mister ed
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I love tube amps
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« Reply #50 on: August 23, 2008, 02:18:18 pm » |
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I tried this on my cathode-biased AB763/reverb.... 560 ohm resistor/25@50 cap on each 6L6, ( 2 6L6s' )... I found that this mod DID drop the output, but in a way that made it sound thinner. The tone was not the same. The effect is like switching-out pre-amp bypass caps. Possibly I'm missing something ?
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rzenc
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TUBES RULE
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« Reply #51 on: August 23, 2008, 06:16:04 pm » |
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Hi...
I came up with this schem for 4 POWER TUBES
What you guys think?
With Respect
Best Regards
Rzenc
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CraigB
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« Reply #52 on: August 23, 2008, 08:39:40 pm » |
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Here's a layout of Geezer's improved 3-selection switch. Looks better if you zoom in. Craig
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« Last Edit: August 23, 2008, 08:41:49 pm by CraigB »
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phsyconoodler
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life is too short to live with bad tone
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« Reply #53 on: August 24, 2008, 09:58:28 am » |
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I just tried the attenuation on an 18 watt lite I just finished and it indeed works.It's hard to say how much it drops the wattage down because the 18 watt is low wattage already,but it dropped it quite a bit.The tone is in debate because I couldn't crank it up yet,but the cleans seem to be alright.
I'll reprt back later today with a real report on the tone differences.
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phsyconoodler
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life is too short to live with bad tone
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« Reply #54 on: August 24, 2008, 01:51:04 pm » |
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I tried it at all volume levels and it definitely works fine.I just used a switch for the caps and it doesn't pop even with no resistors.The low watt sound is good but not outstanding.For bedroom gigs it gets an A.
It works very well with a strat and not bad with humbuckers.I have a PPIMV on this amp too and that rounds it out nicely.
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theundeadelvis
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I love tube amps and bacon...
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« Reply #55 on: September 22, 2008, 11:23:06 pm » |
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Hey everybody! I'm finishing up a fairly straight forward 5E3 and would like to implement this attenuation method. I currently have a 25uF 50v cap and 270ohm 5watt resistor in place. Do I just separate the cathodes of the 2 tubes and add a second cap and resistor of the same values for the other tube? Or do I need to change the values of those components? Thanks in advance!
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phsyconoodler
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life is too short to live with bad tone
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« Reply #56 on: September 23, 2008, 12:42:20 am » |
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You need to double the resistor value with separate ones.Thw same value cap will be fine,but usually you halve it when using two.
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tubenit
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« Reply #57 on: October 12, 2008, 03:18:28 pm » |
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Does the attached drawing of a DPDT switch look correct here?? I have actually wired one up on a friend's amp and it worked but not sure I have drawn up how I wired it????
Please confirm or correct the drawing, thanks. If it's incorrect can you post a DPDT drawn up in this style to show what it would look like.
Would both of these work as I have drawn them???
I'm trying to draw the one on the top right to be the same as DaGeezer's on the bottom.
With respect, Tubenit
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« Last Edit: October 12, 2008, 03:34:55 pm by tubenit »
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VMS
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I love tube amps
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« Reply #58 on: October 13, 2008, 02:35:41 am » |
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Hi, I think you are missing the caps to ground connection on the full-1/4power switch.
The other one seems to be ok.
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Geezer
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« Reply #59 on: October 13, 2008, 05:19:28 am » |
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VMS (& his added drawings) are indeed correct.
T, how did the mod sound on your friend's amp?
G
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 Cunfuze-us say: "He who say "It can't be done" should stay out of way of him who doing it!"  |
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tubenit
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« Reply #60 on: October 13, 2008, 05:29:19 am » |
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VMS ........ THANKS for your help it is appreciated!
DG, the amp sounded GREAT with the mod. As I heard others say, there was little to no tone difference which I liked alot. It was on a Carolina Blues Special (Bogen conversion) that belongs to my friend (incredible guitarist) who lives up there within a few miles of you. He bought a condo and needed even lower volume to continue playing without the neighbors complaining.
While the wiring values I used were called 2/3 & 1/8 ....... it sounded more like 2/3 and 1/4 to me.
Very useful mod. I'm grateful that you shared your success with it on the forum.
With respect, Tubenit
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Frankenamp
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What does this button do?
