SOLD: RCA BN-2A tube preamp, hybrid OP-6 / OP-7

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emrr
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SOLD: RCA BN-2A tube preamp, hybrid OP-6 / OP-7

Post by emrr » Sun Dec 03, 2017 2:52 pm

Pretty clean working example of the RCA BN-2A portable tube preamplifier/mixer, the next generation OP-6/OP-7 hybrid, being an OP-6 circuit with the essence of the OP-7 tacked on the front end for multiple inputs. 4 input connectors, 2 being switchable, so really 3 microphone inputs possible at once. Adds multiple monitor and cue paths useful for radio broadcast that the OP-6 lacked. Has captive quick release connectors on the top and rear panels for fast access to the insides, and the top cover holds two spare tubes and a spare fuse. The original power connector is included. I can provide a pdf of the manual to the buyer.

This unit had one bad filter cap which I replaced, and all the other electrolytics test at or above spec save one cathode bypass which is slightly low (33 rather than 40). The unit ran properly for a few hours, and sounds as expected. The existing tubes work fine, but have not been tested for overall strength. In any high gain tube amp like this, one could certainly go through a handful of new tubes which have been properly burnt in and select for lowest noise. Response is very consistent across wildly different input/output settings, being flat from 16Hz to 2K, then a 1.5dB rise to roughly 14K, and 1dB down about 20K. An input set to noon (10) and master set the same yields 43 dB gain, 92dB quoted as max gain. The power connector is ungrounded, I would suggest reworking it to include ground for lower noise and safety, as there is a free pin available. It was also a bit fidgety to make filament connection unless seated correctly. VU meter works fine. The ‘P’ input connectors have been modernized at some point with XLR’s, always a nice bonus with these. Output via front panel binding posts, so it will need a pigtail connector or a modification to one of the side panel 1/4” connections for output.

Sold as-is due to age (nearly 70 years), handle responsibly and with proper knowledge, or have your tech do a restoration for utmost in reliability.

$OLD plus shipping and insurance on roughly 34 lbs, box of roughly 20”x15”x15”.

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Doug Williams
ElectroMagnetic Radiation Recorders
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