Hoffman AB763 Trem-O-Nator Upgrade

[purpletele]

I have reviewed the Trem-O-Nator Schematic and the Hoffman AB763 Schematic and Layout.

I enlarged the Layout and performed some Old School Editing to White Out the deleted components and draw in new values or components.

I think I have followed the schematic changes and layout changes as shown on the Trem-O-Lator Detail for the BandMaster, but I could sure use some critique of my artwork for accuracy.

Also, I am not understanding where the Insertion point will be for the Intensity Pot. On my art work I left the right lug of the Intensity Pot Unconnected, not quite sure of how to close this circuit.

As always, I really appreciate the help, my amps continue to improve with all the help and that is very special and important to me

Thanks you

Brian V

 

[shooter]

early eyes,
the bias pot wiper/cap wire to the middle of the 220k's through the INT is eliminated on the layout.
the schematic has it still on the INT pot. you wanna get that wire correct, regardless of trem type

[sluckey]

This should work...

[purpletele]

early eyes,
the bias pot wiper/cap wire to the middle of the 220k's through the INT is eliminated on the layout.
the schematic has it still on the INT pot. you wanna get that wire correct, regardless of trem type

Thank you

[purpletele]

This should work...

That is Gorgeous!!

Thank you

[sluckey]

Just a note on the footswitch... If you use an RCA jack you will have to connect the footswitch for the tremolo to work.

[purpletele]

Just a note on the footswitch... If you use an RCA jack you will have to connect the footswitch for the tremolo to work.

Oh thank you.  If I just disconnect the footswitch will that close the circuit and have the Tremolo work?

[sluckey]

Now what did I just say? 

[purpletele]

Now what did I just say? 

Sorry, typing without digesting what I read.  Foggy head, no amp work for me today

[sluckey]

Just pickin' at you. I had assumed that you used a RCA phono jack like on Hoffman's layout. I used a 1/4" Switchcraft switching jack on mine just so I don't have to plug in a footswitch.

You about done with the mod? Let us know what you think.

[purpletele]

Just pickin' at you. I had assumed that you used a RCA phono jack like on Hoffman's layout. I used a 1/4" Switchcraft switching jack on mine just so I don't have to plug in a footswitch.

You about done with the mod? Let us know what you think.

I'll be getting the parts Tuesday or Wednesday, and I'm excited about making the change.  I used the RCA phono jack, but I don't ever use the footswitch, I like the idea of the Switchcraft jack.

Blossoms, rain and wind is intoxicating to me so today is a good day to just play guitar.

[shooter]

Foggy head, no amp work for me today

I call it crayon time, usually after 6:20 pm 

[purpletele]

Trem-O-Nator Update

All systems are working!  The tremolo seems much better than before, I will have a chance to AB it with my other Deluxe.

The drawing was fantastic, thank you for that!!

I used the 50K RA Intensity Pot and I added the .022 cap nearest V4 in lieu of the .01.  The Mod schematic had .022, let me know if that is incorrect.

The Tremolo is very smooth and sounds lush, I am getting spoiled but I feel like there could be a bit more Intensity.  Is that possible to tweak any components for more intensity?

I am going to try the change of the RCA jack to a Switchcraft switching jack.

I'm going to gear up for the Princeton later this week, that Trem could use a boost.

Thank you very much, successful mod!

[tubenit]

Super nice looking build!   

How is the floor noise at idle?  Quiet amp?

With respect, Tubenit

[sluckey]

I feel like there could be a bit more Intensity.  Is that possible to tweak any components for more intensity?

Replace the 10K cathode resistor with a 47K.  Also try with no cathode resistor. Any better?

Edit... I wonder if the Xvive opto is just not quite the same as the Vactec Vactrol VTL5C1? Could be a factor with the intensity. My Vactec has way more intensity than I could ever use.

While you are experimenting I'd like for you to try a Vactec to see if there is a difference with intensity. You can get some from AES...

     https://www.tubesandmore.com/products/optocoupler-vactec-vtl5c1-vactrol-new-old-stock

[purpletele]

Super nice looking build!   

How is the floor noise at idle?  Quiet amp?

With respect, Tubenit

Thank you Jeff, this amp is fairly quiet, my other Deluxe is really quiet.  Haven't determined the difference.  Both have cool chassis' made by a guy on Reverb.  The combo chassis is really light!

It's a souped up AB763, 6l6's with a 40 Watt OT

BV

[purpletele]

I feel like there could be a bit more Intensity.  Is that possible to tweak any components for more intensity?

