The Start of a Plan

[jamaio]

I have a Blues Jr. that I will be converting with the Hoffman kit for my first project.

I was considering a second project. I still have the first amp I bought back in 1995, it's a Fender Sidekick Reverb 35 1x12 combo. It's a solid state amp made in Taiwan. I was looking around online  and came across this video: https://www.youtube.com/watch?v=gmh40eZmG5U

So it looks like my plan will work, I just need to decide which Hoffman kit to use. Since I already have a Fender tube amp I was thinking about a Stout Reverb.

Would the Stout be a good choice or should I use something else?

Thanks,

John

[PRR]

It's like those home improvement and car restoration shows: it sure looks easier when 100+ hours of work are edited-down to a few minutes.

(I like the time Dean and Jan built a large warehouse in 19 screen minutes. At the end they pulled back to show dozens of workers and cranes....)

Get your current project done first. I have part-piles all over that I have not got around to. That first project will also show if you really enjoy hacking and melting metal or just the idea of it.

[sluckey]

♫ Say yes to one. Let the other one ride. ♫

[jamaio]

Get your current project done first. I have part-piles all over that I have not got around to. That first project will also show if you really enjoy hacking and melting metal or just the idea of it.

Thanks for the reply!! I should have mentioned I installed the Fromel Electronic Supreme mod kit in my Blues Jr. about a year ago so I really enjoy hacking and melting metal. The installation went well for the most part, I mixed up 2 caps and had very low bass output. I went through and double checked everything and found my mistake. The amp has played well for the last year and I got the itch for more mods. I ordered an Eminence Cannabis Rex, it will be here tomorrow. The search for tone is endless....

♫ Say yes to one. Let the other one ride. ♫

So I will finish the conversion to my Blues Jr. then come back for opinions on the best option for a complete build using my Fender Sidekick.

Thanks,

John

[sluckey]

I think a lot of us like to think ahead about a next project while finishing up a current project. Especially when the fever is high! But trying to juggle two sets of parts in a single workspace can be an invitation to the gremlins. I think I get more satisfaction when I single task this stuff.

[PRR]

I also think each project teaches a little about what the next one should be. Whether you want to go further in the same direction or go a different way.

[whoops]

I will join the crowd also in advising to think on one project at a time, I also had , and still have the fever sometimes and start 2 or 3 projects before finishing the first one. It happens sometimes when you are waiting for parts or learning new thinks that have links for others things.

Well 10 years down the road on DIY and I have loads of unfinished projects. I don't advise that to anyone.
I realized that I can't start anything new before I finish all the unresolved projects, I still get the rush and fever sometimes but I learned how to control myself.

Anyways sometime soon I will need your help to help me finish my Gretsch reverb restoration and after that my Hoffman Ab763 amplifier that I started 7 years ago and was never able to make it work.

[silverfox]

PRR- "Get your current project done first. I have part-piles all over that I have not got around to."

I count myself fortunate in the parts piles department. I do have another pile in the store room but, I believe, (until the next deal comes along), I believe I'm not going to buy another tube amp chassis parts, shortwave radio recap job, etc... for a while. As for the next project, I've been trying to get back to my amp build but it's been snowing decently here and my work is interrupted by the current project: Building a Bob Sled run.... Originally I hail from NE.

silverfox.

[jamaio]

I ordered the Blues Jr. conversion kit today, ready to start my first "Hoffman" project!! I will be sure to post lots of build pics and I will upload a sound demo when I am done. A friend has a stock Blues Jr. so I will be able to do a side by side demo and he plays guitar much better that me.

Let the fun begin. 

[whoops]

In what does the convertion Blues Junior Kit consists?

I've recorded quite a few Blues Jr and I like the stock sound on those amps.
Some failure problems but the sound is quite good

[jamaio]

In what does the convertion Blues Junior Kit consists?

Information on the Blues Jr. conversion kit can be found here:
http://el34world.com/Hoffman/Blues_Junior_Build.htm

[whoops]

Thanks for showing that, as I dont have a Blues Jr myself I never got into that page in the Hoffman amps section.

I actually like the sound of the stock circuit and prefer to have the reverb myself.

