Yesterday, 09:31 PM
Sorry Murf, technical is what I do.
OK, Unlike the Western Auto Tru-Tones, this True Tone is a Wells Gardner set. The Nostalgia Air schematic is below:
http://www.nostalgiaair.org/PagesByModel...023515.pdf.
Unfortunately, they do not show the pinouts for the speaker plug. if all 5 pins are used, the pins (IN NO PARTICULAR ORDER) would be connected to:
Plate of one 6F6
Plate of the other 6F6
Center tap of output transformer and one leg of the field coil
Other leg of field coil
Chassis ground
If you take out the 2 6F6 tubes and ohm between pin 3 of one 6F6 and pin 3 of the other 6F6, there should be about 560 Ohm. Lift one leg of the secondary connection to the speaker voice coil. Resistance of the secondary, the voice coil and the hum bucking coil all should be quite low. I suspect that these resistance checks will pass and that your issue is elsewhere. My bet is that the wrong power transformer was used or there is an issue with the voltage divider (resistors R22, R23 and R24) that produces "C-".
One possible issue is that your B+ (from rectifier cathode to ground) of 250V is quite low. The schematic lists plate voltage to ground at the 6F6 plate (pin 3 of each 6F6) is 330VDC. The center tap of the rectifier connects to ground through resistors R22, R23 and R24 (the Candohm?) This develops the grid bias (C-) for the Output tubes, 1st AF and Phase Invertor (Balancing Excitor). There should be about -25V between chassis ground and the center tap of the power transformer. Measuring across C44 should yield about 355V. Note that t5h3 can case of C44 does not connect to Chassis ground, it connects to the junction of R24 and the HV Secondary center tap of the power transformer. This point, not Chassis Ground is the most negative point on the power supply. Note that the cathodes of the audio amp and outputs are at Chassis ground, but the 6F6s require a bias of about -25V for grid bias. This is taken from the junction of R24 and they HV secondary center tap.
If R22, 23 and /or 24 change resistance with high current, this may cause your issue. Low B+ (250Vvs 330V) will cause the same issue.
Hope this helps.
OK, Unlike the Western Auto Tru-Tones, this True Tone is a Wells Gardner set. The Nostalgia Air schematic is below:
http://www.nostalgiaair.org/PagesByModel...023515.pdf.
Unfortunately, they do not show the pinouts for the speaker plug. if all 5 pins are used, the pins (IN NO PARTICULAR ORDER) would be connected to:
Plate of one 6F6
Plate of the other 6F6
Center tap of output transformer and one leg of the field coil
Other leg of field coil
Chassis ground
If you take out the 2 6F6 tubes and ohm between pin 3 of one 6F6 and pin 3 of the other 6F6, there should be about 560 Ohm. Lift one leg of the secondary connection to the speaker voice coil. Resistance of the secondary, the voice coil and the hum bucking coil all should be quite low. I suspect that these resistance checks will pass and that your issue is elsewhere. My bet is that the wrong power transformer was used or there is an issue with the voltage divider (resistors R22, R23 and R24) that produces "C-".
One possible issue is that your B+ (from rectifier cathode to ground) of 250V is quite low. The schematic lists plate voltage to ground at the 6F6 plate (pin 3 of each 6F6) is 330VDC. The center tap of the rectifier connects to ground through resistors R22, R23 and R24 (the Candohm?) This develops the grid bias (C-) for the Output tubes, 1st AF and Phase Invertor (Balancing Excitor). There should be about -25V between chassis ground and the center tap of the power transformer. Measuring across C44 should yield about 355V. Note that t5h3 can case of C44 does not connect to Chassis ground, it connects to the junction of R24 and the HV Secondary center tap of the power transformer. This point, not Chassis Ground is the most negative point on the power supply. Note that the cathodes of the audio amp and outputs are at Chassis ground, but the 6F6s require a bias of about -25V for grid bias. This is taken from the junction of R24 and they HV secondary center tap.
If R22, 23 and /or 24 change resistance with high current, this may cause your issue. Low B+ (250Vvs 330V) will cause the same issue.
Hope this helps.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
Best Regards,
MrFixr55
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