Come and go percussion on my B3

[B3 Fever]

After start up there is no percussion on my B3. Its been a while (8 mos) since I've played it but the percussion worked fine then. I've worked all the percussion rockers to no avail. After some time (about an hour) the percussion comes back but cuts out again after varying time periods. It seems this could be a bad tube or going bad? If so, I don't know which one to replace as I don't have a tester and neither do the drug stores anymore ha ha. Where would you start if you where me? I don't have much knowledge with electronics and do not own any testing meters etc. All other features work i.e. chorus, vibrato, drawbars, and presets.

Thanks in advance...Rich

[Goff]

Just a guess, did you check the two 6C4 tubes V5-V6 and the 12AU7 at V7?
After that if it's not the rocker switches grounding out on the metal cover case, check the percussion transformers under the chassis in the AO-28. Has the AO-28 been overhauled yet?

There could also be whiskers (Dendrites) growing on the metal parts where using a battery to nuke them is the usual fix. Depends on where you live and the atmospheric conditions that grow these zinc whiskers.


AO-28 preamp tubes, every B3 owner owes it to have spares and good quality ones at that.

[robb3]

Which transformers on the AO28 are the percussion transformers? I've got an AO28 that works great for vibrato and non-vibrato channels, but I don't get touch percussion. I can hear a very faint signal that doesn't decay of the chosen harmonic when activated, but no decay and very, very soft. Might it be a transformer? I tried this AO28 in another Hammond where touch percussion works, and same issue, so I'm thinking its something in the pre-amp and not whiskers.

[Goff]

Which transformers on the AO28 are the percussion transformers?

From Geo's site it will be T4, T5, T6.


You would best resort to the transformers after checking your percussion tubes first, rocker switches shorting.

Have you fresh tubes for these to swap in to see if it solves it?

If not, you should have those on hand.

Owning a B3 comes with caveats. You need back up parts on hand to use as test solutions.

[B3 Fever]

Thanks for responding Goff. Most of the tubes are still labeled Hammond, so this is suspicious. One by one I removed each tube, brushed Deoxit on the pins, and worked it in and out of the socket a few times. The percussion worked after a cold start up but I doubt I eradicated the problem. A friend of a friend told me to try doing this, and is bringing a tube tester over next week. Regardless, I agree it's a good idea to have backups. The preamp hasn't been overhauled. When you mentioned quality tubes, are some better than others? Can anyone recommend (if allowed) where to have an overhaul done, tube brand, and site to purchase a set.

Thanks...Rich

[KC9UDX]

Don't replace good tubes. Determine they are bad before replacing them. Friend of a friend sounds like he knows what he's doing; let him test the tubes.

Do you always get percussion after a cold start? I don't know much about the B3, but this sounds like an open grid leak to me, I'd suspect that first. Bad tube second.

[Goff]

Thanks for responding Goff. Most of the tubes are still labeled Hammond, so this is suspicious. One by one I removed each tube, brushed Deoxit on the pins, and worked it in and out of the socket a few times. The percussion worked after a cold start up but I doubt I eradicated the problem. A friend of a friend told me to try doing this, and is bringing a tube tester over next week. Regardless, I agree it's a good idea to have backups. The preamp hasn't been overhauled. When you mentioned quality tubes, are some better than others? Can anyone recommend (if allowed) where to have an overhaul done, tube brand, and site to purchase a set.

Thanks...Rich

Rich, it would depend on what type of tube tester your friend has. If it's an "emissions only" tester you won't really find out much. This is why if you had fresh tubes and it doesn't necessarily mean those made yesterday, it could be better quality NOS vintage tubes, or even working used spares, then you could swap the tubes instead of just cleaning the pins on the ones you have in there to see if it's the tube acting up. As it is said, the best tube tester is the preamp/amp, the device using the tube itself.

Good testers cost and the better ones test for a myriad of maladies.

I had an issue with a 6x4 and it had the Hammond label on it. Pulled the tube out and cleaned it, same story, no sound, rotors on fast. Swapped in a fresh NOS JAN 6x4 and the organ came back.

Below is Tubeworld samples. I show you this because this site lists made in USA tubes instead of those made recently in Russia which some Hammond supply dealers sell.

Read the descriptions below carefully. Some of the tubes might say "used" and the rest NOS. The NOS normally come in original boxes unless otherwise noted.

https://tubeworldexpress.com//collections/preamp/6C4

https://tubeworldexpress.com/search?q=12au7

There are other sellers of course but a better tube to me is a vintage NOS tube.

When it comes to the AO-28 preamp, best not to cut corners IMO.

The 6C4's would be NOS JAN (joint army navy) that sellers bought up from the millions of tubes the military stocked.

Usually Hammond parts sellers sell the JAN 6C4 usually Sylvania or Philips, sometimes GE.

But if you want all original made tubes for all tubes in the AO-28, a seller like Tubeworld will have them. Best to get each tube listed on the AO-28, specially the 6x4, the 12BH7. Otherwise you'll be back to square one when a tube goes out, and you without backups.

There are many guys who do quality work. It would depend on where you are, if you don't happen to have a good tech in your city or maybe you lean towards a certain Ham tech.

The Piano Organ Depot looks to be in PA. 570 area code.

You mentioned that you swapped the AO-28 into another organ and the same story, so perhaps the problem is really in your preamp. Many get these rebuilt as a matter of course.

Keep in mind owning a B3 is more and more becoming a rich man's instrument like owning a vintage sports car.

If the AO-28 is not the problem then you'd need to ship the whole organ to a tech if they can't come to your house.

[B3 Fever]

Thanks for the suggestions and help guys! Looks like it was Robb3 that swapped organs to test the preamp. There is a boxed 6X4 taped to the inside cabinet which I presume the original owner has done for some reason. I am the second owner for 20 years now. The good news is after almost three hours of play time the percussion hasn't cut out. KC9, the percussion wouldn't work after a cold start. I would just keep it on and it eventually would work a while, fade a while, and repeat that behavior. I've been playing Hammond simulators for months and thought they nailed the sound, until I fired up the beast that is!

[KC9UDX]

Then it sounds like you have a bad capacitor or a bad tube. Testing or substituting tubes is the first thing to do. If that doesn't result in a fix, then you've got a bad capacitor to change.

[Goff]

been playing Hammond simulators for months and thought they nailed the sound, until I fired up the beast that is!

Yup, happens all the time, just when you thought it was safe to come out from under that rock!

Don't forget those tube sockets. You can get these, dental floss and use some contact cleaner and brush those socket tabs.


I would still order a complete set of tubes for the preamp. Order extra 6x4's as those are known to go out more than the rest.

And tubes like the 6C4, 6x4, 6AU6, 12BH7 are not common tubes.

But there are substitutes under different number systems, mil-spec types of the same tube. Yet still not common tubes like the 12AX7.

The better 6x4 is the GEC CV4005 made in England. These are rectifier tubes.


My bad on the mix up Robb and Rich!:P

[B3 Fever]

You rock Goff! Thanks for your help...Rich

[Wes]

Start by swapping 6C4s around: do the symptoms change?