blues jr conversion project - initial questions

[rsr]

i'm about to start a rebuild of a billm modified blues jr.   
I've reviewed the PDF wiring and layout diagrams (really good) and pictures and i have a few initial questions before i start.  i'm sure there will be others as i go, and i appologize in advance if some of these are dumb questions, but i'm pretty green at this.

The amp has a number of billm replacement components in the circuit. As advised previously, i'll do the hoffman circuit as designed, except as noted below, to start with and see how it sounds and then incorporate some of those mods if it seems worthwhile.

For background, i use a 5771 tube in V1 as i like things a little less gainy (i play a mix of blues and jazz) and also a cannabis rex speaker.  The resulting sound, with the billm mods is just fantastic.  I'm trying to preserve this as much as possible. But, the amp has some sort of intermittent component/wiring/vibration/heat related issue that has been impossible to diagnose. That's the reason for the rebuild. Not to change the tone, but to correct that flaw.

So, the questions...

- i'll be using the billm TO20B output transformer (http://billmaudio.com/wp/?page_id=1546)
Does that change anything in the hoffman circuit or wiring?

- i'd like to re-use the billm filter caps that i have in there now.  Spec-wise they match except they are 450 volts instead of 500.  The billm site says that's still comfortably over the BJR operating voltage of 330v.  This should be fine, right?

- the amp currently has the billm standby switch mod.  i'd like to keep that.  how do i wire that 3 position switch with the hoffman board?

- in the PDF wiring diagram, there are a bunch of little lasso looking things where ground wires from the input jack and pots appear to loop around the shielded wires that go to the tubes.  What do those mean?  My guess is that those ground wires get soldered to the shielding of the RG174 wires. Is that right?

- In the PDF, it doesn't appear to me that the FAT footswitch jack is hooked up anyplace.  Am i missing something or has this been omitted?  I'm fine without it, just not sure how to interpret what i'm seeing.

- the hoffman circuit has V2 jumpered to "give it a little more push" and is described as a mod in the tube board replacement. I like the sound as is so i won't be doing that.  Does that affect anything else in the hoffman circuit?

- the parts list has a mix of 18 and 20 gauge wires.  I think the 18 is only used for the tube board, which i've already done. As far as i see, the PDF and pictures don't really indicate which gauge wire is use for which connections.  I've already done the tube board, and i have a bunch of 18 gauge wire on hand. So, can i just use the 18g wire everywhere?  If not which gauge goes where?

Thanks in advance
roger

[shooter]

for reference this is what I'm looking at
http://el34world.com/Hoffman/files/Hoffman_BluesJunior.pdf

OT;
from your link I got this;

it is ideal for a 2xEL84 or a 2x6V6 amplifier using an 8 ohm speaker

re-use the billm filter caps

you got 4?, all =or> than the uF Doug's using?

how do i wire that 3 position switch with the hoffman board?

Doug doesn't have a standby, so I would post a pick of the schematic section from what you have so we might make sense outta no switch to salvaged switch

FAT footswitch

that's cuz it's a toggle switch, goes tween VOL & TReble

can i just use the 18g wire everywhere?

yup, 18g is bigger than the 24g stranded I use for everything but fil.

[rsr]

for reference this is what I'm looking at
http://el34world.com/Hoffman/files/Hoffman_BluesJunior.pdf

Yep, that's the wiring diagram i'm referring to.

re-use the billm filter caps

you got 4?, all =or> than the uF Doug's using?

I have all 4.  The uF's match exactly, the difference is just the voltage.

how do i wire that 3 position switch with the hoffman board?

Doug doesn't have a standby, so I would post a pick of the schematic section from what you have so we might make sense outta no switch to salvaged switch

I don't have a schematic.  I do have the instructions from billm that i followed when installing it previously.  They say:
- "plug both white wires (that were going to the original switch) to the circuit board P9 and P10"
- "unplug the red transformer wire from P12 and plug it into the angled terminal on the new switch"
- "plug the black wire from the line cord onto the low terminal on the new switch"
- "plug the black wire from the circuit board onto the left terminal of the new switch"

So, i guess all i really need to know is what on the hoffman board corresponds to P9 and P10 from the bjr cream board?
And, i guess  the "black wire from the circuit board" means the wire from the fuse, right?

FAT footswitch

that's cuz it's a toggle switch, goes tween VOL & TReble

Yes, there is the toggle switch on the amp face panel for FAT and is see that in the wiring diagram, but there is also a footswitch jack for it next to the speaker jack.   That's what i'm referring to.

can i just use the 18g wire everywhere?

yup, 18g is bigger than the 24g stranded I use for everything but fil.

Thanks

[sluckey]

As I said a few days ago...

I suggest you do this conversion exactly according to Hoffman's plan. After it's up and running, then tackle BM's mods one at a time. You may find that some of them are no longer needed. You may also find that some cannot be adapted to the Hoffman circuit. We can help you figure all that out.

You need to focus on Hoffman's plans and info and forget about the original BJ or any BillM mods. Just get Hoffman's circuit working first. That will be quite an accomplishment.

