Yet another Blues Jr Build

[southboundsuarez]

Hello, just finally got around to building this and thought I would share my progress. Man , I didn't expect this much wiring! Sure can appreciate the gals back in the day at Fender wiring up the old Blackface amps!
Please comment if you have any suggestions or questions.
Happy Holidays, Southbound Suarez 20211224_035044_HDR_copy_1156x508.jpg

[acheld]

Looks great!   Yup, a lot of wires and components in these amps.     

You will like it -- this amp is a workhorse, sounds great and is much more reliable than the stock Fender BJ.

One bit of advice that may or may not make any difference -- when you're done, pull the heater wiring to the back toward the rear just to increase the distance from your signal wires.   Might reduce hum, maybe not, but easy to do and there should be no downside.

The originals, of course, just have the heater circuit printed on the tube board (and are quiet).  When I built a couple of these, I twisted the heater circuit to the power tubes, and then just placed the wires to the preamp on the board. (As I recall, I borrowed this from Doug Hoffman's build notes.)  No hum in any of them I built, and it made the wiring of the sockets much easier.  By the way, I never again used that fat faux cloth wire ever again -- it behaves well, but gets in the way.

[southboundsuarez]

Yep, I probably over did it with the filament wires. You can't tell in  the previous pictures, and it does look deceiving but my heater wires are actually flying above everything up in the air all alone. Admittedly, they look as though they are indeed laying across all the other wires. I usually have always brought my filament wires straight up and run above the tube sockets. Signal wires always flat against chassis and every signal path at right angle to each other and any other wire. There has been a method to my madness with all zigzag wires of my layout. Not saying that my method is actually proper or sound, or actually based on any true technical or scientific fact that I can fully explain other than trying to reduce capacitance between long leads ran in parallel, choke common mode, with phase cancellation and reduce mutual conductance keeping paths perpendicular.  That said,,,, I don't know how well My wires confirm,,, obviously it doesn't probably help to twist wires that carry only DC , but yet you see it done all the time. LoL!
I am now almost finished with installing my power transformer. Last thing to wire to the xfmr is the heaters and the LED power lamp.  Finally onto populating the board. I already have my Filter Caps and bias supply installed.
I will try to post update pics in just a few.
Thanks for your taking the time to check out my build, I really appreciate the feedback and comments.

[southboundsuarez]

[omg][/img]
Ok let's see if I am uploading correctly? Anyways, the first photo shows the filament leads flying up and above.
The second photo I have mounted my bridged rectifier on the chassis. The B+ is routed back to the board and connected to the turrets where the rectifier was designed to mount. It just seemed to tight a fit and I just didn't like it so close to my pots the AC do close to the Z node filter cap turret. Also I installed an IEC power receptacle for my mains. I used the old power cord hole in the chassis to mount my fuse holder.

[southboundsuarez]

Getting there....

[glass54]

Nice work southbound and lots of (neat ) wiring
Merry Christmas.
Kind regards
Mirek

[Willabe]

By the way, I never again used that fat faux cloth wire ever again -- it behaves well, but gets in the way.

Your referring to the stuff that has a cloth braid over a normal plastic/vinyl insulated wire? That stuff is a pain for tube amps. 

Not the real push back braid wire.

[acheld]

the stuff that has a cloth braid over a normal plastic/vinyl insulated wire?

Yes that's it.   The vinyl insulation is a bit different -- I found it easy to strip once I got the hang of it, and it works fine, except that the wire+insulation is far too thick for the wire gauge, and makes it hard to route groups of wires around the sockets. 

[southboundsuarez]

Interestingly it appears that the fake me out cloth covered vinyl wire is about the only stuff that is certified and rated to 600v specifications... Also it is about the only stuff that comes in more than just two or three standard colors.
I suppose it's all good if you are just going for that cloth covered braided cool poser style of look.....
But it misses the point of why use cloth braided wire in the first place. The beauty is in not having to strip it! Just simply cut to fit actual length and simply push the braid back... Of course use sharp cutters to avoid fraying. I have also doped the ends with thinned out Hide Glue or clear fingernail polish.
On this BJr build I have used just whatever wire I have had on hand. A good portion of it being solid core wire in 22 or 20 guage.... Likely with insulation only rated to 300v ...
My actual preference is for 22g pre-tinned stranded in 600v rated vinyl insulation. As it exhibits "Goldilocks" type behaviour,,,,, as in the way that it is just right. Not too stiff and hard to work with but not too limp, that it stays put and remains bent and will lay down right where you put it.. 
I have pondered how is it that they call out and test the specification that denotes 300v wire insulation vs 600v wire insulation when there is nothing that indicates the actual current at that rating? They so print a temperature rating on the jacket imprinting. Surely the type of wire enclosed and it's conductivity/resistance must play a role with thermal breakdown being a large part of that equation.
One thing certain is that something as ubiquitous as the wire we use and how it is dressed makes up more to the performance of our amp builds than most would often credit.
What about some of that High digit expensive Teflon insulated MilSpec aerospace styles of wire? Anyone ever use that stuff? I love the Teflon dielectric shielded coax cable as used in my build. The braid is like 98% coverage and is a real pain to comb out because it's so tight (I usually just push it back like cloth) but the beauty is in soldering it, because the dielectric can take like a ton of heat and won't melt... Not sure of the impedance of the stuff I got or what type it actually is but it's very thin and flexible with silver tinned conductor that solders very nicely, and it probably has a very high velocity factor. Not that I worry too much about it's electrical properties in a audio amp build. (Those sorta things are beyond my technical aptitude. If it comes to things like tuned RF circuits, transformers and transmission lines I am monkey see monkey do and follow the recipe paint by numbers just as I do here.... LoL ) Anyways just stuff for topicality and conversation .... Whadya think? Oh yeah and where to get the good stuff for reasonable price? Anybody got a good technical/scientific take on the properties of the wire and how it effects our builds? Is wire a component that we often overlook when building for tonal mojo. Perhaps I am missing something like 99% pure oxygen free, nitrogen purged wire that is indeed the secret sauce???
Hmm????
Just throw stuff out there...

