04-07-2017, 09:15 PM
Another tube arrived today, a 6AU6WC military Sylvania.
So this evening I decided to try an experiment.
Not having a full set of 6П14П tubes yet, I reinstalled the original very weak 7189 Fisher tubes, hooked up a pair of speakers, and put the TA-600 on the Variac.
By 90 volts I could see the FM tuning eye (I had it set to FM), and I was obviously tuning in stations as the eye was opening and closing as I tuned across the FM band. So by visual indication, the tuner appears to be OK. I did switch it to AM and also saw the AM tuning eye opening and closing as I tuned across the AM band, though not as much as on FM.
One problem though.
No music...no talking...no noise...nothing.
Silent Night.
Or, if you prefer, The Sounds of Silence.
???
I turned the Variac off and unplugged everything. The 5AR4/GZ34 was barely lukewarm, and the 7189s were cold.
Hmmm...sounded like no B+ to the output tubes to me.
Consulting the schematic (yes, I'll post a copy later, perhaps tomorrow), I noticed that there is a 160 ohm, 10 watt resistor between the 5AR4/GZ34 cathode and the input electrolytic capacitor section.
You guessed it...that resistor is open.
I won't be doing any more Variac tests until after I replace the electrolytics and, of course, that burned out resistor. I'll also check the other power resistors to see if any others are open.
Back to the 6П14П...the seller readily agreed to send me a replacement, and I noticed today that it indeed has been sent as I received the notification from USPS.
I have my price quote from Hayseed Hamfest also, and the cost will be about what I expected it to be.
So this weekend, I need to order the loose electrolytics along with one or more power resistors from Mouser, and get the order going for the new twist-lock cans from Hayseed Hamfest. Yes, I could cut open the original cans and restuff them, but this is a special unit and it deserves the special treatment of new twist-lock electrolytics.
So this evening I decided to try an experiment.
Not having a full set of 6П14П tubes yet, I reinstalled the original very weak 7189 Fisher tubes, hooked up a pair of speakers, and put the TA-600 on the Variac.
By 90 volts I could see the FM tuning eye (I had it set to FM), and I was obviously tuning in stations as the eye was opening and closing as I tuned across the FM band. So by visual indication, the tuner appears to be OK. I did switch it to AM and also saw the AM tuning eye opening and closing as I tuned across the AM band, though not as much as on FM.
One problem though.
No music...no talking...no noise...nothing.
Silent Night.
Or, if you prefer, The Sounds of Silence.
???
I turned the Variac off and unplugged everything. The 5AR4/GZ34 was barely lukewarm, and the 7189s were cold.
Hmmm...sounded like no B+ to the output tubes to me.
Consulting the schematic (yes, I'll post a copy later, perhaps tomorrow), I noticed that there is a 160 ohm, 10 watt resistor between the 5AR4/GZ34 cathode and the input electrolytic capacitor section.
You guessed it...that resistor is open.
I won't be doing any more Variac tests until after I replace the electrolytics and, of course, that burned out resistor. I'll also check the other power resistors to see if any others are open.
Back to the 6П14П...the seller readily agreed to send me a replacement, and I noticed today that it indeed has been sent as I received the notification from USPS.
I have my price quote from Hayseed Hamfest also, and the cost will be about what I expected it to be.
So this weekend, I need to order the loose electrolytics along with one or more power resistors from Mouser, and get the order going for the new twist-lock cans from Hayseed Hamfest. Yes, I could cut open the original cans and restuff them, but this is a special unit and it deserves the special treatment of new twist-lock electrolytics.
--
Ron Ramirez
Ferdinand IN
