New schematic for review

[tubeswell]

Regarding my choice of output transformer I initially reported it as a "Tweed" Deluxe OT but it is in fact a "Tweed" Princeton OT. This transformer is listed as a SE transformer but I "ve questioned its primary center tap myself. I also have seen a similar version of this transformer with b suffix in a "Blonde" schematic with 2 6V6's wired in parallel. Anyway the OT in question is a Custom Magnetics 022913 made in Chicago & listed as a replacement for Princeton Reverb & Tweed Deluxe model amps.

Ahh I don't think that would be for a Tweed Princeton - a tweed princeton OT is definitely an SE OT. If the Primary has a CT, then it is a PP OT and I think they mean that it would be for a Brown Princeton or Princeton Reverb (which is the same type of OT as a tweed deluxe). (And they say it is a replacement for a PR)

I've also got a Hammond Champ transformer

I'd use that one myself

[Howlin' Mad Mac]

Well I understand what you mean about the cap bleeding some AC to ground. I had originally not included a NFB resistor but some of the comments I received indicated I should rethink & include one although I've often removed them from Champ circuits with good results so you tell me. I'll take a look again at BF/SF Champ schematics to get a better idea what's going on. As for the 250K pots I was originally thinking of using 500K pots until I remembered I used the last I had on hand rewiring a Schecter Tempest last month & after looking in the ol' parts box saw I have plenty of 250K pots & 1M pots. Should I use the 1M pots instead? Why? Will I need to adjust any other component values if I do? Which ones & what values? Oops there on the OT ground... good catch & I'm fixing pronto.

[Howlin' Mad Mac]

Why is it wrong (what's different) to use this transformer for SE application? I'm sure your advice is well founded & I want to learn the right way to do things. I picked this particular transformer because 1. I have one sitting on my shelf looking lonely & 2. I was "borrowing" from Ted Weber's 5F2A schematic.

[MWJB]

022913 is the Fender replacement part for a SE tweed Princeton, wired as shown in Mac's schem & mated to an 8ohm speaker.

I'd use 1Meg pots.

[Howlin' Mad Mac]

Final draft take two... and the winner is?

6V6 SE - Main Circuit.pdf

[loudthud]

Why is it wrong (what's different) to use this transformer for SE application? I'm sure your advice is well founded & I want to learn the right way to do things. I picked this particular transformer because 1. I have one sitting on my shelf looking lonely & 2. I was "borrowing" from Ted Weber's 5F2A schematic.

There was a thread a while back, http://music-electronics-forum.com/t16311/ where the OP built a single ended amp and had endless problems. At one point I think he re-built the whole amp and it still had problems. It dragged on for almost 2 months. I don't want to spoil the ending, but you need to read it

[Howlin' Mad Mac]

Ok, well I read the entire thread & yea there was some interesting stuff there but I didn't see anything related to using a CT OT for a SE application. Did I miss something or should I have caught something else?

[MWJB]

Loudthud, I don't believe for a minute that the poster in that thread had issues, soloely from using a PP transformer. Pull a power tube out of a super Reverb or a bassman, any static, crackling? No. Power drops, but they run in SE.

[Howlin' Mad Mac]

There was a thread a while back, http://music-electronics-forum.com/t16311/ where the OP built a single ended amp and had endless problems. At one point I think he re-built the whole amp and it still had problems. It dragged on for almost 2 months. I don't want to spoil the ending, but you need to read it

Doh! Nevermind... didn't see the thread continued on a 2nd page. So his problem was just that using a PP transformer for SE application. Makes sense they're constructed differently although I don't understand why the manufacturer says this is the replacement model yet it is not designed to work as expected. Yea! Modern manufacturing. :-P

[Howlin' Mad Mac]

Well made another revision with OT & NFB reconfigured... hope this one gets a passing grade from my professors.

6V6 SE - Main Circuit v2.pdf6V6 SE - Power Supply v2.pdf

[loudthud]

Loudthud, I don't believe for a minute that the poster in that thread had issues, soloely from using a PP transformer. Pull a power tube out of a super Reverb or a bassman, any static, crackling? No. Power drops, but they run in SE.

That's a valid point, but the amp worked a hole lot better with an SE transformer. Enough better that all the imagined problems went away.

[redelephant]

Going ultralinear? (think u got a typo in the output, 1kohm in series with plate...)
Looks good to go. Are you aware that tone - volume connection gives a highly interactive response? As you vary the volume you also vary the tone response a little.
My preference with loop NFB in a SE job is 'Just say NO!' A tube running class-A single ended should be given the freedom to run unconstipated so it can provide you with sweet warm juicy 2nd H even when at low clean levels, and when cranked you get that screaming dist with nice warmth. Saves you the possibility of unwanted oscilations as well, not to mention the parts.

[redelephant]

Oh, forgot. Why the SS diode in series with the rectifier? What voltages are you estimating. Nice using choke input filter if you have the voltage to spare.

[J M Fahey]

I was "borrowing" from Ted Weber's 5F2A schematic.

Excellent idea.
Borrowing is fine in my book, a perfectly valid way of working.
Why don't you save yourself a lot of time and "borrow" it in full, at once?
After all, that's where you are heading, step by step.
I was going to chime in about the somewhat poorly biased 12AX7's (why deviate from the datasheet suggested 100k/1k5 unless you have a valid reason to do it?) until I saw Ted Weber had it right.
Why doesn't that surprise me?
As a personal point of view, I "borrowed" almost all of Jack Darr's book, from 1969 on (fond memories), and it was the right thing to do.
*Now* I design, after studying and experimenting a lot along the way, but still, 40 years later, 90% of the time I agree with the classic designs.
Well, they became classic for some reason.
Or, as Art teachers usually say: "*first* follow the rules; when you fully master them, *then* you can start bending them for creative purposes .... but not before"
Good luck.

[Howlin' Mad Mac]

I get what your saying & have rearranged things accordingly (check later post of 6V6 SE v2 schematics) & tell me if I've got things right yet. However aren't the 1st two 16mfd in parallel & therefore equal to a single 32mfd cap? Still he wants to use this to record with so I agree noise & hum are going to be an issue therefore I did add a 9mH/70ma choke prior to the reservior & rectified & filtered the fillament supply. Also my heartfelt thanks, your comments & those of many others have been a big help to me.