Rickresource Rickenbacker Forum

I have a mystery transformer bolted to the inside of my M-3, which drops the Australian mains voltage down from 240V(RMS) to around 195V(RMS), before it powers the input transformer of the valve amp. The voltage was measured with my new RMS digital voltmeter, which consistently displayed about 236V(RMS) from the power point, showing that it's functioning as it should.

The M-3 is a 1960 234V/50Hz 'export' model as confirmed by the specs listed on the serial number plate, and additionally with the "234V 50/60Hz" stamped on the amplifier chassis.

The mystery transformer looks original to the organ - It's old, rusty and uses Bakelite plugs, which have not been legal in this country for many years. It was assumed that the amplifier was a regular US 117V model, with a step-down transformer for Australian mains power. We theorised the "234V" chassis stamp and serial plate were correct if the mystery transformer was considered an integral part of the organ's power supply. That said, an organ expert in the UK said he'd never seen a step-down transformer in a 220/240V Hammond as all the organs he'd seen had dedicated 220/240V amplifiers installed at the Hammond factory.

Now that I have taken the voltage measurements, I believe that the amplifier is a genuine "234V" amp (as the stamp suggests), but now can't work out what the mystery step down transformer is doing. I'm fairly sure 195V into a 117V appliance would fry things fairly quickly, yet 195V into an amp that is expecting 240V would certainly run things a little cold. I'm really tempted to bypass the mystery transformer and just plug 240V straight into the amp and see what happens. Any suggestions?

For those of you who are saying "Why would you want to mess with something that currently works?", the reason is because I am adding a reverb amplifier and a Leslie connector to the organ, and the mystery transformer sits right where the new reverb amp needs to sit. Otherwise I'd just leave it as it is...

I just worked out the obvious way to determine whether the mystery transformer is necessary, and can't believe I didn't think of this earlier. I've been missing the most important aspect of this problem the whole time -

The voltages in the mystery transformer, and the primary voltage in the amplifier's mains transformer don't matter squat. The only thing that matters is the secondary voltages in the amplifier's mains transformer. As long as the heaters get +3V / -3V, and the rectifier gets 5V on one side and +320V / -320V on the other side, then nothing else matters.

If the secondary voltages on the amp's mains transformer are found to be approximately 20% less than they are supposed to be, then the mystery transformer will get ripped out.

If the secondary voltages on the amp's mains transformer are found to be spot on, then the mystery transformer will unfortunately have to remain.

Does anybody know what kind of voltage tolerances such an amp should be able to handle? Say for instance, the heaters get 8V, and the rectifier gets 6.5V/400V, or conversely, if it runs cold at 5V, 4V/270V what kind of effect would this have on the performance and safety of the amp?

Greg and some others know more than I do about this, but I'll pipe up here. I think that 8V is considerably more than you want 6.3V heaters to work at. I know a little less about the over voltage to the rectifiers, but my guess is that you really want to hit within about a 10% range. I think you want to knock down voltages if they are higher.

At which point they become functional, tubes will last longer under voltage than over voltage on the heaters.

I have no idea what that mystery transformer is doing in there.

In the US, the line voltage is more like 125v instead of the 110 or 115v that it was in the 60's, and that affects all of the voltages inside the amp, which often read high. If your filament voltage is really high, then it can cause problems with less tube life, but the only way you can really fix that is to change transformers, put more current load on that line by adding a tube or lamp for example, or use a variac rated for the full current daw of the whole organ.

I'd suggest to search google if you haven't already for sites and forums specializing in Hammond organs and see if anyone at one of those could possibly have some info.

Greg