Well, 2-3 weeks ago I finished the driver board and measured the whole amp. It is better than expected even though output tubes were JJ KT77.
Later I will upload more graphs, here you can see 20Vpp 20kHz sqr signal into 4R5, non-gnfb.
Later I will upload more graphs, here you can see 20Vpp 20kHz sqr signal into 4R5, non-gnfb.
nice work. I assume that the squarewave is with just Cathode feedback around output. What level of global feedback do you propose to deploy. Keen to see more
...very nice work
...very nice work
frequency response at 30Vpp into 4R5 (UL+CFB+GNFB_12dB)
17Hz: 0dB
100kHz: -3dB
thd vs freq at 10W into 4R5
green trace: UL+CFB+GNFB_12dB
gray trace: TR+CFB+GNFB_12dB
17Hz: 0dB
100kHz: -3dB
thd vs freq at 10W into 4R5
green trace: UL+CFB+GNFB_12dB
gray trace: TR+CFB+GNFB_12dB
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Can you then confirm that the amount of CFB is indeed what they claim? They state 10% of Ra which is a rather unusual way to define it. That's 24% CFB in terms of turn (or voltage) ratio between cathode and total anode + cathode.
A while ago someone else was maligning about those OPT's hinting they are a bad copy of the Plitrons and so 10% is turn (or voltage) ratio.
Your amp design and test results confirm my experience building with with Toroidy CFB transformers. They are a very nice transformer. Will use them again. My next design will use John Broskie "Blumlein Garter Revisited". This will ensure good current balance in the transformer, as I understand that balance is more critical with Toroidal transformers.
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Ah OK, but what is not true is what they STATe in their website!!! It's not me. I had not noticed your reply in that thread. So Peter was right. I asked directly to Toroidy about that funny definition and they replied that it was indeed 10% Ra. Now it's clear that they do NOT know what they are talking about. I have to admit that Peter was right and they have probably copied the Plitron transformer. Bad copy of course, because the Plitron has quite better bandwidth and headroom.
Just to avoid mis-understandings and discussions I copy and paste their response here again:
"Thank You for contact us.
There are two cathode windings - one for each half of the primary winding.
TTG-CFB4000PP has a 4k Raa (anode to andode) - 2k between the anode and the center tap.
Each CFB winding is calculated as a 10% of a half, so 10% of a 2k."
That's quite clear. And it means 24% CFB which is not what it is in reality. Enough for me to NOT trust all the other specs. It might be cheap respect to other options but not worth the trouble for me. For others it might be. At their own risk of course....
"Thank You for contact us.
There are two cathode windings - one for each half of the primary winding.
TTG-CFB4000PP has a 4k Raa (anode to andode) - 2k between the anode and the center tap.
Each CFB winding is calculated as a 10% of a half, so 10% of a 2k."
That's quite clear. And it means 24% CFB which is not what it is in reality. Enough for me to NOT trust all the other specs. It might be cheap respect to other options but not worth the trouble for me. For others it might be. At their own risk of course....
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