Ampeg VT-40, has no sound...

[69toronado69]

i recently acquired a 1971 ampeg vt40, the guy i got it from said that it smoked or smelt bad or something, but would amplify a guitar fine. i took it home, fired it up and it made a loud hum. my dad who's an old jazz rock keyboardist (who used a vt-40 for a rhodes) insisted that it was no good and had me proceed with taking it apart and cleaning the tube contacts.

I noticed a master volume that was soldered into the main boards inside. could that have roasted the amp?

anyway, we cleaned the contacts and made her look nice then put it all back together. when we then attempted to fire it up again, it made no noise, and does not register a signal from an instrument or any frequency...so that was a waste of money...

dad said to replace the power tubes as they were microphonic. i bought two matched JJ 7027A's and the damn thing still wont make noise. before i pay $150 to have an amp guy 'look' at my amp, i was wondering if any of you guys might know what is wrong.

Thanks much, Sean Murphy

[rf7]

I noticed a master volume that was soldered into the main boards inside. could that have roasted the amp?

Maybe, maybe not; anything is possible. Are any components touching that shouldn't be touching?

Are all of the tubes lit up? Do the power and standby lights come on? Is your speaker cabinet working?

There is usually an external amp out connector on the back panel of the amp. If you run that out to another amp, do you get any output? If so, then your preamp is working.

Is there any noise at all coming out of the speaker cabinet, like hum or hiss?

Can you swap in new preamp tubes?

Take a look at Geofex for more help.

Your amp guy could probably knock this out in an hour, if you're lucky,but that would cost money. It could just be a bad preamp tube, or it could be a multitude of things and that could get costly. Those are 40 year old amps after all.

[69toronado69]

hey, so yeah, i think ill run the pre out into my acoustic head and see if i get a signal. im pretty sure its the power amp section. the tubes in the pre amp section fire up just like they should, i cleaned them all, polished the contacts and windexed the tubes themselves. i used contact cleaner on everything and it seems like nothing in the inside is fried. would youy say that the interface between the power and pre amp is roasted? im convinced that its the power transformer that has melted due to having fried tubes in it for the past 20 years...

hope to hear back,
sean

[techineer]

You should hope it's not the power transformer. Those are expensive and probably not available for that amp.

If it has an effects loop or Preamp Out/PA in jacks, try plugging a guitar into the Return jack or PA IN jack. See if you get anything in the output. If so, the PA is fine.

As 'rf7' suggested, you can also try connecting a cable from the SEND or Pre-Out jack to the input of another amp. Plug a guitar into the VT40 input and see if it plays through the other amp. If so, the preamp is good.

If neither of these work, it's probably time to head to your local amp tech. With 500 volts or so at high current floating around inside it, these things can kill you if you don't know exactly what you are doing. Even with the power off, charged filter caps can knock you across the room.

[69toronado69]

[QUOTE=techineer;112015]You should hope it's not the power transformer. Those are expensive and probably not available for that amp.

Do you know what a transformer for the vt-40 might cost, im fairly certain its the transformer.
sean

[Dave Curtis, dB AudioTech]

Do you know what a transformer for the vt-40 might cost, im fairly certain its the transformer.
sean

What makes you fairly certain?

Did you try sending signal to another amp? If it's marked like my VT22, it'll say "Ext Amp" next to a pair of jacks.

[rf7]

Do you know what a transformer for the vt-40 might cost, im fairly certain its the transformer.
sean

Around $150 from Fliptops.

Are you getting all of the correct voltages at the tubes?

So which transformer are you certain is bad? There is 2 of them in there.

Just because the tubes light up and you cleaned all of the contacts, does not mean that those tubes are working.

Just because there is no sound coming out of your amp, does not automatically mean a transformer is bad. If you spend $150 on a new transformer, and the amp still does not work, then what are you going to do?

[69toronado69]

well. the ext out, shows a slight signal, im unsure of which transformer, but their is reason to believe that one is fried as the tubes are all lighting well and their is no other evidence of any other damaged components... does anyone know any good tube amp shops (fair priced) in or near seattle?

[Dave Curtis, dB AudioTech]

Mike Schway has a shop in Musician's Center in Bellingham. Tell him Dave Curtis sent you.

[Enzo]

That is not much evidence. Tubes lighting up tells you one thing and one thing only - the tubes are getting heater power. Doesn;t tell you anything about high voltage supply - which I suspect you no longer have.

Your transformers are WAAAAY down the list of suspect parts.

Did you remove that master volume you were concerned about? After mentioning that was when your problem came up. Perhaps it was not properly removed - you'd have to restore the old circuit.

A wire could have broken off the board somewhere.

Bad parts usually don;t look any different from good parts. You can spot burnt things, but a simple open resistor can look fine yet stop the whole show.