My BF-Tweed Champ

[printer2]

Not the best executed, too small a chassis, made some mistakes (How did I drill the holes for the controls on the wrong side? Guess we are doing a Marshall layout.) old power transformer that does not take kindly to me bending the leads, but it works. What is so special about it? Rather than just use a ground lift on a Blackface tone stack to get a Tweed amp, I figured out how to use the treble pot for a tone pot when in the Tweed position.



More or less the layout I used, moved things around a little and I forgot the 220k resistor for the 6V6 grid.



Still planing on adding a spring reverb although SS. Not the tidiest build but it works. A little more hum than I want with the volume turned up all the way but otherwise quiet. Still needs a feedback resistor, might make it switchable.

[PRR]

Love the wood.

6V6 is happier with a grid resistor.

I think your bridge rectifier is drawn wrong.

I do think, with a decent speaker, you want either NFB or another stage of filtering before the OT tap to get low hum/buzz. (With a dinky speaker in a teeny cab, it hums but you don't hear it 2 feet away.)

[DummyLoad]

attached bridge-recto correction. please don't be offended.

very nice woodwork and nice build. cool idea w/ tone-stack switching.
 
respectfully,

--pete

[printer2]

Well look at that. Never even bothered to look at the bridge, it is a ready made symbol in the software I use to draw up my circuits. I have been copying and pasting the same PS into my schematics and just changing the values. No bother you taking liberties, we need as many as we can get.

No hum in the output with the volume turned down. I can not remember the first cap value, might have used a 220uF or a 160uF. Hum is 60 Hz not 120 Hz. I do want some NFB though, I just did not have time to determine how much. Wanted to get it all together and get back to making my acoustic guitar. The body is made and need to do the neck.

[eleventeen]

I like the cabinet a lot. Sweet looking!

2 questions: what are the values of the 2 twin resistors you've used to make the synthetic center tap on the heaters? Looks like 51...something?

What is that blue cap-like component sitting on the IEC AC-input receptacle?

[printer2]

I have 120 ohm resistors on the socket doing center tap duty tied to the cathode. i am guessing you are asking about the two resistors on the right. They are 0.7 ohm, the PT is from a radio and I am not drawing enough current so these two are eating up about a volt to keep the heaters happy. The blue things are caps, pulled the IEC jack from a piece off equipment and it had them on it. Thought it would not hurt to keep them. Thanks about the cabinet. It was my first attempt at doing box joints and I used some spruce boards as test pieces. Made a couple of small cabinets and planed for 8" speakers, this one is a 10" though, old 60's hifi speaker. The grill cloth are plastic place mats I picked up at a dollar store. They are open weave and work ok. The cabinet height was determined by them.

[eleventeen]

"I have 120 ohm resistors on the socket doing center tap duty tied to the cathode."

Not to ground?

Place mats!   Very clever!

With the exception of the extra pot hole, that amp has nothing to apologize for! Looks very cute.

[printer2]

"I have 120 ohm resistors on the socket doing center tap duty tied to the cathode."

Not to ground?

Place mats!   Very clever!

With the exception of the extra pot hole, that amp has nothing to apologize for! Looks very cute.

Elevating the heaters using the power tube cathode is an old trick. Starts to get busy on the socket though when you have the two balancing resistors, the screen resistor and the grid blocker. Was a pain to unsolder the heater supply when I found I had 7.4V on the heaters.

Hopefully the extra hole will have a reverb pot in it within a month. I was thinking of putting a push-pull pot in there and have it do double duty as a master volume or as a reverb return. I have to keep slapping my hand and remind myself this was suppose to be a simple amp.

[printer2]

Darn, never going to live down that schematic. The amp does not even have a bridge rectifier in it, just a sloppy cut and paste job.  Sorry about the labeling, that does make sense. It was just a working drawing and I never really concern myself with the power supply section when building or the switch labels. Me bad.

Nothing for sale. I just show what I cobble together so that if anyone else has the desire they can use some of my ideas. The extra hole is slated to be for a reverb pot. I did some preliminary work on a SS spring reverb but I do not have the time to work on it now.

[terminalgs]

Elevating the heaters using the power tube cathode is an old trick. Starts to get busy on the socket though when you have the two balancing resistors, the screen resistor and the grid blocker. Was a pain to unsolder the heater supply when I found I had 7.4V on the heaters.

You had 7.4v with tubes in the amp?


Place mat looks good.  Guitar looks great!

[printer2]

Elevating the heaters using the power tube cathode is an old trick. Starts to get busy on the socket though when you have the two balancing resistors, the screen resistor and the grid blocker. Was a pain to unsolder the heater supply when I found I had 7.4V on the heaters.

You had 7.4v with tubes in the amp?


Place mat looks good.  Guitar looks great!

The power transformer was used to having three more signal tubes and a 6V rectifier on it.



First one that mentioned the guitar. It is a real cutey being about the same size of a Baby Taylor. It really infuriated some builders, they thought it a waste of time using the humble woods it is being made of. Then there are others who can not wait to find out what it will sound like. Mind you I did search through hundreds of boards to find the right one. The sides and back is made of scrap pine and the top is made of a cedar fence board. I put it aside to build this amp. I need to do a little tweaking of the amp, I find the 0.1uF tone cap is too large and the bass is usually around 10-15%. Used a large output transformer and the speaker can take the bass so it does not fart out. Given the capacity of the PT I probably could have done a tube reverb with trem. But this was to be a quick build.

[printer2]

Printer2,
From your comment, I was being obnoxious, and I apologize.

What is the your wall socket voltage?  I've seen a few 128 and 130v at wall sockets.  The high heater voltage is likely a result of higher voltage.  From the schematic of the Westinghouse donor, the P/T was designed to have a somewhat lower voltage. 
With a higher wall socket voltage, your heater voltage will also go up. 

Speaking of your guitar.  I remember going to junior high with one of the Pimental brothers, who made guitars in junior high woods shop.  Some of the Pimental guitars are of humble woods, and those command premium prices.  I remember reading several years ago, about a guitar maker who made a body of paper mache (sic), to prove a point.      What types of strings are you planning to use?   

I am a little slow sometimes, I missed that.

I have a variac and I always set it up for 120V once I am convinced nothing will blow up.


The guitar maker that did the paper mache thing was Torres, the father of all modern day guitars. He was showing that the top was the most important element in the guitar. I will be using regular steel strings, the string length is 22 3/4". Oak fretboard and bridge which will be blackened. The neck will be Fir. It started out being a prototype build to get the jigs and methods down to build a guitar with better materials. If I made mistakes on this one it would be no big deal.

At least that is the theory. With the time I put in this one and with it turning out not too bad I want to do just a good job on it also. Minor mistakes I made but that is the learning experience. I have made a hollow semi-hollow body before this so the neck will not be a completely new experience. Still need to put a final bridge on it and maybe a single coil pickup at the neck.

[Willabe]

Hey now, that looks real nice!


            Brad