In Reply to: RE: Webster output transformers posted by Tre' on November 30, 2019 at 17:21:28:
the whole small gap thing is actually hugely misunderstood when it comes to EI lams. The only way to get a gap "suitable" for any DC offset is to have a completely discrete gap with all of the E's on one side and the I's on the other. I think much of the misinformation about alternately stacking the E's and I's in groups to decrease the size of the airgap comes from Rueben Lee
I find that this graph will work well for predicting AC permeability at a given excitation level but has no relation to DC saturation characteristics. In other words a 0.001" gap with EI lams alternately stacked in groups of 4 will behave very differently with respect to DC than a well polished C-core with the same effective gap.
I have mentioned this before in the John Hogan amp discussions and essentially adding a substantial DC offset to a PP output transformer actually linearizes the inductance as can be seen in the plot below of a ST-70 output.
given that the inductance you end up with is not huge, the listening reports seem to support that it can still sound really good and the math says response down to 40 hz shouldn't be a problem.
dave
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Follow Ups
- RE: Webster output transformers - dave slagle 06:56:15 12/02/19 (14)
- RE: Webster output transformers - Tre' 08:02:34 12/03/19 (12)
- RE: Webster output transformers - dave slagle 09:54:10 12/03/19 (0)
- RE: "I wonder what a HK Cit2 OPT with 60ma. standing current on it would sound like?" - Ivan303 08:41:33 12/03/19 (10)
- RE: "I wonder what a HK Cit2 OPT with 60ma. standing current on it would sound like?" - PakProtector 05:48:59 01/02/20 (1)
- RE: "I wonder what a HK Cit2 OPT with 60ma. standing current on it would sound like?" - Tre' 12:12:06 01/02/20 (0)
- RE: "I wonder what a HK Cit2 OPT with 60ma. standing current on it would sound like?" - Tre' 09:10:15 12/03/19 (7)
- "you are there" - buffy 11:35:54 12/03/19 (6)
- RE: "you are there" - Tre' 12:13:17 12/03/19 (5)
- RE: "you are there" - buffy 13:05:45 12/03/19 (4)
- RE: "you are there" - Tre' 16:20:43 12/03/19 (3)
- RE: "you are there" - buffy 17:08:29 12/03/19 (2)
- RE: "you are there" - Tre' 20:01:08 12/03/19 (1)
- RE: "you are there" - buffy 12:06:40 12/04/19 (0)
- RE: Webster output transformers - tube wrangler 09:29:18 12/02/19 (0)