813 SE build

[Hearinspace]

Originally Posted by tubelab.com

I built an 845 SE and I needed to use DC on the filament to get rid of 60 Hz intermodulation products. If you use AC and play a 1KHz tone through the amp you can see 940 Hz and 1060 Hz IMD products in the output. They are masked by the level of the fundamental tone so you dont hear them in musical applications, but they cause listener fatigue. All my DHT amps have used DC heating, but the DC must be clean. Sawtooth ripple on DC is worse than clean AC because of the higher order harmonics.

Thanks for that little gem. I've seen that before but didn't know what I was looking at (and where it might be coming from).

[santa]

Thanks to Rod Coleman i now have the components for the 813 heaters.
Still trying to get the chassis sorted. It is the hardest part for me.

[santa]

I'm down to the sanding clear coats on the wood bases so now I can continue on with the build.
For HV filtering, I was going to use some electrolytic caps I had laying around but I think I should at least use new parts for this build.

Considering the rectifiers in use (6D22S) and CLC filtering, what should I do for PS caps?
I would like to avoid the use of the big old paper/oil caps as I dont really have the room for them.

[santa]

I'm thinking some panasonic TSUP bypassed by some PP caps would do the job.
What would be a better sounding choice?

[Rod Coleman]

Stacked TSUP are good sounding electrolytics. Many Nichicons are known-good too, and Mouser has the KX series at 450V.

For ~900V dc, if the electrolytics are straight after the rectifier, then 400V rated parts, stacked 3 high (and balanced with 150K/2W) will be just enough.

To improve on that setup, I prefer LCLC, with Panasonic stacked MKP 1uF/1600V at the rectifier, 5H, Panasonic TSUP or Nichicon KX, 2H, then Proper audio MKPs, eg: AMPOHM/LCR

http://uk.farnell.com/ampohm-wound-p...30v/dp/1636651

Some like MKP motor caps here, but they sound worse than electrolytics to me.

[Steven-H]

Any updates ?

[santa]

I have been slowly getting the parts together for this project and doing some testing.
I finally sent the brass to a metal shop and had them polished and lacquered as I just could not keep the tarnish at bay.
They came out looking so good that my wife likes them and will keep them dust free for us to enjoy.
My goal for these is to have an amp that would look at home in a grand manor or castle.

I have pretty much all the parts so now I can begin assembly.

[radiostar]

Looks great!!!

[Steven-H]

Agreed - looks awesome. Cannot wait to see it finished.

[santa]

I have made room for a toggle switch that would allow Triode/UL switching.
With 900 VDC on the contacts the switch could prove to be a safety hazard if it does not fail (which many would) at power up.
For this kind of VDC and the isolation needed I feel I may need to go to a RF type relay and use the switch in the coil trigger circuit to maintain acceptably high breakover voltages at the switch itself.
Any opinions here?