I have been doing a little research on Fender "ultralinear" taps and this is pretty interesting...from DIYTube. This is from a conversation about replacing a OPT in a Studio Bass with a Hammond OPT that usually will put out about 160 watts RMS non ultralinear.
"The 1650T transformer with screen taps would be a marginal transformer choice for the super twin -- and it would require more circuit modification than indicated to make it perform even at a marginal level.
Many people in the guitar amp world mistakenly refer to the Fender tapped screen circuit as an Ultralinear design. It is not, and the taps were not intended, nor are they capable of producing Ultralinear operation. Typical Ultralinear operation for 6L6 class tubes requires a 43% tap (based on turns ratio), which is about what the Hammond transformer provides at 40%. True Ultralinear operation results in much lower distortion, and much lower power output -- about 35 watts is the absolute maximum RMS power output that a pair of 6L6s can give in an Ultralinear design. Therefore, when using the tapped version of the 1650T in the Super Twin, the amp would not produce much more than about 110 watts continuous RMS output. For this transformer to work to it's best ability, the screen taps would need to be taped off, and then have a standard choke type filter system installed for the screen B+ take off. Under these conditions (strict pentode operation), the amplifier would produce about 165 watts continuous RMS output.
As for the actual design of the Fender tapped screen circuit, the purpose of these taps was a cost saving measure on Fender's part, in that they eliminated the need for the choke to provide adequate filtering for the output stage. That was it, and nothing more. This is not an opinion, but a fact that came out of a conversation I had with the circuit's designer. As such, the taps are appropriately placed at only 12.5% of the winding -- enough to provide a small amount of B+ filtering, but hardly enough to reduce power output and cause Ultralinear operation.
Finally, contrary to what was claimed, the Super Twin is quite capable of putting out 200 watts continuous RMS -- if the P-P impedance is correct to allow for it. In this case, the original Super Twin transformer has a P-P impedance of 1500 ohms, which is proper for six 6L6s in Fender's tapped screen design. This is why the Hammond transformer, as a 1900 ohm unit, will not allow full power output to be produced even without screen tapped operation.
When the impedance mismatch, inappropriate tap positioning, and power rating of the transformer are all considered, you can see why I maintain that this transformer would be a marginal choice at best."
Taking this into consideration, it might be best to investigate as to whether the OPT in a Twin 2 (which uses a choke) would be able to put out 100 watts driven by two KT88's as it shows 465V before the choke and 460V after the choke on B+ on the Twin 2 schemo. It might be a little marginal on the 88's? It would certainly drive them at a lower output and that would give it some reserve on "depth" or reserve current which is what a person would want in a bass rig. I would guess and venture about 75 watts RMS and about 150 peak or program burst. I would prolly gain a bit on the simplified preamp as far as reserve also."
Who needs a Sunn anywho? lol. It turns out that I found a Sunn 200S is a 60 watt amp and not the 100 I thought it was. It follows this same theme by using the 88's instead of 6L6G's with would take away the reserve of the tube which Sunn capitalizes on to sound so loud, like idling a 454 cu in snow blower. For brut force there is no substitute for cubic inches and nitro ... ditto on tubes it seems.
I'am putting the Blackface on the rear burner. Back to the BFA, I'll post a schemo soon. Been working on this one about two years gathering info.
