Looking for some recommendations for some of you SX62 experts. I recently acquired a nice one. It functions very well on all AM bands. There are three small problems I would like to get some advice on.
1. Crystal calibrator is almost unusable. It has no tone and only provides a hissing sound with a zero beat in the middle. I believe it is suppose to have a good tone.
2. CW has no effect when switched on.
3. FM band functions but has vague tuning and considerably less output and quality compared to the AM band
The previous owner said he replaced the line capacitors and a couple others that were not working. I have tested and replaced three marginal tubes. That is all I have done to the set. I'm enjoying it too much. I am hoping that some of you might be able to provide me some ideas to get to these minor problems directly. Im fairly adept at aligning a set (last one an SX25). I have never ventured into FM. I have no desire to get into complexity of aligning this set as it works so well.
Your crystal calibrator symptom is due to the BFO not working. It will only make an audible tone with a functional BFO. The BFO may need alignment.
The SX-62 has a lot of capacitors that are likely to need replacing and the power transformer doesn't have any real safety factor so it is important to take care of some of the "danger" caps before going further. At the very least, replace the output stage cathode bypass capacitor and the coupling caps from the phase inverter to the output tube grids. Excessive leakage of any of these caps will cause failure of both the audio output transformer and the power transformer. The capacitors in the tone control circuit are also capable of causing a lot of collateral damage and should be replaced.
Realistically, the SX-62 is a nice receiver but for it to perform as it should you should replace any remaining wax paper, black beauty, and similar high failure caps. The difficult to reach capacitors in the front end can all be replaced without taking apart the band switch area but it does require some maneuvering with long jaw needle nose pliers. Many of these otherwise difficult to access capacitors can be accessed easily once the removable shield cover and chassis brace on that side of the chassis is removed. You will likely also find several resistors well out of spec in the SX-62 including some of the higher wattage resistors.
Some have experienced burnt contacts on the band switch in the SX-42/62 receivers but it has not happened in any of the 5 I have around. I think this is likely due to my replacing the troublesome caps in the front end AND cleaning the band switch of dust/debris before sustained operation.
I have yet to repair a SX-62 (or its SX-42 close relative) that did not have a poorly functioning FM detector due to leakage of mica caps in the FM discriminator transformer. Even minor leakage in these caps will greatly reduce FM performance and I highly recommend you just replace them. Clip the old capacitors and replace them, the new mica caps are much smaller and fit easily in place of the old ones. I would not unsolder the old leads because you are likely to damage a winding in the process. I have found a few bad mica caps in the regular IF transformers but these will be easily found during alignment when you will note there is either no peak or a very broad and shallow peak for the affected transformer. Like the discriminator "can" these can be replaced with the transformer still in the receiver, there is no need to unsolder it.
Once you have it aligned properly, FM tuning is different with a discriminator detector as opposed to the ratio detector used in later FM sets. The discriminator is capable of better performance but it is dependent upon limiter stages so the ratio detector was a cheaper choice for consumer gear. With a discriminator detector you will find triple spot tuning on FM. The FM detector will slope detect on either side of the proper point and the correct tuning is the center response point. Until you get used to this (and you will quickly) you will find it easiest to tune the FM signal in the AM mode before switching to FM. With proper alignment, tune for MAXIMUM distortion in AM mode which is perfectly centered on the station and then switch to FM. The discriminator drifts some during warm up so don't align it until the receiver has been on 15 minutes or so and then count on it drifting a bit for the first 5 minutes every time the receiver is turned on.
I have several of this family of receivers and they sound very good on FM when operating properly.
Joined: Jan Thu 01, 1970 1:00 am Posts: 6306 Location: Raleigh NC USA
Many thanks for all the info, Rodger. I have an SX-62A half done in the 90's but waiting in the service queue for a complete job ever since, that is, if I can ever get around to it! Meanwhile, I'm always glad to pick up info about it.
Thanks again and 73's,
_________________ It don't make a go if it ain't got that GLOW!
Thanks for the great info and insights. At the moment I have not even looked inside the set. I'm enjoying it too much. It has no problems other than the minor ones I already addressed. I suppose though if I want to continue enjoying it I had better dive into it and see what has been done and what still needs to be done.
Only thing I am not looking forward to is the alignment. I have read over the instructions a few times now and it looks like quite an involved process that I'm not sure I have the equipment or expertise to do. I enjoy aligning basic sets. I have an eico signal generator and a DX398 to verify the generators output but that is it. Frankly, I do not understand some of the instructions. Recently I had my first challenges trying to align an SX25 that I completely restored. Terms and processes like wobbulate and wobbulator and 1000khz tones are not things I have found many references or equment for.
I have to find some re written alignment instructions oriented to someone with good basic restoration skills and basic equipment. Thanks for the great information and insights. I am sure that I will reference your info for quite some time.
As pointed out earlier, this probably means the BFO is not working. In that regard you might find this article interesting relative to the BFO in your receiver. http://w2dtc.com/w2dtc-sx-62-receiver-page.htm In this case the BFO was not running because a connection had over the years pierced a piece of tape inside of a shielded can and that was all that was wrong with it.
There was also some information in the associated PDFs about the alignment.