Hammond 125A 3 W Universal Push-Pull Tube Output Transformer
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Create Free Business AccountKey Features
- 3 W universal push-pull output: 1,200 to 25,000 ohm primary range
- Matches 1.5 to 15 ohm speakers via secondary solder lug selection
- 20 mA max DC bias per side; 14.94 H primary inductance
- 150 Hz - 15 kHz at full rated power (+/- 1 dB max, ref. 1 kHz)
- Compact 2.06 x 1.25 x 1.19 in open frame, 0.19 lbs
- 1500 V, 60 Hz primary-to-secondary hipot
- RoHS and REACH compliant
The 125A is the smallest member of the 125A-125E universal push-pull tube output family, rated at 3 audio watts. It is designed for general purpose or replacement use in push-pull tube output circuits, which makes it a practical choice for radio restorers, guitar and hobby amplifier builders and technicians who need one transformer that can match many plate-to-plate impedances and speaker loads.
Selecting different secondary solder lug pairs gives a total primary impedance anywhere from 1,200 to 25,000 ohms (blue wire to brown wire) with speakers from 1.5 to 15 ohms. For example, an 8 ohm speaker across lugs 4&6 reflects 12,800 ohms, while a 4 ohm speaker across lugs 1&4 reflects 5,800 ohms.
The 125A handles up to 20 mA DC bias per side and has a primary inductance of 14.94 H. The series is specified for 150 Hz to 15 kHz at full rated power (+/- 1 dB max, ref. 1 kHz). Production test data on the drawing includes a primary DC resistance of 295.0 ohms ±20% (blue to brown), a 1500 V, 60 Hz, 1 second hipot between primary and secondary, and a maximum excitation current of 4 mA at 130 V, 400 Hz.
It is an open style unit with primary leads at least 5 inches long and solder lugs for the secondary. Overall dimensions are A 2.06 in (52 mm), B 1.25 in (32 mm), C 1.19 in (30 mm) and D 1.75 in (44 mm), with 0.19 in (5 mm) mounting holes, and it weighs 0.19 lbs (0.09 kg). For single ended output stages, the 125SE Series is the intended alternative. The part is RoHS and REACH compliant.
Ideal For
- Replacement output transformer for small push-pull tube radios and amplifiers
- Low-power push-pull tube output stages
- General purpose tube output matching to 1.5-15 ohm speakers
Overview
| Series | 125A-125E Series Universal Push-Pull Tube Output |
| Application | General purpose or replacement use (not Hi-Fi) in push-pull tube output circuits |
| Description | Audio transformer, universal push-pull tube output, 3 watts |
| Part Number | 125A |
| Short Description | AUDIO TX OUTPUT SE OR PP |
| Single-Ended Alternative | For single ended use, see the 125SE Series |
Dimensions
| A (Overall) | 2.06 in (52 mm) |
| A (Drawing) | 2.063" ±0.063 |
| B (Overall) | 1.25 in (32 mm) |
| B (Drawing) | 1.250" ±0.125 |
| C (Overall) | 1.19 in (30 mm) |
| C (Drawing) | 1.188" ±0.063 |
| D (Overall) | 1.75 in (44 mm) |
| D (Drawing) | 1.750" ±0.063 |
| G (Drawing) | 0.187" ±0.015 |
| Weight (Table) | 0.19 lbs |
| G - Mounting Hole | 0.19 in (5 mm) |
Electrical
| Audio Watts | 3 |
| DCR BLU - BRN | 295.0 Ω ±20% @ 20°C |
| Drawing Marking | 1.2k TO 25k primary; 1.5 TO 15 secondary; 25mA DC; 150Hz - 15kHz ±1 db MAX, REF. 1kHz; 3WATT |
| DCR PIN 1 - PIN 6 | 1.200 Ω ±20% @ 20°C |
| Max. DC Bias Per Side | 20 mA |
| Primary Impedance Range | 1,200 to 25,000 ohms |
| Excitation Current (Iex) | 4 mA max @ 130V, 400Hz, BLU - BRN |
| Hipot Primary - Secondary | 1500V, 60Hz, 1 SEC |
| Secondary Impedance Range | 1.5 to 15 ohms |
| Primary Inductance (Table) | 14.94 H |
| Frequency Response (Series) | 150 Hz - 15 kHz at full rated power (+/- 1 dB max, ref. 1 kHz) |
| Secondary No-Load Voltage BLU - RED | 65.00 V ±2% @ 130V, 400Hz on BLU - BRN |
| Secondary No-Load Voltage PIN 1 - PIN 2 | 0.967 V ±2% |
| Secondary No-Load Voltage PIN 1 - PIN 3 | 2.174 V ±2% |
| Secondary No-Load Voltage PIN 1 - PIN 4 | 3.431 V ±2% |
| Secondary No-Load Voltage PIN 1 - PIN 5 | 5.026 V ±2% |
| Secondary No-Load Voltage PIN 1 - PIN 6 | 6.766 V ±2% |
Identifiers
| UPC | 623980188607 |
| UNSPSC | 39121301 |
Hook-Up Data
