SF to BF Twin Project

[p2pAmps]

I have a young man in Florida who decided he wanted his old Twin Reverb tore down and restored to a AB763 BF Twin.  Here's is where it sits now.  I broke my own rule of having more than one build at a time going.... Slap me please 

[Fresh_Start]

As I looked through the pics, I started thinking "it looks like MadMax has been in there with a soldering gun."  Especially liked the 1/2 watt (apparently) resistors where something in the 2-5 watt range would be necessary. Solder joints and melted insulation looked terrible.

This isn't so much a conversion to Blackface as it is a rescue operation!

Chip

[sluckey]

Tell us how you cleaned that chassis. Or is that a new chassis?

[tubenit]

My guess is 120 grit 5" orbital sander.   


And I could be wrong.


With respect,  Tubenit

[eleventeen]

That's a lot deeper than most would tear down an amp. I can only assume that both you and your client have some idea of what this is going to cost.

Just asking, not as a prelude to criticism:


Are you going to reuse *any* parts? (Obviously you will reuse the trannies)
Pots?
Tube sockets?


Your work on your PRs has been completely stellar, but this is pretty time consuming. It's somewhat of a time savings of course when you have a perfectly clean playing field on which you're going to work. It just seems to me that the final bill on this is going to be about 1.5 used Twin Reverbs,

[p2pAmps]

I clean chassis with a National Detroit DA sander with 80grit, works great.  I also use green scotch bright pads, steel wool, whatever I need to get em cleaned up.  But a DA take 10 minutes so its fast too...

Cheers,

[p2pAmps]

That's a lot deeper than most would tear down an amp. I can only assume that both you and your client have some idea of what this is going to cost.

Just asking, not as a prelude to criticism:


Are you going to reuse *any* parts? (Obviously you will reuse the trannies)
Pots?
Tube sockets?


Your work on your PRs has been completely stellar, but this is pretty time consuming. It's somewhat of a time savings of course when you have a perfectly clean playing field on which you're going to work. It just seems to me that the final bill on this is going to be about 1.5 used Twin Reverbs,

You know in many ways, its faster and better when I just tear these down and start fresh.  Client knows his parts costs will be higher but in the end they have a new amp again.  I always replace tube sockets, pots, new wire, and new board.  I do reclaim the trannies of course and any blue ajax caps I find.  This guy mailed me a full set of blue caps to use so we are good on that front.  I can tear down and complete a rebuild in 7 hours on these. 

[p2pAmps]

Here are some more pics.  Hoping to finish her up this weekend...

[jojokeo]

As I looked through the pics, I started thinking "it looks like MadMax has been in there with a soldering gun."  Especially liked the 1/2 watt (apparently) resistors where something in the 2-5 watt range would be necessary. Solder joints and melted insulation looked terrible.

This isn't so much a conversion to Blackface as it is a rescue operation!

Chip

What a mess it was indeed. I especially like or don't like to see this stuff (depending on your perspective). Great job as always Mike.

[p2pAmps]

Drum roll............

All done...  NEXT!

If you are bored find all the pictures here: 
http://p2pamps.com/twin

[HotBluePlates]

Beautiful!! First-rate rebuild!

Reminds me of a guy who used to hang around here (Darrell?) who built Fender repros so good they bordered on forgeries.

[Willabe]

WOW!   

[clyde]

Nice work, and pretty speedy as well.  I also know a fellow that does this, at first glance you wouldn't be able to tell they weren't factory.  Unfortunately his penchant for using old worn-out parts leads to less than desirable results. 

[DummyLoad]

most excellent work. :-)


--pete

[jojokeo]

With all those sexy wire bends the Fender builders' never looked so good!

What did you do with the extra hole for the ground switch? I like to put in a switched Presence control there. Pushed in and turned down all is stock. Turned up you get another added control and pulled out she's not bitchin' err not feeding feedback negatively... This is a great added feature to a Fender.

[p2pAmps]

With all those sexy wire bends the Fender builders' never looked so good!

What did you do with the extra hole for the ground switch? I like to put in a switched Presence control there. Pushed in and turned down all is stock. Turned up you get another added control and pulled out she's not bitchin' err not feeding feedback negatively... This is a great added feature to a Fender.

Thanks guys...

I just put the ground switch back in the hole as requested, of course it doesn't do anything.  I do like your idea about the presence control and may do that when I do up my own twin.  I have a stock 76 with JBLs that I would to tear down...

[p2pAmps]

I do have one question for you guys.  The tremolo on the amp sounds great at the slowest speed but when I turn the speed up it dies around 7...  Now I am using all the stock values for the trem circuit.  Could I have a bad bug perhaps?

[sluckey]

Could I have a bad bug perhaps?

Maybe, but I'd suspect the tube first. Get a handful of 12AX7s and use the one that gives the strongest fast signal. It's pretty common for the trem signal to be weaker at the faster speeds. All those oscillator circuits will quit working at some higher speed. The signal just gets too small to sustain oscillation. You can replace the 2.7K/25µF on the oscillator cathode with a red LED to increase the trem signal well above the fast end drop out point.

BTW, that looks fantastic. I wish my TRRI looked like that!

[p2pAmps]

Could I have a bad bug perhaps?

Maybe, but I'd suspect the tube first. Get a handful of 12AX7s and use the one that gives the strongest fast signal. It's pretty common for the trem signal to be weaker at the faster speeds. All those oscillator circuits will quit working at some higher speed. The signal just gets too small to sustain oscillation. You can replace the 2.7K/25µF on the oscillator cathode with a red LED to increase the trem signal well above the fast end drop out point.

BTW, that looks fantastic. I wish my TRRI looked like that!