But of course a well done turret board circuit and wiring will be more reliable and easy to service

[Ed_Chambley]

I have seen this video and wondered what he is doing with the knob in the triangle.  Anyone know?

[jamaio]

My parts came for my Hoffman Blues Jr conversion, I cleared my bench off and got right to work. Here are a few pictures of my progress so far.

I found an PT at work, not sure if it will fit!!


Clean bench ready to start!!


Chassis removed.


Ready to start adding new parts.

I have seen this video and wondered what he is doing with the knob in the triangle.  Anyone know?

I'm not sure what he is doing with the knob, there are several ways to change the tone of an amp with knobs or switches. I posted the video so that everyone could see the platform for my next build.

[jamaio]

I found an old post by sluckey, this is the plan I will follow along with the process outlined here:
http://el34world.com/Forum/index.php?topic=17701.0

Here's what I do... There is never only one 'big power on' event. Instead, I power up in stages as the build progresses. LOOK, LISTEN, FEEL, AND SMELL during all phases of the build when power is applied!

PHASE 1. The PT primary circuit is the first thing I wire up. As soon as the power cord is in place (but before the secondaries are connected) I plug in for the first time. I make sure the power switch, fuse, indicator light, etc. work and that the unloaded secondary voltages are as expected.

PHASE 2. Next I wire the 6.3v filament circuit. (If you're fond of the Fender style overhead filament string, this step would come later.) Then power on again and measure voltage across the filament pins of each socket. All tubes are then plugged in and visually checked for glowing filaments. REMOVE ALL TUBES.

PHASE 3. Rectifier tube is wired (nothing else). Check for proper filament and HT voltages on the recto socket. Then plug in the recto tube and check for B+ at the cathode. There are no filter caps at this time, so readings will be low. At this point the entire PT circuit has been checked, except for a possible bias winding that's still flying loose.

PHASE 4. Wire in the board(s), pots, input/output jacks, etc. IOW, complete all remaining wiring. Use the schematic and an ohm meter to verify that grid and cathode resistances measure expected values to ground and that plates are correctly connected to the proper B+ nodes. Visually trace the schematic (not the layout) and compare to your actual build. Verify polarity of ALL electrolytic capacitors and bias diode.

PHASE 5. No tubes in yet. If you have a fixed bias amp, power up and verify proper negative bias voltage is present on the control grid pin of every output tube socket. If adjustable, be sure the range is adequate and then set it for max negative voltage. DON'T PROCEED UNTIL THIS IS RIGHT!

PHASE 6. Plug in the rectifier tube ONLY. Power up and check for plate voltages on every empty tube socket. They will be high.

PHASE 7. Plug in all tubes and connect a speaker. Power on and see how it sounds. If you've successfully gotten this far, there shouldn't be too many surprises. Watch for red plates, smoke, etc, and listen for howl, hum, buzzes, bacon frying, etc.

If this is a NFB amp, there's a 50/50 chance you may need to reverse the OT plate leads. There may be an obvious howl, or you may just have a bad or weird sound, possible squeal/howl on certain notes, the kind of things you can't explain. Just reverse 'em. Hey, you may find out that it was right to begin with, but at least now you'll know for sure. I recommend not trimming the OT plate leads to length until you know for sure.

Play guitar for a short time. Then measure plate, grid, and cathode voltages for all tubes. Measure on the socket.

That's basically what I do. You may have to adapt details for different amps, but the idea is to power up in stages. Divide and conquer. You'll have confidence built up for that final complete power up.

[whoops]

I found an PT at work, not sure if it will fit!!

LOLOLOLOL
That's a big Monster!

Isn't the stock Power Transformer fine?

[jamaio]

Isn't the stock Power Transformer fine?

Yes, the stock PT is good, I saw that PT at work and started thinking... I think thats where most of us get in trouble!!  That PT is for an L.E.D. sign, its 48v and it weighs about 50 lbs. with the chassis and extra large caps.

I made it through my first phase of powering up and testing without the tubes. I found the heater voltage high, after a quick look I realized I did not ground the pull down resistors, rookie mistake. Fixed the ground and retested without the tubes first then with the tubes, everything is good now.

