Fender Hot Rod Deluxe to Single Channel AB763

[emerson909]

Thought I would post some details of my second build, I got a hot rod deluxe for a good price and after the success of my Bassman conversion decided to have a go at a single channel AB763. It was quite tight for space to add additional preamp valves so only added 1 for the reverb and went for a MOSFET driven bias wiggle tremolo. I also wanted to use the high impedance tank that came with the HRD so went for Merlins transformer less reverb from the valve wizard website. These were both late changes after I had built the turret board as well as switching to radial filter caps so the final layout is a bit congested in the preamp but works ok. I’ve kept the HRD 4K:8 ohm output transformer so using the 4ohm tap with an 8 ohm speaker and JJ 6V6’s. While reading about this I noticed I had installed the NFB resistor values for the multi speaker AB763s so switched the feedback to the 4 ohm tapping and kept the resistors.

The build went well but the start up has been a somewhat humbling experience  I’ll list some of the issues I had and the fixes in case it might help anybody or if anybody has any comments as to what I could have done better! I don’t have a scope so the troubleshooting has been a bit hit and miss.

I had an oscillation on initial power up leading to a high pitch squeal, no problem I thought, swapped the OT primaries and the squeal went away until I maxed out all the controls. Once the treble was on full I had another oscillation leading to loud squeal. Lots of swapping valves, moving wires, checking solder joints etc but nothing seemed to make a difference so I put a 47pF cap across the LTP plates. That seemed to tame the oscillation but not eliminate it. Then came across a post by pdf64 suggesting caps across the preamp load resistors so put 47pF caps across V1A and B and the oscillation was gone!

I was then noticing a trailing distortion on the lower notes, lots of reading led me to think this was blocking distortion caused by another oscillation. Cue lots more valve swapping, bias changing, chop sticking, moving leads, resoldering etc but no improvements. I hooked up the speaker from my other amp and turned out it was the speaker. I should have picked this up far sooner as the output volume was also really low.
 
Swapped speakers and everything was sounding good until I turned the reverb up over 3. I would get a nasty ringing sound. I tried wrapping the tank in all sorts, moving it into a different room, put the bright cap on a switch, clipped the 10pF bypass across the 3.3M resister (no improvement to reverb but sounds better so kept). Put a 2200pF cap over the recovery grid leak, no improvement. Increased said cap to 0.1uF which I initially thought had worked but it had just rolled of the highs, so I now had a mid-range ringing.

I put 10K grid stoppers on all of the preamp valves which made no difference so on the suggestion of another forum post I removed the 100uF reverb driver cathode bypass which has stopped the ringing. I went back to the 2200pF grid leak bypass cap to brighten up the reverb, it’s not as deep as before but good enough for what I want. Not sure how I could tweak it to get slightly more depth?

The tremolo was also making a thumping sound so added a diode across the intensity pot as suggested by Slucky which got rid of the thumping.

Need to get a new speaker once funds allow but otherwise very pleased with the outcome.

[emerson909]

Schematic

[emerson909]

Pictures

[stratomaster]

...everything was sounding good until I turned the reverb up over 3. I would get a nasty ringing sound. I tried wrapping the tank in all sorts, moving it into a different room, put the bright cap on a switch, clipped the 10pF bypass across the 3.3M resister (no improvement to reverb but sounds better so kept). Put a 2200pF cap over the recovery grid leak, no improvement. Increased said cap to 0.1uF which I initially thought had worked but it had just rolled of the highs, so I now had a mid-range ringing.

I put 10K grid stoppers on all of the preamp valves which made no difference so on the suggestion of another forum post I removed the 100uF reverb driver cathode bypass which has stopped the ringing. I went back to the 2200pF grid leak bypass cap to brighten up the reverb, it’s not as deep as before but good enough for what I want. Not sure how I could tweak it to get slightly more depth?

You can try a 560pF plate to cathode cap with the cathode bypass cap restored to your reverb driver.

If that doesn't cure it you can try a series resistor with the cathode cap.  Something in the 1k-3.3k range may be enough to increase depth without inducing oscillation.

Finally you can try a split plate load, say 6.8k and 3.3k for a cut of about a third of the voltage from the driver.  Adjust to taste.  8.2k/1.8k would be another good one to try.

[emerson909]

Thanks for the suggestions, I'll try crocodile clipping in some components and report back with the results.

