Mullard 5-10 DC conditions

[ASolderer'sTale]

Hi everyone, I’m new to VR, and much appreciate the wealth of knowledge displayed by members in the threads. I have recently completed building a stereo amplifier based on the Mullard 5-10. It uses a GZ34 instead of 2 x EZ81s, but aside from that adaptation I’ve followed as faithfully as possible the circuits in the 1993 reprint of Mullard’s 1959 “Tube Circuits for Audio Amplifiers”. From first firing up, it sounds wonderful – a rich chocolaty sound, very low hum and hiss. However, I was concerned about the measured DC conditions which varied quite a lot from the published table. Anode voltages especially in the input stages (ECC83, EF86) were much higher. I sweated for weeks trying to figure this out. Then I found an old thread on VR with a link to the PDF for 1954 circuit. Circuit was the same BUT the DC conditions were quite different. In fact they were very similar to my measurements – so great relief there. But it begs the question: what happened within Mullard in those 5 years from 1954 to 1959 to change the DC conditions for the same circuit? The AVO used has same specs. And why does my amp conform to the earlier version and not the later? Any ideas anyone? I attach pics of the two tables …. Aside from that I’m enjoying a sound I’d almost forgotten from 50 years ago … now for the pre-amp …

They are near enough in my book, it would rather depend upon which amplifier on the bench you where measuring. +/- 20% is OK.

[peter_sol]

Both those tables are based on a sample unit. Quite wide variations are nothing to worry about.

[Diabolical Artificer]

It's not the results per se' that are indicative of a helty/faulty amplifier, but the difference between cathode and g1 or screen anode. That's the great thing about working with valves, as long as the measurement's are ish, your fine. They're more relaxed than their uptight cousin's the transistors : )

Andy.

[ASolderer'sTale]

Thanks everyone, a great help - ahh the value of experience! I'm not sweating anymore (except for the heat given off by 9 valves and 3 trannies). As I consider making the stereo pre-amp in Mullard's book, using the HT and heater supplies from the main amp, I am a little stuck trying to find a suitable HT connector system (plugs and sockets). I can only find conventional systems 240V rated. Does anyone know if there exists a 6 pin plug & socket system suitable for 300v plus?

I have used D connectors at 350VDC, some are rated 500V and 5A, should be enough!