20-09-2022, 04:51 PM
Hello All,
I have a well worn Ekco PTP301 1966 vintage 6-transistor radio that I'm working on. It's back in operation and, seemingly, working quite well, but the quiescent current is at odds with the value quoted on ERT Service Chart 1620. This quotes 6 mA, but I'm seeing nearly double at 11.6 mA after thermal stabilisation. The line up is:
2SA73 mixer-oscillator
2SA49 1st IF
2SA53 2nd IF
2SB54 driver
2x2SB56 output pair
All are germanium PNP
My measurements indicate 3.9 mA taken by the first four transistors, approx. 1.45 mA in the output pair biasing network and the rest (just over 6mA) though the output pair.
3.88 mA for mixer, IF amps and driver doesn't seem unreasonable to me, and the 1.45 mA in the biasing network is non-negotiable. My question is, therefore, whether the output pair quiescent current is excessive/worth bothering about or if it's within reasonable bounds of component variation.
Any suggestions?
I have a well worn Ekco PTP301 1966 vintage 6-transistor radio that I'm working on. It's back in operation and, seemingly, working quite well, but the quiescent current is at odds with the value quoted on ERT Service Chart 1620. This quotes 6 mA, but I'm seeing nearly double at 11.6 mA after thermal stabilisation. The line up is:
2SA73 mixer-oscillator
2SA49 1st IF
2SA53 2nd IF
2SB54 driver
2x2SB56 output pair
All are germanium PNP
My measurements indicate 3.9 mA taken by the first four transistors, approx. 1.45 mA in the output pair biasing network and the rest (just over 6mA) though the output pair.
3.88 mA for mixer, IF amps and driver doesn't seem unreasonable to me, and the 1.45 mA in the biasing network is non-negotiable. My question is, therefore, whether the output pair quiescent current is excessive/worth bothering about or if it's within reasonable bounds of component variation.
Any suggestions?
My name is Steve, but I answer to most things like "Oi, you!".
