Help - SPL Goldmike with no input/output sound

[doma2001]

Hi, I hope someone can advise me. I have recently acquired an SPL Goldmike (9844). I can't get an input signal to show up at all.
It powers up fine and all LEDs light up including the VU display. However, neither channel shows any indication that an input signal is there at all.

The mic (48v used) and lead are tested to be working fine.

If the tubes are dead would this result in 100% no audio?
I can't see any tube glow but I assume they don't glow much anyway.
I understand the 9844 in an integrated circuit design with the tube simply adding 6bd of gain but would this still allow audio to pass through if the tubes were both dead?

Happy to source and replace the tubes if this is the problem so advice on how to match them also appreciated.

 

[rob aylestone]

The tubes are an amplifier - so in the unlikely event they are dead, then they are dead - and there won't be any output. Tubes would die by heater filament failure, and an instant stop, or they'd become microphonic and sensitive to vibration of just distort nastily until death.

 

[doma2001]

Thanks for reply, so if the tubes are dead no sound, ok.

Why do you say in the unlikely event they are dead?

 

[TekTrax]

Rule of Thumb... if you can see the glow of the filaments, most likely you have power supply problems.
If you don't see a glow of the filaments, and I mean all the tube filaments... you might have a power transformer problem.
The filament glow but no audio is most times, an easier fix than replacing a power transformer because of the filament side opened up.
I've seen it both ways including a dead tube filament which is rare.
Do you know of a tech locally that can troubleshoot tube circuits without a diagram?