without these filters in place, the receiver won't operate in SSB and CW modes. Different SSB bandwidths could be specified with 2.4, 2.75, and 3.1 choices stock CW was 800 hz bandwidth with 300 hz bandwidth optional. In stock form, the 51S1 should have a pair of SSB filters (USB and LSB) along with a CW filter mounted under the filter cover as FL2,3, and 4 respectively.

Collins 51s-1 receiver