I have a problem with a Quad II power transformer; the 6.3V winding. (Found no previous reference to this):
The voltage is 7,2V unloaded, and down to 6,9V under 5A load; more than the demanded quantity, with mains voltage as specified. I have refurbished a number of Quads previously, but have never encountered the 6,3V this high although it was always on the high side. (Other voltages were roughly as specified.) No undue heat build-up under full load; in fact it operates rather on the cool side, ambient temperature 23° C. (I recall other's experience of Quad power transformers getting quite hot.)
The transformer appears to be original. Any other experiences in this regard?
Thanks!
The voltage is 7,2V unloaded, and down to 6,9V under 5A load; more than the demanded quantity, with mains voltage as specified. I have refurbished a number of Quads previously, but have never encountered the 6,3V this high although it was always on the high side. (Other voltages were roughly as specified.) No undue heat build-up under full load; in fact it operates rather on the cool side, ambient temperature 23° C. (I recall other's experience of Quad power transformers getting quite hot.)
The transformer appears to be original. Any other experiences in this regard?
Thanks!
Thanks Cerrem,
I should have mentioned: Correct taps used, 240V in my case, mains adjusted with a Variac. All other voltages within 5% including other primary taps. I do not have the necessary equipment to measure the low d.c. resistance of the 6V winding accurately but can make a hook-up, even so I doubt whether the original value would be known to anybody.
One found all manner of funnies over the years, but it is the first time I have encountered one power transformer output voltage off with the rest in order and no apparent shorts/malfunctioning otherwise. (I do have another Quad here - its mate for stereo - but there the power transformer was rewound, measuring correctly.)
If no experience by others I must just accept it as a fluke and add some resistance. (Ouch! - a 'degrading' action at any time!)
I should have mentioned: Correct taps used, 240V in my case, mains adjusted with a Variac. All other voltages within 5% including other primary taps. I do not have the necessary equipment to measure the low d.c. resistance of the 6V winding accurately but can make a hook-up, even so I doubt whether the original value would be known to anybody.
One found all manner of funnies over the years, but it is the first time I have encountered one power transformer output voltage off with the rest in order and no apparent shorts/malfunctioning otherwise. (I do have another Quad here - its mate for stereo - but there the power transformer was rewound, measuring correctly.)
If no experience by others I must just accept it as a fluke and add some resistance. (Ouch! - a 'degrading' action at any time!)
Get two 0.05 to 0.07 ohm 5-10 watt resistors and put each one in series with each 6.3 volt transformer tap. Try to find two that are well matched. A cheap and easy solution to your problem. Whoever wound that transformer, probably put an extra turn or two on that winding when the transformer was made.
Oh, I see that you already came up with this. I should read posts in their entirety...
Oh, I see that you already came up with this. I should read posts in their entirety...
Thanks Dan,
Yes, the solution is not too difficult, it is the reason that puzzles. Extra turns in error seem to be the only explanation - but then either side of the center tap - that is still exactly in the middle voltage-wise. One presumes these transformers were wound as a batch, so how does an error occur for one only - unless it was the lot of the batch, in which case it was not noticed by quality control?? It is noticable that the KT66s 'light up' over-bright. (For completeness sake: I said the transformer looks exactly like an original. I have however no guarantee that was not neatly replaced after a rewind.)
Thus, to put my question a little different: Has anyone found such a discrepancy with any tube amplifier before?
Yes, the solution is not too difficult, it is the reason that puzzles. Extra turns in error seem to be the only explanation - but then either side of the center tap - that is still exactly in the middle voltage-wise. One presumes these transformers were wound as a batch, so how does an error occur for one only - unless it was the lot of the batch, in which case it was not noticed by quality control?? It is noticable that the KT66s 'light up' over-bright. (For completeness sake: I said the transformer looks exactly like an original. I have however no guarantee that was not neatly replaced after a rewind.)
Thus, to put my question a little different: Has anyone found such a discrepancy with any tube amplifier before?
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