TEMPO II AMP IN 403

Hello, my question, is it ok to plug a tempo 2 amp into a 403 jukebox to test. are voltage and plug the same or will it cause damage?

thank you, nick.

Hello Nick

I think, the voltages will fit, but I am not sure, if the power plug will fit. The Tempo 2 amp has a 5-pin plug. If I remember right, the 403 has only 4-pin. if you only want to test the amplifier, you may temporarily connect the power supply to the amplifier with 4 test leads. There are two independent circuits, one for the filament voltage (6.3 VAC) and one for the high voltage (about 150VAC).

The mute switch doesn't need to be connected for the test.

The speaker connection will probably not fit. I would recommend to connect two external speakers. The speakers must be connected to terminals MAIN LEFT and RIGHT. The selector switch next to the terminals will be set to STEREO. Operation without a speaker can damage the amplifier. In this way you prevent a further problem. The Tempo2 - amplifier needs an anti-phase input signal for proper operation of the internal (mono) speakers. For stereo operation, it is not necessary.

Finally, I would like to point out the high voltages (close to 400 VDC) in the amplifier. You should only work on the amplifier if you have the necessary knowledge and experience.

Best regards - charly49

hi charly and thanks. it was the input voltages i was concerned about. i will double check and pay close attention to the input/output before i power on.
it seems to be a small problem with the amp but i am having trouble tracking it down. there is unwanted 'vibrato' within the overall sound. other than that, the amp is good and strong. could be a valve problem but that would be an expensive guess to swap them all out!

thanks again

Hello Nick

It is difficult, to evaluate the "vibrato" without hearing it. The internal speakers are connected to both channels in a bridge circuit. Thus, you could not hear, whether it affects both channels or only one. With separate external speakers you can hear it. If both channels are affected, it is obvious that the fault lies in the power supply. You should observe the operating voltage with an oscilloscope. To the DC voltage on the electrolytic capacitors may almost no low-frequency voltage or oscillation be superimposed. If only one channel is affected, you can swap the tubes of the two channels. If the error occurs after that on the other channel, a tube is the cause.

If you do not have the necessary equipment and knowledge, you should give the amplifier to a specialist for repair.

Best regards - charly49

hi charly, point taken. i read up on the phase inversion part of this amp....unusual and i was thinking along the lines of the 60's record players that were mono but had carts stereo wired. i see now this is very different with a stereo ouput inverted to mono. i think i will wait until i have the original box to check it out further. many thanks for your help