I'm about to drive a stake thru the heart of my Aikido linestage

[BillEpstein]

Actually, I'll just dismantle and re-build the snake-bit blankety-blank thing

It was fabulous (oh, what bass and clarity!) from first start-up but always had a smidge of left channel hum I couldn't chase.

Then I needed the Hammond 373BX for another project so swapped in a Heyboer power tranny at 30 volts less B+ and lost a little bass but the 3 amp Heyboer permitted a 5U4 which worked out well. Hum still there.

Most recently the PEC pot became noisy and the channel-to-channel tracking went to hell.

Swapped the PEC for a 23 step attenuator which is awesome in the Simple SE. Once fully warmed up, the music now momentarily fades out and back in every few minutes.

Nothing left to do but destroy it!

[Andrewbee]

Before you terminate it, did you compare the voltages between both channels and even before that did you try swapping the tubes ?

[athos56]

We have the technology, to rebuild it, stronger, better!

[Andrewbee]

We have the technology, to rebuild it, stronger, better!

LOL

I built an all 12SN7 Aikido and it really is very clear and for me noise free. My only issue is excessive gain which I knew would be an issue for me but thats what voltage dividers are for.

With one side being noisy the first thing I would do is swap tubes around and then consider layout (actually layout would be the first thing), e.g. is one side of the circuit close to a PT or AC wires?

I assume (never a good thing I know) that he is using one of J.B.'s boards so the ground for both channels is shared on the board so I doubt its there.

If its none of the above then perhaps an incorrect value component hence my original suggestion re voltages.

Maybe a cold solder joint.

If the music fades in and out I would look at my power supply and see if its "pumping"

[BillEpstein]

I assume (never a good thing I know) that he is using one of J.B.'s boards so the ground for both channels is shared on the board so I doubt its there.

If its none of the above then perhaps an incorrect value component hence my original suggestion re voltages

Quite right about the grounds which are identical from both boards with 1 channel being silent so it's not that.

Prior to installing the attenuator the voltages were all equal within 1% on each of the 2 octal, mono boards. I haven't measured since installing the attenuator, but...

I don't know what 'power supply pumping' means. The supply is tube rectified with a 47uF to 6H coil to 100uF with the requisite voltage divider.

I had the boards out once to re-solder and check all values and used the occasion of swapping the power transformers to move it out of the box, take the power switch from the fron to the back and move the rectifier as far from the boards as it would go.

I'm used to building, finding the occasional stoopid mistake and then listening. This sort of tomfoolery has me reaching for the hammer

In the meantime, theres much worse things than what my little passive box with the Taiwanese attenuator and Mountain rotary switch offer as a pre-amp. I do miss the weight of the Aikido, tho'.

[Andrewbee]

Okay,


How about switching channels on the acutator to see if the problem follows along to the other channel?

Are the input wires shielded and following the same route?

Input jacks. Is the noisy channel input jack properly installed and insulated from the chassis?
Any stray wires perhaps from the input signal wire (if its stranded wire) making contact with the chassis?
Did you check the input jack to make sure there is no continuity between signal and ground? Sometimes there may be a stray strand of wire or overheating of the jack may have melted the insulation which creates an issue.

Pumping meaning the power supply coming up to voltage and then discharging in a repetitive cycle. More likely to happen with an LC supply with incorrect resistor to size the current draw.

[BillEpstein]

Originally posted by Andrewbee

Pumping meaning the power supply coming up to voltage and then discharging in a repetitive cycle. More likely to happen with an LC supply with incorrect resistor to size the current draw.

Nothing changed in the power supply between the time it worked perfectly, except for the bit of hum, and the new attenuator was installed. Once installed, the left channel hum continued as before, then, after about 20 minutes, this 'pumping' began.

At any rate, this Nosferatu ( I've re-named it as it has sucked the enjoyment out of the music) pre-amp is totally stripped from the chassis and laying in pieces on the bench.

Sgt. Bilko would be pleased!