Orange AD15 Style Amp

[frankenxtein]

It has been a while since I've built a amp.
Since we have a couple people that come over that use small Orange amps , I thought I should build my version of one.
Going to try and get it as close as I can , sans the GZ34 rectifier.
So , that will be quite different I guess. These things are always an experience for me.
Using a nice Voice of Music power transformer #12552-2 300-0-300  HT 120ma and just over 3A of 6.3v. The power transformer was removed from a tiny chassis that had 6au6-12ax7-two 6bq5's and a ez81.
That chassis was in a console either the model 557 or 562
The output transformer (#12553-1) in said amp is nice but , set for a 4ohm load. (8k x 4ohms)  So , I'm using a Musical Power Supplies Inc OT20PP 8k x 4-8-16ohm 

[thetragichero]

i've built an amp from hammond organ iron stealing the output section of the ad15. sounded quite nice

i used a musical power supplies output transformer (ot22pp i think? something like that) in a recent build and sounds a lot better than the first version i did with a hammond ot. contacted them about custom wound transformers and they got back quickly even though gmail flagged it as spam, and the pricing was quite decent. i love supporting smaller companies

anyway, excited to see how your build progresses

[frankenxtein]

 Here's a photo of the donor amp.
Spent the day laying out the new chassis 13.75" x 6" x 2.5"

 A real nice organ output transformer is a Baldwin C-512-023628C weighs about 2 lbs. 25:1 6k2 x 8ohms. I put one of those in a PP el34. I have a A0-20936-2 from a Hammond that thing is like 10k x 4ohms. I just don't want to build something that needs two speakers right now. The OT that was in the donor amp is about a 1 lb , it was on the inside of the tiny chassis.

[frankenxtein]

Still have that same rat gnawing the hole for my IEC jack. 
The hard work is done.
The transformer placement is the same as I used for another amp , no noise even without the shields on the preamp and PI tubes. I did the headphone trick again hoping to be able to put the transformers next to each other. I ended up having to arrange everything the same as before.   
I used the same tag board on that other amp also.
       That amp has a big Basler Power transformer (I added a bell cover and that PT stands up) , Baldwin C-512-023628C (no covers) , Bridge rectifier , 2 -6Н2П ,2 -EH el34 and has a cathodyne phase inverter. Pretty much a 5e3 preamp with a Matchless power section. 

[frankenxtein]

Well , I must say I was getting ready to start making up my jacks and getting my parts laid out for the board. Then I looked at the input jack.
I picked this design for a few reasons but , wasn't expecting to be stifled by the input jack(s).

The Combo doesn't have two input jacks and from the drawing , it appears there's a connection bypassing the gain ,directly to pin 7 on V1b.   

https://www.ampbooks.com/mobile/classic-circuits/orange/

[sluckey]

The Combo doesn't have two input jacks and from the drawing , it appears there's a connection bypassing the gain ,directly to pin 7 on V1b.   

No, that connection is only used to ground the grid of V1b to keep the amp quiet when nothing is plugged into the input jack. The jack is a standard Cliff jack. Once you insert a phone plug that connection is broken and does nothing.

[boots]

I will be watching your build with interest!  EL84's are my favorite....

[frankenxtein]

Just a few photos of what I've got done so far. I bought four of these chassis they're 18ga. steel , really a bear to work with. I don't know what they were made for but , they were cheap. I still have two more to build in.
The power tube sockets and rectifier , are complete as far as can be done at this point.
I put a couple blanks on those unused socket holes. Just need to get the 12ax7's wired up with , what can be added before the board and pots are put in.
It's a real job putting two 20gauge wires in these little sockets.
The hot pink on the unused pins is a piece of shrink tubing. The rectifier has backup diodes. 
The heater wires for the 12ax7's  cross under the board in what will be the the filter section. The board sits 3/4" above/below the chassis.
This worked the last time so , if it ain't broke.

The amp before this one had a lot of heater current (6amps) and is SS rectified. Where the rectifier sits in this one , is where I used two 0.1ohm 5watt resistors on a couple tag strips to remedy that. On this amp I'll leave a space at the end of the board to put a couple of those resistors if needed. This one should be close
      Those 0.1ohm resistors knock just a little off the 6.3v supply. That other amp has el34's so who cares how much voltage the HT is. Most of my amps are built from junk and have to use a bucking transformer. That one doesn't thanks to those resistors on the filament supply.

[frankenxtein]

Good enough for a stopping point today.
I need to repair my soldering iron.

[frankenxtein]

Getting there , making a few changes to aid in construction.  After I do some stuff , I see how I could do it better.

[frankenxtein]

I hasn't caught fire , but I'm not trying to set it on fire. LOL
Surprised that I didn't get the controls mixed up.
It's been too long since I built an amp so , I'm not good at getting the numbers right
My screens are 100 volts below my plate voltages. 360v plate 260v screen.
I have a pair of 6p14p-ev's that match pretty close.

I have separate cathode resistors 250 ohm , 8.5v across the cathode resistors.
The schematic is hard to read some of the numbers.
I changed the (R1)680ohm resistor to a 2k , the next node was 22k , I changed that to 10k and changed the 150ohm screen resistors to 100ohms.

I didn't notice that they used a 260-0-260v PT in the AD15. This one is 300-0-300v the schematic for the Voice of Music amp looks as though they were getting B+ after the first node. There is a note in the parts list that says ,"some units use a ez81"

[frankenxtein]

I had the darn screens coming off the 3rd node. 
It works now.  6P14P-EV , the rest of the tubes will be replaced with JJ's
Plates 317v Screens 312v , Cathode current about 35ma (10.55v. per/300ohm resistor) 
A-318v
B-312v
C-251v
D-217v

 I switched everything back to the Orange AD15 specs.
Added current limiters (250ohm 5w resistors) They each drop about 9 volts. (ez81 Rt.) 200ohms would be closer.