Hoffman Fender Blues Junior Conversion

[Strat-ish]

Hi all,

This is my first re-build, so I apologize for my newbie questions, but just may need a bit of hand-holding. Also sorry if the answers are on the site and I missed them.

I have my boards mounted and laced and am ready to start my initial connections, so I have a series of questions to make sure I don’t mess things up at the get-go. (measure twice…)

Any help is greatly appreciated!

On/Off toggle:
The stock amp has the power transformer connecting to the front lugs and power chord to the back lugs (meaning towards the back of the chassis, which are the 2 angled lugs). In the schematics and the build photos it ‘looks’ like it’s the other way around. Or am I seeing/reading it wrong?

I am inclined to keep connected the way it is unless there’s a specific reason it changes from the stock?

Power LED
I’d like to be sure I know where to connect the stock LED. Is it just directly to the filament wires and the tube board (with the 180 resistor)? Does it matter which side the resistor is on?

Speaker Jacks
I’m having trouble discerning how the second speaker jack connects. I have an OT with the same wiring as stock (black and green). In the photos I’m seeing a green wire and an orange wire each going to a different jack, so it’s not translating to me. Or, is simply that they get jumper-ed to each other (green to green and ground to ground + the middle lug)?

Grounding
Is it better to make a new spot to mount grounding wires to the chassis? Or (if I can manage it) is it ok to just use one of the PT mount bolts?

Thanks in advance!!

[vampwizzard]

a lot of us have required hand holding. no worries there.

On Off Switch: Mimic what you see. It shouldnt matter which half is wired to which half of the on off circuit just as long as you go 1A:1B and 2A:2B.. dont cross lugs.

Power LED appears to be LD1 on the schematic. Make sure youre connected to R34/CR6 correctly as well as the V1 pin 9 rail

Speaker Jacks: cant help you here, ill leave that to others more knowledgable

grounding: mimic what the original did. It is better to give it a separate ground lug than to a PT lug.  info: https://el34world.com/charts/grounds.htm

[sluckey]

Read https://el34world.com/Hoffman/Blues_Junior_Build.htm again. Special attention to this note near the top of the page...

Note that Hoffman boards are not assembled by looking at my builds.
I do test builds first and change the designs based on those builds.
You assemble Hoffman boards using the documents listed below.
The Layout Diagram, Schematic and BOM for this board are on this page


...and this note too...

"My customer sent me an Allen power transformer as an upgrade.
He also wanted an upgraded output transformer and so I installed a 768 Heyboer output transformer"

As stated, the OT in the pictures is not the original OT. The upgrade has multiple output impedances so Hoffman wired a second jack with a different OT impedance tap. But you have the original single impedance OT so wire a single speaker jack as shown in Hoffman's documents.

[EL34]

Steve already pointed out info that you should have seen by looking at all the documents on the library page here
https://el34world.com/schematics.htm#Hoffman_Blues_Junior_Conversion

Make sure you look at all the info

[Strat-ish]

Thanks everyone for your responses!

I have gone through the schematics, I know the photos are for an altered build (with a different OT), and understood them in theory, but in practice I was getting a bit lost. Like I said, a total newbie.

What I may do (if you don't mind), is edit the schematic to show how I'm reading the connections and if someone would kind enough to let me know if I'm reading it right.

With the on/off power toggle, if the connection side doesn't matter (won't break or blowup), is there a way to discern which direction is on or off by the connection so it corresponds to the labels on the amp face?

I appreciate info on the LED, but it went over my head, but I'll add it as I understood it to my schematic and see if I got it.

If I get this together maybe it'll be helpful to other folks.

Thanks again, you guys are great!

[sluckey]

With the on/off power toggle, if the connection side doesn't matter (won't break or blowup), is there a way to discern which direction is on or off by the connection so it corresponds to the labels on the amp face?

Use your ohm meter.

[Strat-ish]

How does this look? (See if I interpreted it right)

[sluckey]

I suggest to remove the jumper between the switch and ground lugs on the right speaker jack.

[Strat-ish]

Got it, thanks! Everything else works?

[sluckey]

The speaker jacks jumped out at me and I didn't look further.

[Strat-ish]

Hello all,

I wanted to update this thread. I've been off my project for various reasons and would love to get back into it.

I've revised my schem, would anyone be able to look it over and check my work? (I'm a very visual person, so being able to properly see the connections is key to me)

I appreciate any help. Thanks in advance!

[mresistor]

Note - that is a layout   not a schematic. 

[Strat-ish]

Thanks! Any other corrections?

[mresistor]

That looks like Hoffmans layout,, what exactly have you changed on it?

[Strat-ish]

I've included the connections to the OT, PT, and power chord (as I interpreted them) to have it all in one. As I mentioned at the top of the thread, I'm a newbie and want to be sure I'm interpreting things correctly. (connect them on paper before the board—measure twice, cut once) Thanks!

[mresistor]

so far looks ok to me ..   

[Strat-ish]

Thanks!

[acheld]

One thing to know about Hoffman's layouts:  the preamp ground is intended to be close to the input jack, with the ground bus connected there, NOT close to the Meat pot as it appears on the layout.   It's just the way he drew these layouts back in the day . . .

My recollection is that there is not a distinct ground connection from the bias winding from BJ transformers -- I'm assuming you drew that in to tie up the loose end?

It's a sweet little amp!

[Strat-ish]

Thanks for the comments acheld. It is from the original diagram, I figured that the ground next to the meat pot was simply to indicate that the bus wire was a ground. I see that the ground from the input goes to a lug on the circuit board. Is that all that's needed for that section?

For the PT (original BJ), I have two wires (brown-ish) that I presumed were the wires that go to the bias and to ground. Is that what you're referring to and do I have it correct?

Much appreciated, I am looking forward to bringing this to life!

[sluckey]

I see that the ground from the input goes to a lug on the circuit board. Is that all that's needed for that section?

Yes, if using Switchcraft jacks. Hoffman's layout depends on the Switchcraft input jack ground lug to provide a good connection to the chassis. If using isolated Cliff style jacks you'll have to use a short wire between the jack ground lug and chassis.

For the PT (original BJ), I have two wires (brown-ish) that I presumed were the wires that go to the bias and to ground.

That is correct.

[Strat-ish]

Thank you!