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Fender Twin Reverb Mod's

 
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foureyees



Joined: 22 Feb 2007
Posts: 15

PostPosted: Wed Feb 28, 2007 5:55 am    Post subject: Fender Twin Reverb Mod's Reply with quote

I heard that you're able to modify a fender twin reverb into a single 12" amp running less wattage by disconnecting a speaker and removing some tubes. is it true? is it safe?
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foureyees



Joined: 22 Feb 2007
Posts: 15

PostPosted: Wed Feb 28, 2007 7:04 pm    Post subject: Reply with quote

bump
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randyc



Joined: 14 Sep 2006
Posts: 407
Location: Eureka, CA

PostPosted: Wed Feb 28, 2007 8:01 pm    Post subject: Reply with quote

Yes, a Twin (or any tube amplifier that uses quad output tubes) can be easily and safely modified to perform as you suggest. Here is the non-permanent modification prodecure:

Remove one 6L6 output tube from each HALF of the output stage. (Note that this is a push-pull stage, each half has two tubes wired in parallel. Make sure that you are removing a tube from each half of the stage and not both tubes from ONE half of the output stage.)

You must now operate the amplifier with a speaker configuration that is TWICE the impedance of the original cabinet. For Twins and Dual Showmans, this means a single 8 ohm speaker instead of two 8 ohm speakers wired in parallel (4 ohms).

The resulting configuration will give you around 50 watts output, will sound quite a bit like a Bassman (that's a good thing) and will impose substantially less stress on the power transformer, choke and output transformer - they'll last forever Smile

To restore original configuration, re-insert two tubes and attach output to 4 ohm speakers.

cheers,
randyc
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foureyees



Joined: 22 Feb 2007
Posts: 15

PostPosted: Thu Mar 01, 2007 5:25 am    Post subject: Reply with quote

just finished doing the mod and the amps sounds wonderful! thanks for the help randyc!! much appreciated!

ps maybe bc i havnt used it in a while but, the reverb sounds really REALLY intense now...is that normal?
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randyc



Joined: 14 Sep 2006
Posts: 407
Location: Eureka, CA

PostPosted: Thu Mar 01, 2007 12:55 pm    Post subject: Reply with quote

Quote:
maybe bc i havnt used it in a while but, the reverb sounds really REALLY intense now...is that normal?


A modification in the output stage shouldn't affect the reverb sound. The twin is a five stage amplifier (5 individual gain "blocks"), the reverb is positioned between stages two and three so it's not likely that a change in stage 5 (the output stage) would be significant.

I'm glad that you liked the results of the simple modification. I did the same to my Showman and configured it for dual 12 inch speakers (wired to 16 ohms), instead of the single factory 18 inch speaker in the HUGE factory cabinet. It's a very nice sounding rig.

I only wish that cutting the power in half would also reduce the weight by half !!!

cheers,
randyc
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Gorecki
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Joined: 06 Oct 2005
Posts: 62518
Location: Davis, CA

PostPosted: Thu Mar 01, 2007 4:57 pm    Post subject: Reply with quote

Just a note, thanks randyc for jumping in with your vast electronic's knowledge! I wasn't going to touch this one with a 50" pole! Laughin my arse off
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randyc



Joined: 14 Sep 2006
Posts: 407
Location: Eureka, CA

PostPosted: Thu Mar 01, 2007 9:31 pm    Post subject: Reply with quote

Quote:
I wasn't going to touch this one with a 50" pole!


Aw shucks, Brian, I'm sure that you knew the answer. You were just holding back to test me, LOL.

cheers,
randyc
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Gorecki
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Joined: 06 Oct 2005
Posts: 62518
Location: Davis, CA

PostPosted: Thu Mar 01, 2007 10:01 pm    Post subject: Reply with quote

randyc wrote:
Quote:
I wasn't going to touch this one with a 50" pole!


Aw shucks, Brian, I'm sure that you knew the answer. You were just holding back to test me, LOL.

cheers,
randyc


Honestly my first thought was yeah sure, go ahead and pull those tubes so when their sockets fill with enough dust to cause a short .... watch the amp go KABOOM! Laughin my arse off
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foureyees



Joined: 22 Feb 2007
Posts: 15

PostPosted: Fri Mar 02, 2007 6:10 am    Post subject: Reply with quote

Gorecki wrote:
randyc wrote:
Quote:
I wasn't going to touch this one with a 50" pole!


Aw shucks, Brian, I'm sure that you knew the answer. You were just holding back to test me, LOL.

cheers,
randyc


Honestly my first thought was yeah sure, go ahead and pull those tubes so when their sockets fill with enough dust to cause a short .... watch the amp go KABOOM! Laughin my arse off


you're joking right? my amp won't explode if dust gets into the socket....will it?
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Gorecki
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Joined: 06 Oct 2005
Posts: 62518
Location: Davis, CA

PostPosted: Fri Mar 02, 2007 8:17 am    Post subject: Reply with quote

foureyees wrote:

you're joking right? my amp won't explode if dust gets into the socket....will it?


Oh goodness, sorry to scare you man. When I said that, I was thinking of my own amps being more along a Marshall design. Tubes are on the bottom of the box pointing up...basically a dust bucket. In the case of a twin, the exact reverse. Your tubes are facing downward from the top (inverted), making dust collection basically impossible.

You're okay, and really, randyc knows what he's talking about, he's convinced me and I'm a really hard sell. Wink
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Frank Sottile



Joined: 17 Apr 2007
Posts: 1
Location: San Marcos, Texas

PostPosted: Mon May 26, 2008 5:36 pm    Post subject: '65 Twin Custom 15 Reply with quote

I got a Custom 15 ('65 Twin Ressue with a 15") the speaker is rated at 4 Ohms.

I came up with this mod, it is simple but you will need to be able to replace the output transformer (or you could have me do it for you).

This mod sounds great and saves money as you no longer need to buy 4 output tubes!

One real cool thing is that you can now run any 8-Pin Power tubes you like (EL-34, 6550, KT-88 or 6L6).

Here is what I do, first (the chassis is already on the bench) I remove the old ouput tranny, and rewire the tube sockets. The first two scockets are now the output, and the second two will be for my Dual Tube Rectifier Mod (more about this later).

Install a Fender #0041754000 Output tranny (this is a 60 Watt rated tranny), Install a pair of output tubes and adjust your Bias voltage. That's it for that mod.

The '65 Reissue is a good amp that can be made better, I repair and mod amps and I have not had many '65 Twins come in for repair. As for mods, I offer a AB763 Board, built with Eyelets or Turrets (if that is what the customer wants). A Tube Rec and Dual Tube Rec Mod. With the AB763 Mod I also offer the Fender "Mod Switch" Mod.

I hope this give you something to think about.
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