[pdf64]

... Once the treble was on full I had another oscillation leading to loud squeal. Lots of swapping valves, moving wires, checking solder joints etc but nothing seemed to make a difference so I put a 47pF cap across the LTP plates. That seemed to tame the oscillation but not eliminate it. Then came across a post by pdf64 suggesting caps across the preamp load resistors so put 47pF caps across V1A and B and the oscillation was gone!

My guess is that the convoluted layout may be causing an excessive degree of unintended coupling between early and later stages, forming feedback loops sufficient to result in free running oscillation. eg the tone stack components are mounted over by V3 and 4 components / circuits.

It's best for the layout to follow the schematic; the input and output sockets, valve sockets and front panel controls are part of that, it's not just the circuit board. But with any real world build, there's a compromise, hence it's best to follow known good chassis / and board layouts.

... everything was sounding good until I turned the reverb up over 3. I would get a nasty ringing sound. I tried wrapping the tank in all sorts, moving it into a different room, put the bright cap on a switch, clipped the 10pF bypass across the 3.3M resister (no improvement to reverb but sounds better so kept). Put a 2200pF cap over the recovery grid leak, no improvement. Increased said cap to 0.1uF which I initially thought had worked but it had just rolled of the highs, so I now had a mid-range ringing.

I put 10K grid stoppers on all of the preamp valves which made no difference so on the suggestion of another forum post I removed the 100uF reverb driver cathode bypass which has stopped the ringing. ...

The layout may be contributing to that too.
But grounding could be playing a part. I think R31, R32 and its bypass cap, and the return from the tank, need grounding to C36 B node cap -ve lead. ie don't let them ground out anywhere else.

Rather than completely remove the R32 bypass, try a resistor in series with it, start with 470R same as R32. Reduce it if that's totally stable, eg try 220R.

[emerson909]

Thanks for the feedback (no pun!), massively appreciate it. Yes this might have to be my prototype board, switching to radial filter caps and moving the power tube screen resistors to the sockets freed up lots of space towards that end of the board. I also realised there's no need for the trem circuit to be where it is and it would be better off over by the bias circuit. I could then also swap the position of the reverb driver and recovery circuits so the wires aren't crossing. If I’d realised this all at once I would have redone the board but it sort of developed as I was going after I’d staked all of the turrets! I’ve really enjoyed building it so will be fun to have another go.

I moved the tonestack to where it is to keep the wires to the pots as short as possible after seeing the Psionic audio deluxe reverb PCB conversions.

it's best to follow known good chassis / and board layouts.

Yeah I started off based on the Hoffman single channel but then changed the trem and couldn’t find a layout for that circuit so had to go freestyle, then squeezed the reverb load resistor and that giant 1uF cap in  .

But grounding could be playing a part. I think R31, R32 and its bypass cap, and the return from the tank, need grounding to C36 B node cap -ve lead. ie don't let them ground out anywhere else.

I did also think this and separated out all the tremolo grounds but I had the reverb grounded to the preamp bus per the Hoffman design so it was going to be more difficult to separate and it went in the ‘if all else fails’ category! Maybe one to look at for Rev 2.

Rather than completely remove the R32 bypass, try a resistor in series with it, start with 470R same as R32. Reduce it if that's totally stable, eg try 220R.

This is the way I’m going to go, will clip some resistors in over the weekend and see how it goes. Thanks again!

[emerson909]

Decided I'm going to redo the board as attached, hopefully this will get rid of some of the gremlins!

[pdf64]

...
I did also think this and separated out all the tremolo grounds but I had the reverb grounded to the preamp bus per the Hoffman design so it was going to be more difficult to separate and it went in the ‘if all else fails’ category! Maybe one to look at for Rev 2.
...

The reverb drive circuit is very different though to the trad arrangement used with Hoffman, the transformer is a bandpass filter and provides galvanic isolation.
So for V2 keep it simple if you wish, but I suggest to make provision in the layout to keep things in line with Merlin's guidelines, eg add a few suitably placed turrets http://www.valvewizard.co.uk/Grounding.pdf

Also reading through that might explain why referring the bias winding to the HT rectifier negative lug doesn't seem good practice.

The V2 cathode bypass cap will need an extra turret for a series resistor?

