HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

The top plate of my existing 45 amplifier has been hacked about so much that it resembles a colander. The chassis has seen everything and has been weighed down with a ton of iron in the past, hence all the holes.
I decided to look into building a more compact setup: neater, no screws visible and more in keeping with the dinky dimensions of the valves themselves.
As a result of this pondering, I came up with this: It’s a midi-sized component, made from a translam construction using seven bamboo chopping boards I got from Poundland for £2 each. Five of them have had their middles jigsawed out, to make a set of half-inch thick frames and two have been left solid to serve as top and bottom panels. Over the past week, six have been stacked, glued, clamped and sanded to within an inch of their lives, with the seventh (bottom panel) made detachable. I’ll detail the build as usual, but the circuit and power supply themselves are just the same as before, so not much new there.

It's a 'Poundland' projct in more ways than one. Of course the case is made from Poundland chopping boards as previously mentioned, but also the output transformers are a pair of push-pull ones I rebuilt myself as single ended.
I've tried not to skimp on the audio circuit components, but the signal coupling caps are Mojotone Vitamin T guitar amp jobbies, and the valve sockets are bog standard nickel plated Chinese units. The 45s are of course not budget and the black Gate WKz final PSU cap is a loaner from Nick (Lurcher) so I'm not counting that as budget either.
In terms of driver valves, it's just an ECC88 twin triode with both channels in a single bottle. It's a Philips Holland NOS, so not modern production. It does however sound great in the amp that exists at the moment. I also have a few Miniwatt PCC88s with the 7V heater, so I'm good for a long time with these.

The underside of the top panel will be part of a stainless steel, door kick plate I picked up for a few quid and everything will attach to that from below with self tappers apart from the earth bond and the 0V signal bond. These will be on bolts, with recesses for the heads sunk into the underneath of the wooden top plate.

Once this is built, there is no scope for changing the driver valve. To mod it apart from maybe coupling cap changes will be nigh on impossible. This is how I want it, as I want this to last me a long time. I've proven the circuit to my satisfaction and am more than happy with the sound quality. There seems little to be gained by going beyond this point unless I spend very big (which I can't) and I want some stability in the old sound system, so I can sit back and appreciate what I've got.

Really nice piece of woodwork there, Steve.

Cheers Fret.

Circuit diagram:

When you say you will not be able to change the driver valve, does that mean if it stopped working for any reason, the only way to change it would be un-glueing the chassis? As normal Steve, I shall be looking forward to see the finished product.

antonio66 wrote: ↑Tue Jun 29, 2021 1:23 am When you say you will not be able to change the driver valve, does that mean if it stopped working for any reason, the only way to change it would be un-glueing the chassis?….

I’ll be able to change the driver for others in the ECC88 family, but that’s as far as it will go. I’m making the case as a quality piece of furniture, quite deliberately. This means that any drilling and modifying will ruin the whole thing. It gives me an incentive not to muck about with it externally once it is built. I’ve proved the circuit on the bigger chassis, so I see no reason, once I’ve built it to do any more with it.

Progress so far: It looks bigger in this pic than it actually is.

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:

I think it look great, what a clever way to stop yourself forever changing stuff.