Ready to install the board.


Power and ground wires on bottom of board.


Turrets laced and soldered.


Board installed.

[jamaio]

I have a question about cap sizes, the schematic shows c12 and c13 as .1/250v, however, in the parts list they are .1/630v caps. Is it ok to use the .1/630v? The caps I received in my order are .1/630v.
http://el34world.com/Hoffman/files/Hoffman_BluesJunior.pdf

Parts List
http://hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&thispage=Amp_BluesJuniorConversion.htm&ORDER_ID=!ORDERID!

The BOM for the Blues Jr kit lists them as .1/250v, was there a change that was not made in the schematic but was updated in the parts list?
http://el34world.com/Hoffman/files/Hoffman_Blues%20junior_BOM.pdf

Thanks,
John

[PRR]

> .1/250v, ... Is it ok to use the .1/630v?

I need a dog-porch. I have, say, 250 pounds of dogs. I found some dog-porch framing made for 630 pounds of dog. Is that OK?

Yes, if the physical size is not a problem (not too deep for a Corgi to climb on to), and if it does not blow the budget or the truck springs getting it home.

Usually in dog-porch (or house) framing we try to stay small because the cost of lumber and delivery and heavy labor adds-up. This is also true when Fender builds a million amplifiers and hopes to turn a profit. In DIY electronics, weight and cost are secondary factors. So much so that we often do not stock lower-Voltage caps if a higher-Voltage part is not real expensive. Or if 90% of caps in most amps need a 400V or higher rating. Just pay the penny (or less) more for all 630V caps.

In *this* case it is very unlikely these caps will ever have 250V on them. But (and especially in DIY where Mistakes Happen) it is nice to know they can take the full B+ of an unloaded B+ supply.

[jamaio]

Thanks for the quick reply, I thought it would be ok, just wanted to make sure. Will it fit? Like trying to get 10 gallons of shit in a 5 gallon bucket!! 

Huge cap in a tight space.

[sluckey]

There's a note on Hoffman's capacitor page that says that .1µF/250v cap has been discontinued.

http://hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Capacitors&ORDER_ID=!ORDERID!

[jamaio]

There's a note on Hoffman's capacitor page that says that .1µF/250v cap has been discontinued.

Thanks, Only place I did not look.

[jamaio]

I have another question about caps, what does the f stand for? The Xicon coupling caps on the Hoffman site all start with f, I found a cap locally but it does not have the f prefix, only 104k 250v.

Thanks,

John

[sluckey]

I think that's probably just some Xicon part number identifier. It doesn't tell you anything about the capacitance value or voltage rating of the cap.

[jamaio]

I think that's probably just some Xicon part number identifier. It doesn't tell you anything about the capacitance value or voltage rating of the cap.

Thanks, I will probably just use the 630v caps because I know they are good quality, I'm not sure where the ones I got locally are made and if they are high quality.

[whoops]

Huge cap in a tight space.

It seems that the Dog porch is bigger than your house, but it's fine since you don't mind to loose a bit of the garden area to make it fit!

[jamaio]

I am close to being done with the assembly of my conversion, just a few more wires to connect then test voltages and adjust bias.

[jamaio]

I have sound!!! Well it's more like noise....ok, it's a loud hum!!!   I went through my voltages, tried to set the bias, found a few problems, made some corrections. Bias is now perfect, all my voltages appear to be correct but all I get is a loud hum when I plug in a speaker. I have 30 years of electronics experience but no experience with troubleshooting a tube amp.

Problems I found:
No ground at R26 to bus on pots
C1 polarity backwards ... oops I checked it, does not appear damaged
no under board connection at C- to C- This fixed my bias problem

Link to schematic
http://el34world.com/Hoffman/files/Hoffman_BluesJunior.pdf

The hum only increases when I turn the master volume and the meat, there is no change when I turn any other knobs. The amp is totally quiet with V2 removed, not sure if that is a valid test but I tried it.

I have been through everything several times and I am not sure where to go from here.

Thanks!!

[whoops]

Congrats, you completed step1.

