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Topic: Fender mod -reducing output?? |
Dave Zirbel
From:
Sebastopol, CA USA
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Posted 13 May 2010 9:13 am |
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I know nothing about electronics!
For awhile I was thinking about beefing up SF Deluxe Reverb with '69 BM tranny. Some say it can be done, some say no. I decided to leave it alone since they are great amps they way they are (and still too loud in some cases according to certain sound men)
Are there any mods to gear down a Fender to have less watts? I have a 70 watt Super Reverb with a SS rectifier. Could I have my tech drop the BM tranny and have myself a Pro Reverb?? The Super on 2 is louder than my Vibrosinic on 4-5. Something like a Pro would be perfect for me. I can't afford to buy one!
Thanks
Dave
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Mike Neer
From:
NJ
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Posted 13 May 2010 9:35 am
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Dave, you talk to an amp tech about this, but he can wire in a switch that will cut off 2 power tubes for 1/2 power. The thing you would need to do is then rewire the speakers to get the correct impedance, since with 2 tubes removed the impedance will change.
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Links to streaming music, websites, YouTube: Links |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 13 May 2010 9:53 am
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Thanks Mike but the SUper has only two power tubes.It sounds great for steel. Wants a 4 ohm load and has an 8 ohm JBL and still crazy loud.
BTW, I only tried one 6SJ7 tube and it works. I still intend to return the favor! 
Thanks again
Dave
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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J Fletcher
From:
London,Ont,Canada
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Posted 13 May 2010 10:01 am
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Hi Dave
I don't think it's worthwhile trying to turn your Super into something else. My advice would be sell it, and buy the amp that does the job for you. But, you could try using an outboard power attenuator to dial in whatever amount of power you need for the job. Weber Mass or Power Brake etc. Though I've never used one. I have many amps, and use the one I need for the particular gig. Jerry |
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John Groover McDuffie
From:
LA California, USA
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Posted 13 May 2010 10:09 am
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Hi Dave;
1) output topology: If your Super Reverb is truly 70 watts it is a late '70s ultralinear model. (Ultralinear topology is a different way of operation using a different transformer and wiring the screen grids differently.) It is probable that a tech can wire this amp to run in normal operation instead of ultralinear, which would make it more of a 40-50 watt amp. It might require the addition of a choke (like a small transformer), which the UL amps didn't have.
2) rectifier: If your amp has a socket for a tube rectifier it is possible that a tube rectifier with more voltage drop could also make your amp "softer", but might also require re-adjustment of the bias. So that also would be best done by a tech.
Regarding the amp being louder on 2 than the Vibrosonic on 4, this could be a function of the taper of the volume pot being different on the different amps. Pots come in linear and also audio taper, but audio taper pots aren't always made to be the same taper, and there are always manufacturing differences. You would need to measure the resistances of the Super vol pot and the Vibrosonic vol pot to find a true comparable setting.
If the Super is in fact an ultralinear model, and the Vibrosonic is not, the difference in actual wattage would only be about 30%, not enough to make a big difference in perceived loudness if both amps were set for the same degree of output amp distortion. (apples to apples) The difference between 4 lower efficiency 10" speakers and one 15" JBL (high efficiency) will contribute a greater difference in the "audio experience" of playing the amp. If you could swap the speakers (you can't because of speaker impedance differences) the VS through the 4x10s would probably sound much like a slightly cleaner Super Reverb, and the Super through the 15" would sound like a slightly warmer version of the VS. |
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John Groover McDuffie
From:
LA California, USA
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Posted 13 May 2010 11:39 am
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| I did some quick research on the amp forum. Apparently it would be fairly simple to rewire this amp to run in normal mode (40-45 watts) or to make it switchable between ultralinear and normal. |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 13 May 2010 12:08 pm
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Thanks John. Can you post a link to the info? I'd like to print it out and take it too my tech.
Dave
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Mike Neer
From:
NJ
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Posted 13 May 2010 12:22 pm
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Ah, yes, what was I thinking.... All the SRs I've known were 40 watt amps, so I think John's right.
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Links to streaming music, websites, YouTube: Links |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 13 May 2010 12:26 pm
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It's a 70 watt 4 ohm with a solid state rectifier.
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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John Groover McDuffie
From:
LA California, USA
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Posted 13 May 2010 12:48 pm
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Here's the thread, although it is not very detailed, and not complete enough to be a "tutorial". But your tech, if he is worth his salt, should know how to convert from ultralinear to standard pentode operation if you just ask him to do that.
http://music-electronics-forum.com/t19761/ |
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Ben Feher
From:
Austin TX
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Posted 13 May 2010 1:06 pm
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Forgive my ignorance, by why can't you just turn it down?
Or switch the preamp tube to something with a little less gain?
Why mess with the poweramp unless your looking for poweramp distortion (unlikely with a pedal steel). |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 13 May 2010 1:41 pm
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I like the sound of lower powered amps pushing the speaker and tubes to get a little compression. I don't like plugging in extra electronics in the signal except for a volume pedal.
