Uploaded March 2015 | Updated September 2026, 17 hours ago
Don't matter who you are, working on an amplifier with the back cover off is very dangerous. Please only attempt this if you are competent and have knowlege of electical equipment. As a favour for a friend, I was asked to repair this Bird Talisman amplifier. I thought I would make a youtube movie out of it because it might be of use to someone else having a similar problem. The Talisman is Bird's answer, as stated on the Net, to Selmer's Little Giant, Clubman and amplifiers having a similar output and valve line-up. As may be heard, when I try to play a 'power chord' from a connected guitar, the amp responds to the loudness peaks only. This infers faulty bias conditions in the active components. As it is a direct coupled, also known as DC coupled, design it is likely that one or two of the resistors has gone high. (they don't usually go low)
It is possible to obtain a greater level of fidelity using DC coupling but a huge amount of current from the mains PSU is dissipated as heat in the EL84 cathode resistor of 560 ohms. 32 volts across 560ohm = 58mA. 32 x 58mA = about 1.9 watt. When the engineers designed this amplifier, they certainly weren't thinking about energy efficiency! They probably chose this design resulting from copyright issues of amplifiers such as the Selmer Little Giant and Watkins Clubman. In these latter examples the EL84 cathode resistor dissipation is less than 0.4W.
Don't matter who you are, working on an amplifier with the back cover off is very dangerous. Please only attempt this if you are competent and have knowlege of electical equipment. As a favour for a friend, I was asked to repair this Bird Talisman amplifier. I thought I would make a youtube movie out of it because it might be of use to someone else having a similar problem. The Talisman is Bird's answer, as stated on the Net, to Selmer's Little Giant, Clubman and amplifiers having a similar output and valve line-up. As may be heard, when I try to play a 'power chord' from a connected guitar, the amp responds to the loudness peaks only. This infers faulty bias conditions in the active components. As it is a direct coupled, also known as DC coupled, design it is likely that one or two of the resistors has gone high. (they don't usually go low)
It is possible to obtain a greater level of fidelity using DC coupling but a huge amount of current from the mains PSU is dissipated as heat in the EL84 cathode resistor of 560 ohms. 32 volts across 560ohm = 58mA. 32 x 58mA = about 1.9 watt. When the engineers designed this amplifier, they certainly weren't thinking about energy efficiency! They probably chose this design resulting from copyright issues of amplifiers such as the Selmer Little Giant and Watkins Clubman. In these latter examples the EL84 cathode resistor dissipation is less than 0.4W.