Now you go on to Step 2:

Step 2 starts by reading and applying these threads:

http://el34world.com/Forum/index.php?topic=19361.0

http://el34world.com/Forum/index.php?topic=17701.0

http://el34world.com/Forum/index.php?topic=5.0

[jamaio]

Thanks for your reply! I will go over every thing again tomorrow evening, I have printed a fresh sheet to go over with a highlighter again, that's how I found my other problems.

Does anyone ever get them right on the first try? I thought I would, I was so thorough, I checked and rechecked, found and fixed mistakes. After finding each mistake and fixing them I thought maybe this was the "one" then I found and fixed others.

It's only my first Hoffman build, I have learned a lot here and I still have a lot to learn.

[jamaio]

Thanks for all the help, I have found my problem, it was right at valve 2 where I isolated it with my crazy test. Some of the juice was leaking out of valve 2, I made some adjustments and bingo we have sweet valve sound!!! Amp sounds awesome!!!  I still have some clean up work to do and mount the chassis back in the cabinet. Once I get everything together I will post a sound demo of a stock Blues Junior and my new Hoffman Blues Junior in a side by side comparison.

Not bad for a rookie, I received my parts last Friday and I finished in under a week. I'm ready to start my second Hoffman build.

[whoops]

Congratulations,
It's amazing how fast you did everything. I'm happy it's working and working well


Regards

[jamaio]

Is it bad luck to work on an amp on Friday the 13th?

My excitement did not last long...  I cleaned up some wiring today, installed chicken head knobs, bench tested my amp and everything sounds good. I installed the chassis in the cabinet, plugged in the speaker, plugged in my guitar, plugged in the amp, powered it on, wait for it to warm up... nothing, not a sound. Look at the input jack on my guitar, its loose, grab another guitar, plug in, nothing, not a sound. Unplug guitar and start checking voltages, checked tubes ... make sure I did not knock one loose, swap tubes, still got nothing. Turn all knobs to lowest position, checked voltages again, all appear ok. Turn volume up, plug in guitar, amp plays and sounds great. Wiggle wires, beat on amp, still plays well. Poke around everything with plastic stick, everything still works good, sounds good. Turn off amp, wait for caps to bleed down, turn amp back on, let warm up, no sound, nothing, no buzz, no hum nothing, check voltages, turn all knobs to lowest position, turn everything up, amp sounds good, plays normally.

I have a bad case of the gremlins!!! Back to square 1, will check everything in the morning with fresh eyes.

What a wonderful hobby!!

[whoops]

LOLOLOLOL

And when you were ready to start you second project!!!!!!

Not bad for a rookie, I received my parts last Friday and I finished in under a week. I'm ready to start my second Hoffman build.

[jamaio]

The gremlins continue to plague me. I have isolated my latest problem to low voltage at V3, my voltages are as follows.

Y = 306.7
V3 pin 1: 230.2; pin 2: 45.3; pin 3/8: 64.8; pin 6: 226.1; pin 7: 47.7

Link to schematic
http://el34world.com/Hoffman/files/Hoffman_BluesJunior.pdf

Any help would be appreciated.

Thanks.

[sluckey]

Those voltages look fine. Which ones do you consider low?

[PRR]

> V3 pin 1: 230.2; pin 2: 45.3; pin 3/8: 64.8; pin 6: 226.1; pin 7: 47.7

Look fine to me. The G1 voltages are skewed by meter-loading. The cathode is 65V. In ~~39K tail resistance this is 1.66mA. So expect 0.83mA per tube. In 100K plate resistor this is 83V drop. 83V down from 306V is 223V. The 82K side will sit a bit higher. Which is all pretty-near what you got, and what we expect of this stage, which is surely capable of slamming EL84s even if it is a bit off.

[jamaio]

Those voltages look fine. Which ones do you consider low?

> V3 pin 1: 230.2; pin 2: 45.3; pin 3/8: 64.8; pin 6: 226.1; pin 7: 47.7

Look fine to me. The G1 voltages are skewed by meter-loading. The cathode is 65V. In ~~39K tail resistance this is 1.66mA. So expect 0.83mA per tube. In 100K plate resistor this is 83V drop. 83V down from 306V is 223V. The 82K side will sit a bit higher. Which is all pretty-near what you got, and what we expect of this stage, which is surely capable of slamming EL84s even if it is a bit off.

