Transmit 2
The Transmit 2 is the ultimate version of the Broadcast, combining features from the 24V Dual and the AP, with additional features and options.
Transistors:
The original Broadcast has featured several different germanium transistors over the years, and many others have been used in reproductions. The germanium transistor I use may vary batch to batch, but I have used all of the following in this circuit and all work very well: OC71, TG5S, 2N527, 2N404A, AC128
The silicon transistor is an NOS Motorola 2N4033, rumored to be used in the Broadcast AP. A bit higher gain than the germanium, with more chime and excellent breakup as gain is increased.
The first stage transistor is an NOS Micro Semi BC549C.
Voltage:
Should only be used with a 9V center negative DC power supply. It has an internal charge pump to boost the voltage internally for the selectable 18V and 27V. Select higher voltages for more headroom and output.
Note: the silicon transistor doesn't like higher voltages. It will not work at 27V and at 18V it oscillates at higher gain, which actually sounds kind of cool, so feel free to experiment with that. Update: I found that using the 2N4037 transistor retains the characteristics of the 2N4033, but allows operation at 27V up to a point. at 27V, oscillation starts a bit after 12 o’clock on the Gain. But again, you can definitely get some interesting sounds with the oscillation.
Tone:
The low cut control is a staple of the Broadcast, but the Transmit 2 also includes the most requested feature for the circuit: a high cut control. Especially useful at high volume for cutting down the peaks to optimum levels.
Also included are selectable ranges for the cuts, normal and maximum.
Output transformer:
I decided to use the Hammond 142A in the Transmit 2. It features the same specs as the Triad and OEP transformers used before, but to my ears they seem to hold the low end a bit better.
Trim Pots:
There are two internal trimpots to adjust the gain range of each channel. I set the low (left side trimmer) to slightly less than the middle and the high slightly above. These can be adjusted to suit your taste.
All other components used are premium, including Lumberg DC jack, Alpha pots, 105C electrolytics, 1/2W carbon film resistors, and SBP enclosures.
The Transmit 2 is the ultimate version of the Broadcast, combining features from the 24V Dual and the AP, with additional features and options.
Transistors:
The original Broadcast has featured several different germanium transistors over the years, and many others have been used in reproductions. The germanium transistor I use may vary batch to batch, but I have used all of the following in this circuit and all work very well: OC71, TG5S, 2N527, 2N404A, AC128
The silicon transistor is an NOS Motorola 2N4033, rumored to be used in the Broadcast AP. A bit higher gain than the germanium, with more chime and excellent breakup as gain is increased.
The first stage transistor is an NOS Micro Semi BC549C.
Voltage:
Should only be used with a 9V center negative DC power supply. It has an internal charge pump to boost the voltage internally for the selectable 18V and 27V. Select higher voltages for more headroom and output.
Note: the silicon transistor doesn't like higher voltages. It will not work at 27V and at 18V it oscillates at higher gain, which actually sounds kind of cool, so feel free to experiment with that. Update: I found that using the 2N4037 transistor retains the characteristics of the 2N4033, but allows operation at 27V up to a point. at 27V, oscillation starts a bit after 12 o’clock on the Gain. But again, you can definitely get some interesting sounds with the oscillation.
Tone:
The low cut control is a staple of the Broadcast, but the Transmit 2 also includes the most requested feature for the circuit: a high cut control. Especially useful at high volume for cutting down the peaks to optimum levels.
Also included are selectable ranges for the cuts, normal and maximum.
Output transformer:
I decided to use the Hammond 142A in the Transmit 2. It features the same specs as the Triad and OEP transformers used before, but to my ears they seem to hold the low end a bit better.
Trim Pots:
There are two internal trimpots to adjust the gain range of each channel. I set the low (left side trimmer) to slightly less than the middle and the high slightly above. These can be adjusted to suit your taste.
All other components used are premium, including Lumberg DC jack, Alpha pots, 105C electrolytics, 1/2W carbon film resistors, and SBP enclosures.
The Transmit 2 is the ultimate version of the Broadcast, combining features from the 24V Dual and the AP, with additional features and options.
Transistors:
The original Broadcast has featured several different germanium transistors over the years, and many others have been used in reproductions. The germanium transistor I use may vary batch to batch, but I have used all of the following in this circuit and all work very well: OC71, TG5S, 2N527, 2N404A, AC128
The silicon transistor is an NOS Motorola 2N4033, rumored to be used in the Broadcast AP. A bit higher gain than the germanium, with more chime and excellent breakup as gain is increased.
The first stage transistor is an NOS Micro Semi BC549C.
Voltage:
Should only be used with a 9V center negative DC power supply. It has an internal charge pump to boost the voltage internally for the selectable 18V and 27V. Select higher voltages for more headroom and output.
Note: the silicon transistor doesn't like higher voltages. It will not work at 27V and at 18V it oscillates at higher gain, which actually sounds kind of cool, so feel free to experiment with that. Update: I found that using the 2N4037 transistor retains the characteristics of the 2N4033, but allows operation at 27V up to a point. at 27V, oscillation starts a bit after 12 o’clock on the Gain. But again, you can definitely get some interesting sounds with the oscillation.
Tone:
The low cut control is a staple of the Broadcast, but the Transmit 2 also includes the most requested feature for the circuit: a high cut control. Especially useful at high volume for cutting down the peaks to optimum levels.
Also included are selectable ranges for the cuts, normal and maximum.
Output transformer:
I decided to use the Hammond 142A in the Transmit 2. It features the same specs as the Triad and OEP transformers used before, but to my ears they seem to hold the low end a bit better.
Trim Pots:
There are two internal trimpots to adjust the gain range of each channel. I set the low (left side trimmer) to slightly less than the middle and the high slightly above. These can be adjusted to suit your taste.
All other components used are premium, including Lumberg DC jack, Alpha pots, 105C electrolytics, 1/2W carbon film resistors, and SBP enclosures.