[R-390] constant voltage transformers

[Bernie Nicholson]

A reason that I have experienced for CVT s to run hot , these units are usually ferroresonant devices and if the capacitor that resonates the transformer goes open circuit they run hot and buzz, you can check the cap easily if you have a clamp meter and measure the cap ac current or you can disconnect the cap and put your ac amp meter in series ,    [SOLA units are particulaly prone to this problem]   but I have never known a 390 or 390a power transformer to burn out and we run them on 240volts , in Australia our power is not balanced to earth as in the U.S.  , our newtral is earthed at everyones power board and this has caused a lot of the line filters to fail due to the capacitors inside them not being desighned for this service, but i have never known anyone having trouble with the transformers .  51J rxs are a different story I have seen a number of these burn out also I have been using my recievers 390A for 25 years and I dont use the 3TF7 ,I have substituted 12BA6 tubes in VFO&BFO and used the 3TF7 socket as a double triode prod det as per Fundamentals of SSB handbook and a miniture relay to switch the audio lines fed from the bfo ht , so only the IF module is modded and when the BFO is switched  off it reverts to the original circuit, also I bought some 51J4 audio output transformers from FairRadio and they are the same package as 390A O/P transformers BUT they are for a 6AQ5 and they have a 3 ohm as well as 600 ohm windings  so I have converted the audio modules and now have heaps of audio and at the right impedence. sometimes I think people worry unnecessarily about 3TF7 s and other probs these recievers ran in service for over 20 years and  I am a great believer in NOT reinventing the WHEEL   HI  best regards to everyone Bernie N    PS Using a Hp5245 counter on the PTO I havnt been able to find any difference in rates of drift WITH  OR WTHOUT the 3TF7 and in corrospondence with various  retired Collins engineers they reckoned the regulator in the 390A was overkill.