Build a Twin Reverb with 2 6L6 ?

[joesatch]

Is it possible? I ask because i want to build a bridge rectifier AB763 and the only layout/schematics i've found that retain vibrato/Reverb are for the Twin but i am doing a conversion and only want 2 6L6 .

[SILVERGUN]

Yes.
Read this:
AB763 parts (el34world.com)

[joesatch]

Too many unknowns without a published schematic. Same filter caps? Same voltages/ transformers or can i use a smaller transformer?  Not enough info

[mresistor]

I think obviously 2 x 6L6 are going to use a different OT than a twin.  Maybe a Super Rev OT is a good option.  Take a look at the Super Reverb and then look at the rectifer in the Showman.  Shouldn't be too hard to make a Super with a SS Recti.  Selection of the Power transformer is based on the Voltage you want after rectification and filtering. Just look at some Hammond PTs.  It's possible that a Super Reverb PT would be what you need.

[SILVERGUN]

Typing while mresistor was...so, I agree

Too many unknowns without a published schematic. Same filter caps? Same voltages/ transformers or can i use a smaller transformer?  Not enough info

Yes, you could save some money on iron once you eliminate the "Twin" factor.

I'd do a single channel Super Reverb spec'd circuit with a Hammond 290CX PT and 1760J/ K/ or L OT . Just replace the GZ34 with diodes.

Fender_super_reverb_ab763_schem.pdf (el34world.com)
sorry, I linked the wrong schematic the first time

[sluckey]

Is it possible? I ask because i want to build a bridge rectifier AB763 and the only layout/schematics i've found that retain vibrato/Reverb are for the Twin but i am doing a conversion and only want 2 6L6 .

Why bridge rectifier? The only AB763 with a bridge rectifier I know about is the '65 Twin Reverb Reissue. Just build it with only two tubes and a vibroverb output transformer.

     https://el34world.com/charts/Schematics/files/Fender/Fender_65_twin_reverb_manual.pdf

[Willabe]

I'd do a single channel Super Reverb spec'd circuit with a Hammond 290CX PT and 1760J/ K/ or L OT . Just replace the GZ34 with diodes.

Watch the B+dcv with SS diodes.

The only reason Fender used SS rectifier on the Twin was a single GZ34 couldn't handle the current demand. So unless you just have to have the sound of a SS rectifier, then just go with a GZ34 rect. tube. Do some research on the difference between the 2 if you don't know. They do sound different and have a different feel to playing, once you turn them up a little.   

[joesatch]

Bridge rectifier because my PT has no CT.  Would it be easier to build a Super Reverb with a diode rectifier? Anyone done that?

[Willabe]

Bridge rectifier because my PT has no CT.  Would it be easier to build a Super Reverb with a diode rectifier? Anyone done that?

What PT do you exactly have? Brand, model? Can you post a spec sheet for it?

Your PT might not work for a SR. It has to deliver the right dcv's and be able to handle the current demands of the amp.   

[sluckey]

You say you are doing a conversion? Which amp are you converting? Got a schematic? What are the secondary voltages of your PT? Got a separate bias winding?

Super Reverb with a diode rectifier is just as easy to build as a Super Reverb with a tube rectifier.

[joesatch]

This is the PT i'm using. I do not want to build a Bassman. I want an AB763 circuit with Vibrato and Reverb.

http://www.classictone.net/40-18018.html

[Willabe]

That should work fine.

But with the B+ current available for 4 x 6L6's and a SS rectifier, it will be on the cleaner/stiffer side, less forgiving. The power supply wont won't sag, which is fine, depends what you like.

Edit;

But with the B+ current available for 4 x 6L6's

That's a "2- 6L6" PT he posted
I got that wrong, it is for a 2x6L6 SR amp.
But, given that SR amps had the largest PT in the AB763 2X6L6 amp lineup. It that had to supply the highest B+ dcv and the highest B+ current, it was rated at 40w compared to all the other 2X6L6 AB763 amps; only 35w, and given that HBP noted that modern (quality) PT's have less internal resistance and that they use grain oriented steel lamination's which run cooler/more efficient that original Fender PT's, this PT is probably stronger/will have less sag than an original Fender SR PT. Add this with a SS rectifier and it will be a stiffer PSU with less sag. How much? 

