TomH
Joined: Mar 15, 2006
Posts: 766
Oberlin, Ohio, USA
|
Posted on Dec 07 2010 09:48 AM
I tried searching for this topic to no avail. Yet, I'm pretty sure that this has been discussed. So, forgive me if this is old hat.
I just bought an early 70s Vibrosonic amp with a JBL D130-F 15" speaker. It hasn't arrived, yet, but I'm really excited about getting it. It's 100 watts. I've read that you can remove either the outer two 6L6 tubes or the two inner 6L6 tubes in Fender amps to cut the wattage in half (50 watts). That's appealing to me, because I won't need 100 watts for 90% of what I do with the amp. Is doing this harmful in any way to the amp? Thanks!
|
skeeter
Joined: Feb 27, 2006
Posts: 2063
Virginia, USA
|
Posted on Dec 07 2010 10:26 AM
I tried this once on my Dual Pro 100 watts.
The only thing I noticed is that the volume knob maxed out at 5. I didn't really notice any tonal difference from 1-5 though.
So it was really just like creating half an amp, volume wise, rather than making it a 50 watt amp. Your mileage may vary.
— Paul
Atomic Mosquitos
Bug music for bug people is here!
Killers from Space
|
Ruhar
Joined: Jun 21, 2007
Posts: 3909
San Diego, CA
|
Posted on Dec 07 2010 10:37 AM
I've tried it, and it really didn't have much of an effect at all for what I was trying to achieve. I just use a smaller amp instead.
— Ryan
The Secret Samurai Website
The Secret Samurai on Facebook
|
elreydlp
Joined: Sep 04, 2009
Posts: 1800
Temecula, CA
|
Posted on Dec 07 2010 10:58 AM
Tsunami_Tom
I tried searching for this topic to no avail. Yet, I'm pretty sure that this has been discussed. So, forgive me if this is old hat.
I just bought an early 70s Vibrosonic amp with a JBL D130-F 15" speaker. It hasn't arrived, yet, but I'm really excited about getting it. It's 100 watts. I've read that you can remove either the outer two 6L6 tubes or the two inner 6L6 tubes in Fender amps to cut the wattage in half (50 watts). That's appealing to me, because I won't need 100 watts for 90% of what I do with the amp. Is doing this harmful in any way to the amp? Thanks!
You can do it, but like some others, I would just use a smaller amp. The output will change from 4 ohms to 8 ohms into a 4 0hm load which is okay.
|
Pyronauts
Joined: Feb 27, 2006
Posts: 1165
Northern CA
|
Posted on Dec 07 2010 02:52 PM
Dave Wronski once told me (and maybe he can confirm this) that I could remove two of the four power tubes in my Twin Reverb to achieve a lower volume, but make sure to either remove the inside pair or the outside pair. Not the two on the left or the two on the right.
|
elreydlp
Joined: Sep 04, 2009
Posts: 1800
Temecula, CA
|
Posted on Dec 07 2010 02:57 PM
Pyronauts
Dave Wronski once told me (and maybe he can confirm this) that I could remove two of the four power tubes in my Twin Reverb to achieve a lower volume, but make sure to either remove the inside pair or the outside pair. Not the two on the left or the two on the right.
That is correct. Tsunami-Tom stated that at the start of the thread.
|
dboomer
Joined: Jan 05, 2009
Posts: 262
Port Hueneme, CA
|
Posted on Dec 07 2010 02:58 PM
Yes ... pulling a pair of the output tubes cuts the current output and you get roughly half the power (in Watts). Remember, that doesn't mean half the loudness. It's just a -3dB change which is slightly noticable.
|
TomH
Joined: Mar 15, 2006
Posts: 766
Oberlin, Ohio, USA
|
Posted on Dec 07 2010 03:35 PM
Thanks everybody for your advice. It sounds like I can at least give it a try without damaging the amp. I really don't want to buy another smaller amp, at least not so soon after buying this amp. I have a small cab and a Crate Powerblock that I use for playing at friends' houses. I was hoping that removing the two tubes would make this Vibrosonic sound like a 50 watt amp with a 15" speaker, which would be cool, but your comments have told me that's not what it will sound like. Oh well. By the way, the Vibrosonic is an 8 ohm amp and not a 4 ohm amp, like the Twin reverb. So, does removing the two tubes make it a 16 ohm amp?
Thanks again!
|
elreydlp
Joined: Sep 04, 2009
Posts: 1800
Temecula, CA
|
Posted on Dec 07 2010 04:15 PM
You're right!
I was assuming (DUMB!) that it was like the mid-90's Custom Vibrasonic which was based on the '65 Twin Rev. RI. It had a 4 ohm OT.
