Poundland 45

[Ali Tait]

My eyes are pies and yours are lies.

[Cressy Snr]

Valve sockets and most of the inside hardware fitted. Here’s an idea of what it will look like when finished.
It’s minus the feet at the moment, but the pic gives the general idea:

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[steve s]

Like it steve...

[Dave the bass]

put a full up cigarette ashtray on it .

The you'd have a ...

[Cressy Snr]

[Paul Barker]

Cute

[Cressy Snr]

We have a set of glowing heaters:

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[Paul Barker]

Steve as a friend I’m worried about the crowded transformers.

[ed]

Steve as a friend I’m worried about the crowded transformers.

at least it's not on a steel chassis.
crowded transformers on steel chassis are great fun...

[Cressy Snr]

Well it either works or it doesn’t. Not a lot I can do now. I’ve put every possible strategy in place to prevent interaction between the iron and minimise the possibility of it humming.
Everything is wired and tested: inputs, outputs, power supply and heaters. There is just the audio circuit to do, but not today.

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Non magnetic stainless steel plates and copper foil, screen the top from the underneath. Mains and heater transformer are under the large can on top. Can is earthed to the stainless plate via its fixing screws. Choke is oil filled in a can which is also earthed to the stainless plate with a copper strap, via one of its fixing bolts. The strap can just be seen sticking out below the left hand side of the Black Gate cap.
The only transformer under the top plate is the 5V rectifier heater transformer on the right hand cab wall.

[Cressy Snr]

Audio circuit is finished:

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[Cressy Snr]

After checking out the voltages, There’s a resistor in the power supply that feeds the input stage (more on that later) that needs altering in value: nothing major, but I couldn’t wait to try the amp out on some music, so here it is playing. It is propped up on a couple of bits of wood to give some clearance on the underside. The rectifier is a GZ34 at the moment just so that when it was upside down being checked over, it was more convenient, ie no need to prop it up on books to get clearance, so I wouldn’t melt the carpet.

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It’s absolutely fine in terms of noise levels. There is a tiny amount of filament hum, just audible with an ear to the speaker but I used 47R resistors to create centre taps rather than using humdinger pots, so the residual can’t be completely tuned out. However the improvement in SQ over a wirewound pot across the filament is well worth the negligible increase in noise.

With the resistor changed and a baseboard with feet to make, the project is almost done.

[RhythMick]

Looking good

[izzy wizzy]

Hope it sounds as good as it looks. That 'milled from a block' style is lovely and I like the form follows function layout.

[Cressy Snr]

Aye, it sounds really good.
In terms of looks and layout, I think it’s the best thing I’ve done in years. The translam construction is incredibly strong and rigid. With the additional stainless plates bonded to the underside of the top panel, it is completely inert. The dead structure of the cabinet could be a major contributor to the excellent sound quality.

The small size of the cabinet has forced some compromises. There is no split power supply anymore, because the choke required for the input stage branch simply could not be accommodated within the cabinet. Instead the supply is a back to basics, CLCRC.
The power stage is tapped off after the initial CLC. Beyond that, an RC section feeds the input stage. To be honest, I’m not missing anything soundwise by using the simplified PSU.

Up on top, the physical layout of the two 45s and the single ECC88 driver stage, means it is completely impossible to mess with; there simply isn’t the room. I took a conscious decision with this amp to deliberately make it difficult, if not impossible to modify. There can be no alternative drivers apart from those in the ECC88 family. There can be no octal driver substitutions, no room. There can be no DC modules for the 45 filaments, no room. No HT regulators: solid state or otherwise, no room. No fancy stepped attenuator, no room. The amp is basic, is what it is and is forced by its small size to remain so, which is good.