833a Amp

[pre65]

The extra choke and caps have now been fitted, the caps on a blue acrylic plate that fits where the EL34 and 6SN7 used to sit.

To be honest it's not cured the bit of hum I have still got, BUT I've gained a bit more lovelyness.

[pre65]

I use a DC blocker in the mains feed to my pre amp, and now I've incorporated a DC blocker into each of the 833a monoblocks.

If anyone is interested read this article. Mine is as fig 8 but with a couple of modifications.

http://sound.westhost.com/articles/xfmr-dc.htm

[pre65]

I see it's a year since my last report.

I don't use this amp very often, but It's in use this morning. I'm trying out a new preamp and thought I'd dust off 833a and warm the room up a bit.

It is still a most amazing sound, powerful yet sweet and detailed.

[flapland]

Originally Posted by pre65

I see it's a year since my last report.

I don't use this amp very often, but It's in use this morning. I'm trying out a new preamp and thought I'd dust off 833a and warm the room up a bit.

It is still a most amazing sound, powerful yet sweet and detailed.

Suspect they could warm a very big room. I am new on the forum and just read through this thread and I am impressed by what members are attempting although I have to admit you wouldn't get me attempting anything like this though, just don't have the skill or the gonads.

[pre65]

Originally Posted by flapland

Suspect they could warm a very big room. I am new on the forum and just read through this thread and I am impressed by what members are attempting although I have to admit you wouldn't get me attempting anything like this though, just don't have the skill or the gonads.

I never thought I would.

[flapland]

Originally Posted by pre65

I never thought I would.

Thats what scares me, I can see some DIY DAC being built by year end.

[pre65]

Even more scary.

I'm rebuilding it with choke input sometime in the future, and have ordered a pair of 1500-0-1500 Hammond transformers and matching chokes.

Expensive, but then the best normally is.

[pre65]

I've started on the rebuild.

The mounting holes for the new mains transformer and reactor (choke) have been drilled as have the mounting holes for the four smoothing capacitors.

The caps are BHC 1000uf @ 450v so will end up as 250uf @ 1800v, should be enough.

I'm now waiting for some stainless hardware to hold things down so not much more progress for a few days.

[pre65]

Bugger all done for 5 years, where does the time go ?

Anyway, I've changed my mind about 1250v HT, and I've got some new toroids to keep the HT at 1000v.

Today I've got one of the units on the bench, and have fitted a filament choke (Russian) and have powered up the filament to do a soak test.

The SMPS unit needed a very slight tweek on the adjustment pot to get back to 10V (@10A).

When that's finished (after 1 hour) I'll do the same to the other unit.

[pre65]

Both units have the preliminary work done, so now for the main task.

One unit has received the new mains transformer and the new choke and MKP type capacitors in the power supply.

Also a new 6.3v transformer to power the two 6D22s damper diodes used in the hybrid bridge.

The second unit is on the bench awaiting the same.

They will be essentially the same as the last iteration but with a more robust power supply.

Next plan is a built in driver stage using a 112a triode and an interstage transformer coupling to a transistorised A2 drive buffer which James Doddington is designing for me.

The way the Covid situation is progressing I need to be kept busy.