audio-talk

Damn ! - that just reminded me I had that problem with a Dell one I used initially for the GK-71 - mind you, that was specced too close to the limit. I got a 20V 5A afterwards and that one started OK. So it is surprising this 20A one is not happy. Can you put a beefy 0.1R resistor in each connectio...

Got the SMPS. Good news is it can be adjusted to 10V. Bad news it won't start up both the fils when cold. It can start one so I think I'll have a delay relay for the 2nd which is a bit irritating. At least the SMPS will be up to power the delay circuit. Unless anyone has some better ideas? Cheers, S...

That's the difference between you and me dave, you have full proper cad drawing and plan to build something, I have a picture in my head and maybe a scribble or two on the back of a fag packet! I may have to look at getting some sort of cad package at some point....... Or Sketchup for free. Steep l...

My experience so far is that there's not a lot of hash and it's more or less at 50 to 60kHz with some higher. I think I remember 40mV as a number from one I used. Just try a 'cough big resistor first and see how it goes. Well I could just turn the voltage down a bit. Why just a big resistor? But as...

A 12V 20A SMPS arrived today. It has adjustable voltazge which is a bonus. I'm betting there will be a load of hash on the output. Any tips on dealing with that at 10A?

Cheers,
Stephen

I use a 30A 12v SMPS for each 833a, Chinese off Ebay. (filament 10v @ 10A) I drop it down to 10v with two resistors and two caps. For the next iteration I may use two Rod Coleman 10v @ 5A supplies in tandem. :) I was looking at his suggestions for power supply before the regs. Blimey! That's one ve...

Yes, but ignoring the fact that I have not tried a SE 813 amp so don't know, unlike a 50Hz AC heater supply in a PP amp via a transformer for each valve, the HF signal from each supply will not be in any way phase locked, one may be at 50kHz, the other 51kHz, so not only would you not get cancellat...

so there is definitely cancellation with the PP output stage Yes, but ignoring the fact that I have not tried a SE 813 amp so don't know, unlike a 50Hz AC heater supply in a PP amp via a transformer for each valve, the HF signal from each supply will not be in any way phase locked, one may be at 50...

Daft question, but i thought on the 813 the top cap is the anode, could the top cap lead be picking up noise from the transformers with it being fairly close to the iron on the bottom level? It ain't close to the bottom tier when it's up the right way :) I only flip them up the wrong way when testi...

Does that leave DC as my only option for the fils or is there something else that's possible? Do the ultrapath thing - put me out of my misery ! I put 30u on the top part and 200u on the bias resistor. No effect on hum/buzz. Annoying huh. The issues I'm having might all be down to 813s are a bloody...

Stephen, I got a couple of capacitors some time ago for my 833a project. They are 130uf @1900v dc @40A. AVX polypropylene. You can borrow them to try if you like for the cost of postage both ways. The Ebay supplier is out of stock at the moment. Thanks but I don't think capacitance is the issue. Ad...

Turning the HT off doesn't reduce the hum/buzz so surpringly, adding a choke between the cap banks doesn't do anything either.

Does that leave DC as my only option for the fils or is there something else that's possible?

Cheers,
Stephen

Well, if I understand where you are, you have got the output stage as quiet as you can using hum pots. I would guess the next place to go in DC heaters. The last scope trace I saw didn't show any signal that looked like it wasn't the heaters. You may find that getting the driver stage going you get...

Other buzzes seem to have pretty much gone. The hum now is very low 4.2mV true RMS so the scope says. I now have two channels going ... sort of. Two output stages going with a minor bit of buzz/hum. Can't make too much noise coz young people in bed. Now to decide how to pursue this hum/buzz. having...

I once built it as a stereo amp, the first one. It was about 1m square :shock: and so heavy, it was built in situ. Flippin' 'eck :shock: Well exactly. They were made for the Acoustats and it made me think, if I need an amp like that to make them sing, then I got the wrong speakers so the amp was pu...