issue with Hammond CV

[Basil McJagger]

Hello,
I have a Hammond CV. It has sat rather dormant for a few years (less than 10). When I turn it on it sounds really great - at first. After about 15 minutes there is a noticeable decline in volume and a bit of distortion. It just gets quieter and more distorted the longer it's on.

I purchased a new tube set hoping that would fix the problem, but it didn't.

After reading a few threads here, I feel like it may be a capacitor issue. I have read all the many warnings, and so I know to be cautious with this. How do I test to be sure that's what the problem is? And if that IS what it is, what's my first move? Specifically which caps should I change out first?

Also, if you have a favorite method for discharging caps (or a link to your favorite method), I'm all ears.

Thanks!

[muckelroy]

Well first of all, if it's a stock CV, you have to be using it with a tone cabinet. What type of tone cabinet are you using? Did you put new tubes into the organ preamp only, or the tone cabinet as well?

Provide as much details about the setup as possible (tone cabinets? Leslie in use? Dedicated B+ power supply? Non-stock preamp?)

[sfp1954]

All the electrolytic caps in both the CV preamp and whatever tone cabinet you are using should be replaced.
Lifetime of such devices is usually rated at 20 years.
The electrolytic fluid in the caps has probably all dried up or leaked out.
They absorb enough moisture from the air to function for a few minutes - but as soon as they warm up they dry out and fail.
I doubt you'll have much to worry about with the caps, if they aren't holding a charge with power on they probably won't have much of a charge with power off.
But check them with a volt meter to see if they do have a charge just to be safe.

To discharge one all you need is a low value resistor and a pair of wires with alligator clips or probes on the ends.
You can also use a standard light bulb.

http://forum.allaboutcircuits.com/th...pacitor.39002/

[Wes]

There are five caps in the CV preamp that are paper/foil. One electrolytic and paper/foil in the rheostat box (going by memory). None of these will likely cause your issue. There is a .5uF in the amp also, big oil block, almost certainly still good.

I would start by looking at your DC power supply, probably in the tine cabinet..

[Basil McJagger]

In 2001 I took the CV to Vintage Hammond of Houston. They installed a Trek II percussion and wired it with two 1/4" outputs.

It came with a DR20 tone cabinet and a D20 tone cabinet. One never worked right, and the other caught on fire a few years ago... I use a Leslie 760 and a Leslie 147 interchangeably with the organ. I use the 1/4" outputs from the organ and combo pre-amp pedals for the Leslies. The organ does the same thing with both speakers - but I've used my digital Hammond SK1 with both speakers and no problem. That's why I think the problem is in the CV.

[enor]

In other words, you have an added-on separate B+ power supply unit in your organ. This is the unit to troubleshoot first, not the amp!

[David Anderson]

All the electrolytic caps in both the CV preamp and whatever tone cabinet you are using should be replaced.

Number of electrolytic capacitors in CV preamps = Zero.

[Basil McJagger]

In other words, you have an added-on separate B+ power supply unit in your organ. This is the unit to troubleshoot first, not the amp!

Ok.
Is this the added-on B+ power supply?



The power transformer had a lot of white powder on the outside of it. What goes bad in this? It looks like an older reverb amplifier or some such. Would I be ahead just to replace the whole thing with a new B+ power supply?

[Wes]

That's indeed a reverb amp, but it could easily be made to work as a B+ power supply. The white powder is oxidization, and of no concern. This explains a lot, actually -- why your organ has symptoms of an old power supply, but a recent "upgrade".

I can't guarantee your problem is that amp, but I'd guess 95% chance that it is. You can probably recoup most of the cost of a new B+ supply by selling that guy on eBay.

My CV had an antique Northern Electric amp as a B+ supply....I sold the amp for more than I paid for the organ. :D

Wes

[Wes]

PS - you should be able to test that supply with a simple DC voltmeter. Make sure it can handle at least 400V. There are GND and B+ terminals on your CV's preamp....don't touch B+ with your finger, you will get the shock of your life!!!

[muckelroy]

Hmm. I've got a spare AO-35. The necklace reverb unit is garbage, so I might repair the AO-35 and make it into a B+ supply for my CV eventually.

Nice option if I don't find any other use for the AO-35.

[Wes]

I would be happy to build you a B+ supply in exchange for your broken AO-35, and pick up shipping both ways. Provided the transformers and chassis are good.

Wes

[Basil McJagger]

I could just remove it and replace it with one of these, right?

[Wes]

Yep, those are good

[Basil McJagger]

I installed the new power supply and voila! everything works as it should.

Thanks Organ Forum - for your patience and assistance. Much appreciated!