[emerson909]

So for V2 keep it simple if you wish

Ha ha no I thought I had separated them but looking at it yes can see there's a few issues, back to the drawing board!

Also reading through that might explain why referring the bias winding to the HT rectifier negative lug doesn't seem good practice.

I can't see what you mean on this one, I've got one side of the bias winding connected to D15 and 1 to the power section earth point (along with the HT rectifier negative). Not sure where else I would ground it, it seems to follow Merlin's scheme but maybe I'm missing something??

The V2 cathode bypass cap will need an extra turret for a series resistor?

Yes I've got this one although just got a link in for now as hopefully I won't need it

Thanks again!

[emerson909]

With regards the reverb I've moved R31 and R32 to B node ground. Presumably R94 and R33 are part of the input to V3A and should be grounded to the D node per the attached schematic?

I hadn't really realised until you mentioned it earlier regarding the transformer providing isolation between the stages, think I can see the issues a bit better now.

[AlNewman]

So you're still using the original reverb tank?
If so, you're trying to build a tube reverb into a tank that was designed for transistors.
There was a thread recently regarding a transformerless reverb, and there are different driver tubes that work better with different impedences, and there may be options for building a voltage divider that works with your tank, but that would take far more intelligent people than me.
The end result in that thread turned out that the best solution was a new tank.  Coupled with a certain driver and voltage divider.

[emerson909]

So you're still using the original reverb tank?

Hi Al, yes it is the original 600 ohm tank, I've followed Merlin Blencow's design here;https://www.valvewizard.co.uk/reverbdriver.html

I've measured 4.9V across the 12AT7 470R cathode resistor so I think the 12AT7 is correctly biased for 10mA as needed.

I've been out with the soldering iron this morning and separated R31, R32 and it's bypass cap and R94 from the preamp ground bus. They're now grounded direct to chassis on one of the reverb jack tabs.

R33 was previously grounded to chassis but I've wired that to the preamp ground bus, I had to increase the bypass capacitor slightly to 3.3 nF as I couldn't reuse the 2.2 and didn't have another.

I've got a 470R wired in series with R32 cathode bias. Looks like the updated schematic attached.

Initial signs are promising, it's too early to test with any volume but with the channel volume up and master volume down I'm not getting the ringing where I would previously.

Will hopefully get a chance to do some mor testing later.

[stratomaster]

Based on info in a thread about cathode bypass caps and hum I'd recommend swapping the locations of the 100μF and the 22μF. 

Also, there's good reason to believe the grid leak bypass cap forms an RLC resonance circuit with the reverb tank output transducer, and can actually peak the treble instead of cut it.  If you want to shape the treble try leaving that cap out and instead place a 330-680pF cap across the plate resistor.

[emerson909]

Thanks, the 560pf caps you recommended arrived earlier, managed to install one across the driver load resistor and I think the cumulative effect of today’s mods has worked. Still not had chance for a proper test but it’s definitely better than before. Thanks again

[emerson909]

OK so got chance to test the amp this morning and I'm really happy with it, the reverb is totally usable and  much deeper than with the cathode resistor unbypassed, I don't get the ringing at any realistic setting now.

I recorded a quick demo of the reverb and trem, I'm a terrible player so please try to ignore that!

https://www.dropbox.com/scl/fi/icv8zpd2ryt3gfm99bglu/AB763-reverb-and-trem.wav?rlkey=56tncb8ft46s2bjdaaeok7bh3&st=gpc476nc&dl=0

I'm playing a les paul, bridge pickup into input 2 with volume around 2.5 and master volume on 10, reverb around 3.5

I'm still going to do a second version of the board but not in so much of a hurry now.

Thanks for everyone's help.

[emerson909]

This is how the Reverb is wired now with the revised grounding and plate bypass cap installed

[pdf64]

...

Also reading through that might explain why referring the bias winding to the HT rectifier negative lug doesn't seem good practice.

I can't see what you mean on this one, I've got one side of the bias winding connected to D15 and 1 to the power section earth point (along with the HT rectifier negative). Not sure where else I would ground it, it seems to follow Merlin's scheme but maybe I'm missing something??

