Paramour 1 with various upgrades - zero voltage on 12AT7 [resolved]

[Paul Birkeland]

What AC voltage do you see across the speaker posts? 

Your amp gain still seems a little low to me, but these test are still helpful.

[patrickamory]

2.5 VAC across the speaker terminals.

[Paul Birkeland]

2.5V at the speaker terminals is just under 1W into 8 ohms.  This is audible.  There is a decent chance that you amp is working fine but you have a cable issue.

[patrickamory]

I was thinking that too, but I switched both the interconnects and the speaker cables (testing each combo separately) to the other Paramour and they work fine. Both speakers are fine (the good Paramour was driving the left and is now driving the right), as are the channels from the preamp.

I thought it might be the jacks in the problem Paramour, but I measure continuity between the center and the outside of the RCA jack and the connections underneath. Same for each speaker binding post.

I'm stumped!

[Paul Birkeland]

It could be something that's moving when you flip the amp over.  I've had this happen before, it can be pretty tedious to figure it out!  (It's also one of the reasons that we now put so many tie down points in our amps)

[patrickamory]

Do you think it could have something to do with the big Auricap, which has come loose from its doublestick tape that fastened it to the inside of the wood frame?

I'm going to try hooking up the amp again while it's on its side (which is how I have it while I'm measuring), tomorrow.

Thanks for all your help Paul - it's really appreciated!

[Paul Birkeland]

It sure could big.  Big caps loose in an amp will bump into things.

[patrickamory]

So I hooked up the amp while still on its side. I used the same interconnect and speaker cables from the good amp to be sure. Everything glowed, no music.

I disconnected the speaker cables and measured across the binding posts - got 0.5 VAC. Would you expect a voltage this low to emit no sound whatsoever (including hum) ?

Re-hooked up the good amp and no problem.

Sounds like I should just secure the Auricap and reheat all the joints?

[Paul Joppa]

0.5 volts rms should be quite audible; it's around 45dB louder than the hum.

Why did you get 2.5v at first, and now 0.5v?

[patrickamory]

Hi Paul J - I measured 2.5 VAC on the work bench, the phone hooked up playing a 60 Hz tone, with the amp on its side.

Per Paul B's recommendation, I carefully hooked it up in the system, playing actual music, with no output, not even noise or hum.

Unplugged the speaker cables and inserted the multimeter leads, and measured 0.5 VAC.

What should I do next? The other amp works perfectly on the same interconnects and cables.

Thanks!
Patrick

[Paul Birkeland]

With the amp on its side, use your phone to play 60Hz into the amp and see what's coming out at the binding posts.

[patrickamory]

Hi Paul B,

Just did that. With the 60 Hz tone on the input and the amp on its side, I measure 2.667 VAC across the binding posts.

Thanks
Patrick

[Paul Birkeland]

Yeah, I bet the Auricap is tugging itself loose when you flip the amp over to run it. 

[patrickamory]

But the 0.5V I measured while hooked up to the system should still have been audible in some way, per Paul J?

I will re-secure the Auricap and re-heat the solder joins, but it feels like there must be something else going on... for no signal/sound whatsoever through the speakers despite the VAC on the binding posts?

[Paul Joppa]

AS I recall, you've measured an output with speakers disconnected, and heard nothing (but not measured the voltage) with them connected. That suggests a mechanical problem with the speaker terminals and/or wires.

Or - here's an exotic one - if you measure an AC voltage but hear nothing, and you know the speaker is working, the amp might be oscillating at an ultrasonic frequency.