The Vibrosonic Rev. was an 8 ohm output, so yes, removing a pair of tubes would make it 16 ohms. It shouldn't hurt the amp. Try it.
|
CrispyGoodness
Joined: Apr 06, 2009
Posts: 565
North Cackalacky
|
Posted on Dec 07 2010 04:22 PM
I thought about doing this with my Twin, and after asking around, it was suggested that maybe the bias on the remaining power tubes get adjusted first. before I took the thing out for a spin. So possible food for thought there.
--Crispy
|
LHR
Joined: Aug 23, 2006
Posts: 2123
The jungle
|
Posted on Dec 07 2010 04:37 PM
I think you are barking up the wrong tree. I would not do this. Forget the change in plate voltages and load on the output transformer, this is just not really so different a sound as to warrant risk. Stick with the design spec (a quartet) and be happy you did.
Have you thought about putting in less-efficient speakers or using some sort of power sink?
— SSIV
|
skeeter
Joined: Feb 27, 2006
Posts: 2063
Virginia, USA
|
Posted on Dec 07 2010 04:38 PM
There's also THD Yellow Jackets, tube converters.
I have no experience with them whatsoever, so I can't say if they're good or bad.
http://www.thdelectronics.com/product_page_yellowjacket.html
— Paul
Atomic Mosquitos
Bug music for bug people is here!
Killers from Space
|
JObeast
Joined: Jul 24, 2012
Posts: 2762
Finknabad, Squinkistan
|
Posted on May 13 2015 08:36 PM
25% Off Sale on Yellow Jackets at Tubes&More
Might be a worthwhile experiment in tone modification.
— Squink Out!
|
derekirving
Joined: Nov 03, 2011
Posts: 660
|
Posted on May 13 2015 09:28 PM
I did this to an old Twin Reverb. Helped a bit but not much, even 40-50 watts of blackface tone is loud.
|
ncgalt1984
Joined: Nov 27, 2013
Posts: 235
Greenville, NC
|
Posted on May 13 2015 10:53 PM
I had this same issue. I'm running a 100 watt Gomez Surfer head and I wanted to be able to push it to get better tone out of it. I decided against pulling the tubes simply because it's only a 3db difference. I ended up getting a Weber Mass 200 attenuator and couldn't be happier. Of course, it doesn't sound as good as it would if it were completely un-attenuated and cranked up. But, it sounds much better than it did when I was playing it on low volume and not pushing the amp into its "sweet spot".
Also, if you were to go with an attenuator, everything would just stay at 8 ohms impedance so there's no need to unplug a speaker or swap them out.
— Kevin
The Out of Limits
www.facebook.com/theoutoflimitsband
https://theoutoflimits.bandcamp.com/
|
SlacktoneDave
Joined: Jul 01, 2006
Posts: 657
|
Posted on May 14 2015 11:42 AM
If you pull two power tubes from a four tube amp, in my opinion it would not be wise to mismatch the speaker impedance to output transformer.
All you guys with your 6L6 tube amps that are too loud when you get them turned up to generate some harmonics should think about changing to a E34L power tube. It has 20% more headroom than a El34, and will generate harmonics sooner that a 6L6.
|
dboomer
Joined: Jan 05, 2009
Posts: 262
Port Hueneme, CA
|
Posted on May 14 2015 12:06 PM
Is an E34L a pin to pin match with a 6L6GC? otherwise you would need to make some modifications in a typical Fender circuit.
As far as mismatching the output transformer ... well it will change the frequency response a little. That could be good or bad depending on what you expect. But the impedance of speakers varies all over the place, usually from about about -30% to about +500% over the entire frequency range. It is usually not damaging to the output transformer if the transformer was designed with a little headroom in the first place.
If you are really concerned you could use an Autoformer to match the impedance. If you need one I have a big 200W new one I'll sell you.
But was others have pointed out ... Half power down not equal half volume. Most people can barely hear the change. The way human hearing works you have to cut it by a factor of 10 to perceive the change as "half volume".
|
SlacktoneDave
Joined: Jul 01, 2006
Posts: 657
|
Posted on May 14 2015 12:21 PM
I know that half the volume= 1/10 the power.
Generation of harmonix happens at different rates with different power tubes. El84 generates much more and much sooner than a 6l6.
|
SlacktoneDave
Joined: Jul 01, 2006
Posts: 657
|
Posted on May 14 2015 12:24 PM
I forgot to say mismatching speaker to output transformer can cause arcing in the primary, is my understanding.
|
Las_Barracudas
Joined: Apr 24, 2011
Posts: 1087
Surf City, NC
|
Posted on May 14 2015 01:38 PM
Congrats on the amp purchase. My bud had a Vibrosonic and it sounded great at volume, though not exactly a clean machine.
That said I wouldn't pull any tubes for the reasons stated and others.
Sounds like you just have more amp than you need. If you can't use it for 90% of your gigs I'd suggest a lower wattage rig; something in the 30-40 watt range.
— METEOR IV on reverbnation
|
April Birthdays 
