Building parafeed EL84 DC 2A3 amp

[Bas Horneman]

I’d suggest try it with ac filaments first to see how much of an issue it is.

I'm tempted. However the talk of IM distortion of AC scares me. But then again...it seems less of an issue with 2a3 or other low voltage filaments.

On the other hand in my case I was thinking to also use the filament transformers for the rectifiers...since my main transformer only has HT.

The filament transformers do 6,3VAC/7,6A.

 

[Bas Horneman]

Power transformer prepped. 415-0-415 / 300mA. Ugly so I'll probably fit under the top plate.

 

[Bas Horneman]

The output stage will probably end up something like this. (Ultrapath connection to be able to forego a bypass cap on the output stage)

 

[Bas Horneman]

Ebonizing the feet for the amp.

 

[Bas Horneman]

Pretty black especially after the blo.

 

[Bas Horneman]

Alu top plates were just delivered...the fun can begin...although I always find it nerve wrecking to cut into that plate.

 

[Bas Horneman]

Spacers done. Using them because the transformer is not a standard size. So no cover commercially available. Decided to hang it under the top plate.

 

[Windcrest77]

I'm tempted. However the talk of IM distortion of AC scares me. But then again...it seems less of an issue with 2a3 or other low voltage filaments.

On the other hand in my case I was thinking to also use the filament transformers for the rectifiers...since my main transformer only has HT.

The filament transformers do 6,3VAC/7,6A.

Is this a Triad flat pack transformer where you added some copper shielding tape? This model has 6.3 v 7.6 A:

Just wondering because I was just looking at this series:

Item # FP12-3800, PC Mount Flat Pack™ Power Transformers On Triad Magnetics

 

[Bas Horneman]

Is this a Triad flat pack transformer where you added some copper shielding tape? This model has 6.3 v 7.6 A:



Just wondering because I was just looking at this series:



Item # FP12-3800, PC Mount Flat Pack[emoji769] Power Transformers On Triad Magnetics

Yup...that's the one I have.

 

[Bas Horneman]

Here they were naked

 

[deepgroove]

Whilst I am no magnetician
If you read Hammonds lit, (same tranny design) it already has low emi
Low Voltage PCB Mount - Low Profile - 2 VA to 48 VA (229 Series) - Hammond Mfg.

Are you going to use a coleman filament regulator

Erica

 

[Bas Horneman]

Yes. Coleman regs.

 

[Bas Horneman]

And good to know that they are low EMI. Just worried they will influence the plate chokes.

 

[Bas Horneman]

Here we go.

 

[6A3sUMMER]

Good!
Keep us posted!

 

[Bas Horneman]

A lovely winters day to do some drilling.

 

[Bas Horneman]

 

[Bas Horneman]

 

[Bas Horneman]

Mock up el84 subchassis

 

[egellings]

I am a little worried that the DHT 2A3 filament will be warm long before the EL84 indirectly heated cathode is warm.
Also, I expect the 5U4G filament to warm up long before the EL84 indirectly heated cathode is warm.

That means all 475V will appear on the 2A3 grid, and slowly fall to 157 as the EL84 warms up, and the EL84 starts to draw plate current.
Thee will be Lots of 2A3 current at power-up time.

I like the circuit, but just take care to get the EL84 cathode warm first.

You might select a pair of slow warming Damper Diodes instead of the 5U4G.

What about that large positive voltage that will be on the 2A3's grid? Won't that just drive the tube into saturation?