[acheld]

Well, most wire is not tested at 600V, it's not worth the cost to the manufacturers.

There are some out there, however, that are 600V rated, with different colors.   This one works ok, but there are others I am sure.

https://www.tubesandmore.com/products/wire-weico-22awg-stranded-top-coat-pre-tinned-600v-50-feet

[sluckey]

Interestingly it appears that...

Way too much focus on wire!!!

[glass54]

....don't forget Leo used the cotton covered solid tinned wire that was the cheapest that he could get his hands on and easy to use 
History tells us that he got it pretty right with wire choices and no amount of Oxygen Free Copper would improve the tone 
I am not damning OFC, as NASA would tell you, there is a place for it.
If you were building serious Instrumentation Amplifiers for critical measurements, you would explore Teflon, Mil spec cables and balancing your inductance, resistance etc and compensating for stray capacitance but here were are having fun with tube guitar amplifiers amplifiers.
As I said before, Nice and neat work southbound 
Regards
Mirek

[PRR]

> 600v wire insulation when there is nothing that indicates the actual current

Current is about the copper.

Voltage is about the insulation.

In most tube-amp work, mechanical robustness is more critical than ratings.

[southboundsuarez]

Hoffman Blues Junior Turret design is a winner!

Ok, I just about have this Blues Junior build wrapped up.
This was my very first Hoffman designed turret board build.
It was all fine business success.
I had read somewhere within the pages of this forum that there was a certain rule in place called "Hoffman's Law" .
The rules definition is that if you build one of the designs from the builds he features in his EL34 marketplace, and you follow the recipe, paint by the numbers and within the lines,,,
Well it only dictates that the end results are cake. 
With his Blues Jr you can have your cake and eat it too.
My build fired up flawlessly with a set of old groove tubes it came to life after a quick run up and down the voltage of my mains supply I observed no undue current draw and decided to pop in an old set of tubes. (I don't use a light bulb test but instead I have a variable output  isolation transformer with large built-in
digital LED  amp & voltage meters).
As I ramped up the voltage with all amp control pots set at midpoint, the amp came to life revealing a weakly but steady 12kHz test tone.
I continued to ramp up the voltage and at around 90 Volts the tone was looking just a tad fuzzy on the scope. The amp was grossly overbiased.
A quick rotation of the bias pot with my magic golden screwdriver I lowered the bias and the tone became very clear and steady , I slowly increased the mains voltage and readjusted the bias by ear and noted no  Ill effects. At 120 Volts I unplugged the test tone removed the test probe and plugged in my cheap  Japanese humbucker guitar, strummed a couple full cords and played some low and high notes. Readjusted the bias, backing off and allowing for more plate current. Started playing for ten minutes before changing to a Mexican tele with Abigail Ybarra wound single coils.
The amp really shines. Not exactly Classic Fender territory but maintains the basic Blues Junior versatility but in a much clearer and defined way. Lots of separation of notes with each note ringing out when playing chords.
I would say so far this has been a success. The amp with the volumes maxed out remains mousefart quiet. The only noise that came thru very pronounced we're the nousefarts caused by the cellphone placed right smack next to the uninstalled amp chassis on my bench. I moved the phone less than a foot maybe 10" away and no more noise.
I did also note that a old Groove tube was a bit microphonic when a drill gun accidently was dropped upon the bench . A quick tap of a chopstick revealed it to be the second position 12AX7.  I replaced it with a known good Telefunken from my coveted set of standard control test tubes.
I will be loading her up with a new set of reissue Tung-Sol and Likely bias it up for around 10watts +/- of static idle dissipation then button her up back into original cab.
I must say that the Hoffman design is a two thumbs up.
I did note that there is alot of circuitry to populate the board inside the confines of a smaller chassis. This makes substitution of any cap larger than the Xicons he uses a bit more of a challenge. But overall if that is my only critical bitch than we are all good fine business. I also like that it utilizes both triode halves of the second tube, I believe that this helps the definition of the musical notes. A reverb would be nice but not necessary, as this is a Blues Jr tonefulness and not a classic  AB763
The purist would probably want to build something else inside of one of these.
For a quicky maybe a Deluxe....
I am looking forward to more Hoffman Turret board purchases and will be downloading the DIY board creator.
If anyone is on the fence about building one of these, I say jump in. It doesn't get any better than this....

