First time Build VJ to Baby Will conversion

[Hollytron]

Hi there I've been putting together a baby will (Lite 2B) as a converted valve junior and I have some questions that the spotty manual and online materials that are provided for the build did not answer. These forums have already been super helpfull BTW.

I have the baby will PCB, the MPS OT20PP output transformer and the PT275.2 power transformer. Its all wired up and ready to test voltages but I ran into some info that has made me reticent to plug it in.

-Do I need to run a 4A slo blow on the heater supply? (this tidbit was hidden in one sentence in the manual and not shown in any of the schematice or layouts ) I do have a 2A slo blow on the power supply.

-Im pretty confident that I have the the High voltage secondary attached correctly but I have the two 275v leads going to t1 and t2 on the PCB and am not using the "center tap" on the PT. The stock tranny had a 0V and 260V which were the options. Is the 0V the "center tap"?

Thanks much and please let me know if you have any tips on how to improve my work. Ive done a bunch of guitar setups and build a handfull of pedals but this is my first crack at an amp and I'm sort of regretting trying the cheap thing first.

[JMPGuitars]

Your PT has more than 2 wires if it's the model you stated. It actually has 4 leads on that part of the secondary. 275-0-55-275. You would be using the 275-0-275; the 0 (orange wire) being the center tap. It looks like from their layout/schematic you connect the CT to ground:
https://www.guitaramplifierpcbs.com/sit ... c-v5_0.pdf
https://www.guitaramplifierpcbs.com/sit ... ode-v1.pdf

I built their Plexi SE into a VJR around 12 years ago. It was a cool little amp.

[Hollytron]

Your PT has more than 2 wires if it's the model you stated. It actually has 4 leads on that part of the secondary. 275-0-55-275. You would be using the 275-0-275; the 0 (orange wire) being the center tap. It looks like from their layout/schematic you connect the CT to ground:
https://www.guitaramplifierpcbs.com/sit ... c-v5_0.pdf
https://www.guitaramplifierpcbs.com/sit ... ode-v1.pdf

I built their Plexi SE into a VJR around 12 years ago. It was a cool little amp.

Ok great I had been looking at that schematic but was not sure what went to ground. Im glad I never turned it on without doing that. That is awesome info.

Any tips on the fuse question?

[Bieworm]

I never put fuses on the heater supply. Always on mains though, and sometimes on the B+. In the event your heaters would draw excess current, the mains fuse will/should blow.
I would desolder the heater and high voltage wires an twist each pair tightly before soldering them back in. The way they are now may cause hum.
Also, do you have a schematic for this particular build? I don’t see a center tap wire for neither heater or HT winding. If there is none for the HT you’d probably need to add the missing diodes on the PCB to create a FWB rectifier. The heaters need a CT wire too ofcourse. If there isn’t one you need to make an artificial CT with 2x 100 ohm resistors. I think they are on the PCB, but I can’t be sure without a schematic and layout of this amp

[Hollytron]

Also, do you have a schematic for this particular build? I don’t see a center tap wire for neither heater or HT winding. If there is none for the HT you’d probably need to add the missing diodes on the PCB to create a FWB rectifier. The heaters need a CT wire too ofcourse. If there isn’t one you need to make an artificial CT with 2x 100 ohm resistors. I think they are on the PCB, but I can’t be sure without a schematic and layout of this amp

https://www.guitaramplifierpcbs.com/sit ... ode-v1.pdf

https://www.guitaramplifierpcbs.com/sit ... c-v5_0.pdf

These are the layout and the schematic for the amp I am building. I have added the CT for the HV to ground like was suggested above and I think the schematic shows the artifically center tap for the heaters although my Power Transformer does have a 0V on the heater side. Thanks for the tip on the twisty wires, I thought I had twisted them enough but I am going to take your advice and redo that part.

[Bieworm]

In case the 100 ohm resistors are soldered as an artificial center tap for the heaters, you can snip off the CT wire from the transformer.
If it were my amp, I would desolder the resistors and connect the CT wire to ground at the 1st filter cap. That way there is no danger that the 100 ohm resistors can fail.

[Hollytron]

Ok cool so I have been going over the schematic and see where I can attach the heater center tap and while doing so stumbled upon another post on this site where JMP guitars advises another person with the same amp as mine to connect the heater CT to ground. It seems like this would be a better plan than trying to get it on the board after the first filter cap. Although there is an open spot on the board labeled "ground" that could be there for just this purpose (see my first photo I am pointing to the spot with tweezers). Does this correspond to the Ground on C1 that is shown in the schematic and if so, can I just connect the heater CT at that spot?

IMG_1339.jpg

Furthermore I read the post on grounding schemes and decided to not have all of my grounds on the same post and thus devised two more in my chassis. This is my second photo. Anyone see any problems with these?

IMG_1337.jpg

Thanks much yall!

[Hollytron]

Here is the schematic

Screenshot 2023-12-24 185448.png

[Daviedawg]

There is a whole big forum on Wattkins devoted to the Baby Will. Unfortunately despite being on there quite recently I have not been able to get on there in the last few days.

Dd

[Hollytron]

I can't even figure out how to request access.

[Daviedawg]

No. Some sort of block on it. One day I was on the next access denied.

Dd

[Hollytron]

I finally got this thing done! It turns out it sounds great and is really quiet as far as idle hum is concerned. I am really happy with how this amp turned out, its louder, cleaner and brighter than I expected. All good things in my book.
Thanks much for all of the help with this thing, I learned a ton from this experience and want to build something else soon.

IMG_1350.jpg

IMG_1351.jpg

[Daviedawg]

Well done. But look forward to a fixation with amp building and related stuff.

Dd