M Fowler wrote:What I don't understand about these Hammond organ transformers is how the hell does a small OT like that put out such good power and tone?
The apparent small size of the output is due to the comparatively large power trans which carries a heavy filament current requirement.
My RD50 also has a visibly small OT. It plays plenty loud, but not the cleanest low end at volume.
M Fowler wrote:What I don't understand about these Hammond organ transformers is how the hell does a small OT like that put out such good power and tone?
The apparent small size of the output is due to the comparatively large power trans which carries a heavy filament current requirement.
My RD50 also has a visibly small OT. It plays plenty loud, but not the cleanest low end at volume.
rd
I have an 18 watt amp built by Doug Roccaforte. The disparity between PT and OT is just like what you guys are discussing. The amp has a fair amount of headroom, but to look at that tiny OT......
I should post some pics I guess.
For a 2 x 6V6 amp that OT looks plenty big and well made too. Some of the best sounding 6V6 amps like Tweed Deluxe, the Princeton series, Deluxe Reverb etc... have OT's that size and smaller.
If the distortion is being generated by the tubes (6V6's do break up easily esp. at lower voltages and with the sag of a 5U4) changing your OT won't do a thing except remove money from your wallet...
This chassis is made of the same material old Hammond chassis are, so it was hard to drill through. So it is strong. I didn't think it was that good when I first received it about 6 or 7 months ago off ebay.
I like the amp better with 5ar4 rectifier and 6L6's go figure huh, never was a 6V6 guy.
Looks great Mark!
On the Hammond amp I got the OT was small as well but it used a field coil speaker so I don't know if that changes anything other than it is used for the choke in the power supply.
I didn't try using the OT and rather used another I had laying around.
FWIW, the OT in an older Hammond will drive a modern speaker just fine.
The problem is that the speaker field coil gets power from the center tap on the PT secondary. Both that and the negative end of the first filter cap (weird) are grounded through it (plus that circuit supplies some oddball negative voltages to the rest of the organ). So if the field coil is gone and you float the CT, or ground it, the power supply will be unhappy either way.
The elegant solution is to substitute a choke for the coil. A power resistor with a heat sink works too.
Sorry to hijack, but I learned all this recently while restoring an M3 and needed to share.
Philoffline no problem not hijacking at all. In the past I built the Gibson EH150 which originally was field coil speaker as well and on my new build I used a schematic from a book noting the use of a choke to replace the field coil in these old circuits.