audio-talk

Just re-reading 4th edition of Valve Amplifiers by MJ and when discussing sources of distortion and the onset of grid current, he refers to the point at which grid current starts to flow, about Vgk of -1V, as the contact potential point... seems a bit of a misnomer to me...

This point seems to be determined by a whole range of factors, however I still can't see how a gold-plated vs. solid nickel grid makes much if any difference...

Just FYI most of my 300B's, when I was using them, of both Chinese and Russian, suffered air leaks over time which eventually resulted in crackling noises, sometimes quite alarming! (one Svetlana made a noise like gunshots) usually when starting up. And later while running too, after more usage time had elapsed. Some only lasted a few months. The Guiguang ones I used latterly are still OK so far but gone brown inside the glass. Guiguang now renamed as ~ P-Vane?

Think what I'm saying is, not surprised.

BTW Paul's right about 6SN7's these can do it too, depending.

I had completely forgotten until the other day that some time ago I snagged one of the loudspeaker cables with my food jolting the amp forward a few inches on the shelf. I didn't notice any noises until weeks later or else I would have connected the events.
I've just ordered a new valve. Although it seems to be ok once the amps has warmed up I didn't want to take any chances with the speaker or amp.

Avinunca1 wrote:.....snagged one of the loudspeaker cables with my food jolting the amp forward a few inches.....

That must have been a pretty substantial meal you were carrying there ?

IslandPink wrote:

Avinunca1 wrote:.....snagged one of the loudspeaker cables with my food jolting the amp forward a few inches.....

That must have been a pretty substantial meal you were carrying there ?

Even with MY gluttony I couldn't manage that!

Well Hotrox called me about three weeks ago to tell me that they didn't have any valves in stock with the correct values for a match. I said I didn't mind waiting and I'm still using the defective valve. A few days ago they told me they had received a new delivery but they were all matched pairs.
Just hope the dodgy valve doesn't do anything nasty while I'm waiting. It gives quite a loud pop when powered up but behaves ok afterwards.
I should hate to have to buy a new op trannie.
May have to buy a new pair. Anyone used the budget Psvanes?

A single ended 300b with one valve per channel won't normally need matched output valves, I would ask them for the closest single they have and that should be fine.

When my Svetlanas went noisy had to unplug the speakers before turning them on, else sounded like a firing range. They finally expired of course, one with snapped filament. A set of four had been bought on Barclaycard, and I think the first one went before I'd finished paying for them!

I had bought a new matched pair from tube doctor in Germany before I realised a matched pair wasn't necessary. I'm still using the valve with the start up crackle though. I'm really bowled over by the purity of this amplifier. It should sound even better with Andrew's heater boards. I must order the
transformer.