I'm going to give that a shot Steve.  The amp owner asked to use the orig tubes which are not all that great to begin with.  I have some UBGs (Used but good) I'll try and see if I have something a little better.  Thanks

[PRR]

> I just put the ground switch back in the hole as requested, of course it doesn't do anything.

To be too cute: run a 0.1uFd 600V cap, a 1Meg, and a 10 Ohm in series from raw B+ to ground. This gives about 0.1mV of raw buzz. Return your first stage cathode networks to the 10r instead of straight to ground. Wire the ground switch to short this.

Now it does something. And something familiar to 1960s players. When switch is set "wrong", the amp buzzes more than when set "other way".

To be more authentic, set one end to short the 10r not with a short but with another 10r. Gives 0.05mV buzz.

Assuming the build has zero buzz (this gimmick only makes sense if the build is super quiet), then the 3-way switch gives 0.05mV, 0.1mV, zero mV buzz in the three settings. This is very-like how the original worked in many rooms with 2-pin wall plug (except "zero" buzz hardly ever happened).
___________________

> I'd suspect the tube first.

Agree (maybe) about keeping "original" tubes in the signal path.

However signal does not go *through* the trem oscillator. It just jiggles at the user-set rate. Effect on signal comes further down the line. As as Steve is suggesting, in this circuit a hardly-weak 12AX7 may fail to jiggle itself, or not at high rate. Unlike a signal stage where low gain is just low gain and you can cover it with a higher VOL setting, the trem jiggle has a _minimum_ gain below which it just won't work.

So find a tube which does what it has to do, and don't worry if you end up with microphonic asian junk or even a MOSFET; that's not "the sound", just a side mechanism.

[p2pAmps]

Ha!  The Buzz gag would be cute...

I'm going to toss a good strong 12AX7 in her tonight and see what happens.  Thx fellas

[p2pAmps]

She is packed and ready to ship...  next!

[tubenit]

That is a BEAUTIFUL amp inside and out!  You have raised the bar on classy looking amps builds and wiring. Stellar job! 


Thanks for sharing!  With respect , Tubenit

[Fresh_Start]

Beautiful craftsmanship. And I know it sounds just as good as it looks based on other sound clips!

Chip

[sluckey]

That looks like a blonde on silver! Very nice look.

I'm curious, is this in the same shop as the BGE? If so, how 'bout a pic showing the entire shop?

[p2pAmps]

Yeah Steve, same shop.  My wife calls it our garage!  I will snap a few pics when I get it cleaned up a little :)

[silat]

You look like an expert since you have already built one of these and I have just started mine...  It is going to be a split chassis. The letters on the layout D and Y and X Etc. Are those  linking components on the back of the board? I see you have yours on the top of the board. It looks like really nice work by the way.

[p2pAmps]

You look like an expert since you have already built one of these and I have just started mine...  It is going to be a split chassis. The letters on the layout D and Y and X Etc. Are those  linking components on the back of the board? I see you have yours on the top of the board. It looks like really nice work by the way.

LOL, I am not an expert at all but thanks just the same. 

So what is a split chassis?  I built this Twin as an AB763 and used the Leo Fender layout and Doug's G10 eyelet board. 

Thanks for the comment, I enjoy this hobby and learn more here each day I read...

[silat]

You look like an expert since you have already built one of these and I have just started mine...  It is going to be a split chassis. The letters on the layout D and Y and X Etc. Are those  linking components on the back of the board? I see you have yours on the top of the board. It looks like really nice work by the way.

LOL, I am not an expert at all but thanks just the same. 

So what is a split chassis?  I built this Twin as an AB763 and used the Leo Fender layout and Doug's G10 eyelet board. 

Thanks for the comment, I enjoy this hobby and learn more here each day I read...

Hello mscaggs, I have not done a split chassis yet. But it is for me using the Ab763 preamp and Baldwin organ amplifier to power it. It already has 2 5u4's and 4 6L6's.. Here is what sluckey wrote to me about as he has built one before."I would tackle this as two projects. Project one is to fix the Baldwin amp as it is with no modifications. That Baldwin is just a power amp, like pages 2 and 3 of the pdf I linked. It expects a line level signal. It's probably a very good sound power amp too!

Project two is build a preamp. There's not enough room on the Baldwin to add a preamp so build a stand-alone preamp in a separate chassis. AB763 would be a good choice or if you want grit, build a Marshall style. Really, you have a lot more choices. You can borrow filament and B+ from the Baldwin or you can use a small PT just for the preamp. Use RCA phono cable/jacks or standard 1/4" phone cable/jacks to connect the preamp to the power amp.

Doing a split amplifier allows a lot of versatility. Build several different preamp chassis and plug 'n play." here is the original post...http://el34world.com/Forum/index.php?topic=19220.0

[bnwitt]

I did a few of those rebuilds with right angle wire bends trying to make them look "slo" and found that Fender's original layouts were quieter.

[p2pAmps]

I did a few of those rebuilds with right angle wire bends trying to make them look "slo" and found that Fender's original layouts were quieter.

Barry, this one was so quiet I had to check to see if i forgot to plug in the speaker...  Did I get lucky?  I have done a few that way for fun and so far so good.  I may not go to all that trouble on the current build which is my personal twin. 

[g-man]

Deleted

[p2pAmps]

Sort of off topic...the pics of your re-build are nice and clear. Do you use software to edit them or have really nice balanced lighting in your shop? I sometimes use photoshop "shadow/highlight" to balance out pics with over exposed and under exposed areas. Works well in moderation but creates a washed out look if used too much.

Here's my secret, I use an iphone in a garage that needs better lighting that I have, and I hold it with both hands LOL...  Seriously, that is all I do.  I have a great Nikon and tripod I never use ha!