Tweedle Dee OT question

[Oddvar R]

I am building the Tweedle Dee amp and I have the classic Tone 40-18030 OT with 5K and 8K ohm Primary and a com lead. Any advice on what to use here, and is it any importance on what lead, 5/8k and Com, goes to the 5Y3 tube and the 6v6 tube, are the interchangeable?

[Colossal]

I am building the Tweedle Dee amp and I have the classic Tone 40-18030 OT with 5K and 8K ohm Primary and a com lead. Any advice on what to use here, and is it any importance on what lead, 5/8k and Com, goes to the 5Y3 tube and the 6v6 tube, are the interchangeable?

Oddvar,

Are you building a Tweedle D Champ or Tweedle Dee amp? Unfortunately, Classictone 40-18030 is a SINGLE ENDED output transformer and is not appropriate for a Tweedle Dee 2x6V6 amp build. You need a push pull output transformer. Given the high voltages in a Tweedle Dee, I would use an 8k primary for a pair of 6V6.

[ChopSauce]

That seems to be a transformer for single ended amps, not push-pull ones - like the Dee. Moreover your OT seems to be rated at 5W only. The tweedle dee seems to be "putting" 15W or more...

What you need is a tweed Deluxe OT. If you're in Europe, the Hammond 1750E looks very much like your first choice. Dunno in the US...

EDIT: Colossal answers faster...

[Oddvar R]

Sorry, it's the 40-18031 OT. (I am in Norway)

Building a Tweedle Dee Champ. I thought they might be single ended?

[ChopSauce]

A champ of course! About the OT, I don't know really. I think the original came closer to 8k primary.

[Colossal]

Sorry, it's the 40-18031 OT. (I am in Norway)

Building a Tweedle Dee Champ. I thought they might be single ended?

Ok, that makes sense then. What DC plate voltage are you going to run your 6V6 at?

[Oddvar R]

I haven't thought that long, what would be the better?

[Colossal]

I haven't thought that long, what would be the better?

If it were me, I'd go with a lower plate voltage, probably 320VDC or less. Then for your output transformer...

Vp^2/Max Diss = center-biased load impedance (ohms)
SQRT(Primary * Max Diss) = ideal plate voltage for a given OT primary impedance for center-biased singled ended operation
For your 8k tap...
SQRT(8,000 ohms * 12W) = 309V
or (309VDC^2)/12W = 8,000 ohms

The 8k tap is the way to go

[Oddvar R]

Great info, thanks. Does it matter what wire goes where? Se picture.

[Colossal]

Great info, thanks. Does it matter what wire goes where? Se picture.

Yes, it matters. Refer to the wiring diagram for the OT and to Charlie's layout drawing. RED is the 8k primary and goes to the power tube socket. Blue (COM) goes to the rectifier socket plate pin or B+1 cap.

[Oddvar R]

Òk, great, thanks.

[Colossal]

Òk, great, thanks.

My apologies! I reread my response and quoted it backwards. I've gone and revised my response.

In summary...

Dumble Champ Power Amp.jpg

[Oddvar R]

That's great, thank you.

Is the brass plate necessary? Or could the ground go directly to the chassis?

[Colossal]

That's great, thank you.

Is the brass plate necessary? Or could the ground go directly to the chassis?

No need to use a brass plate. Ground the preamp and its supply cap via bus wire, to the chassis at a single point over by the input jack. Ground the power amp and its supply caps via a bus, and any transformer center taps, to a single point over on the "AC side" of the amp. Don't use a PT chassis bolt for this, use a dedicated ground tab on the chassis itself for this purpose. Finally, use a dedicated and separate chassis ground tab for the Mains ground wire, placed over where Mains power enters the chassis.

[ChopSauce]

Thx Colossal. This is of interest for people willing to build a tweed as well, I guess. At least, that seems to me.

About the bus bar, also:

- I suppose that the best solution is to have its "non chassis-connected" side held by the physical connections (bits of solid wire) between the pots and the ground?