1650P Hammond PP Übertrager 6,6k 60W 0,2A 4/8/16 40% UL

Hammond 1650P – 60 W ultralinear output transformer with a 6.6 kΩ primary

The Hammond 1650P is an enclosed and shielded push-pull output transformer for high-quality valve amplifiers. It is intended for two output valves, a 6.6 kΩ plate-to-plate load and up to 60 W RMS. Its secondary windings support 4, 8 and 16 Ω speakers.

Two 40% screen-grid taps support ultralinear operation. The 1650P may also be used in correctly designed triode, pentode or tetrode push-pull stages. Because its secondary windings are interleaved, both secondary windings must be used in every load configuration according to the Hammond connection diagram.

Suitable applications

• Push-pull output stages using two EL34, KT88, 6L6GC, 6550B or 5881 valves
• Correctly designed circuits using 807 or 6146B valves
• Ultralinear output stages using 40% screen-grid taps
• Triode, pentode or tetrode push-pull circuits requiring a 6.6 kΩ plate-to-plate load
• Mono amplifier projects up to 60 W with 4, 8 or 16 Ω speakers

Technical data

Product type

Push-pull audio output transformer with ultralinear taps

Primary impedance

6.6 kΩ plate-to-plate, centre-tapped

Secondary impedances

4, 8 and 16 Ω

Power rating

60 W RMS

Operation

Push-pull using two output valves

Maximum DC current

200 mA per primary side according to Hammond; not a permissible DC-imbalance figure

Ultralinear taps

40% taps for both screen grids

Frequency response

30 Hz to 30 kHz at full rated power, maximum ±2 dB referenced to 1 kHz

Primary inductance

305 H typical for brown–red at 60 Hz, 10 V with the secondary open

Leakage inductance

11.8 mH typical for brown–red at 60 Hz, 10 V with the secondary shorted

Primary DC resistance

160.5 Ω between blue and brown, typical

Secondary DC resistance

0.230 Ω black–green and 0.370 Ω black/yellow–yellow, typical

Dielectric strength

2,000 V RMS

Temperature range

-40 to +105 °C

Construction

Enclosed and shielded housing for above-chassis mounting; not epoxy potted

Mounting

Four-slot Hammond Type X mounting

Connections

Insulated flexible flying leads at least 8 in or approximately 203 mm long

Dimensions

Approx. 79.4 × 96.8 × 108.0 mm according to the Hammond drawing

Mounting pattern

Approx. 63.5 × 74.7 mm; slots approx. 5.16 × 9.53 mm

Shipping weight

Approx. 3.63 kg according to Hammond

Primary connections

Plate connections

Blue and brown to the two output-valve plates

Primary centre tap

Red to the high-voltage supply

Ultralinear tap on the blue side

Blue/yellow to the associated output-valve screen grid

Ultralinear tap on the brown side

Brown/yellow to the associated output-valve screen grid

Secondary wiring notes

The 1650P uses two interleaved secondary windings. Their connections change with the required speaker impedance. Both windings must be engaged in every 4, 8 or 16 Ω configuration according to the Hammond diagram to achieve the specified performance.

The secondary must therefore not be treated as a conventional common-plus-taps winding. Connect black, green, black/yellow, green/yellow and yellow exactly as shown in the manufacturer diagram.

Comparison with the 1650PA and 1650PAP

Hammond 1650P

Classic interleaved secondary windings, shielded enclosure and flexible flying leads

Hammond 1650PA

Electrically related easy-hookup version with simplified secondary wiring

Hammond 1650PAP

Epoxy-potted version in the same power class; mechanically and physically different from the 1650P

Selection and application notes

The 6.6 kΩ plate-to-plate impedance is a target value for the complete operating point. Plate voltage, screen-grid voltage, bias current, operating class and expected output power must suit the selected valve.

The 200 mA figure is the maximum per primary side. It is neither an automatically suitable bias current nor a permissible current difference between the two push-pull halves. Excessive DC imbalance can magnetise the core and reduce low-frequency headroom.

When using the 40% taps, recalculate the screen-grid voltages and dissipation. Changing from pentode to ultralinear operation alters the valve characteristics, gain and required operating point.

Lethal voltages may be present on the primary wiring. Mount the transformer with adequate touch protection and discharge all filter capacitors before servicing.

Questions about selection and use

Which output transformer suits a 60 W push-pull stage requiring a 6.6 kΩ plate-to-plate load?

Hammond 1650P is intended for correctly designed two-valve push-pull stages requiring a 6.6 kΩ plate-to-plate load and up to 60 W. Hammond suggests valve families including EL34, KT88, 6L6GC, 6550B, 5881, 807 and 6146B.

Which output transformer provides 40% ultralinear taps and 4, 8 and 16 ohm outputs?

Hammond 1650P provides 40% screen-grid taps, a 6.6 kΩ centre-tapped primary and secondary matching for 4, 8 and 16 Ω. Both interleaved secondary windings must be used according to the Hammond connection diagram.

Can the Hammond 1650P also be used without ultralinear operation?

Yes, the Hammond 1650P can be used in correctly designed triode, pentode or tetrode push-pull circuits. Screen-grid wiring, supply voltages and operating points must suit the selected operating mode.

Is the 200 mA figure for the Hammond 1650P a permissible current per primary side?

Yes, Hammond specifies a maximum of 200 mA DC per primary side. This is a winding limit, not a permitted DC imbalance or an automatic recommended bias current; calculate the operating point separately.