[PRR]

> a certain rule in place called "Hoffman's Law".

Josef Anton Hofmann theorized that when woofers are mounted in speaker enclosures, the designer would have to accept that there are three trade-offs.

Hoffman's Law: temporary solutions become permanent.

Hoffman's First Law - Quantum measurement hints that observers may create microphysical properties. Computational theories of perception hint that observers may create macrophysical properties. The history of science suggests that counterintuitive hints, if pursued, can lead to conceptual breakthroughs.

The version seen here most is "If you built it like I drew it, it would be working already".

[southboundsuarez]

Hope that I am ok to bump an ancient thread but just wanted to update...

It has been several years and this little amp has seen some serious use being gigged by its owner, professionally, nearly every weekend in a variety of venues for the last couple of years.
Reportedly, fantastically and favorite go to amp!

It has finally come back to me for a new set of tubes and rebias.

A basic looking over...
Everything initially seems all good, it plays strong and full, with low noise floor.
My ultra critical observation is but maybe a little underbiased and sterile. (This is strictly ancedotal and extremely critical observation and opinion).
Generally the amp is working fine and no problems... 
Everything seems OK and as expected...
Especially for an EL84 output amp that is regularly used live in a band!

Pulling and replacing tubes...
 I simply shotgunned a whole complete set of Tung Sol reissues.

I didnt measure the old set of power tubes.
The previous set of theTung Sol reissue EL 84s (did T.S. ever really produce an orig. EL84 if even an actual 6BQ5?). They did not look too worse for wear.
The glass looking clean with  much of the gettering deposits on the glass still shiny and opaque. Just a small transluscent perception of brown upon the edges of the silver mirrored gettering deposits. 
Probably the best looking set of used EL84s that can remember ever pulling from an amp with this many hours!
Anyways,
At this point I didnt take the time to measure the idle current or dissapation with the old tubes present.
I just replaced with a new set and rebiased at 70% with probably only about .05 milliamps more adjustment over the previous settings.
(Why dont I ever log this type of stuff whenever I start out or keep decent records? Shame on me!) 
But as an afterthought I checked them on my Hickok and noted that they were about 80% and 85% transconductance accordingly for whatever thats worth...

 I dont remember the original bias
But I probably biased the same.  I biased around 70%  and then adjusted to ear as well as watching crossover on the scope?)
I dunno, cant say for sure....

Now not so sure what has happened!!???!!!!?? 

FULL REPLACEMENT WITH T.S. reissues and suddenly the amp has become torally tube finnicky.

The first two stages very microphonic  and tube dependent.

I have spent way too much time tube rolling so many different tubes old and new, not sure what worked best where, and/or when.

All  the tube positions are having very inconsistient results.

Suddenly it seems like this once bulletproof stable rig has ended up very unstable and inconsistient.
Something obviously not right!

I have continued to dick around with tube placements and exchanging tubes every which way, the amp has become more and more sensitive with bad personality disorder and wants to misbehave! The gremlins pop up one place and disappear to another...

I AM CHASING GREMLINS THAT HAVE NEVER APPEARED IN THIS AMP UNTIL NOW!!!
 
My best and most consistient results are with my most coveted set of control tubes used only for testing purposes.
A very lovely set of Diamond stamped red tipped vintage audiophile Telefunken$ . However maybe its because they are lower gain than all the various newer production tubes I have been now rolling thru for hours on end?

Been chopsticking the amp and something isnt right.  I am having problems with the tube sockets and wire dress suddenly being super sensitive
Reflowed solder, changed plate resistors and grid stoppers.
De-Ox-It and retensioned pin contacts  moved grid leads around and plate leads too.
Unfortunatelty the issue just isnt consistient!
 I must obviously have an intermittent somewhere but have not found it..

Just a simple tube change out on a otherwise super stable and reliable amp shouldnt have this effect!

Its weird how it suddenly became so sensitive and I am waisting my time and sanity going off in every direction trying to chase the inconsistency.

I think maybe a bad or intermittent ground?

Unsure, but I know that this circuit was ultra stable and had no issues up until changing tubes.
 
Now, seems like whatever tube I roll it is inconsistient and unstable with either microphonics or ultrasonic oscillations that show up at different stages.

ARGHHH!!!!
I am sure its something stupid silly.

I need to relax and methodically go over everything,

I have probably strayed off of course in too many directions. 
Okay okay okay going to take a break and relax and regroup. 
Kiddos  let this be a lesson and dont do what I do,,, be methodical and take notes and measurements before you begin and when everything is fine.
I will start making measurements of voltages and take notes with power supply unloaded and loaded up and report back.
I wanted to brag about how great this amp was still doing!  DOH!!!