SE 45 DIY Amp Question

[setup1]

There are a couple of JE Labs versions. This one shares the filament trafo. No doubt the isolation is better with separates, but I could also do dual monos on the same chassis if it matters.

This schematic was a reverse engineered version of the original Simple 45 amp below. This was the very first SE amp I built using whatever parts I had in my bin. The OPT actually came from a trashed HK 500 integrated - PP, no air-gap. This was the mid 90s.

All subsequent versions of the Simple 45/2A3 were based on the schematic below.

As many have stated above, it's best to use separate filament transformers in SE configuration.

 

[trainbuftony]

+1 for using that "flathead" transformer
You could brag about it having period correct "flathead" power.
In the 1940s into the 50s, prior to the small block Chevrolet engine the ford flathead v8 was what the hot rod kids souped up.
Flathead power would indeed be perfect.

 

[Squidward]

As an aside (because that never happens here at AK), I've developed a habit of reading through parts catalogs to see what interesting parts other industries use and if they can be adapted to audio. I especially love reading about transformers, capacitors, and resistors. I think there are some amazing industrial parts that rival or better boutique "audiophile" parts that are sometimes touted.

One of my "discoveries" has been the Flathead line of transformers. With dual primaries and secondaries, low cost, and small form factor they make excellent flexible filament and bias supply transformers.

 

[HowardK]

I use this for two heater supplies in a 45 stereo amp. I use two .25 dropping resistors per channel and two 49 ohm to form a center tap per channel.

 

[Squidward]

I use this for two heater supplies in a 45 stereo amp. I use two .25 dropping resistors per channel and two 49 ohm to form a center tap per channel.
View attachment 2480368 View attachment 2480367

Are those green resistors KOA Speer?

 

[HowardK]

Vishay wirewound .24r 3 watt.
I guess wirewound are ok for dropping resistors.
Correct me if I'm wrong.

 

[analog addict]

Triad magnetics F1x transformer makes 3 amps at 2.5v

$10 each here. Work great for any 2A3/45/71A build. Used them for all of these.....

Triad Magnetics F1x at Allied Electronics & Automation, Inc