Replace the 10K cathode resistor with a 47K.  Also try with no cathode resistor. Any better?

Edit... I wonder if the Xvive opto is just not quite the same as the Vactec Vactrol VTL5C1? Could be a factor with the intensity. My Vactec has way more intensity than I could ever use.

While you are experimenting I'd like for you to try a Vactec to see if there is a difference with intensity. You can get some from AES...

     https://www.tubesandmore.com/products/optocoupler-vactec-vtl5c1-vactrol-new-old-stock

I installed the 47 K resistor without noticeable results.

I thought the same thing about the Chinese Part, but I wanted to root out any mistakes that I might have made.

I will make a video in the next day or so but it really sounds exceptionally nice,  but it's not a dizzy warble. 

I'll order up a few from AE and test it again in a few days.

I just played it again and it is really cool, that was after a few beers.  I'm kind of hoping the Chinese LED's are not as powerful, I'd like to get a little more juice in the soup just to know it's there.

These amps that I have at home are getting really nice, thank you!

Brian Vallis

[sluckey]

I installed the 47 K resistor without noticeable results.

Now try it with NO resistor.

[purpletele]

I installed the 47 K resistor without noticeable results.

Now try it with NO resistor.

Just saw this, I'll give a try shortly

[purpletele]

I installed the 47 K resistor without noticeable results.

Now try it with NO resistor.

I lifted the 47K resistor an I couldn't discern any difference.

Update, the intensity feels a little more pronounced

[RWood]

Hi, purpletele, really nice build and great implementation of the tremolo. Could you provide some more info about your chassis? It looks to be the missing link between the Princeton Reverb and two-channel Deluxe. How wide is it? I did a little searching on Reverb but did not see one like it. Thanks

[purpletele]

Hi, purpletele, really nice build and great implementation of the tremolo. Could you provide some more info about your chassis? It looks to be the missing link between the Princeton Reverb and two-channel Deluxe. How wide is it? I did a little searching on Reverb but did not see one like it. Thanks

Hi,

The chassis is essentially a copy of the Princeton Reverb chassis such as the Mojotone.

I found Steven O'Conner of Synaptic Amplification on Reverb.  I asked him to reproduce the Princeton chassis but I gave him a dimension to cut in an IEC.  I had to give him the dimension's for the record, and he will need to know the face angle.  It seems I was about 70 degrees, I was matching the angle on the cabinet.

I used a Princeton Tall Boy Cabinet from Mather Amp Cabinets.  I had to cut a leg off of the back panel to expose the IEC. 

I used the strap bolts that go through the chassis.

When I have Synaptic's build me a chassis for a Champ I have Synaptics deliver the chassis to Mather and I have him mount the chassis, that is when I have bought a new cab.

The chassis is really light and easy to drill.

Let me know if you need other photos or info

BTW the last photo is a Princeton in a Champ, it's cool!

Brian V

[RWood]

thanks much! Nice looking amplifiers.

[purpletele]

Trem-O-Nator Update

The American NOS parts from Antique Electronic changed the game! 

Great suggestion

Much more pronounced, I took some quick video with a mic, that will come later.

I filmed a couple of chords with the Chineese component installed and then made the change and video taped that.

After that I re-installed the 47K resistor that I had previously pulled out.  Couldn't tell if it made a difference, I will have to listen to the sound on the video.

Always fun when a component makes such a difference.

BV

Modified Update: I'm getting a static/Microphonic sound on the V3-7 Wire going up to the the 470K resistor that ties to the middle lug of the Reverb.  I changed the tube but that didn't change the static.

Any thoughts on how that became affected?

[purpletele]

Trem-O-Nator Update

The Trem-O-Nator is working better than anticipated, but the changes caused some imbalance on the Reverb circuit.

I V3-7 is a hot wire and the voltage at that pin is 283, and I should see +-200V based upon my previous records.

On the T-o-N circuit I have replaced the 47K resistor with the 10K as designed.

Any thoughts on trouble shooting the voltage increase at V3?

Thanks,

BV

[sluckey]

I V3-7 is a hot wire and the voltage at that pin is 283, and I should see +-200V based upon my previous records.

I hope not! V3-7 should be zero volts. According to your voltage chart you have 283V on V3-6. Probably what you meant?

I notice that V3-1 has also increased. I bet that power supply nodes B, C, and D are all higher too. What say you? The ton mod removed one triode that was fed from B+ node B. I would expect all the downstream voltages to increase. Don't know how much.

283V is quite normal for the bigger 6L6 AB763s. Other than the increased voltage, is the amp misbehaving?