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« Reply #61 on: October 13, 2008, 09:19:52 am » |
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This idear has really got me curious: I see it implemented with a pair of EL84's- will it work with 6L6's (such as my Red-Headed Stepchild)? It looks simple enough that a ham-handed tube novice such as myself. How would that affect the adjustable bias mod? (Or is this too complicted fer my pea-brain?) ;)
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This problem calls for a bigger hammer!
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sluckey
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« Reply #62 on: October 13, 2008, 09:29:35 am » |
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This circuit applies to a cathode biased amp. I think your stepchild is a fixed bias amp.
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VMS
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I love tube amps
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« Reply #63 on: October 13, 2008, 02:34:18 pm » |
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Glad to help!
This mod is something I'm definitely going to try in some future build.
Maybe 6bm8 amp with even lower wattage. :)
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Frankenamp
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What does this button do?
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« Reply #64 on: October 13, 2008, 02:35:53 pm » |
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Hmmm, (doin' my best Arsenio Hall impersionation) http://www.el34world.com/charts/fenderservice5.htmI think the above link details how to change from fixed to adjustable bias. Is this the same thing? Or is my profound lack of knowlege rearing its ugly head (again)? Got my money on 'ignorance'- but I could be wrong! ;D (Yer gunna have to think of me as that kid in the corner with the thick crayons) ;) |
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This problem calls for a bigger hammer!
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sluckey
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« Reply #65 on: October 13, 2008, 04:15:19 pm » |
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I think the above link details how to change from fixed to adjustable bias. Yes. But it doesn't change to CATHODE bias. Fixed bias applies a negative voltage to the control grid in order to bias (control) cathode to plate current. Adjustable bias is a form of fixed bias with a pot to fine tune the negative voltage applied to the grid, thus providing fine control to the cathode to plate current. Cathode bias uses a resistor between cathode and ground to develop a positive voltage on the cathode that will control the cathode to plate current. Your amp is fixed bias (even if you can adjust it) and this circuit applies to cathode bias circuits ONLY. (Upper case used for emphasis, not shouting) :) |
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Frankenamp
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What does this button do?
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« Reply #66 on: October 13, 2008, 05:00:06 pm » |
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OK, that makes sense :) So, Fixed = PLATE bias Now, the sixty-four dollah question: is there a way to do something similar to a fixed (plate) bias amp? or is there an adjustable bias configuration that will work with my iron? I wish I'd bet real money on my ignorance... coulda hada winnah. (Upper case used for emphasis, not shouting) :)
('s OK, I'm used to gittin' shouted at, wife does it all the time) ;D She sez it's fer emphasis too... but I don' think so unless it's followed up by the fryin' pan, now THATS emphasis! |
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This problem calls for a bigger hammer!
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sluckey
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« Reply #67 on: October 13, 2008, 08:48:14 pm » |
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So, Fixed = PLATE bias
I've never heard of PLATE bias.
Now, the sixty-four dollah question: is there a way to do something similar to a fixed (plate) bias amp?
May have to think outside the box.
or is there an adjustable bias configuration that will work with my iron?
Sure.
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Frankenamp
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What does this button do?
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« Reply #68 on: October 14, 2008, 09:44:23 am » |
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So, Fixed = PLATE bias
I've never heard of PLATE bias.
Don't mind me I'm either low on caffiene, or stuck on stupid... same difference, just tryin' to hone my 4H electrical skills ;) Just making a gallant attempt to follow the bouncing electron with my thick crayolas. |
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This problem calls for a bigger hammer!
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tubescent
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« Reply #69 on: January 18, 2010, 10:05:38 am » |
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just wanted an update:
how many of you guys are still using this mod and happy with the sound?
also any problems with wear on the transformers? (someone mentioned to me it might be an issue with this mod)
thoughts much appreciated before i go ahead and drill my 5e3
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chocopower
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« Reply #70 on: September 03, 2011, 01:23:11 pm » |
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I've read something like this would work, but have not tried it myself. It was described as sort of getting a psuedo
single ended sound from a push/pull amp. One of the forum guys a few yrs ago did it and stated it worked.
With respect, Tubenit
In the cathode biased amp i tested coneccting to ground one of the tube grids and it work REALLY WELL. Even better thant split cathode resistor/cap with the caps switch. How could it be done in a fixed bias amp? I suposse that bypassing one of two 220k bias resistor will work, but i´m afraid about bias voltage going crazy. any idea? |
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« Last Edit: September 03, 2011, 01:26:21 pm by chocopower »
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Spanish Revolution NOW.
David
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