eniam rognab wrote:still wondering about choke coupling, is this an issue?
Possibly! I had a 50-watt built with PT and OT placed about four inches apart, and the choke between. I had the OT hooked up to headphones. I found that placement of the choke DID affect the level of hum out of the OT--because of its ability to bend the magnetic field, I suppose.
So check out choke placement using the headphone trick. Though I have no idea whether this affects output hum under operating conditions.
I build and repair tube amps. http://amps.monkeymatic.com
eniam rognab wrote:xtian, was the choke energized during the test? do i need it energized?
xtian might be fixing his strap button so I'll jump in, hope it's OK.
Interesting question. I'm sure the choke position would make a difference in how much hum the OT "hears" from the PT. BUT it will be used in its energized state, and because of that the choke will emit its own hum field, probably a lot smaller than the PT but still a noise contributor. It's the sum of the PT and choke fields you need to minimize in the OT. So clap on those cans, fire up your amp with the choke loose and find a prime spot to sock it down.
As a safety consideration, remember chokes have a voltage rating and it's often ignored. Even if you're within the safe rating, might be super safe to slide that choke around with some chopsticks or similar. If there's any current leakage you don't want to find out the hard way.
well i am working kind of off the Malou rocket as far as choke placement and i went ahead and bit the bullet. i figure: mount the OT where there is 0 read on the meter and the choke is far enough away and the emitted juju is weaker than a (leo insert something tasteful here please)
something about mountains and molehills and i dont wanna be that guy that is all like crazy and rambling about some shit that dont matter
so here we go guys and gals! next stop tyoooobs!
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Wow this thread has all kinds of great advice and examples already. Thanks to all for contributing. Phil, can you share why you don't like the zener (or the resistor drop) idea? Because "it isn't necessary" is what I got from your examples (which would indeed be best). Or is it the heat generated. Change in tonality/response? All of the above...
Passfan I saw that build in the for sale section and it's a really great build. My issue is, I built a Wreck Express, and even with the 28 watts of 6v6 in it now, it's still so freakin' loud I have to back the LarMar style master to 2/3 in the clubs we play - and it's a bit sizzly fizzly there. I was hoping to try an 18 watter full up or close (without an MV). And I don't play quiet...people were plugging their ears last Sat. on some of the high harmonic pinches...heheh.
Xtian, I have to hand it to you for a creative approach. I don't think re-using the "umbilical" ever crossed my mind but that's really good.
Looks like the kid (Rognam) is going to beat me to the finish line....but that's OK, slow and steady and like Preset, I gotta make it with small dollars so I'm not going to rush and buy parts I'm not necessarily needing. Next step is get it to a power switch and take actual volt readings.
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Be sure your tinfoil hat has a good low impedance ground.
I've always wanted to do something with an AO-43 but just never found one cheap enough. I've converted a couple other Hammond reverb amps though. Here are the links...
donzoid wrote:Very cool Steve. How many watts does the PeeWee get you? I would guess it sounds really good with the deluxe front end.
I never even calculated or measured the power. It sounds a lot like a Princeton or Deluxe, but breaks up sooner. That could be because of the original tubes in it. Those little dudes are more expensive than the entire amp!
OK I powered up the PT with a 5u4 on it, and "unburdened" it's measuring at 358 on pin 8 (B+ raw).
Turns out the choke on this chassis was used for the reverb loop, and schematic says it has 250VDC B+ for the 12BH7 and about 140mA of capacity. Unless smarter (than me) folks on here say otherwise, I am not thinking that is enough to place right at the B+ but I will look around here maybe I have others that can handle more. In any case Phil_S was right, it's not as high as I thought it would be even with the 120vac we have now as supply. So that's encouraging because it won't have to get "clamped" as hard to bring it down a little.
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Be sure your tinfoil hat has a good low impedance ground.
I built a Plexi6V6 from a Hammond AO-29, used the Hammond iron and chassis and it came out terrific! Put it in a Line6 1x12 cabinet and it's now my go-to amp for "Marshall-y" sounds.
I have another AO-29 here and my next project is a full-featured low-power portable amp in a smaller cabinet. I'm inclined to build a Princeton Reverb front end and a Vibro Champ back end, separated by a DC-coupled cathode follower like the one in the heart of the Plexi. Here's the circuit:
I just worked on a blackface tremolux, and the transformer set was at least similar. The plate volts for the original set were 432 at pin 6...(but this one was 6L6). If it's cathode bias you can probably get into the same neighborhood with some tweaking looks like most of the people who are re-purposing these are using 6v6 with great results.
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Be sure your tinfoil hat has a good low impedance ground.
I have one other Hammond conversion that may be of interest. It's a stand-alone true pitch shifting vibrato unit rather than a guitar amp, so mods please delete this post if it doesn't fit the thread.
I used a Hammond AO-41 Vibrato module for this project. Here's the link...