[purpletele]

I V3-7 is a hot wire and the voltage at that pin is 283, and I should see +-200V based upon my previous records.

I hope not! V3-7 should be zero volts. According to your voltage chart you have 283V on V3-6. Probably what you meant?

I notice that V3-1 has also increased. I bet that power supply nodes B, C, and D are all higher too. What say you? The ton mod removed one triode that was fed from B+ node B. I would expect all the downstream voltages to increase. Don't know how much.

283V is quite normal for the bigger 6L6 AB763s. Other than the increased voltage, is the amp misbehaving?

The amp is misbehaving!  I get a very distorted notes on the Lower register Strings,  But the Trem sounds swirly!

Voltages at the Nodes:

A = 450 V
B = 444 V
C = 442 V
D = 429 V

Note regarding 6L6 tubes: I believe the original voltages taken in 2018 had 6v6 tubes installed.

V3-6 is the Hot wire and not V3-7

[purpletele]

Steve,

Any thoughts on modifying components in the Reverb Circuit to accommodate the added voltage from the T-O-M?

I seem to have some time on my hands, and I would love to help make this amp great again.

BV

[sluckey]

Replace R68 and R69 with 10K 3W resistors. These are the values for a DR.

[purpletele]

Replace R68 and R69 with 10K 3W resistors. These are the values for a DR.

Thanks, this is the fun part.

It will be tomorrow for the work I have Boglevirus right now.

[purpletele]

Replace R68 and R69 with 10K 3W resistors. These are the values for a DR.

I replaced R68 & R69 with 10K 3W resistors with limited improvement.  I'll check to see if I have 20K 3W resistors and see if that knocks it down.

Thanks

BV

[sluckey]

I'll check to see if I have 20K 3W resistors and see if that knocks it down.

Don't bother. This is just going deeper into a rabbit hole.

Let's rewind a bit. so, you have "very distorted notes on the Lower register Strings". Did this just pop up since the tremolo mod? Do you suspect the tremolo mod caused this behavior? If so, pull the trem tube and disconnect the wire on the wiper of the INT pot. This totally removes the trem circuit. Still distorted?

[purpletele]

I'll check to see if I have 20K 3W resistors and see if that knocks it down.

Don't bother. This is just going deeper into a rabbit hole.

Let's rewind a bit. so, you have "very distorted notes on the Lower register Strings". Did this just pop up since the tremolo mod?
The amp was performing well without any distortion on the lower register strings prior to the Trem Mod.  I can't imagine not noticing such nasty distortion

Do you suspect the tremolo mod caused this behavior? If so, pull the trem tube and disconnect the wire on the wiper of the INT pot. This totally removes the trem circuit. Still distorted?  I pulled the wire on the middle lug of the Intensity Pot but I still have light distortion on the D String.

I still have the changed 10K resistors on the B+ Rail

I replaced the 10K resistors with the original 1K and 4.7K.  With the Intensity wiper disconnected and the V4 tube pulled out I had a nasty reverb scream.

I am leaving it with the original B+ resistors in place.

[sluckey]

Symptoms keep changing. I suspect we are dealing with collateral damage that is not related to the trem mod. I notice that your reverb pot wires are routed directly under the VTL and parallel to the wire from the INT pot. Unsolder both white wires from the reverb pot and reroute them directly/diagonally from the board to the pot. If this helps the reverb scream I suggest using shielded wire for both of these wires, shield connected to the pot buss.

[purpletele]

Symptoms keep changing. I suspect we are dealing with collateral damage that is not related to the trem mod. I notice that your reverb pot wires are routed directly under the VTL and parallel to the wire from the INT pot. Unsolder both white wires from the reverb pot and reroute them directly/diagonally from the board to the pot. If this helps the reverb scream I suggest using shielded wire for both of these wires, shield connected to the pot buss.

I moved the reverb wires into a Flying Posture and that quieted the Demon.  I'll replace those with Shielded wires.

I have the original resistors in the B+ Rail.  The amp is more quiet than before.  I have the Trem circuit disconnected and I still have the distortion on the E, A & D strings

V3-6 and V3-7 remain microphonic

That is a little forward progress

[purpletele]

Looks like I'll have a little more time, we just shut down a 28 Million dollar construction project.

Steve,

Do you think we should move forward with trying to resolve the distortion issue?  Or do you think I should revert to the original design?

If you have ideas, I have the time.  It would be cool to work through the Princeton down the road.