Nothing wrong with that, some might like it better. Just be aware of this.

[SILVERGUN]

But with the B+ current available for 4 x 6L6's

That's a "2- 6L6" PT he posted

Super Reverb with a diode rectifier is just as easy to build as a Super Reverb with a tube rectifier.

yup, you don't have to overthink it

[PRR]

I want an AB763 circuit with Vibrato and Reverb.

As Silvergun suggested, do the Super Reverb, exactly, EXCEPT instead of the vacuum rectifier do a solid rectifier ('cuz four hollow diodes is way too much work/heat). Expect a couple extra Watts, you'll survive.

[joesatch]

That should work fine.

But with the B+ current available for 4 x 6L6's and a SS rectifier, it will be on the cleaner/stiffer side, less forgiving. The power supply wont won't sag, which is fine, depends what you like.

That PT was made for (2) 6L6.  Should i build a Super Reverb with a diode rectifier? What else would i need to change if i did that?

[SILVERGUN]

That PT was made for (2) 6L6.  Should i build a Super Reverb with a diode rectifier? What else would i need to change if i did that?

Read reply #13

[PRR]

Fender sometimes forgot to note the CT on the 72V winding.

[joesatch]

Fender sometimes forgot to note the CT on the 72V winding.

There is no CT on the HV for this PT. Am i to assume CT is internally grounded? Is there a way to test?

[sluckey]

There is no CT on the HV for this PT. Am i to assume CT is internally grounded? Is there a way to test?

Not talking about the HV winding. Talking about the bias winding. Brown/Yellow is the tap but it's doesn't appear to be a center tap.

[joesatch]

There is no CT on the HV for this PT. Am i to assume CT is internally grounded? Is there a way to test?

Not talking about the HV winding. Talking about the bias winding. Brown/Yellow is the tap but it's doesn't appear to be a center tap.

So brown/yellow goes to the bias?.  getting back to the HV.  The diagrams i see for diode rectifier (ex. twin) have the CT on the HV grounded. There is no CT on this PT . Is it internally grounded?

[sluckey]

As you said, there is no CT on the HV winding for this PT. You must use a bridge rectifier. Look at this schematic...

     https://el34world.com/charts/Schematics/files/Fender/Fender_65_twin_reverb_manual.pdf

[Willabe]

The diagrams i see for diode rectifier (ex. twin) have the CT on the HV grounded. There is no CT on this PT . Is it internally grounded?

No, it is not grounded internally.

The Twin uses a full wave rectifier, not a full wave bridge rectifier. On a FWB the B+ is grounded at the bridge, not the PT CT as with a full wave rectifier. Amps that use a FWB rectifier do not have a CT on the B+as Sluckey said. 

[Willabe]

So brown/yellow goes to the bias?.  getting back to the HV. 

Look at hi-lighted schematic in PRR's reply, #16. Then look at the PT spec sheet.

Brown wire #5 and brown/yellow wire #6.

[sluckey]

The Twin uses a full wave rectifier, not a full wave bridge rectifier.

Several of the later TRs, including the '65 Twin Reverb Reissue, do use a bridge.

[joesatch]

The diagrams i see for diode rectifier (ex. twin) have the CT on the HV grounded. There is no CT on this PT . Is it internally grounded?

No, it is not grounded internally.

The Twin uses a full wave rectifier, not a full wave bridge rectifier. On a FWB the B+ is grounded at the bridge, not the PT CT as with a full wave rectifier. Amps that use a FWB rectifier do not have a CT on the B+as Sluckey said.

Hey thanks. do you know of any layouts that incorporate a FWB that can use my PT (AB763 circuit)?