From the Merlin grounding document -

Fig. 15.4: Current flows around the transformer-rectifier-reservoir in short heavy pulses that may be a source of buzz.
 ...
To minimise the interaction of ripple current with the rest of the circuit, the transformer-rectifier-reservoir must be treated as a single, self-contained circuit block.
In some schematics this is emphasised by drawing the circuit in a more compact fashion, as in fig. 15.5, and the circuit should be physically built in a similarly compact way.The rest of the amplifier will then be connected directly to the
terminals of the reservoir capacitor. Connections to any other points on this noisy current loop are not allowed, and no part of this network may be connected to the chassis if a quiet ground scheme is to be maintained!

So the reservoir cap negative terminal should be the local star point / start of the common bus.
Whereas your layout shows the rectifier negative terminal used for this.

Furthermore -

In a fixed-bias amp the negative bias supply should be considered to be a tiny power supply in its own right, so the same grounding logic can be applied. The whole bias supply is built with its own star (or possibly bus) ground scheme, and the last stage
-often a bias adjustment pot-is finally connected to the audio circuit, as in fig. 15.13.

[pdf64]

With regards the reverb I've moved R31 and R32 to B node ground. Presumably R94 and R33 are part of the input to V3A and should be grounded to the D node per the attached schematic?
 ...

Sorry, it's probably not significant but R94 should be referred back to the B node cap too.
More significantly, so should the shield lug of the reverb drive RCA socket. ie to do that, insulated washers will be needed to prevent it connecting to the chassis.

Whereas R33 should be referred to the local D node star point, same as the cathode resistor of the stage it's related to.

Keep in mind the heavy-ish current loop driving the tank, and the miniscule current loop at the inputs.

I recorded a quick demo of the reverb and trem

Well done, it sounds great, I especially like the trem!

[emerson909]

Right, I think I see what you mean, moving the existing wire from ground to rectifier to the filter cap ground (purple arrows in attachment). I was thinking both were electrically similar but not thinking about current flow. I can make that change pretty easily.

[pdf64]

Right, I think I see what you mean, moving the existing wire from ground to rectifier to the filter cap ground (purple arrows in attachment). I was thinking both were electrically similar but not thinking about current flow. I can make that change pretty easily.

Yes, that's it 

[emerson909]

Sorry, it's probably not significant but R94 should be referred back to the B node cap too.
More significantly, so should the shield lug of the reverb drive RCA socket. ie to do that, insulated washers will be needed to prevent it connecting to the chassis.

I've got both of these grounded to the chassis atm, it's going to be difficult to get the insulated washers on the RCA jack so will leave that for when I redo the board, there is a noticeable buzz on the reverb once it gets over midway so this could be the cause.

Well done, it sounds great, I especially like the trem!

Thanks!

[Willabe]

Right, I think I see what you mean, moving the existing wire from ground to rectifier to the filter cap ground (purple arrows in attachment). I was thinking both were electrically similar but not thinking about current flow. I can make that change pretty easily.

Yes, that's it 

No, that's not it, it's close but not right.

That next filter cap C36 can't be directly attached to C34. Has to be a wire between the 2.

The way it's wired now, it's wired directly into that 1st filter cap loop.

[emerson909]

ok will have to design that into the rev 2 board. I already re wired the existing amp! Looks like this now. It's really quiet with no signal, just a bit of hiss.

[emerson909]

This is what Rev 2 is currently looking like incorporating previous comments,

I've hopefully now got reverb driver and trem circuits grounded to the B node which is separated with a bit of wire from the A node. Will add insulating washers to J8 when the board is out.

I also swapped the master volume and trem pots around to shorten the leads and avoid crossing.

[pdf64]

The grounding seems a bit convoluted, doesn't make sense to me, eg the controls seem to be connected to the C node?

Have a look at how Michael at Modulus arranges things with local star points that get linked together and then the input stage cathode return is connected to the  chassis near the input.
https://download1655.mediafire.com/uod54furnnjgbv1swTr78UYkbEvrefPdf9QtUJG37W6M2D_BzaKqw9iI0Yte4-RGoF1CZisldeLxEMQu263g3WYrZAFQaCZq4_xk_9BCYQ6YbMJLkHiaGeeEHEI2iO3yzn3kAReS2elFKEAO9YvKriMkpwa2T1F3JpIgTFU/hma7541vr8kou1z/GTS-20+Layout.pdf

I suppose as the current arrangement isn't hummy, it's a somewhat academic point :)

[Willabe]

I'm would think his grounding scheme works, or he wouldn't post it, but,

He's got the heater CT connected with the 1st filter cap ground and PT B+ CT.

