Paramour 1 - 27 mv hum problem

[patrickamory]

Oh right - I completely spaced on that 

So I have installed the new caps and am reading -2VDC at terminal 5 and 15. Resistance check shows open at terminals 1, 2 and 4.

Did I fry the diodes?

[Paul Birkeland]

You'll have to be a bit more generic with your voltage values; I have no idea where my Paramour 1 manual is at the moment and I don't have an electronic copy.

If you have -2V coming out of the positive side of your rectifiers, then there's a problem (blown fuse?).  As always, posting photos can be helpful.

-PB

[patrickamory]

Hi Paul -

Sorry for the vagueness.

The fuse is intact.

Attached are photos of the voltage readings page of the manual, and a photo of terminal strip 1-5. I did move one of the diodes from the top to the bottom hole of terminal 5 because it was getting a bit crowded on top.

Thanks,
Patrick

[Paul Birkeland]

If a diode body shorts the two terminals where the capacitor connects, you will get no voltage out of the rectifier bridge or full wave rectifier and you will damage your power transformer (though the fuse should pop first).

[patrickamory]

So it sounds like I have an open connection somewhere... will check tomorrow, thanks Paul.

Patrick

[Paul Birkeland]

No, I think you have a short between two adjacent terminals.  It looks like those two terminals where that capacitor is in your photo are connected together.

[patrickamory]

Hi Paul -

I don't think so? Please see more detailed photos attached.

I read increasing and decreasing megaohms between the two terminals which I'm assuming is the effect of the capacitor.

Please let me know what I'm missing...

Thanks,
Patrick

[Paul Birkeland]

That last angle does show separation.

You can measure the AC voltage between brown and purple to ensure that the power transformer is still delivering the goods.

[patrickamory]

Hi Paul,

I measure 642VAC across brown and purple. So the PT is alive?

I should have mentioned that both tubes glow, and the C4S diodes light up.

Thanks again,
Patrick

[Paul Birkeland]

the C4S diodes light up.

Then your high voltage DC rail is operational. 

[patrickamory]

Thanks Paul - I just measured VDC at 5 and 15 now and they are fine.

Hooked up the amp and the hum is almost inaudible (the gain is slightly less too - but only slightly actually the gain is much lower).

So on to the next unit now - hopefully replacing the filter caps has solved the problem! Thank you once again for all the help.

[patrickamory]

Now I've done the other amp, voltages all check out correct, but I'm getting a tiny, distorted signal.

I did replace the binding posts - I'm guessing there's a poor connection there if all voltages are on point? Will try reheating tomorrow.

Getting there.

[patrickamory]

Second amp is putting out a very low, distorted signal. I read 0.19 VAC on a 60 Hz test tone, input jack shorted. I switched both tubes - same result. Voltages all check out as do resistance readings.

Solder joints for the 3 replaced caps all seem fine.

Any suggestions on what to check next?

(The good news is that the hum is down to 2.6 mV.)

[Paul Birkeland]

You can play the 60Hz test tone, then measure the AC voltage at the RCA jack, at pin 3 of the 4 pin socket, and at the speaker binding posts, then report those readings here.

[patrickamory]

Hi Paul,

Here are the readings at those points with the 60 Hertz test tone, plus T25 (where the positive end of the parafeed cap connects to the blue wire from the OPT):

- RCA jack: 0.03 VAC
- A3: 11-13 VAC
- Binding posts: 0.08-0.10 VAC
- T25: 17 VAC

Thanks again,
Patrick