[Willabe]

The Twin uses a full wave rectifier, not a full wave bridge rectifier.

Several of the later TRs, including the '65 Twin Reverb Reissue, do use a bridge.

Yes.

Didn't cross my mind. It's my mind set of nothing after the BF Fender amps. 

[Willabe]

Hey thanks. do you know of any layouts that incorporate a FWB that can use my PT (AB763 circuit)?

I don't but it's probably out there.

Not a big deal, just use the AB763 layout and put the FWB in between the PT and the end of the eyelet board closet to the PT. They sell self contained FWB rectifiers that are fully insulated, you just bolt them to the chassis.

Or you could have Doug make an AB763 eyelet/turret board and leave it a little long to mount the FWB on the board, or have him add the eyelets/turrets needed to use separate SS diodes.

[joesatch]

looking at rob robinette's layout of the Blackface Twin. It shows a center tap on HV to ground (but it is a dashed line). Is this a FWB and what do i do in this case i dont have a CT? 

[sluckey]

THAT IS NOT A FWB!

[joesatch]

THAT IS NOT A FWB!

Youre right i need this.; but i havent seen a AB763 layout that uses this

[Willabe]

Youre right i need this.; but i havent seen a AB763 layout that uses this

Fender black face amps didn't use FWB rectifier set ups. There's many different kinds of power supply rectifier set ups, half wave, full wave, full wave bridge, half wave doublers, full wave doublers, etc.

Read up on rectifiers for power supplies;

http://www.valvewizard.co.uk/bridge.html

http://www.valvewizard.co.uk/psu.html

[sluckey]

This is the simple wiring change to use your PT with rob's layout...

[joesatch]

This is the simple wiring change to use your PT with rob's layout...

Awesome you the man!

[joesatch]

This is the simple wiring change to use your PT with rob's layout...

with this i am left with an additional brown wire. where does it go?

[SILVERGUN]

This is the simple wiring change to use your PT with rob's layout...

with this i am left with an additional brown wire. where does it go?

Nowhere OR anywhere where it won't impart it's evil ways on your power supply.
It is just not needed and can be taped off, never to be seen or heard from again.

[Willabe]

..... Talking about the bias winding. Brown/Yellow is the tap but it's doesn't appear to be a center tap.

with this i am left with an additional brown wire. where does it go?

Look at the PT spec drawing, keeping in mind what Sluckey said. The brown/yellow/#6 looks like a CT, but it's not a true CT, because it's not in the center. It's a split winding at 2 different acv's with a common brown/yellow/#6 to both sides of the wind. True CT wind would be say; 30/0/30acv. This is like 73/0/34acv. They saved themselves from winding 2 low acv winds for the PT bias wind (and a wire fly lead).

Between brown/#5 and brown/yellow/#6, they show ~73acv. Between brown/#7 and brown/yellow/#6, they show ~34acv. Clever. 

Edit: It IS a CT. See replys # 16 and # 37. Willabe

[joesatch]

..... Talking about the bias winding. Brown/Yellow is the tap but it's doesn't appear to be a center tap.

with this i am left with an additional brown wire. where does it go?

Look at the PT spec drawing, keeping in mind what Sluckey said. The brown/yellow/#6 looks like a CT, but it's not a true CT, because it's not in the center. It's a split winding at 2 different acv's with a common brown/yellow/#6 to both sides of the wind. True CT wind would be say; 30/0/30acv. This is like 73/0/34acv. They saved themselves from winding 2 low acv winds for the PT bias wind (and a wire fly lead).

Between brown/#5 and brown/yellow/#6, they show ~73acv. Between brown/#7 and brown/yellow/#6, they show ~34acv. Clever. 

