[Big D]

Hi all,

I have had some limited success with the interphone system in the BC-604 transmitter. I had to do some more fault-finding and with the assistance of a radio forum I worked out that one of the vacuum tubes in the set was faulty. I replaced this and the audio stages in the set started to work.

The BC-604 mounted in the FT-237 does allow you to test sidetone, which is a test on the interphone circuit. The BC-604 now works but it has a wee problem which I may or may not be able to resolve in the short term. I am told that in the Interphone mode, the dynamotor in the BC-604 should run continuously (can anyone confirm this?). This makes sense as the dynamotor powers up the audio stages in the set which are required for the interphone audio to operate.

On my set however, I seem to have an intermittent problem which is likely to be caused by the S104 radio/interphone relay. I had the BC-604 in the FT-237 radio tray and for a short time the dynamotor was running continuously in the interphone position (which I’m told is correct). However, then the dynamotor stopped running continuously and now it won’t run in interphone mode unless I key the microphone. I figure that one of the contacts in the radio/interphone relay is the cause of the problem but there seems to be no easy way to get at the contacts to clean them. It is a complicated relay with lots of connections and I don’t really fancy the idea of trying to replace it, even if I could source a replacement!

As it stands, when using the interphone, one has to key the microphone and pause for a second or two before talking to allow the dynamotor to fire up the audio. At this stage, I’ve found the audio is a bit noisy and there is some dynamotor whine in the audio so I intend replacing the capacitors on the dynamotor to see if that helps. I have also ordered some replacement vacuum tubes for the audio stages, just in case one of the existing ones is not quite right. Not an ideal situation, but when it does work, it does work! If I’m not happy with the performance, I do have a NOS BC-605 that I could fit instead of one of the BC-603’s and this will provide interphone capability.

I have tidied up the BC-604 and the two BC-603’s. I didn’t do a complete strip down and paint of all the panels on the sets. There was just too much involved in removing all the control panels and besides, the appearance of these was not too bad as it was, and I may replace the French sets with US ones at some point anyway. The new paint on the exterior panels has freshened up the appearance of the three sets though.

I am still having some issues with the DM-34D dynamotor that I needed to work on to get it to run and I am ready to admit defeat on this one. More often than not it won’t start. The resistance measurements I’ve done on it suggest that there are some open windings on the armature, so I will keep an eye out for a replacement. If anyone has a good spare they want to part with, I’d be interested.

In the meantime, a few other bits and pieces have arrived in the post (thanks to Brent and Jean-Marc).

Next week I hope to have some progress photos on the hull sandblasting.