Re: Hoffman Fender Blues Junior Conversion

[afireworship]

Thank you for confirming where to place the choke leads! I got the new board assembled and installed. Now I have a weak very broken/ distorted signal - but no smoke  The weak signal seems to be directly affected by the bias pot. That's my next question, how do I check and where do I adjust my bias too?? In the PDF diagram it shows only a resistor on the master pot, in the pictures there appears to be a silver mica cap - where is the proper placement for this cap?

[EL34]

Thank you for confirming where to place the choke leads! I got the new board assembled and installed. Now I have a weak very broken/ distorted signal - but no smoke  The weak signal seems to be directly affected by the bias pot. That's my next question, how do I check and where do I adjust my bias too??

The schematic shows a general voltage you can set your bias too -12.3 at the point shown in the schematic

You set the bias by measuring the voltage drop across the 1 ohm resistors on the board in millivolts
25 millivolts = 25 milliamps of current flowing through the tube

Set it to 25 millivolts as a general
http://el34world.com/Hoffman/files/Hoffman_BluesJunior.pdf

In the PDF diagram it shows only a resistor on the master pot, in the pictures there appears to be a silver mica cap - where is the proper placement for this cap?

I am not sure where you are seeing this?
The layout diagram and the schematic do not show any cap on the master

You need to make sure you have the later version of the PDF
Make sure you hit refresh on your browser after you click on the link
http://el34world.com/Hoffman/files/Hoffman_BluesJunior.pdf

Make sure you read this post
http://el34world.com/Forum/index.php?topic=17468.0

[afireworship]

Thank you again sir! I'm really enjoying this project!

[afireworship]

I had a time figuring out my issues but it was a broken lead on the rectifier section of the power pt. It was intermittent. I've now gotten it up and running seemingly ok except some of the controls. The bass, master, and meat controls seem to have no effect. The treble, volume and mids seem ok. I was able to get the bias to idle in at 25 millivolts. Any ideas about how to diagnose the controls issues?

[EL34]

This is how I do it
http://el34world.com/Forum/index.php?topic=17701.0

[afireworship]

Thank you for your help sir!! With that great idea I found an incorrectly terminated resistor on the meat control as well as the biggy, a broken wire on the center term of the master control at the board! likely from moving it around so much trying to figure out the output tranny issues. It is now running seemingly correct, not a lot of influence by the bass control but some, as a whole a very thick and warm tone with larger than expected sound from a small amp. I'm using a vintage 30 but plan to move to an alnico speaker / head config. If I wanted to brighten the over all tone and maybe lose a bit of the gain would I be correct in thinking that I should change out the silver mica 250 cap for a lower value and undo the V2 mod and ground half of it out? Would I be better off to try a lower gain tube in v-1 or 2 or both?? Thanks for making this fun!!

[EL34]

Try lower gain tubes first
Also a smaller negative feedback resistor

[afireworship]

 
okay, I am getting closer! I seem to have torched a few pots. I got a new soldering station and the watts are a lot bigger than what I used before, lol. Now I know for this time around, I just ordered all new pots! I only toasted two of them but I plan on custom building a chassis to function with an added presence control and to be a part of my pedal board mounted with the tubes facing the audience and the controls facing up near the rear of the board!

Two specific questions to anyone who can help;
1. if I wanted to add an effects loop where would I do so?

2. If I wanted to add a tube rectifier how would I do it?

Thank you EL34 for all your help so far! This is a truly edifying experience!

[Ross]

Your enthusiasm and vision are admirable but to have "torched a few pots" should give one pause. For the safety of you, your loved ones (and even the unloved) I would strongly suggest showing your project to an electronics technician or such before you proceed. Please.

[afireworship]

Well I got this thing up and running and am loving it so far! It wasn't as bright as I expected, I normally play really bright. I mimicked a presence circuit off of one of my other amps and it brought me into the zone. I still want to do a tube rectifier and I think I see and understand how to do it. I would also like to add a reverb and vibe or trem unit by copying the circuit on your AB763 layout.

My question is will those circuits be likely to function and sound okay with the EL84 power tubes and in the blues jr. conversion??

Thank you!

[tubenit]

I still want to do a tube rectifier and I think I see and understand how to do it. I would also like to add a reverb and vibe or trem unit by copying the circuit on your AB763 layout. My question is will those circuits be likely to function and sound okay with the EL84 power tubes and in the blues jr. conversion??

I would not recommend that and I am not sure where you would have room to do that?

Simple solution is to install a passive effects loop & use reverb and/or tremolo in the loop.

Use Hoffman's Switchcraft 12A jack. 

with respect, Tubenit

[afireworship]

Thank you for the schematic to add a passive loop. I am actually going to build a new chassis / cab and will have plenty of room. I thought about using a loop and pedals as that's what I'm doing now with my current rig but I was hoping to raise the bar on the effect quality, there is nothing like bias based trem. With the new chassis lay out I'll even have room for one of the long accutronics verb tanks.

[tubenit]

I am actually going to build a new chassis / cab and will have plenty of room. 

Oh, my apology then.  Yes, you can use typical Fender reverb and tremolo design.

OR you can use a "1 tube" reverb IF you don't need Fenderish "surf" reverb. 

http://el34world.com/Forum/index.php?topic=7957.0

And there is some decent info about tremolo mods here:

http://el34world.com/Forum/index.php?topic=604.0

OR ............ you could add an active FX loop with info here:

http://el34world.com/Forum/index.php?topic=10208.0

And here is a schematic with an idea for you that would allow you to get Fenderish reverb and tremolo with only 2 tubes.
The reverb is a hybrid of the Fender topology but with some Dumblish type reverb component values (which perhaps gives a slightly warmer sounding reverb)

With respect, Tubenit

[afireworship]

Great! Thank you very much! I am anxious to check out these links and get started! There are many of us who are not pro amp tech's but still have a passion for tubes and tone and this forum has been very helpful for me. Thanks again!