JMI AC30/6 NO SOUND

[Travis8]

Hi, my JMI AC30/6 turn on, everythin is working but it doesn´t make any sound, no hum no hiss (Nothing!)

Some recommendation about how to check where is the problem??

Thanks.

[xtian]

Google is your friend:

https://robrobinette.com/Tube_Guitar_Am ... ooting.htm

[Stevem]

If it was working the last time you played it and turned it off then the chances are really good that a output tube blew on you when you fired it back up, and that took out the amps internal DC power supply fuse.

[Travis8]

Thanks, How can I check if tubes are un good conditions?

I build and repair some amps but I'm still learning

[Stevem]

If you have another amp there look into the output tubes when you take it off standby and into play mode, you will see a blueish white flash as the tubes get there needed DC power.

If this does not happen to any of the 4 output tubes in the Vox then DC supply is open .

You can further check with a voltmeter by hooking it up to pin 1 or 6 of any of the preamp tubes.

With that check you should read at least 90 volts DC on any of those pins.

Can you post up a schematic of this model Vox for us?

[Travis8]

It´s like this one http://www.pisotones.com/Alfonso/JMI/JMI_30-6.htm

So I must read pin 1 or 6 of preamp tubes?

Thank you guy

[pdf64]

Vintage Vox don’t got no stinking standby

If there’s no hiss / hum, it’s probably most expedient to check pins 1&6 of the LTP phase splitter V2, at ghe far end, below the tone control.

Are you sure that the speakers are connected?

[Travis8]

Yes, speakers are connected. I will check pins 1 and 6 of V2 today!


Thanks again

[Travis8]

Vintage Vox don’t got no stinking standby

If there’s no hiss / hum, it’s probably most expedient to check pins 1&6 of the LTP phase splitter V2, at ghe far end, below the tone control.

Are you sure that the speakers are connected?

this one??



http://www.pisotones.com/Alfonso/JMI/3493.jpg

[pdf64]

Yes, speakers are connected…

Are you sure they’re good?
It would be regrettable to wreck an OT due to a failed speaker being assumed to be ok.

[pdf64]

this one??



http://www.pisotones.com/Alfonso/JMI/3493.jpg

No, that’s the top boost valve / circuit.

AC30/6 schematic https://el34world.com/charts/Schematics ... 301960.pdf

[Travis8]

Yes, speakers are connected…

Are you sure they’re good?
It would be regrettable to wreck an OT due to a failed speaker being assumed to be ok.

I try some cabinets and also with Torpedo Captor

[Travis8]

0.685 on pin 1
0.740 on pin 6

[Travis8]

All 12AX7 same values around 0.7

[pdf64]

So have you got any decent HT voltage anywhere in the preamp chassis? eg on the big filter caps.