Thanks for the quick replies. I thought the voltages at pins 2,3 and 8 were low. My symptom was very low output volume. After reading your posts and seeing the voltages should be fine I plugged everything in and the amp is back to normal, go figure. I did swap different tubes in and out and moved them to different locations to see if anything changed while I was checking voltages, maybe I found the right combination of tubes in the right places. I have my original Fender GT 12ax7's in and 2 JJ el84's. I will continue to test and see if any other issues come up.

Thanks for putting up with my rookie questions.

[jamaio]

And just like that it is back to sounding like crap, low volume, when I strum the output sounds crackly....


Now, without touching anything it is back to sounding normal.

The fun of electronics!!!

[jamaio]

I was comparing my voltages to the voltages I found here:
http://el34world.com/charts/valve/ValveData.php?e=view&f=18341

Voltages all checkout, sometimes it works, sometimes it doesn't. Going back through all my solder joints, looking for bad/lose connections, i'm at a total loss. I was an auto technician for 20 years, I traced all kinds of electrical problems, I have never seen anything like this.

Can I just toss it all out and start over??

I am sure I will find it, just takes time.

[sluckey]

You cannot trust the voltage charts you see on that link. Most of those voltage charts were posted by people because their amp was not working.

[jamaio]

You cannot trust the voltage charts you see on that link. Most of those voltage charts were posted by people because their amp was not working.

Thanks!!

[whoops]

You cannot trust the voltage charts you see on that link. Most of those voltage charts were posted by people because their amp was not working.

Thanks for the info Sluckey.
where do you think is a good place to check for trusted reference voltage charts?

thanks

[sluckey]

I don't know. I put voltages on my schematics when I finish a build. I trust my voltages. But most of my stuff is not mainstream so not much help to others. I do wish Hoffman would include voltages on all of his builds. A lot of people build his stuff. I think it would be very helpful.

[jamaio]

The gremlins continue but I have made some progress. During a time when I had no sound I was checking voltages to see if they were different, I went straight to the pin on the back of V2 socket, the meter lead shipped and shorted pin 2 and pin 3 together, now I have sound, amp sounds good, however, the Treble Mid and Bass controls have no affect on the tone of the sound. With the Master and Volume both set to 2 the amp seems a little overdriven, more so with the Fat switch on. The Meat knob changes the tone.

So my question, why would shorting pin 2 and 3 on V2 start the flow of sound? Am I charging or discharging a cap? I ordered all new replacement caps from Doug, I do not trust the condition of the caps with all my mistakes. Also would a bad cap cause the issue I am seeing with Treble, Mid and Bass?

If I make it through this built I will be well seasoned for my next build.

[jamaio]

I don't know. I put voltages on my schematics when I finish a build. I trust my voltages. But most of my stuff is not mainstream so not much help to others. I do wish Hoffman would include voltages on all of his builds. A lot of people build his stuff. I think it would be very helpful.

I found a service manual from Fender for the Blues Jr online, they include voltages through the signal path using a 1 khz input signal. Of course they are no good with the Hoffman build, but interesting reading to see how the signal changes through the path.

[whoops]

I ordered all new replacement caps from Doug, I do not trust the condition of the caps with all my mistakes.

That's overly exaggerating.
I don't see any reason to change all the caps.

I don't see any reason at the moment to change any Cap at all

[jamaio]

That's overly exaggerating.
I don't see any reason to change all the caps.

I don't see any reason at the moment to change any Cap at all

I do not have a cap tester on my meter at home but we have one at work. If I remove the caps to test them I may as well replace them. If the caps test good then I will have spares for my next build.

[whoops]

If I remove the caps to test them

Remove what Cap?

And Why do you want to remove any cap at the moment?

[sluckey]

So my question, why would shorting pin 2 and 3 on V2 start the flow of sound?

Probably just a coincidence. There are three jumpers on V2 socket. Are these jumpers soldered securely and on the correct pins?