The Mullard 3-3

[atnaat]

Hello, what's the general opinion of the mullard 3-3? I want to build some valve amplifiers and my previous experience is restoring valve radios and servicing amps. I need a small amp to build to be connected to my computer. I'm levitating to wards the Mullard 3-3 because it's not a kit but in the book it's laid out very simply, which could help over come the learning curve.

Thing is though, I don't want to build it if there's something that I can build that will perform better, relative to price of course. Opinions?

[Eli Duttman]

Along with the 3-3, Mullard published several other designs. All of the designs were intended to promote sales of their tubes.

FWIW, I've been involved in a project based on a Mullard design that employs the 6BM8/ECL82. Look here. With only 2 bottles and inexpensive, "universal", power "iron", the design could easily be "perfect", for use with your PC.

[ray_moth]

I built a 3-3 in 1963 to put in a record player. With the little elliptical speaker I used, I couldn't really tell how good it was but it was a heck of a lot better than the usual run-of-the-mill record player amps in those days.

There didn't seem to be any technical issues with the 3-3 that I can remember..

[dtut]

I built a 3-3 a little over a year ago. Interesting amp with very interesting - and I thought - enjoyable sound. I had trouble getting it quiet and getting the OPs settled down because they are so mutually effected by the behavior of the tubes actually in the amp. Eli's suggestion would be easier to build and get right, I think.

[Tubes4e4]

Hi atnaat,

the 3-3 circuit was discussed controversely over at the German forum of Jogis Röhrenbude (I don´t give a link here because that thread by now is in an access password protected archive and completely in German).

Quite some people expressed their doubts on the driver stage. To shed som light on facts, I made a plot of EF86 at the almost starving, current trickling operation point it is used in the Mullard 3-3, click here. Also, note how intelligently the DC for the driver stage screen grid is derived and how this method stabilizes the operation of the whole amp circuit. Well, those guys at Blackburn certainly knew what they were doing

Given a decent OPT to be used, you cannot do much wrong having a try at it for your intended purpose - after all, it is simple and cheap enough to be build just for testing wether it will suit your intended application. I am sure it will

Regards,

Tom Schlangen

[rjb]

I threw together a 3-3 when it first came out- with a cheap OT. If I remember correctly it was a bit temperamental as to the brand of EF86 used. Might have been the breadboard layout of course.

I had more success with their push=pull designs, much more tolerant as to components and layout.

[atnaat]

I think I'll build it, I already have the tubes and sockets lying around. Where is best to buy transformers in the UK? I've googled and it would appear that it's best to buy them over the internet from America.

[ray_moth]

You could try Sowter - good reputation but not cheap.

[Eli Duttman]

Atnaat,

Nose around for a UK distributor who deals in Triad Magnetics stuff, perhaps Farnell. The voltage doubler B+ supply shown in the 6BM8 amp should be adequate for a stereo "3-3" too. Totally cheaping out on the O/P trafos is a bad idea, but saving a few coins elsewhere is quite sensible. IMO, there is no more cost effective solution to the quality B+ PSU problem than a well executed voltage doubler. If you try doubling a Triad N-68X, use larger caps. in the stack. Here, you want to keep the rail voltage up.