Hello!
When ordering a ll1679PP transformer I was asked whether I want a PP or PPZ (parafeed zero gap) transformer.
No specification for a PPZ is available. I have only found out that they have twice induction comparing to a PP and no air gap.
Does anybody have experience in using such PPZ OT? What would be the best for KT88 based PP?
When ordering a ll1679PP transformer I was asked whether I want a PP or PPZ (parafeed zero gap) transformer.
No specification for a PPZ is available. I have only found out that they have twice induction comparing to a PP and no air gap.
Does anybody have experience in using such PPZ OT? What would be the best for KT88 based PP?
No experience, but found this on the Internet: https://jacmusic.com/lundahl/tech-papers/PPZ-SPECIFICATIONS.pdf
You would either have to use a parafeed push pull configuration which would be a massive waste of time and money.
Or you would somehow have to guarantee that the two tubes would be drawing the exact same amount of current which would limit you to class A operation.
Further to what Tjj226 wrote, since you r amp will be push-pull, you want the PP not the PPZ. The PPZ is designed for zero DC voltage across the primary -- which you get in parallel feed amps (typically a choke-loaded output tube with signal taken from the anode via a "parafeed" (DC-blocking) capacitor to the primary of the OPT). PP (small gap) is designed to handle the small amount of DC voltage you get with with push-pull.
cheers, Derek
cheers, Derek
Guys, thank you! I did not manage to properly translate "parafeed" into Russian, so I did not understand it is for a different design
push-pull amps are usually balanced if loaded with matched tubes (best)or it
has individual bias adjustments (cheapest)
by the way, what power can you get from a parafeed amp comparing to the regular PP configuration?
Same power as with series feed.
And no, transformer designed for paraded cannot be used in regular push-pull, no matter how good tube matching is. DC offset, even in microampere range, will eat up the inductance and degrade transformer performance. Tubes drift.
And no, transformer designed for paraded cannot be used in regular push-pull, no matter how good tube matching is. DC offset, even in microampere range, will eat up the inductance and degrade transformer performance. Tubes drift.
^ I have no practical experience with this but would a garter cathode bias create enough balance to use a 0 gap transformer?
Hammond is so much easier with their detailed website and their transformers are rarely liquid/creamy looking
Gapless requires a largish capacitor to prevent dc saturation. The high pass filter generated by the lrc circuit can be calculated using the primary resistance, core primary inductance and the chosen capacitor.
This could be simplified to the rc high pass filter using the primary impedance (chosen frequency) and chosen capacitor.
Maybe consider feeding the anode with the output transformer opposed to clamping it across anode and ground/or cathode. aka not using para(lyzed) feed.
Push pull does not have to be parafeed. It just is "two" tubes on one output transformer.
edit: changed low pass to high pass, whoops, tired
Gapless requires a largish capacitor to prevent dc saturation. The high pass filter generated by the lrc circuit can be calculated using the primary resistance, core primary inductance and the chosen capacitor.
This could be simplified to the rc high pass filter using the primary impedance (chosen frequency) and chosen capacitor.
Maybe consider feeding the anode with the output transformer opposed to clamping it across anode and ground/or cathode. aka not using para(lyzed) feed.
Push pull does not have to be parafeed. It just is "two" tubes on one output transformer.
edit: changed low pass to high pass, whoops, tired
Last edited:
it is very hard to adjust for exact same current on both halves of pp. therefore zero gap is problematic.