Stout chassis AB763 Lite... Got some tuning done :-)

[ToneJunkie]

So I purchased the parts (Transformers, chassis and such) and I already have the parts on hand to build a board... I have a couple of design wonderings though.


1. I have only built amps that have a fender style layout with the tubes at the back.  It looks like the AB763 Lite board is laid out like a traditional fender (Sluckey's design PDF is attached). But the stout chassis has the tubes AND controls at the front.  Will I have any hum problems running the control wires from the pots over the tubes to the back of the board?  General layout shown in picture.  In the picture I sized the chassis to be 12" and the board to 8" its a little tight but I think it should work. 

2. When doing an amp with the tubes and controls in the front is there any big considerations I should know about?


Also a quick pre-build thanks for all the help here on the forums and a special thanks Doug Hoffman and Steve Lucky for all the info and guidance you provide!

[labb]

For consideration and comments: I am building the AB763 lite right now. Tore down a Fender 5B3 and am using what is left to build the Lite...I am going to do this build without a standby switch. Been some discussion(Merlin) as to whether  or not a guitar amp needs one...Guess I am going to find out....re: your question as to where to locate the standby switch.
http://www.valvewizard.co.uk/standby.html

[shooter]

Will I have any hum problems

If you follow all the *best practices* on grounds, HV, and signal, you should be fine.  My last 2 builds were in stouts and are dead quiet.  They both have bottom plates but without the plates they will pick up room noises.

[sluckey]

If you do my board you may consider this simple mod... Swap places with the 250pF and 100K. Move the two short jumpers from the bottom of the board to the top of the board. Now the three tone control wires will be on the same side as the tube wires. See pic...

[ToneJunkie]

I am going to do this build without a standby switch.

I just got one of the switches with off standby and on... I have not seen that article that website is great.  I got some reading to do.

Will I have any hum problems

  My last 2 builds were in stouts and are dead quiet. 

Cool I hope mine are dead quiet too :-)

Now the three tone control wires will be on the same side as the tube wires. See pic...

Awesome!  thanks I just built the board and put the mod in. 

[ToneJunkie]

I want to try and make this amp the quietest I have ever made...  I have been studying on how to do this.  And there seems to be an issue with using a can cap... it would be impossible to do a grounding scheme where the preamp section should have the smoothing capacitor as close to it as possible including using the same ground connection.  So should I just use the can cap for the main power section (So only use part of it the 40uf and maybe one more 20uf) and then have a couple other 22uf caps that connect directly to the board I left some space for more turrets on the edge if I need them? 
 
 
 

   

[sluckey]

If I had that cap can I'd use it for all the filter caps. Works pretty good on a Princeton Reverb.

Maybe put three turrets in place along the edge and wired to nodes C and D. And arrange them such that you can put the two 10K dropping resistors between the turrets. Then you can add the preamp cap and PI cap later if not happy with those caps being in the can.

[ToneJunkie]

Just got my transformers... Ehh, I may have overlooked some measurements.  Take a look at these pictures of how close the choke is to both the OT and PT.  So can you guys weigh in about what to do here...


Idea 1:  Ohh, thats not too close go for it.
Idea 2: Find a smaller choke... I have tried to find one.  The transformer pictured is a 4 Henry 100ma unit.  Could I go with a smaller 4.5 Henry 75ma unit?  I think they used something like that in a Vibrolux... It will still be pretty close
Idea 3: That OT is too big find a smaller one and use a smaller choke.
Idea 4: Don't use a Choke


Any other options or do you have a favorite options in the ideas I have so far.

[shooter]

Not sure on your cab, might try and *dry-fit* it like I did my OT's

[sluckey]

I would either give up the tube rectifier for silicon ***or*** I would move all the tubes one space to the left (as seen in your pic). Then put the choke where the rectifier hole is. Kinda like this pic...

[ToneJunkie]

Well, Hmm.   Still not sure what to do... This choke does not fit in the position Sluckey suggested and may try the dry fit and see if it affects hum.  What is the lowest choke current rating acceptable for 2 6L6's and 1 12AX7 and one 12AT7? I'm going to do some more reading...


From Aiken
If, on the other hand, you are selecting a choke for a capacitor input supply (such as the typical Marshall or Fender design), then the requirements are relaxed quite a bit. The purpose of the choke in these type supplies is not for filtering and voltage regulation, but just for filtering the DC supply to the screen grids of the output tubes and the preamp section. The screens typically take around 5-10mA each, and the preamp tubes draw about 1-2mA or so (for the typical 12AX7; 12AT7's are usually biased for around ten times that). This means that you can get by with a much smaller choke, and, in addition, the preamp supply current doesn't vary that much, so you can get by with a higher DC resistance, which means smaller wire can be used to wind the choke, which means higher inductance for a given size core. Just add up the current requirements of the screens and preamp tubes, and add a bit more for margin. For a 50W amp, a typical value might be 50-60mA.


