The Nemesis 813 PP Amplifier

[Nick]

Edit : actually with PP cancellation , you might not hear that 50kHz intermodulation as much.

You could use the same argument to say you would not need to use hum pots

[IslandPink]

Me and Paul played with them many years ago.

Just to clarify for Stephen, this was lighting transformers.

[Nick]

Me and Paul played with them many years ago.

Just to clarify for Stephen, this was lighting transformers.

Yes, modified to remove ripple and alter the voltage out.

[IslandPink]

Edit : actually with PP cancellation , you might not hear that 50kHz intermodulation as much.

You could use the same argument to say you would not need to use hum pots

Err, not quite , I think if Stephen tried to use AC heating on an SE 813 amp, we'd not be talking about anything that was useable - so there is definitely cancellation with the PP output stage

[Nick]

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 50kHz, the other 51kHz, so not only would you not get cancellation, you may get a 1kHz difference tone. The reason you get cancellation with 50Hz heaters is that the two signals are correlated.

[izzy wizzy]

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 50kHz, the other 51kHz, so not only would you not get cancellation, you may get a 1kHz difference tone. The reason you get cancellation with 50Hz heaters is that the two signals are correlated.

I think I'm already hearing and seeing the mix of 100Hz and 50Hz on the scope - the little wiggles on top of the 50Hz; some look like 200Hz, some a bit less and so on. I wouldn't fancy that with higher frequencies. Plus I don't fancy yet another project on top of this one so for me, HF AC heating is out. I've done quite a bit of reading on the subject from the RH amp man and TriodeKingdom on AA but they're all single ended apps.

LED supplies are fairly cheap but 12V however if they have an HF element on the output, some LC filtering would not only drop some volts but maybe clean things up a bit. Has anyone experience or know of anyone doing that with these things in that fashion?

Cheers,
Stephen

[Mike H]

That might noise on your mains supply. Where I used to live (South Essex) I can remember being shocked at what I saw by just 'scoping the mains - i.e. by just looking at the AC on a heater winding. One time I remember seeing the peaks being clipped, ( . . . ! ) another time spikes, evidently caused by a dimmer switch type of thing, (triac turning on part way thru each half cycle) but we had no dimmer switches in our place. So must be somebody else in the road!

[Mike H]

LED supplies are fairly cheap but 12V however if they have an HF element on the output, some LC filtering would not only drop some volts but maybe clean things up a bit. Has anyone experience or know of anyone doing that with these things in that fashion?

The PCL86 amp I've just made uses SMPS supplies. Both HT and heater. The amp has a common mode rejection filter for each, where they come into the amplifier case. (Two separate PSU units.)

However you'll need a CMR filter for 10 Amps.

[Mike H]

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 !

Thicko question, what is ultrapath? (If I knew I've forgotten. )

[Nick]

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 !

Thicko question, what is ultrapath? (If I knew I've forgotten. )

https://www.tubecad.com/2008/08/blog0147.htm

[IslandPink]

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 cancellation, you may get a 1kHz difference tone. The reason you get cancellation with 50Hz heaters is that the two signals are correlated.

I was assuming you could find an SMPS that would supply 2x 813 .

[Mike H]

Thicko question, what is ultrapath? (If I knew I've forgotten. )

https://www.tubecad.com/2008/08/blog0147.htm

S .. P .. L .. A .. S .. H ...

Thanks.

'Course I remember it now.

[pre65]

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.

[izzy wizzy]

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 cancellation, you may get a 1kHz difference tone. The reason you get cancellation with 50Hz heaters is that the two signals are correlated.

I was assuming you could find an SMPS that would supply 2x 813 .

Yup saw some on Amazon last night. Might be worth a punt to settle this for good ..... maybe.
https://www.amazon.co.uk/Redrex-Univers ... 3H675NQB06

I realised something when we were discussing HF AC and in phase cancellation and all that. The second channel had way more buzz/hum much like the first one originally and then thought, better check the phase of the wiring as it made a difference on the first one. Doh! Wired them up wrong again so hopefully will get less when I wire them up properly. Too tired for much else tonight having got up at 3:30am to drop the wife off at the airport. Might even be best not to play with 1kV either .... if I can resist.

Cheers,
Stephen

[izzy wizzy]

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 very expensive way of doing things. I know his stuff is good but it would have to be some improvement to go that route. The size of the transformer he recommends

Cheers,
Stephen