So the charging pulses can be pushed into the heaters wiring, I wouldn't do that.

[pdf64]

Good point 
To eliminate the potential for heater buzz interference, I recommend DC elevation of the heater circuit.

But yeah, as it works fine as is, then theoretical improvements beyond that becomes an 'angels on a pin head' kinda thing.

There's nothing wrong with that though, provided we don't let 'best' become the enemy of 'good enough' :)

[emerson909]

The grounding seems a bit convoluted, doesn't make sense to me, eg the controls seem to be connected to the C node?

I was thinking the same 

It might not be clear from the layout as to where the grounds actually are as I don't show the earths on the tag strips. Also not clear that the input jacks are isolated from the chassis. I've uploaded another layout showing the grounds and slightly rearranged preamp bus.

There are 4 connections to chassis;

1. Safety earth for 240VAC supply connected direct to chassis via bolt and star washer with nothing else.

2. Power Section earth for A and B node bus and bias 50VAC neutral connected to chassis via 1 of the tag strip grounded terminals.

3. Heater artificial centre tap connected to chassis via 1 of the tag strip grounded terminals.

4. C and D node bus connected to chassis via 1 of the tag strip grounded terminals near the input jacks. The other end of this bus is insulated from chassis.

I'm trying to follow the principle of having 2 main ground busses, It would be difficult to implement a scheme like Michael's as I'd have around 9 terminations to make on the pre amp filter cap -ve terminal, so would end up having to do some sort of bus arrangement anyway.

I noticed I had sort of run another bus for the preamp in the last layout I posted, I've split this up for each stage now with a single connection to the main bus in circuit order per Merlin's 'improved bus' scheme

As you have pointed out I think I'm getting to the point of diminishing returns as it's already a quiet amp although I obviously want to make it as good as I practically can. I think elevating the heater currents will be one for a future build :)

Thanks once again for all the feedback, you've all really made me think about some aspects of the design!

[Willabe]

There's nothing wrong with that though, provided we don't let 'best' become the enemy of 'good enough' :)

Just have to move that 1 wire. 

[Willabe]

Schematic

I want this schematic close, so we don't have to scroll all the way back to almost the start. 

https://el34world.com/Forum/index.php?action=dlattach;topic=32112.0;attach=116012

[emerson909]

Had to make a small change, I had the tremolo supply connected to   B+.

[pdf64]

...
I'm trying to follow the principle of having 2 main ground busses, It would be difficult to implement a scheme like Michael's as I'd have around 9 terminations to make on the pre amp filter cap -ve terminal, so would end up having to do some sort of bus arrangement anyway.

I noticed I had sort of run another bus for the preamp in the last layout I posted, I've split this up for each stage now with a single connection to the main bus in circuit order per Merlin's 'improved bus' scheme

To continue discussing how to make an amp that doesn't hum less hummy  -

Rather than Merlin's improved bus, by having the separate power amp and preamp connections to the chassis arrangement, what's happening is that charging / ripple current for the C and D nodes is passing from the reservoir, via the chassis, through the preamp chassis connection, to the caps. See the red ripply current path below :)



I suggest that to better approximate Merlin's layout, you lift the power amp, reservoirs etc off the chassis, and make a wire link between the B and C cap negative terminals.

[emerson909]

To continue discussing how to make an amp that doesn't hum less hummy  -

Yes we will get rid of this hum whether it exists or not! 

[emerson909]

Finished the Rev 2 build, the new layout definitely makes more sense, I'm away for a week from tomorrow so not going to get chance to test it until I get back, will let you how it goes.

[emerson909]