You're a sharp guy Will. I'm reading about all this stuff the best i can. I built a JTM45 kit years ago but never really understood what i was doing and it worked cause i followed the diagram closely. This amp is a '93 Concert Amp (essentially all same trannies as a Deville) i want to use all this iron and pull the pcb to build a AB763. I'm thankful for your input i was about to wire it like the original Twin Reverb

[sluckey]

Looking at the '93 Concert schematic and this PT data I've come to the conclusion that the mystery winding is really a 27vac-0-27vac winding. It is a true center tap. You will have to measure the voltages between the BRN/YEL and each BRN wires. Should get about 27VAC for each reading. Then measure voltage between the two BRN wires. Should be about 54VAC. If this is true, then to use this PT in rob's layout, you will tape off the BRN/YEL wire and connect one BRN to the bias board and the other BRN to ground. Joesatch, measure these voltages and report back.

The data sheet voltages are a bit confusing until you look at the schematic. Then they make sense. Wires 5 and 6 will deliver -72VDC when using a HWVD (half wave voltage doubler) and wires 6 and 7 will deliver +34VDC and -34VDC when using a Half Wave Split rectifier.

[Willabe]

Looking at the '93 Concert schematic and this PT data I've come to the conclusion that the mystery winding is really a 27vac-0-27vac winding. It is a true center tap.

Ahhhh. 

You're a sharp guy Will.

Not sharp enough.     

[PRR]

... ...I've come to the conclusion that the mystery winding is really a 27vac-0-27vac winding. It is a true center tap.....

Wasn't that conclusion offered in Reply #16, 23 posts back?

[joesatch]

I haven't torn it apart yet. I'll let you know how it goes.  It has such a small choke only 50ma so i'll need to change that.

[sluckey]

... ...I've come to the conclusion that the mystery winding is really a 27vac-0-27vac winding. It is a true center tap.....

Wasn't that conclusion offered in Reply #16, 23 posts back?

Wasn't clear to me. I thought the focus was on the missing CT. And you called it a 72V winding. That little schematic snippet you posted showed the missing CT in violet but also on that same pic the lower half of the winding is clearly labeled 27VAC, which would make that a 54VAC winding. My focus was on the VIOLET.

[PRR]

I said it was a centertap. You said it was a centertap. I apologize for the confusion.

[EL34]

Too many unknowns without a published schematic. Same filter caps? Same voltages/ transformers or can i use a smaller transformer?  Not enough info

The AB763 reverb circuit is all of these amps

Deluxe reverb, Vibrolux reverb, Bandmaster reverb, Pro reverb, Super reverb, Twin reverb and Dual Showman Reverb?
https://el34world.com/Hoffman/AB763Notes.htm


Just pick the transformer set to make any of those amps using a AB763 circuit
Tube rectifier or solid state rectifier is your choice
Use a bridge rectifier if you need one

[acheld]

The AB763 reverb circuit is all of these amps

Deluxe reverb, Vibrolux reverb, Bandmaster reverb, Pro reverb, Super reverb, Twin reverb and Dual Showman Reverb?
https://el34world.com/Hoffman/AB763Notes.htm

I'm hesitant to stick my nose under the tent on this thread, but . . .

Doug has done us a big favor with his AB763 notes, but for a new guy (like me) to get the best out them it is really helpful to print out the schematic in color, and then print out the BOM.   All the differences in the circuit components are shown in blue on the schematic, and you can look up the corresponding part number on the BOM.

This is really helpful when designing your own build, mixing and matching components as needed. 

[EL34]

It sounds like it is being made more confusing than it really is

You start with a AB763 reverb board
Build any one of many different Fenders using this same board

Add what ever transformer sets you want to make a different amp
The AB763 circuit is still the same

Change the DC power source to what ever you want
If you have an electric device and you need to give it power
Example: Use 4 x AA batteries or use a wall wart
This can be a Tube rectifier or solid state diodes for the AB763 circuit
This is the rectifier board in a Fender amp

If you have a car that has a 3.7 liter engine and you change it to a 5.0 liter motor, it is still the same car
The car itself is the AB763 circuit

I have already outlined this in this document
https://el34world.com/Hoffman/AB763Notes.htm