So according to this I would need around 20ma for my 6L6's and 4ma for my 12AT7 and 12AX7 so it would seem that I could use a 4 Henry 75ma Choke and see if that fits a bit better.   

[sluckey]

Just use the small 125C3A Fender choke that Doug sells. Very first item on his transformer page.

[ToneJunkie]

Got some work done  .  Decided to not do the can cap.  Got a tube socket and the small Choke coming Friday. 

[ToneJunkie]

I just finished it and played through it for about an hour... sounds great!  Nice feel with a 5U4.  I'm pretty damn excited to play this one out!  I decided to do a no cabinet build so there is a 1/4" aluminum plate on the bottom with feet and there will be a tube cage soon.  I had a local metal worker build one for around $25.  It should look cool.  Here are a couple of pictures and some #'s.  Its my quietest amp to date as far as hum!  Awesome!  Here are the voltages on the tubes
12AX7 1A   201    0     1.69     
12ax7 1b    200    0     1.68


12AT7 2A    181    48    77
12AT7 2B    189   49.4   77


TAD
#1 6L6WGB      0     AC     391     394     -37     0       AC      41mv 
#2 6L6WGB      0     AC     390     393     -37     0       AC      32.5mv

[sluckey]

That turned out great! Do you have plans for the extra tube and pots? A raw control is very easy to do and provides a lot of gritty sounds.

[eleventeen]

Looks great! Well done! I kind of like the multiple-cap board for the preamp e-caps.

[ToneJunkie]

Thanks guys!  Yeah I am thinking about that raw control looks cool and no plans for the tube though.  I'm not getting a faceplate so the extra pots will just cover the holes... I got some sweet aluminum knobs coming too (I think I'll call the amp the "Aluminati"... Joke).  I will be trying to voice this amp a little over the next couple of weeks and also put that cage over the tubes which I want you guys to check out... it will look a little different than the usual build.  I will probably say this several times more but Slucky thanks for the help and all the work in those layouts and documents.


I do have a question about bass response as far a EQ goes.  I'm putting the bass somewhere around  8 o'clock - 9 o'clock area so really low.  I have had this experience on a similar circuit before.  Is there anything you guys do bass EQ wise in the circuit to tame the bass?  I can of course just turn it down but I am curious if others have had the experience and what you do.

[sluckey]

Replace the two 25µF cathode bypass caps on V1 with 10, or 5, or 2, or .68. Experiment with it to taste. Many people like to use a SPST center off mini toggle to allow three choices.

Also replace the two .1µF coupling caps between the PI and power tube grids with .047 or .022. I like the .047s.

[eleventeen]

Well if it's any consolation, I've never been able to turn a Fender amp bass control above "4" without the thing turning into mud.

[Willabe]

Well if it's any consolation, I've never been able to turn a Fender amp bass control above "4" without the thing turning into mud.

Same for me too.

[ToneJunkie]

I did some tuning today with my new 1x12 rear ported cabinet with a Celestion G1265 (Fedex brought it today) which I think sounds great.  I put in a 12AX7 for the phase inverter, put in the Raw control and a Soul control (a NFB pot).   I play clean a lot in the bands I play with so what I'm looking for is a nice big clean sound that feels good... to me what feels good is a fairly soft attack and even when clean single strings sing a bit.  I don't play loud enough nor am i trying to have the amp breakup.  So for me the 12AX7 made the amp feel softer and the Soul control did that as well although with a 10k pot i did not use much of it to get what I wanted (Note it just adds resistance past the 820 resistor).  As for the Raw control I could see using it as an effect that you switch in but as for a base sound I get all the mids I need with the 10k mid pot (I will keep trying to find sounds I like with it).  I also got the aluminum knobs which I think look cool... the lighting was a little odd tonight for the pictures.

[Ambugaton]

Man, I am going to pretty much copy this if you are ok with it. Down to the aluminum knobs. Exact look that I love.

[ToneJunkie]

Ambugaton go for it!  No cabinet and no faceplate makes the build a bit cheaper and lighter     I got the aluminum from metals online its 1/4" T6 aluminum and the knobs are from Mammoth electronics.

[Ambugaton]

I noticed that you used all metal film resistors on this build, does this help with making the amp quieter? I wonder if I should do the same.

[ToneJunkie]

Nope those are carbon film (I'm pretty sure)... I have heard that metal film do make amps quieter but I think lead dress, layout, and grounding scheme are the main things to keep in mind when your trying to make an amp hum free.

[eleventeen]

The blue Rs are metal film, the beige ones are carbon. When they are new, there is probably no perceivable difference. When I am recapping a 35 y/o old Fender, I myself routinely change the 100K plate resistors with higher-watt MFs. OLD carbon comps in that plate resistor position typically generate lots of hissy and rat-like thermal (I think) noise that simply will not go away no matter what you do until you replace them. If I am ordering 2-3 watt R's for those, I usually just get the inter-node R's in the power supply also MF, also 2-3 watt. We're talking the absolute cheapest parts there are, if you are replacing resistors of *any* size/type/position IMO it's silly not to go with the MFs. That's just me.