HELP! - did i damage my AMP - AMI continental 1

Hello,

I am working for two months on my AMI Conti 1 - managed to get it running and amazing !

I did the last job today - adding an original Volume Remote Control unit (from Ebay)
apparently what happened is that i plugged a 13.5 Ohms potentiometer instead of the original 5.5 Ohms.
(it was suppose to be identical, numbers on the unit... mono potentiometer....)

now i dont hear the music any more, some hmm (regular) amp sound does come and the volume does control it, but no music.

I need some help here as to what is the damage ? any test to perform before dismantling the AMP???

any help here would be highly appreciated

eitan

Eitan,
Like I wrote on the other thread--
I doubt you have done any "damage"--It would almost be impossible to damage this with a volume control, as all the amp does is look for a varying resistance ?
Check your connections--sounds as if one or more is open/shorted--
Remove the volume control wires from the AMP. Measure them at that point--have someone turn the control for you if you can't reach it. I'll bet you do not get any movement in the reading----which will tell you if the wires are shorted, or open--Ron Rich

This control is supposed to be 5K-ohms as in 5000 ohms. 13 Ohms won't harm anything -but you won't get sound from such a low load.

Put the connections back as per normal with the internal volume control and you'll have sound again.

Rob

yes 5k ohms. and i used a 13.5k ohms potentiometer.

i did measure the potentiometer after replacing back the 13.5 with the original 5.5.

i get get good reading from the potentiometer ...

i will try again to check all that can be checked

eitan

This looks real wrong
I cannot figure out what happened
the potentiometer is giving the right reading - as before
some hmm volume noise (as usual) is there and the potentiometer does increase/decrease it (with some nice static noises) but no music
it looks like the needle terminal is not connected (but it is)

any ideas ?

can i disconnect the preamp plug from the amp to see if it makes a difference - as i suspect the preamp if at fault because the terminals for the volume are located at the pre-amp?

can i use the input inlet (how) to test the amp?

should start thinking of taking the AMP out ?, are there any other tests to perform ?

eitan

Hו
looking for solution i found one post with same problem
(he ended replacing a tube)

so one suggested tapping on the tubes with a pencil eraser. When doing so nothing happened for me but tapping on the can capacitor of the preamp would make indeed heavy static noises.

i guess this is not normal ? any other test that can be done before i take away the AMP?
eitan

Eitan, if you are certain that you have connected the volume control correctly, you can try replacing the preamp tubes one at a time.

This amp is 55 years old and if it has not been rebuilt in at least the last 25 years it is way over due. it can be patched up but you will be often dealing with cruddy little problems like this and there is always the danger of a major failure that takes out one of the transformers. It likely won't perform as well as it could if rebuilt.

Rob

Thanks for responding Rob

1. is there a way to test the tubes, i.e. if they lit does it says they are ok, or can it be that a lit tube is faulty ?

2. if all the tubes lit does it say that the transformer is ok ?

3. do you know what can be plugged into the input socket at the main AMP in order to test it, I do suspect the preamp is malfunctioning

Sure the best thing is to rebuild the AMP, unfortunately Israel has very few people who knows tube AMPs, jukeboxes never got here... and my AMI Continental is the sole one in Israel - i will do my best to find an expert, but chances are low, very low

eitan

Hi Eitan,
The fact that tubes are lit is irrelevant, as for the quality of the tube. The only indication of a bad tube, is one that is not lit !
The only "test" for them is to use a GOOD "tube tester", then use the tube in a circuit--as it may still be bad.
As Rob said--that's a fairly simple amp, and anyone with any experience on tube equipment, should be able to check/repair it. Ron Rich

Eitan, Ron covered most of your questions here, but if you have a decent 12AX7 it can be subbed for any tube in the preamp as well as the driver in the power section.

If you want to plug in an external source to test the power amp -just use the other RCA plug on the power amp. Any volume control connected to the machine will affect the test so it is best to disconnect it from the 3 terminals. The test source you use needs to have some sort of volume control, otherwise it will be too loud and might damage the speakers. An IPod or phone will be fine.

Rob

Thanks Rob,
I have spare 12AU7 (not 12AX7)
for the purpose of the test can i use 12AU7 in place of the 12AX7 ? or just the opposite?
eitan

The 12AU7 will work well enough for test.

Rob

Rob, Ron
please forgive me being an amateur
i just used my spare 12AU7 and instead one of the preamp 12AX7
I have music again
stopped it immediately - i will get a proper 12AX7
yes those are old machines and mine didnt work for so many years (more than 20)
it came back alive because of your help ...
so thank you for all your patience
no one else to consult here ... no where to buy replacement tubes (or proper oil)
so i will dance again soon
thanks!
eitan

Eitan,
Glad you found the problem--you might try the "bad 12AX-7" in another position, if there is more then one, as sometimes the tube socket will not make good contact with a tube ?? Ron Rich

this was an easy one
even managed to buy one already in the local guitar store...
its not RCA or nice quality (eastern europe "JJ") but for me its super now
just you advice - is there much difference in sound between different tubes brands?
i guess there is but not sure how dramatic it is and also regarding those specific 12ax7 - are those the most important ones re sound?
eitan