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47
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Ceriatone / Overtone / 100k
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on: May 20, 2008, 03:38:34 PM
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Well, time for some major tweaking. I totally redid all the cathode, plate and grid values to match the Dumble values. Here is the latest schematic. Soundclips to follow.
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48
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Ceriatone / Overtone / Re: possible bias issues
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on: May 20, 2008, 12:35:03 AM
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???So, should i lower the current or raise it? Is it running to hot at the moment or not?
Your bias voltage is a negative voltage and it 'slows down' your tubes bias current. If I understand correctly, you are getting too much bias voltage. Raising the 1.2k resistor will lower your range of bias voltage and allow you to make your tubes run in the usual range 30-35ma or so. If the highest you can get your bias current is 25ma then your tubes are running cold. |
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49
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Ceriatone / Overtone / Re: possible bias issues
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on: May 19, 2008, 01:09:25 PM
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Its a JJ 6L6GC, and i am sure the valve can hhandle the extra current, its just the amp doesnt provide that extra current, the bias pot is maxed!
There are two resistors that alter the range of the bias adjustment. Your bias voltage is too high; lowering it will make your tubes run hotter. There may be a 1.2K 1W resistor on the rectifier board that can be raised (3.3K is the Dumble value here). There is also a resistor that bleeds the bias voltage to ground. There may be a 15K resistor there. The Dumble value for that one would be 27k. Not sure why he changed the bias circuit, but it may have to do with giving people the range to run EL34s. |
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51
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Ceriatone / Overtone / Re: Ceriatone cleans
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on: May 11, 2008, 02:44:11 PM
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I have substituted a spectrum of values for the screen resistor in many Fender and home made amps. If anything I would recommend going to a higher value; maybe as high as 5k for the screens, this seems to yield a more grainy sounding texture. Higher value screen resistors also tend to protect the output transformer to some extent in case of tube failure. As always; the proof is in what you like to hear and how you want to sound , so experimentation will yield the "correct" configuration for the individual player.
I agree with you on these points. I have 1.5k screens on my ODS and am frequently consider going from 470 to a higher number on Fenders. |
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52
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Ceriatone / Overtone / Re: Special Overtone Project
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on: May 06, 2008, 02:36:04 PM
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What an incredible sounding build! You do amazing work!
Do you have a layout or something that shows what you did to make the 100 watt version?
How did you wired up the 50/100 switch, the standby switch and, the 2 resistors to 'lift' the heater voltage from ground?
When you write that you strictly adhered to Dumble's grounding scheme and lead dress. What exactly does a builder do to emulate his technique?
Are the transformers you used the Hammond 100 watt 125A29A & 022889?
Those sounds are so sweet!
I have a schematic that shows everything! It shows how the 50/100 switch is wired and exactly where it is grounded. The schematic shows all the grounding points. Lead dress was copied exactly from the #124 pictures on the internet. To make it easier I tried to copy the wire colors also (but did not have enough of some of the colors, though) Lets see if the schematic will post... |
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53
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Ceriatone / Overtone / Re: Tweaked Layout
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on: May 06, 2008, 02:26:35 PM
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Good work jzucker on the layout.
One question. What about the 10k trimmer for the PI. #124 and the original Overtone had 5k. Should this be in RED also? And the 100k Level pot (from 250k)?
Yes, I'll have to double check mine. I guess it depends on which version you have. Mine already had the 100k level so I didn't see a change. Mine still has a 10k trimmer. I don't know about that one. I'll ask ayan. Ok, so it looks like those were changes to the Overtone Niki already put into production. Maybe those could be annotated on the layout for those with the original, older versions that want to upgrade. Not to complicate things, but it looks like Niki may have given you a layout file that did not incorporate his update to the way the switches in the back were wired. #124 used slide switches, but the Overtone uses toggles, and the pins on the toggle are "opposite" the throw of the lever. |
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54
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Ceriatone / Overtone / Re: Tweaked Layout
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on: May 05, 2008, 03:49:26 PM
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Good work jzucker on the layout.
One question. What about the 10k trimmer for the PI. #124 and the original Overtone had 5k. Should this be in RED also? And the 100k Level pot (from 250k)?
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55
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Ceriatone / Overtone / Re: Special Overtone Project
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on: May 01, 2008, 05:42:00 PM
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I don't have a dedicated speaker for the Dumble yet. I have been using the speakers in the various combos I have. Currently my favorite is a Celestion Modern Lead 70 that happens to be in a Sundown 50w Combo. My second choice (of the speakers available to me) is a 4x10 Alnico set that resides in a Mesa Blue Angel combo. I have Celestion vintage 30s in a 2x12 combo and in a 2x12 closed back Mesa cabinet. Neither sounds real good with the Dumble. So, I'm still looking for the best speaker...
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57
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Ceriatone / Overtone / Re: My OT build
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on: April 28, 2008, 02:14:44 PM
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I was not sure of the measurements on the original, but I used 1/8 inch by 3/4 inch aluminum with counter sunk screws for mine and it looks very close. I see what you mean about the cutout, my cabinet does not have it correct. I don't have a wood working area, so I just did some mods to Nik's Ceriatone cabinet.  Here is a closeup of a real Dumble for comparison:  |
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58
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Ceriatone / Overtone / Re: My OT build
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on: April 28, 2008, 11:38:09 AM
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Cabinet looks nice, though it is styled after a later model Dumble. Here is a collage I put together to show the different chassis and cabinets Dumble used.  |
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59
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Ceriatone / Overtone / Re: Special Overtone Project
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on: April 27, 2008, 05:46:28 PM
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One thing I forgot to mention. I am using an output transformer with a single 4-ohm tap and I am running this into an 8-ohm speaker or cabinet. From what I can tell, lot of 100w Dumbles were used this way.
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60
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Ceriatone / Overtone / Re: Special Overtone Project
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on: April 25, 2008, 09:42:30 PM
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I cannot really say. The tube I chose that allowed me to get a perfect DC balance may have just been a better sounding tube (irrespective of its 'balance'). There is not enough range of the balance trimmer to really get my tube 'out of balance' enough to hear any difference to easily compare.
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to keep the forums alive.