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

[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.

 

[patrickamory]

Hi guys,

I just had another thought. I have a little DPST switch in there just before the binding posts, to switch between transformer windings (4 ohm and 8 ohm).

I just measured continuity across the switch terminals and the binding posts and I'm seeing continuity between both poles and the center terminal, and the binding posts, in either switch position. Surely one set of windings should be closed off depending on switch position?

Does this imply that the switch might be fried? If so, should I try bypassing it? And if so (million dollar question), how do I figure out which OPT wires represent which speaker impedance? My speakers are 16-ohm Valencias.

Thanks for the continuing help and advice.

 

[patrickamory]

Amazingly, I was able to dig up my spec sheet for the upgraded OPT (attached).

I'm going to take the switch out of service and connect directly to the 16-ohm (yellow) secondary.

 

[Paul Birkeland]

The 0-4-8-16 ohm winding is a continuous piece of wire with very low DCR.  Regardless of the switch position (unless it has a center "OFF" position), you're going to read lots of shorts between everything.

 

[patrickamory]

PROBLEM SOLVED.

With the switch out of the system and the binding post connected to the 8-ohm wire, I read 6 VAC across the speaker terminals.

Hooked the amp up, and music.

Thanks for your help, everyone.

 

[patrickamory]

Btw... they sound absolutely killer. Garrard 301, Shindo Masseto, Valencia drivers in custom cabinets with original crossovers.

My Cortese is headed back to Japan for service. The Paramours aren't as quiet, but otherwise are completely holding their own in the system.