Hoffman sells that three position switch. The listing for the switch also contains a link to detailed generic instructions for wiring this switch. It's easy to do. There are no specific instructions for the BJ. We can help. Quit looking at those BillM instructions! They will not give you any useful info on wiring this switch to Hoffman's circuit.

Just connect a wire from the front panel FAT switch ungrounded lug to your footswitch jack.

[rsr]

As I said a few days ago...

I suggest you do this conversion exactly according to Hoffman's plan. After it's up and running, then tackle BM's mods one at a time. You may find that some of them are no longer needed. You may also find that some cannot be adapted to the Hoffman circuit. We can help you figure all that out.

You need to focus on Hoffman's plans and info and forget about the original BJ or any BillM mods. Just get Hoffman's circuit working first. That will be quite an accomplishment.

Yep, and as i said, i think that's good advice, that i intend to follow, mostly:)
The only real deviation i have is the filter caps at 450v instead of 500v.

Hoffman sells that three position switch. The listing for the switch also contains a link to detailed generic instructions for wiring this switch. It's easy to do. There are no specific instructions for the BJ. We can help. Quit looking at those BillM instructions! They will not give you any useful info on wiring this switch to Hoffman's circuit.

Ah, i found the link http://el34world.com/charts/SwitchDPST.htm.  That should do the trick. Thanks.

Just connect a wire from the front panel FAT switch ungrounded lug to your footswitch jack.

OK, i think i'll be able to figure that out when i get there.

The one question yet unanswered is the little "lasso connections" shown in the PDF between the ground wires and the RG174 wires going from the pots to V1 and V2.   Can you confirm or correct my guess that that means to solder the RG174 shield to the ground wire?


Thanks again.

[sluckey]

The lasso represents the braided shield on the cable. Connect to ground at the pot buss wire. Notice that the shield  has no lasso on the other end of the violet wires? That means the shield is not connect at that end.

[rsr]

The lasso represents the braided shield on the cable. Connect to ground at the pot buss wire. Notice that the shield  has no lasso on the other end of the violet wires? That means the shield is not connect at that end.

Thanks.  I it hadn't occurred to me to wonder about what to do with the shielding on the tube socket end of the cable yet, so that'll head off a question later on:)

[rsr]

A while back, i was asking about connecting the footswitch jack for the FAT toggle switch, and sluckey said

Just connect a wire from the front panel FAT switch ungrounded lug to your footswitch jack.

I get the ungrounded lug on the toggle switch part, but does that wire go the to tip or shield of the footswitch jack, and what do i do with the other lug on the FS?  Run it to ground or jumper to the other or ... ?

Thanks

[shooter]

but does that wire go the to tip or shield

look at the schematic, think about your jack, with your jack installed, get out a meter and measure resistance from chassis to ring, then tip to chassis, should solve your delema

[rsr]

but does that wire go the to tip or shield

look at the schematic, think about your jack, with your jack installed, get out a meter and measure resistance from chassis to ring, then tip to chassis, should solve your delema

probably would, if i had ever done this before and/or knew what i was doing.
but since neither of those is true, was hoping for an answer not in the form of a riddle.
but, i'll take a shot...

i think the answer is that the wire goes to whichever of the lugs on the FS jack is not grounded to the chasis, which i'm guessing would be the tip, so that's what i'll try first.

it's 50/50 chance anyway.

[sluckey]

That was a good logical guess.

Please keep all this BJ conversion discussion in a single thread so there will be some continuity.

[shooter]

Kinda confused, is bilm a version of BJ, or mod too

as to bias, on the linked pdf by Doug, it shows 12.5, 3.5 seems a big enough span to clear up

reasons I like a continuous thread; links, ALL the data is handy, compartmented data requires a security clearance

[rsr]

billm (http://billmaudio.com)  is (was) i guess kinda internet famous for a set of mods, most notably for blues juniors, that turned them from turds into really great sounding amps.  He made several videos on youtube and explained things nicely for amateurs like me.  Unfortunately, he died a couple years back.  His son andrew continues to operate the site, as far as i know.

What i've learned since, fwiw, that even though these modded BJRs can sound really great, they still have all the maintenance problems as they always did, due to PC board construction and all that.   If i'm lucky, the hoffman conversion will sound close to as good as before (without the mystery fizz), and is now built to last.  I'll find out tomorrow.   And if not, i learned a lot and had a good time doing the project.

As to the bias, i'm not finding anything in the PDF that shows such a bias setting. The schematic shows -12.3v in red at the C- between R31 and R32.  Is that what you're talking about?

Kinda confused, is bilm a version of BJ, or mod too

as to bias, on the linked pdf by Doug, it shows 12.5, 3.5 seems a big enough span to clear up

reasons I like a continuous thread; links, ALL the data is handy, compartmented data requires a security clearance

[sluckey]

As to the bias, i'm not finding anything in the PDF that shows such a bias setting. The schematic shows -12.3v in red at the C- between R31 and R32.  Is that what you're talking about?

-12.3 is a ballpark setting. The actual setting is for 25mV at R98 and/or R99.