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Hello Folks. I am working on a new SE amp. Problems with the 6.3V heaters. I measure 3.2V at each pin (both socket and pin). Neither the 6SJ7's nor the KT88's heat up. What is my DOH??
Follow Ups:
Do you mean that the voltage of each tube socket heater pin to ground measures 3.2Vrms?
The voltage 3.2V suggests that you are getting only half 6.3V. Are you sure that you have used the correct pair of transformer leads? Perhaps you are using one live and the CT by mistake.
Bill
I suspect a faulty supply. With the CT grounded, I have 3.2v on one lead and .33 on the other.If I ground the .33 lead, and test the others, referenced to ground, they test about 17V.
Disconnect from circut & then measure winding itself, end-to-end & end(s) to center tap.
Below are the results.
Test A had DMM common on center tap.
Test B had DMM common on lead 2.
Test C had DMM common on lead 1.Test A) 1 2.22V CT 3.36V 2
Test B) 1 ??V --> 2
Test C) 1 <--??V 2
Tests B and C are NOT stable. Voltages vary from 1.8-3.2 V
Continuity tests positive from CT to 2. Negative from CT to 1 and from 1 to 2.
The voltages out of the transformer are AC = either test lead arrangement should indicate equally same when meter is set for AC Volts. If you have transformer leads correctly identified, then continuity test shows one side open & AC Volts as measured from that side should accordingly be Zero.
Well, neither side measures zero volts referenced to CT. However, lead 1 does not register on a continuity test. Weird.Below are voltages referenced to ground.
1 .05
CT 17.49
2 15.08
If you can measure AC Volts in referance to circut Common, it would seem you did not bother disconnecting from circut as I suggested. Can't diagnose transformer that way. BUT read further: what is the color code for your filament winding leads? CAUTION: Black/Green is a dual Primary winding lead & NOT a Secondary filament CT lead. Mis-interpreting the transformer lead color code could account for weird readings AND pose a very dangerous situation.
Perhaps I have incorrectly described my observations. I have tried proivde as much information as possible and I appreciate your assistance.The filament leads were disconnected from the circuit. Leads 1 and 2 are green. The center tap is green with a white trace. This is as it is described in the transformer wiring schematic.
These results are with the leads disconnected from the circuit.
Test A had DMM common on center tap.
Test B had DMM common on lead 2.
Test C had DMM common on lead 1.
Test A) 1 2.22V CT 3.36V 2Test B) 1 ??V --> 2
Test C) 1 <--??V 2
Tests B and C are NOT stable. Voltages vary from 1.8-3.2 V
Continuity tests positive from CT to 2. Negative from CT to 1 and from 1 to 2.
Below are voltages referenced to AC ground with the leads disconnected from the circuit.
1 .05
CT 17.49
2 15.08
With leads dis-connected from circut, simply measure AC Volts from lead-to-lead. At AC, there is NO Common test lead (makes no diff black to red or red to black). DO NOT referance AC on secondary leads to SAFETY Ground. I do not know how to interpret your readings per such unusual methods, do you need to review your meter's instructions? I am going to bed for tonite.
That would be these results.Lead 1 to CT often about 2.22 VAC - but unstable sometimes as low as 1.5 -and as high as 3.5 VAC
Lead 2 to CT 3.36V AC - always very stable stable within a few hundredths
Lead 1 to Lead 2 - very unstable from 1.8-3.2 VAC
There is continuity from CT to lead 2 but not from CT to lead 1 or from lead 1 to lead 2.
B+ voltages and 5V heater measure stable. My other tube amps measure stable heater voltages.
The sole purpose of the AC SAFETY Ground connection to chassis is to prevent YOU from becoming a portion of the circut in the event of a fault that places dangerous voltage on the chassis. An Earth Ground connection is not required for normal circut operation EXCEPT as a SAFETY measure. Your household electrical service entrance does pose full potential to that AC Ground. As such, referancing a dis-connected transformer secondary winding to the separate AC SAFETY Ground can also result in erroneous & fluctuating AC voltage results. If your secondary windings are correctly identified, the no continuity between CT & lead #1 (& non-continuity between #1 & #2 follows since CT is in-between) is sufficient to show fault. Hope that helps.
Correct construction implementation dictates the AC SAFETY Ground from power cord (Green wire) connects to a separate chassis point all its' own. Nothing else connected to that point & NEVER direct to circut Common returns. The circut Common current returns should then make their own separate connection to chassis at just one point (Star *ground* or one end of a daisy-chain Buss bar). This allows maximum SAFETY potential.
Try measuring the resistance with your ohm meter to determine which leads are actually connected. If you have unstable reading I suspect that these leads are not from the same winding.
*
Mine goes wacky when the bat is low...
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