Noisy A100

[Drawbar Dave]

I look after a few Hammonds for professional players and visited a studio yesterday to service their A100. A couple of years ago I recapped all three amps when they had just acquired the organ. It has a 26-1 kit. I noticed yesterday that when the organs built in speakers were making a wind noisy (meteorological not gastrointestinal) when the swell pedal was on full tilt. This only seemed to affect the two dry speakers and not the reverb speaker. Is this normal behaviour or could I look at the ceramic disc capacitors or resistors? The organ is a 1968 and sounds fantastic when playing. I ave heard a similar noise to this on one of my Farfisa Compact Duos when I had a bad germanium transistor in the mixer board.

I cleaned all of the tube sockets and they don’t make any noise when wiggled and I also checked all connections were solid on the wiring.

[Sweet Pete]

Is the reverb amp the A044? There is a transistor in there. I once had to replace the transistor in one that had 'wind' noise.
Most difficult part was finding a germanium type replacement.

[David Anderson]

Wind noise is most likely a noisy tube or carbon composition resistor.

[Drawbar Dave]

Thanks guys, that gives me some direction. And yes Pete it’s got an AO44. Luckily I know someone with a warehouse full of tubes and germanium transistors!

[Sweet Pete]

On the one I replaced,the emitter read 0%.Changed a 1.2meg resistor too IIRC.
Have had a few 'tornados' between the 'verb tank and the AO44 over the years.
Maybe a solder reflow would have brought back emissions?I'll never know....
Can never get 'all' the scratchiness out of the verb dial either.
They are old with a few 'worn' or dirty spots.
I call it 'character',producers and engineers call it 'noise'.
,

[David Anderson]

Just curious as to why we're discussing germanium transistors when the Dave stated that he was hearing this noise from the main speakers and not from the reverb speaker. That it apparently tracks with the expression pedal suggests it's in the first half of the preamp. Or am I misreading?

That said, it wouldn't be hard to replace a germanium transistor with silicon in an AO-44. The earlier Ge and later Si circuits are almost identical. Silicon/germanium differences are occasionally critical, but not here.

[Drawbar Dave]

You read correctly David. However I have been asked to help fix another A100 after Christmas that has totally dead reverb so Pete’s experience might help. This ones a 1968 model so should have an AO44 as well?

[Wes]

Make sure you order a couple of spare #12 lamps to have on hand before you start troubleshooting that AO44.

[Drawbar Dave]

I will! And a transistor too. It’s a 2 hour drive to that studio in London for me so I am trying to take everything i can think of just in case!

[Jaim]

AO44 - if the amp is dead. I've seen a shorted ECL86/6GW8 fry the wire from the rectifier to the first filter section. Also the 1K 1W resistor can burn out.

Jim

[tpappano]

Make sure you order a couple of spare #12 lamps to have on hand before you start troubleshooting that AO44.

My reverb was completely "dead", the main problem was the sockets for the little lamps were corroded. Some contact cleaner and removal-reinsertion of the lamps fixed it. The RCA plugs and jacks were pretty nasty, too.

[David Anderson]

Make sure you order a couple of spare #12 lamps to have on hand before you start troubleshooting that AO44.

And spare RCA cables to and from the reverb tank in case the grey originals have opened up inside. Not sure if they used the same cables in the UK.

[Drawbar Dave]

Yes! Good call. I have a few hifi phono leads for this and yes we have the same grey cables over here.

[jgarner812]

Just curious as to why we're discussing germanium transistors when the Dave stated that he was hearing this noise from the main speakers and not from the reverb speaker. That it apparently tracks with the expression pedal suggests it's in the first half of the preamp. Or am I misreading?

That said, it wouldn't be hard to replace a germanium transistor with silicon in an AO-44. The earlier Ge and later Si circuits are almost identical. Silicon/germanium differences are occasionally critical, but not here.

It has two amplifiers. There is a reverb amplifier with one speaker and there is the regular amplifier for the other two speakers. If both reverb and regular had noise, yes, Id' look in the pre amp. But since the main speakers are the only ones making the noise, Id start in the regular amplifier. First, check for bad or loose wires and maybe a bad ground or cold solder joint going to or from the main amp.

[David Anderson]

It has two amplifiers. There is a reverb amplifier with one speaker and there is the regular amplifier for the other two speakers. If both reverb and regular had noise, yes, Id' look in the pre amp. But since the main speakers are the only ones making the noise, Id start in the regular amplifier. First, check for bad or loose wires and maybe a bad ground or cold solder joint going to or from the main amp.

Thanks for letting me know an A100 has two amplifiers. I never would have known that otherwise.

On that topic, the A100's reverb tank is driven by the AO-39 power amp, so any noise at output of the AO-39 will be sent to the reverb tank; however, it might be noise mostly outside the frequency response range of the tank or may be filtered at the input of the reverb amp.

That it tracks with the expression pedal indicates that the noise source is upstream of the expression capacitor.