roy d Posted September 28, 2004 Share Posted September 28, 2004 some months back I raised some questions here about my silverface champ... well, the project has moved along a bit. I replaced the guts with a new board from ceriatone, built a new cab for use with a 12, and loaded it with an alnico Weber Blue Dog. Boy does it sound great and the dog isn't even broken in yet. I still may do the heater mod to get rid of that class A hum although it sounds so good I'm afraid to touch anything. moving to the 12 speaker really makes the amp come alive and is a worthwhile consideration for anyone who loves their champ. The old cab is tucked away in the rafters should I ever decide to sell the amp... NOT! Roy http://www.soundclick.com/bands/8/alexisdmusic.htm "once it stops bein' a mystery it stops bein' true" David Mowaljarlai - Ngarinyin Aboriginal Elder Link to comment Share on other sites More sharing options...
Caevan O’Shite Posted September 28, 2004 Share Posted September 28, 2004 Cool! Glad to hear that you like the way it sounds 'n' all! By "heater mod", do you mean converting the heater filiment supply to operate on DC instead of AC? That will reduce 60-cycle (and threabouts) hum, and improve the sound somewhat as you won't be playing against as much 'out-of-tune', 'flat-Bb' hum. But, any of the things endemic to Class-A operation, particularly that power-supply "ripple", "ghost-note" effect, will still be a part of the whole Class-A thing. Ask yourself- What Would Ren and Stimpy Do? ~ Caevan James-Michael Miller-O'Shite ~ _ ___ _ Leprechaun, Esquire _ ___ _ Link to comment Share on other sites More sharing options...
Big Red 67 Posted September 28, 2004 Share Posted September 28, 2004 Try a Hum-X first. That way it isn't a mod since you like the sound! Big Red's Ride Blog Link to comment Share on other sites More sharing options...
Caevan O’Shite Posted September 29, 2004 Share Posted September 29, 2004 Originally posted by Big Red 67: Try a Hum-X first. That way it isn't a mod since you like the sound!Just so y'know, switching the heater-filiment supply from AC to DC won't change the signal path or gain or power-supply sag or anything like that on an amp; it really won't change the tone at all. What it does is change the current that heats-up the heater-filiments in the tubes- the part that lights up, and warms the tube so that it will work- from AC, which can and does induce extra hum and noise, to DC, which will make the amp much quieter. A true design upgrade! It does need to be done neatly and correctly, though, with particular respect paid to the polarity of the wiring. Any time that someone changes the types of output-tubes in an amp, or adds an extra "preamp" tube for anything, I think that this should be done, along with particular attention paid to the new current-draw requirements, up to adding another small transformer to handle the heater-filiment supply. Often, I guess, this is ignored! Ask yourself- What Would Ren and Stimpy Do? ~ Caevan James-Michael Miller-O'Shite ~ _ ___ _ Leprechaun, Esquire _ ___ _ Link to comment Share on other sites More sharing options...
roy d Posted September 30, 2004 Author Share Posted September 30, 2004 Caevan, I'm not sure exactly what the mod does... (I only follow simple directions and do them carefully). It involves adding two 100 ohm resitors and running new wires from the heaters of each of the tubes to the power light (obviously more complicated than that). Big Red 67, it isn't a ground loop hum so the hum-x wouldn't do anything or even the hum that comes from an unshielded guitar. It is there even when nothing is plugged into the amp. Myles commented that it is typical for a class A design and wasn't concerned about it when he heard my amp some time ago. roy Roy http://www.soundclick.com/bands/8/alexisdmusic.htm "once it stops bein' a mystery it stops bein' true" David Mowaljarlai - Ngarinyin Aboriginal Elder Link to comment Share on other sites More sharing options...
Chipotle Posted September 30, 2004 Share Posted September 30, 2004 Originally posted by roy d: Caevan, I'm not sure exactly what the mod does... (I only follow simple directions and do them carefully). It involves adding two 100 ohm resitors and running new wires from the heaters of each of the tubes to the power light (obviously more complicated than that). The two 100 ohm resisitors form an artificial center tap to the power transformer's heater winding. If your amp has a center tap on the heater connected to ground, you don't need these resistors. Some of the cheaper Fenders would just use the chassis to carry one half of the heater voltage. If your champ was wired that way, you should really rewire the heaters. There will be a big difference! Caevan's talking about building a DC supply for the heaters, which also helps with hum (as opposed to the hiss), but requires some fiddling to get the voltages correct. It's probably overkill on a champ. Do you have any pictures of the reworked champ? Link to comment Share on other sites More sharing options...
roy d Posted September 30, 2004 Author Share Posted September 30, 2004 Chipolte, I have some photos... but no place to post them... sorry sounds like one of these days I'll need to do the mod. roy Roy http://www.soundclick.com/bands/8/alexisdmusic.htm "once it stops bein' a mystery it stops bein' true" David Mowaljarlai - Ngarinyin Aboriginal Elder Link to comment Share on other sites More sharing options...