Brian V

[sluckey]

Do you think we should move forward with trying to resolve the distortion issue?  Or do you think I should revert to the original design?

Let's try to fix it. First, answer these...

Are you using a 50K intensity pot? Is the INT pot ground lug securely attached to the preamp ground buss? Now try this...

Replace the 47K resistor that was removed from the board when you started this mod. Disconnect both INT pot wires at the board. Pull the Tremolo tube. This totally isolates the entire trem circuit from your amp. The amp is now a basic single channel AB763 with reverb but no tremolo. At this point, do you still have distortion? If so, then something has changed while you were doing the mod but it is unrelated to the mod. It's collateral damage. If this is the case, leave the amp wired like this until we solve the distortion issue.

See attached...

[punkykatt]

Yes, put back that 47k resistor. I did the Trem-O-Nator mod last week on Doug`s AB763 6V6 amp I built for a friend back in 2005. I took the 47k out when doing the mod because the original Fender schematic did not have it. The amp had too much gain and sounded over driven so I put it back in and the amp cleaned up nicely.  My $.02  Punky

[sluckey]

Yes, put back that 47k resistor. I did the Trem-O-Nator mod last week on Doug`s AB763 6V6 amp I built for a friend back in 2005. I took the 47k out when doing the mod because the original Fender schematic did not have it. The amp had too much gain and sounded over driven so I put it back in and the amp cleaned up nicely.  My $.02  Punky

Did you use a 50k int pot? The whole purpose of that 47k is to simulate the missing 50k int pot in the Hoffman ab763.

[punkykatt]

Doug`s power tube bias vary trem had a 250k pot which I tried first because it was in there. The trem on the Trem-o-Nator was a bit week, so I put a 50kC pot in and the trem was stronger. Cant remember if I did the 47k removal test with the 250k pot or not. I must have.  Thanks for clearing that up.

[purpletele]

Do you think we should move forward with trying to resolve the distortion issue?  Or do you think I should revert to the original design?

Let's try to fix it. First, answer these...

Are you using a 50K intensity pot? yes, 50K ra

Is the INT pot ground lug securely attached to the preamp ground buss? YesNow try this...

Replace the 47K resistor that was removed from the board when you started this mod. Disconnect both INT pot wires at the board. Pull the Tremolo tube. This totally isolates the entire trem circuit from your amp. The amp is now a basic single channel AB763 with reverb but no tremolo. At this point, do you still have distortion? If so, then something has changed while you were doing the mod but it is unrelated to the mod. It's collateral damage. If this is the case, leave the amp wired like this until we solve the distortion issue.
I replaced the 47K, and disconnected the 50K pot at the board, and pulled V4.

I still have distortion 

[purpletele]

I have taken a current voltage reading throughout, this amp has 6L6's installed.  I believe I had 6 v 6  tubes when I took the original voltages.

The reverb circuit is really sensitive, I'll be installing the shielded reverb control wires shortly.

Let me know if you have any ideas based upon this current info.

Thanks

BV

[sluckey]

I still see the int pot connected!

[purpletele]

I still see the int pot connected!

I had put things back together to see where I was with tone and distortion, and to take a voltage reading with everything connected.  I had previously disconnected the circuit as described and still had distortion after the Tremolo circuit was taken out of service.

I can disconnect the Trem circuit again if you have ideas for tests.

[sluckey]

Wire the trem circuit back up and make sure it's working. It's not a factor with your distortion. But, connect the end of the int pot to the board in a straight line fashion as shown with the green highlight in the attached pic. The way you have it routed now (yellow highlight) is bad. There is guitar signal on that wire and it needs to be kept away from other stuff. In fact, if you ever put shielded wire on the reverb pot wires it would also be a good idea to use shielded wire for the int pot.

Oh, and remove that 47K resistor again. It's not needed.

[purpletele]

I pulled the 47K resistor and installed a shielded wire on the intensity pot wire and it is flying on top.  The tremolo works incredibly well, the amp is really quiet.

I replaced the two reverb control wires with shielded wire and that seemed to intensify the reverb circuit.  It's get's very caverness very quickly.  The distortion is more prevalent now.

[shooter]

thinking out loud;

any chance the board stuff is be coming conductive or oddly capacitive 

[purpletele]

thinking out loud;

any chance the board stuff is be coming conductive or oddly capacitive 

That's Covid 19 incubating!

I'll clean it up, it was starting to bug me as well.

[shooter]

 

 

[shooter]

Symptoms keep changing

If you're bored can you recap, I'm at low notes distort, not sure what high notes do?

thanks