| Speaker On Secondary Lugs 1&2 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 27000 Ω |
| Speaker On Secondary Lugs 1&3 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 5400 Ω; 2 Ω speaker: 7200 Ω; 3.2 Ω speaker: 11500 Ω; 4 Ω speaker: 15000 Ω; 6 Ω speaker: 21600 Ω |
| Speaker On Secondary Lugs 1&4 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 2150 Ω; 2 Ω speaker: 2900 Ω; 3.2 Ω speaker: 4600 Ω; 4 Ω speaker: 5800 Ω; 6 Ω speaker: 8700 Ω; 8 Ω speaker: 11600 Ω; 12 Ω speaker: 17400 Ω; 15 Ω speaker: 21500 Ω |
| Speaker On Secondary Lugs 1&5 - Resulting Primary Impedance (BLU To BRN) | 2 Ω speaker: 1400 Ω; 3.2 Ω speaker: 2200 Ω; 4 Ω speaker: 2800 Ω; 6 Ω speaker: 4200 Ω; 8 Ω speaker: 5600 Ω; 12 Ω speaker: 8400 Ω; 15 Ω speaker: 10200 Ω |
| Speaker On Secondary Lugs 1&6 - Resulting Primary Impedance (BLU To BRN) | 3.2 Ω speaker: 1200 Ω; 4 Ω speaker: 1500 Ω; 6 Ω speaker: 2300 Ω; 8 Ω speaker: 3000 Ω; 12 Ω speaker: 4500 Ω; 15 Ω speaker: 5600 Ω |
| Speaker On Secondary Lugs 2&3 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 18000 Ω; 2 Ω speaker: 24000 Ω |
| Speaker On Secondary Lugs 2&4 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 4200 Ω; 2 Ω speaker: 5600 Ω; 3.2 Ω speaker: 9000 Ω; 4 Ω speaker: 11200 Ω; 6 Ω speaker: 16800 Ω; 8 Ω speaker: 22500 Ω |
| Speaker On Secondary Lugs 2&5 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 1550 Ω; 2 Ω speaker: 2050 Ω; 3.2 Ω speaker: 3300 Ω; 4 Ω speaker: 4100 Ω; 6 Ω speaker: 6150 Ω; 8 Ω speaker: 8200 Ω; 12 Ω speaker: 12300 Ω; 15 Ω speaker: 15500 Ω |
| Speaker On Secondary Lugs 2&6 - Resulting Primary Impedance (BLU To BRN) | 3.2 Ω speaker: 1700 Ω; 4 Ω speaker: 2100 Ω; 6 Ω speaker: 3150 Ω; 8 Ω speaker: 4200 Ω; 12 Ω speaker: 6300 Ω; 15 Ω speaker: 8000 Ω |
| Speaker On Secondary Lugs 3&4 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 16500 Ω; 2 Ω speaker: 22000 Ω |
| Speaker On Secondary Lugs 3&5 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 3300 Ω; 2 Ω speaker: 4400 Ω; 3.2 Ω speaker: 7000 Ω; 4 Ω speaker: 8800 Ω; 6 Ω speaker: 13200 Ω; 8 Ω speaker: 17600 Ω; 12 Ω speaker: 26400 Ω |
| Speaker On Secondary Lugs 3&6 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 1300 Ω; 2 Ω speaker: 1700 Ω; 3.2 Ω speaker: 2700 Ω; 4 Ω speaker: 3400 Ω; 6 Ω speaker: 5100 Ω; 8 Ω speaker: 6800 Ω; 12 Ω speaker: 10200 Ω; 15 Ω speaker: 12800 Ω |
| Speaker On Secondary Lugs 4&5 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 10000 Ω; 2 Ω speaker: 13500 Ω; 3.2 Ω speaker: 21600 Ω; 4 Ω speaker: 27000 Ω |
| Speaker On Secondary Lugs 4&6 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 2400 Ω; 2 Ω speaker: 3200 Ω; 3.2 Ω speaker: 5100 Ω; 4 Ω speaker: 6400 Ω; 6 Ω speaker: 9600 Ω; 8 Ω speaker: 12800 Ω; 12 Ω speaker: 19200 Ω; 15 Ω speaker: 24000 Ω |
| Speaker On Secondary Lugs 5&6 - Resulting Primary Impedance (BLU To BRN) | 1.5 Ω speaker: 8500 Ω; 2 Ω speaker: 11000 Ω; 3.2 Ω speaker: 18000 Ω; 4 Ω speaker: 22000 Ω |
Packaging & Shipping
| Shipping Weight | 0.19 lbs (0.09 kg) |
Construction & Finish
| Style | Open style |
| Primary Leads | Minimum 5" long |
| Secondary Connections | Solder lugs 1-6 |
Compliance & Certifications
| RoHS Compliant | Yes |
| REACH Compliant | Yes |
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Frequently Asked Questions
What primary impedances can the 125A provide?▾
Depending on the secondary lugs used and the speaker impedance, the resulting primary impedance ranges from 1,200 to 25,000 ohms, blue wire to brown wire.
How much DC bias current can it take?▾
The 125A is rated for a maximum of 20 mA DC bias per side.
Can I use the 125A in a single ended amplifier?▾
The 125A-125E are designed for push-pull tube output circuits; for single ended use the manufacturer points to the 125SE Series.
What speaker impedances are supported?▾
Voice coil impedances from 1.5 to 15 ohms, using the hook-up table to pick secondary lugs.
What are its dimensions?▾
A 2.06 in (52 mm), B 1.25 in (32 mm), C 1.19 in (30 mm), D 1.75 in (44 mm), with 0.19 in (5 mm) mounting holes.
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