Caevan O’Shite Posted September 30, 2004 Share Posted September 30, 2004 Originally posted by Chipotle: "The two 100 ohm resisitors form an artificial center tap to the power transformer's heater winding. If your amp has a center tap on the heater connected to ground, you don't need these resistors. Some of the cheaper Fenders would just use the chassis to carry one half of the heater voltage. If your champ was wired that way, you should really rewire the heaters. There will be a big difference!"Thanks for the clarification! 'I did not know that!' That sounds like good info to stash away... Ask yourself- What Would Ren and Stimpy Do? ~ Caevan James-Michael Miller-O'Shite ~ _ ___ _ Leprechaun, Esquire _ ___ _ Link to comment Share on other sites More sharing options...
Philip OKeefe Posted October 1, 2004 Share Posted October 1, 2004 I did DC heater mods to both my Fender Super Champ and my Princeton Reverb II... it did seem to knock down a watt or so from the output, but the reduction in hum was well worth it to me, since I use them primarily for recording purposes. It's a fairly easy mod - just a single cap and a bridge rectifier. I THINK the instructions can be found in the Aspen Pittman Tube Amp book. The reduction in hum and noise was so obvious that I am able to run the amps sans negative feedback (yup, I added a switch to each amp to let me kill that too) and they're still quieter than they were stock. I'll check my Tube Amp book later and see if the schematic is in there or not. Link to comment Share on other sites More sharing options...
Philip OKeefe Posted October 1, 2004 Share Posted October 1, 2004 Well, I don't see the bridge rectifier / capacitor circuit mod in the Groove Tubes Tube Amp book (4th Edition) but I did see a tip that I want to pass along - if your old Fender amp "spits," pops and crackles (background noises), try replacing all of the 1/2 watt 100K Ohm resistors in the preamp circuit(s). That usually cures those problems. Here\'s a link to a PDF with the instructions for the DC heater mod on a Pignose tube amp... the concept is fairly simple - just a bridge rectifier and a cap or two. The instructions won't exactly apply to other amps, and as always with tube amps, if you don't know what you're doing in there, STAY OUT! There are very high voltages in tube amps - even after they've been unplugged - the filter caps can store hundreds of volts for quite a while after you unplug the amp. When in doubt, always refer the servicing to a qualified tech - any good tech should know how to do this simple mod and it shouldn't cost very much to have it done. Link to comment Share on other sites More sharing options...
Caevan O’Shite Posted October 1, 2004 Share Posted October 1, 2004 Originally posted by Philip O'Keefe: "...if your old Fender amp "spits," pops and crackles (background noises), try replacing all of the 1/2 watt 100K Ohm resistors in the preamp circuit(s). That usually cures those problems.Ah, yes! The cure for 'blackface bacon-sizzle'. Done that, it works. And, yes, Mr. O'Keefe's cautions are well founded. Ask yourself- What Would Ren and Stimpy Do? ~ Caevan James-Michael Miller-O'Shite ~ _ ___ _ Leprechaun, Esquire _ ___ _ Link to comment Share on other sites More sharing options...
Philip OKeefe Posted October 1, 2004 Share Posted October 1, 2004 I've done it a few times myself... works great for silverfaces too... I even did it (along with all the other resistors and caps) on my Super Champ and Princeton II with good results. It probably was most effective for me on an old '67 Bassman head and a 65 Bandmaster that I used to own - those amps were monsters - but a lot more than I want or need volume- wise these days. Link to comment Share on other sites More sharing options...
roy d Posted October 1, 2004 Author Share Posted October 1, 2004 the directions for the heater mod can be found: http://www1.korksoft.com/~schem/mods/champvibrochamp_heater_wiring_mod.pdf roy Roy http://www.soundclick.com/bands/8/alexisdmusic.htm "once it stops bein' a mystery it stops bein' true" David Mowaljarlai - Ngarinyin Aboriginal Elder Link to comment Share on other sites More sharing options...
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