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Rich Hlaves
From:
Wildomar, California, USA
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Posted 13 May 2010 2:38 pm
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Dave,
Regardless of what changes you make to the SR it will most likely result in a change in sound or tone you may not like. IMO the SR is one Fender amp that sounds good at any volume. I have two of them. (black face AB763 circuit) I play out with them and use them sometimes for home practice as well. Yes the volume knob is sensitive at low levels but one it is set my volume pedal or pot on the guitar does the rest.
One thing that you may be able to do yourself at home is change the preamp tubes V1(normal channel) & V2 (reverb channel) to reduce gain the the preamp section to make the amp quieter. Stock tubes are 12AX7. A 12AY7 (less gain)or 12AU7 (even less gain) will reduce the output by reducing the gain the power section sees. The 70 watt UL Super also has a master volume so I'm kinda wondering what you are after in total here. If you want it to hair up at a lower volume then the power attenuator mentioned above might work the best with no tube changes.
As an aside, I own a '67 Pro Reverb. Control wise it is much like my Supers and sensitive at low settings. It gets mainly six string use and is blasting clean by 4 on the control knob. Tone wise the Pro is my favorite amp for six string behind only my Fox 5D6B Bassman and it does very well with Steel unless you want it ultra loud. The Twin Reverb is pushed into service then. For low volume stuff a home built Deluxe reverb gets use. I am thinking of building another in a single 15' cab.
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On man....let the smoke out of another one. |
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John Groover McDuffie
From:
LA California, USA
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Posted 13 May 2010 2:52 pm Spinal tap moment
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| Rich Hlaves wrote: |
| For low volume stuff a home built Deluxe reverb gets use. I am thinking of building another in a single 15' cab. |
That's going to be huge! 
 |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 13 May 2010 3:01 pm
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If I had a black face Super I wouldn't consider changing it! The one I'm talking about is late 70's 70 watt with ss rectifier. They're not really one of the more desirable Fenders from what I understand.
I wish I could have one of each!! 
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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John Groover McDuffie
From:
LA California, USA
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Posted 13 May 2010 3:03 pm
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| Does it have pre-punched holes for two more large tube sockets, like the BF Bandmaster has? That would make it relatively easy to convert it to a tube recto. |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 13 May 2010 3:11 pm
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No. It came stock without the socket hole.
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Rich Hlaves
From:
Wildomar, California, USA
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Posted 13 May 2010 3:29 pm
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J. Groover,
That pic reminds me of the old TV show Time Tunnel! Loved that show as a kid. Seriously, a DR set up for a 15 will only be a couple of inches taller than stock. With a JBL in there it will weigh a bit more but hey, it's worth the effort. Probably still weigh less than my 12" amp with an EVM 12L in it. Hmmmm, Weber Neo!
Dave,
I feel your pain. Completely different amps tonally. I think I understand the sound you are after now. I'd sell the UL Super and buy a black line '68 silver face amp with the AB763 BF circuit. These can be had for $1000-$1200. Same guts as the '64-'67. If you get $7-800 for your UL that wouldn't be too bad. Lots of steelers like the ULs. Plan on spending a few bucks to get and used BF Fender tube amp up to par. I have only bought one (traded for actually) in my lifetime I have not had to work on and that was from Ken Fox!
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On man....let the smoke out of another one. |
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John Groover McDuffie
From:
LA California, USA
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Posted 13 May 2010 4:37 pm
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| Rich Hlaves wrote: |
| I am thinking of building another in a single 15' cab. |
Spinal Tap moment I was referring to - notice you typed ' which stands for feet, rather than " which stands for inches.
Remember when Spinal Tap got it the wrong way 'round and ordered the 18" Stonehenge stage prop. |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 13 May 2010 5:01 pm
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Well, the Super is in pretty rough shape although still toneful. I plan on taking it in for a tune up because it makes noise and is very microphonic. Even after swapping out tubes it was still microphonic. (Do tube sockets and pots become microphonic?) I know it hasn't been worked on for years. I thought since someone is going to go through it that maybe it would be the time to also do a mod. Most likely I'll just tune it up and use it and start saving for a Pro.
'69 Bandmaster transformer for sale....
Thanks for the input.
Dave
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Jeff Keyton
From:
Texas, USA
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Posted 13 May 2010 7:46 pm
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Have you thought about trying the tube adapters made by THD called yellowjackets ? They will allow you to run EL 84's in the amp and you don't have to rebias the amp either. They sound real good in my 72 SR. Yes there is a tonal change, but it's still a Super; and you can turn the amp up to 4 or 5, from 2 or 3.
JK |
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Dan Tyack
From:
Olympia, WA USA
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Posted 14 May 2010 9:38 am
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| I'd recommend something like the THD Hotplate, it will reduce volume with really little change in tone. And then if you have to play stupid loud you will have the extra headroom. |
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Olli Haavisto
From:
Jarvenpaa,Finland
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Posted 14 May 2010 9:45 am
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Stupid loud ? What`s that? 
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Olli Haavisto
Finland |
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Rich Hlaves
From:
Wildomar, California, USA
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Posted 14 May 2010 12:54 pm
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Would that be almost as loud as freaking loud?
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On man....let the smoke out of another one. |
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John Groover McDuffie
From:
LA California, USA
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Posted 17 May 2010 3:20 pm
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| Dave Zirbel wrote: |
'69 Bandmaster transformer for sale....
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Is that a Bandmaster output transformer or power transformer? and how much? |
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