Where are the 833 amps? - Page 29

pre65 · 12th August 2011, 10:54 PM

I have a pair of 833a monoblocks. Currently undergoing mods to take them to mk3 version.

rcavictim · 13th August 2011, 12:08 AM

Quote:

Originally Posted by pre65

I have a pair of 833a monoblocks. Currently undergoing mods to take them to mk3 version.

I can feel the radiant heat from here across the pond! Safety aspects aside, that's definitely a fun project! How high is your killer B+ ?

pre65 · 13th August 2011, 06:01 AM

Actually, it's not that high.

I was advised that 1,000V was minimum for good results, but with the PSU bits I had to hand iv'e "only" managed about 950V HT

First version used my 300b SET amp via a 5K output transformer on the 16R tap to drive the 833a grid, sounded very nice. Version 1A used a small interstage transformer at about 1 :4.5 ratio, but that was less successful.

Current version (mk 2) uses a 6SN7 and EL34 (as cathode follower with fixed negative bias) to drive 833a.

Next version will give a negative supply to the EL34 cathode to correct a slight anomaly on the waveform that the scope found.

Philip Ramsey (Bluebell Audio) is trying to get Hammond to make some special interstage ( about 6:1 from memory) driving transformers, as he thinks that is the best way. I'm sure going to want to try them when (or if) they become available.

101audio · 9th February 2012, 11:43 PM

I don't think this circuit going to work, but I am going to post here and asking for your input.
I want drivers and output tube use the same DC supply. Keep power supply simple
Thanks, 101Audio

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12th August 2011, 10:54 PM	#281
pre65 diyAudio Member Join Date: Oct 2005 Location: Essex/Suffolk borders.UK	I have a pair of 833a monoblocks. Currently undergoing mods to take them to mk3 version.

13th August 2011, 06:01 AM	#283
pre65 diyAudio Member Join Date: Oct 2005 Location: Essex/Suffolk borders.UK	Actually, it's not that high. I was advised that 1,000V was minimum for good results, but with the PSU bits I had to hand iv'e "only" managed about 950V HT First version used my 300b SET amp via a 5K output transformer on the 16R tap to drive the 833a grid, sounded very nice. Version 1A used a small interstage transformer at about 1 :4.5 ratio, but that was less successful. Current version (mk 2) uses a 6SN7 and EL34 (as cathode follower with fixed negative bias) to drive 833a. Next version will give a negative supply to the EL34 cathode to correct a slight anomaly on the waveform that the scope found. Philip Ramsey (Bluebell Audio) is trying to get Hammond to make some special interstage ( about 6:1 from memory) driving transformers, as he thinks that is the best way. I'm sure going to want to try them when (or if) they become available.

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