Pye PF91A pre-amplifier and control unit.

[Geordie McBoyne]

The circuit of the Pye PF91A can be found in the 1955/56 Radio and Television book.

The original design employed two ECC40 double triode valves. Although I have these I'd rather use the printed circuit board which appears in the attached pictures. The valves of choice to use with this PCB could be the ECC83 although this valve has quite different characteristics compared to the ECC40 so some component value changes will be called for.

Details of the ECC40:  http://www.radiomuseum.org/tubes/tube_ecc40.html
The Radiomuseum suggests the successor to the ECC40 is the ECC82:   http://www.radiomuseum.org/tubes/tube_ecc82.html
The ECC82 has a much lower gm and ra. than the ECC40.

The tone control pots will be replaced by a eleven position switch to give a centre position flat and five cut and five lift positions.

Geordie McBoyne

[Geordie McBoyne]

Same base connections as the ECC40 are the Mazda 6L1 and the 6L19.   Characteristics are quite different from the Philips/Mullard valve.   The 6L1 is a very low impedance double triode: ra = 4Kohms, mu = 16, gm = 4mA/V.   The 6L19 characteristics are closer to the ECC40. 6L19:  gm = 3.4mA/V, mu = 55, ra = 16Kohms.

Geordie McBoyne.

[pwdrive]

Is that a lump of iron in the schematic or ferrite/dust?

Looks like a decent circuit.

Lawrence.

[Terry]

Is that a lump of iron in the schematic or ferrite/dust?

The core is drawn with broken lines which signifies ferrite/dust -  I would imagine dust in this application.

An iron core, as in a mains transformer or smoothing choke , is signified by solid lines, Lawrence.

[pwdrive]

So it is, I should have looked closer.

Should make an interesting project.

The last home amp I built was the 3+3.................long time ago, the last valve amp I built was for our mobile disco (yeah rock'n roll) that was 807's at around 500 volts, but I did the preamp with solid state, BC107/8/9 can't remember which exactly.

Lawrence.