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Bluebell Audio "Loftin White" Style 2A3 Single Ended Triode Valve Amplifier

With the WAD PHONO II and PSU II safely under my belt I could get to building what I really wanted - a low powered single ended triode valve amp. The beauty of 97db efficient loudspeakers is that they don't require oodles of power to get a nice sound from them. Still being rather unadventurous and a novice in the amp building game I had intended to build the WAD 2A3PSE kit. Unfortunately as soon as I was in a position to construct one WAD went through an "internal restructure" and the 2A3PSE was dropped.

After a bit of head scratching and a few prompts on the old WAD forum I considered a Loftin White style direct coupled amp, inspired by Keith Garrett's website. The originator of this take on the original Loftin White amp is Philip Ramsey of Bluebell Audio. After an initial phonecall in which Philip encouraged and reassured me that I could build an amp from scratch I placed an order, and soon after two big boxes full of strange looking bits arrived. No turning back now. This was the start of a telephone friendship with a man incredibly passionate about valves and music, without whose patience I probably wouldn't be listening to valve amps now. I suppose I should add that I have no connection with Philip or Bluebell Audio other than I provide the cash and they provide the components. Just a happy customer.

Construction

So, I had two big boxes full of bits. One was very heavy and contained all the transformers, the other was smaller and was full of components, valves, fixings etc. Now I had to work out what to do with them.

I spent a long time studying some photographs Philip had sent me of one of his Loftin White builds and sketching out what I thought was going on. It's probably my nature but I wanted to think it all through so I knew what the end would be, not just the beginning. Once I'd got things sorted out, I started to draw the transformers etc. up in AutoCAD and planned how I would lay the amp out. Once happy I printed out the layout and attached it to the 17" x 14" x 4" black powder coated steel Hammond chassis.

Then it was a combination of drilling, filing and hole punches to prepare the chassis. The secret is to be methodical, take your time, and increment the drill size by 0.5mm. The temptation is to jump by a couple of millimeters but a better finish can be achieved by the smaller increment. Generally this creates less swarf so less deburring is needed with a countersink bit. Perhaps more significantly, at bigger diameters an increase of, say, 2 millimeters is quite a lot of material to remove and can result in some work hardening of the steel chassis. Not to be recommended. The worst bit is forming the rectangle-ish shape for the IEC socket. I try to avoid these now and use captive leads that require a simple circle. Much, much easier.

The finished chassis. Philip recommended that I should cover the chassis in masking tape before I started drilling to protect the finish. I rather foolishly thought that by covering it with the printed layout I was doing the same, but all that did was trap swarf between the layout and the surface and inevitably lead to some scuffing. I still use AutoCAD to draft out the layout but I cover the chassis entirely with masking tape and I frequently lift two sides of the layout from the chassis to clean the junk out.

Next job was mounting the transformers, choke and valve sockets. The amp is starting to take shape now. The small 9 pin sockets were probably the most fiddly bit of the whole amp. The holes for the bolts are very close the to hole for the socket and in one case it actually "broke through" when fettling the bolt hole to fit the bolt.

On the rear, the on/off switch, IEC socket (boo!), slow blow fuse holder, phono sockets and speaker terminals.

Internally, the tag strip, Cerafine cap in the PSU, the filament transformers for the 2A3s (AC heated), and the twisted earth bar. I tried to use as many existing valve socket fixings as possible to mount the tag strip, mounting them beneath transformers where there were none.

The first few components connected up - the PSU and output stage.

Now finished, including some mahogany side pieces.

Switching on

Gulp! It's an understatement to say that I was a little nervous the first time I switched the amp on. Thoughts of 400V rippling through incorrectly wired electrolytic capacitors filled me with a little terror, even though I'd checked my wiring, but I thought it important to look confident in front of my better half!

So, standing at arm's length, I flicked the toggle switch and waited. The GZ34 rectifier started to warm up, then there was blue arcing inside and everything went dead. The slow blow fuse had gone. Hmmm, that wasn't supposed to happen.

I tried again, exactly the same thing happened and the fuse blew. Rather frustrating. Over the next few days I had a few conversations, checked all the wiring, scratched my head and waited for Philip to send down another GZ34 and some more fuses.

The following Friday the bits arrived. I got home from work, plugged the new bits in, held my breath and switched on. Success! A smidge of hum from the AC filaments through the Fostex FE208EΣ was very reassuring. I never had another fuse blow after this.

Initial Listening Impressions

It's Friday night, I've been abandoned at home for the weekend, and the neighbours have also gone away. I'm Home Alone with my new amplifier... great! A trawl through all my favourites proved that this amplifier really was as musical as I had been promised. Philip assured me of an "awesome" sound thanks to the direct coupling of the driver stage to the output stage, and that is exactly how it sounded after all those years of solid state amplifiers. The sound seemed so solid, all the grain I heard with solid state gear had been lifted. And even with a seemingly meager 3.5W on tap there was more volume than I could handle at two o'clock in the morning with no-one to wake up. Hell, even Oasis sounded good that night.

Improvements

I had a trip over to see Steve Shiels with the Loftin White. This was the first time I'd heard his Lowthers and rather more esoteric valve amps. Steve has a very nice collection of valves (I'm not doing it justice here) and he was generous enough to try a few different valves. First up was a Mullard GZ32 rectifier which glowed like a light bulb which concerned me a little as I didn't want one of Steve's nice Mullards to expire! It sounded very nice though, quite an obvious difference. I was surprised.

Next up were a few replacements for the ECC83s. Most didn't make much difference to my untrained ear, except for a nice pair of Tungsrams Steve produced. Turns out these were actually made by Mullard. Very nice. Once I got home and heard them in the context of my normal system I could tell they were much nicer than the new production Svetlana 12AX7s they replaced. Result!

Talking to Philip, he said that the components in the amp were already a pretty good spec and without spending significantly there was little to change. He did suggest that I could try some NOS RCA 2A3s though. Which I did...

Dualplates as you can see, don't think I've even seen a photograph of a monoplate. Were they an improvement over the cheap Sovtek monoplate 2A3s? Well, yes I think so, but there's not a lot in it, at least in this amp. The Sovteks are a real bargain though.

Living with the Loftin White

For a year I was really happy with the amp. If it hadn't been for Philip raving about his recent incarnations of the Western Electric WE91 pentode driven 300b monoblocks I might never have listened to another amp. But Philip was so effusive of his new amps I had to try them, and in comparison the Loftin White is limited, particularly in the bass. I had intended to replace the output transformers which I had robbed to build the WE91s and get the Loftin White up and running again. But as time goes by that's not going to happen, slowly I'm taking more bits and it's dying an ignominious death. A little sad really for my "first amp". But it really is a grand little amp, and is so much better than so many comercially available amps it's laughable. Maybe one day in the future I'll rebuild it out of sentimentality. Now, taking inspiration from the Japanese a fully tricked-up Loftin White might be something else entirely...

 

 

 

 

 

TubeCAD Headphone Amplifier
   

WAD PHONO II and PSU II