One Tube SE Guitar Amp -schematic here- I have Power Supply & layout questions

[kagliostro]

I Need help for Power supply design and whole amp layout



I've find a nice 1 tube guitar amp schematic

http://www.solorb.com/elect/musiccirc/squirrelmonkey1/

The tube is a 6AF11 Compactron ( two triodes and one pentode )

EDIT

http://www.tubebooks.org/tubedata/HB-3/Receiving_Tubes_Part_1/6AF11.PDF

http://www.nj7p.org/Tube4.php?tube=6AF11

So is possible to have a 1 tube amp  


My first BIG problem is the Power Supply  

I can't use the schematic used by the author because in Italy we have 220v

so the original PS is not usable here


Other problem is a layout

I'm able to copy a layout and build an amp

but to me is difficult to draw a layout



I arranged a layout for the amp and a new Power Supply schematic

Can you give a look and revise ?

The red wires are on the other side of the board - the 20uf 20nf cap (green wires) is connected directly to the socket.




I'm very confused about the Power Supply

Questions:


Voltage difference

I have 220v transformers - Must I decrease the voltage till 180v and 175v, voltages that the autor used, or can I assume that those voltage are the voltage obtained with the original 120v-120v/28v Power Transformer used by the autor and I can rise a little the B1+ & B2+ voltages ??


Consumption

As I've 2 x 10VA - 220v/9v transformers, is 10VA enough for that amp or I must use 2 x 15VA transformers ?

Thanks

Kagliostro

[PRR]

Be sure you can get that socket in your area.

He has the power stage biased for about 25mA at 180V. 20ma at 200V would be acceptable also.

Preamp stages are 1mA or less each.

Your 220V winding will rectify to 308V DC, a little less because two small transformers. You need to lose 300V-200V = 100V at 25mA. 100V/25mA= 4K resistor able to handle 2.5 Watts of heat. (Your row of 33K is much too much.)

Total power pulled from transformer is 308V*0.025A= 7.7 Watts DC. Your AC VA rating should be 12.3VA. Go ahead and use the 10VA. They will sag but you don't need full voltage. They will run hot but 10VA parts usually won't get hot enough to matter.

Instead of ferrite bead, a 33K resistor will probably work better in this high impedance input.

Rectifier is mis-drawn:

[kagliostro]

Many thanks PRR

Your explanation about consumption is plenty fine

also MANY thanks for correcting my stupid   :shocked:  PS AC connection  

100V/25mA= 4K resistor able to handle 2.5 Watts of heat. (Your row of 33K is much too much.)

OK I'll use 4K resistors - ( three or .............. one is enough ??? ) and than a 5K 2W resistor as in the original project (or not ?).

Be sure you can get that socket in your area.

I've the tube, the socket and some other parts.

Instead of ferrite bead, a 33K resistor will probably work better in this high impedance input.

As the author don't used the 33k input resistor I was thinking he do that as to have max gain at input

so, as I have some ferrite beads, I've think to use one there, for the reasons you well know.

I'll use a more standard 33k resistor as from your council

Kagliostro

[kagliostro]

OH OH .............  NO !!   I was really in a wrong way

My mind was really out of order

I've read newly all PRR wrote about the calculation of the requested resistor

So, if I'm not wrong, I need a row of two resistors

the first as stated by PRR as to reach B1+ at near 200v
~300v - 200v = 100v  -- than -- 100v / 0.025A = 4K resistor

the second assuming B2+ is right at 175v with a B1+ of 200v
~200v - 175v = 25v -- than --  25v / [EDIT 0.025A = 1K] 0.001A = 25K resistor

are this calculations correct ?

B2+ with an increased B1+ (200v instead of 180v) can be set at 175v or must be set higher ?

see new revised schematic


Kagliostro

[kagliostro]

As I discovered that the OT (7kohm/3.5ohm) I have in my junk box can not be used as is demaged

can I use this transformer for this amp ?

http://it.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2106475

http://docs-europe.electrocomponents.com/webdocs/0473/0900766b80473a76.pdf

Thanks

Kagliostro

p.s.: as it is rated for 40mA DC I suppose that is adequate for a Single Ended amp but not sure about

[PRR]

Yes.

The 6AF11 power section is pulling about 25mA, so the 40mA OT rating is fine.

[kagliostro]

Many Thanks PRR

Kagliostro