Can this single transformer be able to power 2 pairs (or four) KT88 power tubes for PP amp?
If using as 6.3V from each half (4-5) and (6-5) does it mean each half can supply 4A each?
Or would it be better to connect each pair of tubes in series and connect two pairs to the 12.6V? Thanks in advance.
If using as 6.3V from each half (4-5) and (6-5) does it mean each half can supply 4A each?
Or would it be better to connect each pair of tubes in series and connect two pairs to the 12.6V? Thanks in advance.
Connect each pair in series, tie the nods/junctions together and connect them to CT 😉.
Best regards!
Best regards!
There is zero, nada, zilch difference between putting them in series for 12.6V or individual to 6.3V. Nothing.
Jan
Jan
Toros are usually wound bifilar to save time at winding. If it is your case, and in case if doubth you can separate both wires and use them in series, parallel or separately, providing the voltage gradient between them is not too high to stress the enamel breakdown potential.
My guess is it’s not a toroid. Those are normally leaded out separately to begin with. Whether a step down EI can have the secondaries separated is a matter of whether the connection is buried. Since toroid primaries (and even secondaries up to 500V) are bifilar, there’s no reason any low voltage center tapped winding can’t be separated safely. But physically doing it without tearing it apart may be another matter.
Hum balance. That cannot be made the same as with a single 6.3V winding, but it may not be an issue. One half of the push pull will always be on one side of ground, and one half on the other (if the CT is grounded like it should be). Polarity will probably matter between channels, and be prepared to swap as needed - just build in the capability to do it easily. If you are running the usual 12A*7 front end, run them in 12V mode so the center is properly grounded. If you prefer GT types, the 12S*7 are also available and usually cheaper than 6V tubes.
Hum balance will work with tubes with singular 12.6 V heaters. The OP's KT88 surely don't belong to these. GU-50's, FL152's etc. would.
Best regards!
Best regards!
It will work fine that way.
Each filament will not be balanced to ground but no big deal, these are power tubes, the last in a long chain, the least sensitive to hum or noise.
Each filament will not be balanced to ground but no big deal, these are power tubes, the last in a long chain, the least sensitive to hum or noise.
Thank you all. I have a separate power supply chassis and wanted to minimize all the wiring as possible. All of my front end signal/driver tubes will be power by DC heater. Any precaution on the wiring scheme especially on grounding/noise that I should be aware of for a separate block chassis?
Yes, as long as both outers are pushes and both inners are pulls. That will keep the hum balanced between channels, and if you hum balance trim the front end it will cancel both at the same time, to the extent possible. Get it backwards and what nulls one channel amplifies the other.
Schematic looks fine would ground the CT. The hum you can get is not usually through the power tubes but the magnetic field generated by the transformer and the heater wires getting into the input wiring. You may wish to twist wires from transformer 4 and 6 together. Little current will flow though the CT wire. You may get better hum cancelation by using 4 for R and 6 for L who knows.
Do you guys understand that the heater current from one tube, through the combined cable resistance, ends up as noise voltage on the other tube on the same wire?
Jan
Jan
Isn't this statement applicable to directly heated tubes exclusively, and for sure not to indirectly heated power tubes?
Best regards!
Best regards!