Well this has turned out to be a complete disaster, I think I‘ve built a Geiger counter with added squeal at max vol and treble.
Amp is just a complete mess of squeal, static, hiss and ironically hum! Video of the horror show;
https://www.dropbox.com/scl/fi/s1qxbo4tnk2ovx133ww8u/20241103_192915000_iOS.MOV?rlkey=3t0jhdrdcovjze78j8h5pn1v4&st=8zhxs02m&dl=0
The static is not affected by the channel volume, but when the reverb is engaged and turned up the static goes??
To try to isolate the issue I’ve done the following;
Chopsticking around V3B grid seemed to have an impact so removed the grid stopper and remade the connections at the valve and board but no change.
Turned off trem and reverb using footswitch
Remove reverb driver (V2) – This gets rid of the oscillation but the static and hiss remain.
Removed V4 (PI), reduces volume of static but still present.
Removed V3, no change
Removed V1, no change
Reinstated V1, V3,
Grounded V1A grid, no change
Grounded V1B grid, no change
Grounded V3A grid, no change
Grounded V3B grid, big reduction in static
As volume has no impact assume V1A is good.
Lifted V1B plate resistor, no change
Lifted V3A plate resistor, no change
Lifted V3B plate resistor, big reduction in static
Replaced V3B load resistor, no change
Replaced R37, R38, no change
Replaced V2 plate resistor R92 and R93, R94, no change
Changed ground scheme to pdf64 last suggestion so A and B node is off chassis and connected to end of pre amp bus bar, effectively connected to C no change.
Seems the issue is something around V3B but I’m out of ideas now other than to go back to previous layout.
All valves and reverb tank were good before the amp was dismantled (destroyed).
Any help appreciated!! 

[Willabe]

You have 2 black wires attached to the 1st B+ filter cap ground lead. They go over to the corner of the chassis. 1 goes over close to the rectifier socket, I can't see what it's hooked up to?

The other goes over to the solder lug strip, and seems to connect with 2 off colored black/dark charcoal gray that come from the PT. What are those wires? Are they the -bias wind fly leads?

And 1 of them is grounded with the 1st B+ filter cap ground lead?

And that solder strip lug is bolted to the chassis for ground?
 

[emerson909]

One goes to the rectifier -ve, one used to go to chassis ground although I moved it to the end of the preamp ground bus, moving it made no difference

[Willabe]

And the 2nd B+ filter caps ground lead has a black wire attached to it coming from what looks like a chassis grommet hole that has OT wires coming through?

Where does that black wire go? What's it connected to?   

[Willabe]

One goes to the rectifier -ve, one used to go to chassis ground although I moved it to the end of the preamp ground bus, moving it made no difference.

This makes no sense.

What are those 2 off colored black/dark charcoal gray that come from the PT?

[emerson909]

2 off colored black/dark charcoal gray that come from the PT. What are

And that solder strip lug is bolted to the chassis for ground?
 

Off colour wires are the 220/230v taps off the pt, they are just terminated on spare terminals. I’m using the black 240v tapping.

Yes the tag strip has 2 grounded terminals, one has heater artificial centre tap and the other has the bias 50vac neutral, used to also have the b+ ground before I moved it

[Willabe]

One goes to the rectifier -ve,

I don't understand this.

What rectifier negative?

And where's the PT's B+ high acv wind's CT?

[emerson909]

Not sure how to explain it then but you can see it better in the pic in reply 23.

It’s the same as it was before when it was working

[Willabe]

I'm asking about the wires at the end of the solder lug strip close to the fuse.

There's a brown wire there that goes from the solder lug strip over to the -bias circuit?

[Willabe]

I'm asking about the 4 wires at the very end of that solder lug strip next to the fuse and next to/just below the red wires.

[Willabe]

Ok, so this PT has no B+ CT?

Your using a SS FWB rectifier?

That's why you said rectifier negative. 

[emerson909]

I'm asking about the 4 wires at the very end of that solder lug strip next to the fuse and next to/just below the red wires.

The pt has no ht centre tap

It has a 50vac tap which is the brown wires. Hot is terminated into the 1st terminal and a wire is taken across to the bias rectifier diode

Neutral is terminated into the second grounded terminal. This used to also have the B+ (black wire) but I moved that to the preamp ground bus so now the second terminal only has the 50vac neutral.

[emerson909]

Ok, so this PT has no B+ CT?

Your using a SS FWB rectifier?

That's why you said rectifier negative.

Yes correct, sorry we’re a bit out of sync with our replies! Trying to be clear

[emerson909]

Its shown on page 3 of the schematic, reply 1

[Willabe]

The pt has no ht centre tap

It has a 50vac tap which is the brown wires. Hot is terminated into the 1st terminal and a wire is taken across to the bias rectifier diode

Neutral is terminated into the second grounded terminal. This used to also have the B+ (black wire) but I moved that to the preamp ground bus so now the second terminal only has the 50vac neutral.

Ok.

This has to be changed.