Is this an UL Power Amp or not ?

[kagliostro]

Here is the schematic of an old italian Davoli Krundaal Guitar Amp

the schematic is confusing me

is an UL configuration or the windings connected to the grid have the only purpose for a lower B+ level with respect to the plates ?

attached some "unusual" configuration from Menno van der Veen

Also the PS seems (at the moment) a bit strange, is a bit late here, and may be my brain didn't compute correctly

Thanks

K

[DummyLoad]

the schematic shows UltraLinear connections to the EL34's.

delon FW voltage doubler for -49V bias (50V winding)
delon FW voltage doubler for 470V B+ (320V winding) to output tube grids.
FWB bridge for 680V to plates & 320V/280V B+ to preamps and connector labled "ingresso unit di potenza" likely a connector that supplies B+ and filament power to a separate pre-amp chassis.

--pete

[kagliostro]

Ciao Pete

So the tubes are configured in UL and the fact that the OT uses separated winding for the grids is attributable to the use of a lower voltage on grids

Grazie

Franco

[HotBluePlates]

So the tubes are configured in UL and the fact that the OT uses separated winding for the grids is attributable to the use of a lower voltage on grids

Yes.

For those playing along at home:
"Normal ultralinear" applies a B+ voltage to the OT center-tap, and has screen taps at a mid-point between the CT and each end of the primary winding. Therefore, the screen voltage is nearly equal to the plate voltage.

But this circuit uses a pretty high voltage for the plates of the EL34's, and so a reduced screen voltage is needed. However, the designer also wanted UL operation. So there is a single center-tapped primary which feeds the screens, and is supplied form a lower B+ voltage. The EL34 plates each have a dedicated winding, both of which are connected to the highest B+ available.

Of course, I'm assuming there is a falling screen voltage when the plate of the same tube has a falling voltage. Otherwise, some of the UL characteristics wouldn't occur (the semi-triode operation of UL).

[DummyLoad]

Ciao Pete

So the tubes are configured in UL and the fact that the OT uses separated winding for the grids is attributable to the use of a lower voltage on grids

Grazie

Franco

yes, it's two separate PS one to g2 and other to the plates - both power supplies are applied to the E34 via output transformer but with the configuration the tubes are running in Ul mode. you'd do the same thing for sweep tubes in UL connection.

that OT could not be replaced with any modern off the shelf OT. seems like it would be a custom winding. perhaps a Lundhal could be made to work in the application? 

[jazbo8]

If you actually have the amplifier, one way to find out for sure, is to disconnect the wires to the tubes and PS to see if there is continuity between the various windings, because sometimes, non-conventional schematic drawing could throw you off. If it is just for theoretical discussion, then it is already well covered in the above explanations.

Jaz

[kagliostro]

Thanks HotBluePlates - Pete - Jazbo8

I'm a collector of the schematics of that brand who aren't easily available

I've a pair of amps of that brand, but not that model

the most part of amps you can find of that brand uses EL500 or EL504 tubes

also units with EL34 may be found, but few with that UL OT

In an italian forum there is a guy who has that model of amp and was asking for the schematic

I had the schematic and posted it for him asking info about the OT

I don't know if he is enough skilled, but I hope he can measure the OT for me

I'm interested to collect all the spec I can about the brand

Franco

[jazbo8]

You must have one of the largest collection of schematic anywhere  , I remember you sending me a whole package of GU50 schematics, I have yet come across one that wasn't already included in your package! 

Jaz

[PRR]

This (below) is NOT an ultralinear design. Instead it is the McIntosh scheme with enormous NFB to cathodes, which requires G2 to follow the cathode (since K-G2 voltage is important); but working at Vp=480V Vg2=300V. Hence separate P and G2 windings.

http://tubebooks.org/Books/lockhart.pdf

[kagliostro]

Thanks PRR

That is very interesting

K