Glasshouse 300BSE (clone??) build.

[Riggers]

Hi All
It has been a few months since I completed this build but wanted to give it a good test run before I published anything on the forum. (just in case I built a death trap or burnt the house down )

I have always been very impressed with my WD88 VA but wanted to dip my toes into the waters of a single ended design. And...the challenge to build an amp from scratch with just a circuit diagram and bom.

It might come as a surprise but I have run the amp successfully driving my WD25T's. You will hear plenty of people say that to experience low power valve amps at their best you need 90+ db efficient speakers but I would go along with Herb Reichart's observation that an easy to drive impedance over the frequency range is more important. I am not playing them to ear-bleeding levels but they can go plenty loud enough and sound great.

Why the Glasshouse design? There are a few SET 300B designs on the internet, I guess it came to having faith in the designer, Andy Grove, and knowing that at least a few of these had been built and used successfully (including Richard from the WD forum).

These days the design is expensive to execute, not least of all the lm323 voltage regulators. I made the choice to go all in with Hashimoto opTx's and decent but not over the top caps. I figured this could well be the last power amp I build as I now have 2 amps of different design approach but that perform well and that I am very proud of.

I have attached a few picks to show my work.

I must thank this forum (and Matthew Snell) for giving me the opportunity to buy my original WD88 amp and the support necessary to get it performing well. I must also thank John Caswell for his patience and generosity for taking multiple phone calls with my list of questions.

I'm interested to hear what you think.

Phil.

[bob orbell]

Looks very well assembled Phil, well done. I have only listened to one 300B single ended and although nice sound, on very quiet passages a low level hum was present and put me off, maybe I should try again. Bob

[colin.hepburn]

Hi Phil
Nice Build Well done Phil

yes my J.E Labs Single ended 6SL7/KT66 Amp I built back in 2011 with lots of help from Richerd and John and others and I am still tweaking it to this day and with an output of about 6 watts it works very well with my old Wharfedale 6 ohm 87db in my room as well as my full range Fostx FE 126 93db Frogle Horns
Now I am reconsidering yet another rebuild of the amp to mono Blocks Any way it is about your amp phil tell us more about it and the music you play on it

[Riggers]

Bob, the thing about this amp is the quite elaborate power supply and DC voltage regulators on the 300B heaters. It makes the amp super quiet. Some argue that DC heaters aren't "rock and roll" or something to the effect that the music is more "digital??" sounding... I can't comment as this is my one and only single ended amp 300B amp and I have nothing to compare it with. It just sounds great.

Colin, I guess I should start with the music. The Dean Martin album I picked up for $2 from the charity shop sounds superb, classical music (even complex orchestral) really draws me in and the most head-bangy 80's rock that I have gets loud enough to annoy the rest of the family.

I went for a bit of a Japan style with the amp, there are a few sites out there to give inspiration including single-ended.net. The chassis is from Takachi. This allows for one to provide a CAD drawing for them to laser cut the chassis to your requirements. Difficult to say if this added cost outweighs the benefit of not needing to buy cutting dies which I would only use once, (but I guess I could onsell on eBay).

Regrets... Always tricky to picture layout in 3 dimensions, I did spend time with large sheets of paper positioning components but did run into a snag or 2 once you consider other components fouling your hard work (such as sockets mounted on side walls impacting boards already mounted to the chassis floor). I could have done with a few less screw holes in the chassis top from a cosmetic point of view, but I did use nice stainless steel screws .

Time will tell whether there is sufficient ventilation in the chassis top. I am relying on the holes for the 300B and 5u4 valves to let hot air escape. I did get an idea from the site aumacoustics for a vented cage for the "hot" valves' sockets to mount to. This seems to work well. (hasn't seen it's first 35 degree Brisbane summer yet!)

Phil.

[John Caswell]

Hi Phil,
Glad to see all your efforts said off. Very neat construction, almost up to my standards. And the fact that it performs well and is quiet is a testimony to thinking about layout and methods of construction. Very good work

John

[Riggers]

Originally Posted by John Caswell

Hi Phil,
Glad to see all your efforts said off. Very neat construction, almost up to my standards. And the fact that it performs well and is quiet is a testimony to thinking about layout and methods of construction. Very good work

John

Many thanks for your kind words and of course your assistance.
Phil.

[Richard]

Lovely job Phil. Have you made it more normal in size than the original? You've certainly put a lot of work into the layout and optimising it electrically



Here're a couple of pics of mine from around 10 years ago which show the internal layout inside the large chassis. It really was a nice amp, one of the best I've had anyway. It had a hum problem which kicked in after a few minutes running. It's hooked up here to a choke John lent me to confirm our diagnosis (choke windings shorting as it warmed up). A new choke fixed it. It was easier to bring the tools to the amp than take the amp to the workroom!

[Richard]

Found a couple more pics which give a better idea of the size of the beast (the only thing left of that system now is the Thorens/Formula4),

[Riggers]

Hi Richard

I did notice that the original build was quite "generous" in chassis size! I managed to get the build done on a more manageable level, the main determiner of chassis size I selected was the height of the choke.

I have to admit that I got some good pointers re connections (especially grounds) from an old post of yours in regards to your choke issue at the time. (and John's advice.)

I have a very quiet amp. The only issue was that originally I managed to ground out the voltage regulators due to a lack of attention. They are mounted to a aluminium angle piece which I failed to de-bur the mounting holes well enough and even with the supplied insulating mica washers I grounded the TO3 bodies At least the only damage was a couple of mains fuses and a 5U4!

Phil.