ORIG. SEX FILIMENTS QUESTION

[najo49]

The filiments went out on one of my sex amps. I dis-connected the wires from power trans. and I got 7.5 volt AC across the 2 outputs. And in the amp got 124v DC at pins 7 and 8 . It seems filiments should be working, anyone got any ideas? Jan Olsen

[Paul Joppa]

If the transformer supplies 7.5 volts (it will come down under load, don't worry) but the filaments don't light, then either the tubes are burned out, or the wiring between filament and transformer is broken. Solder joints can have hidden problems that do not appear for a long time. You can check the voltage between socket pins 7 and 8 - should be 6.3vAC +/-10% if the filaments are lit.

I'm assuming both filaments went out at the same time, so wear on the filaments is an unlikely cause. But a bad voltage surge on the power line could take out both filaments - just measure the DC resistance between tube pins 7 and 8, it's probably a bit over 1 ohm when they are cold.

[najo49]

Paul, I am totally perplexed about this problem. Here is how things are 1. with filiment lead disconnected I get a 7.5 v AC across both of them. I resolderd them and checked the continuity to the lead going to pin 7, and 8 of the other tube. I resoldered everything. upon turn on I get not filiment in either tube. (i check every tube used in the other amp and are all good.) I have no idea what is going on and I hope you do. Thanks J.

[Doc B.]

Did you measure the voltage right at tube pins 7 and 8? PJ was trying to establish if the 7.5 volts is actually getting to the socket. This is a companion test to the continuity check you made that should also be made.

[Paul Joppa]

I do not follow exactly what you are saying, but I THINK you mean you have confirmed the power transformer makes the right voltage, and the wiring is correct, and the tubes are good. One can only conclude the sockets are bad - I am assuming the tubes have unbroken guide pins and are therefor inserted in the correct orientation.

Did you in fact measure the AC voltage between A7-A8 and B7-B8, with the tubes inserted and power applied? If not, that would be the ultimate test of correct wiring. If the necessary voltage is present at the tube socket pins, remove the power, disconnect one transformer terminal (again, sorry!) and measure the resistance between A7 and A8, and between B7 and B8, still with the tubes inserted. This will test whether the sockets are connected to the tube pins. If the measured resistance is low, repeat the measurement with the tubes removed just to be certain that there is not a short circuit in the wiring.

[najo49]

 Let me restate.
1. both filiment were out . I checked both tubes,and the connections 7, 8 on both tubes
2 I de  soldered the filiment wires coming from tranny. I checked the voltage across the two leads it was 7.5 volts. I checked the wiring from tube a to b at pins 7,8. I resoldered these and checked again. I did not connect the  50 ohm resistors to 7 and 8 by the way but I have since tried  it with them re soldered .
3. I re soldered the leads from tranny to pin A 7,8.. The filiments were not operating. This led me to my second request for help. And my statement, this is really unclear to me why they are not working.
4.I hope this helps as I know I am not quite clear sometimes. It seems to me that the trans is putting out 7.5 V Ac and that the solder joints are good and have been checked and re checked. I pulled the tubes partially so I could check the socket connection and found a succesful connection at the tube pin and the soldered connection underneath. seems the sockets are good. I am thinking the transformer when put to service collapses and the 7.5 v goes to 0. meaning the otherwise working . former is not putting out the filiments voltage when in service. What do you think of this. Jan Olsen

[Doc B.]

I am thinking the transformer when put to service collapses and the 7.5 v goes to 0. meaning the otherwise working . former is not putting out the filiments voltage when in service. What do you think of this. Jan Olsen

I think you should measure that and see if in fact the voltage across 7 and 8 does go to 0 volts with the tubes in place.

[najo49]

Doc, it started to blow fuses now when turned on so the transformer is shorted. What would be the transformer that is available that would replace this one? This is one of Tonys amps which you will get I wanted to give them to you in working condition but may be that is not important to you. Let me know

[Doc B.]

Hi Jan,

It's not at all important that they be working. They are just the first amps we sold and I would like them for sentimental reasons. They will go on display next to the original prototypes.