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Old 12th August 2011, 10:54 PM   #281
pre65 is offline pre65  United Kingdom
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I have a pair of 833a monoblocks. Currently undergoing mods to take them to mk3 version.

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Old 13th August 2011, 12:08 AM   #282
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Originally Posted by pre65 View Post
I have a pair of 833a monoblocks. Currently undergoing mods to take them to mk3 version.

Click the image to open in full size.
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+ ?
"There are more worlds than the one you can hold in your hand." Albert Hosteen, Navajo spiritual elder and code-breaker, X-Files TV Series.
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Old 13th August 2011, 06:01 AM   #283
pre65 is offline pre65  United Kingdom
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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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Old 9th February 2012, 11:43 PM   #284
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Default SRPP-833

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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Old 26th December 2012, 04:05 PM   #285
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Send a message via MSN to Peter 807
Smile High power Amp

Why nog make an 4CX250b SE -Amp,about 65Watts and 1000-2000 V ,Anode,grids stabilized.
Big Supply transformator end Big SE trafo.
Used an ECC83,and an EF183 for drive.
Searcing for trafo will be difficult,but fun.

Also PP is possible Output would be around 200Watts,8Ohm use an 4 Ohm tap,to drive the 8Ohm will make an very stable Amplifier,with around 85Watts.

For more info please contact me.
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Old 18th January 2016, 01:44 AM   #286
JBLman is offline JBLman  United States
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Originally Posted by ReinoutdV View Post
Good afternoon,

you must admit.....this thread is getting longer/better every time. It started all with Protos asking for 833-amps and now it seems there are serious plans and even builded amplifiers with this tube !

NickC: your right about the open structure of the tube socket. It is rather exposed. Nonetheless the anode-connection with 1000 V (in my case) is more a problem. A standard topcap will fit perfectly for the wire, but a part of the connection (metal !) is still exposed. Although the heat of the tube will certainly make you think twice of touching it........can you take the risk with children ? That's why i've build an open frame with ventilation holes in it. If there are visitors with children i simply install the frame. The tube cn still loose it's heat but the holes are to small for even tiny fingers to touch the 833 at all. It works but i do not like it; so now i'm experimenting with a teflon pipe that slides over the top cap. If i'm happy with it i'll post a picture. Now you have to do with the frame-solution (picture in next post).

Back to the tube sockets. I am happy to have found a pair. But asking for 4 for your PP-design is pushing. But i will be on the look-out for you (and all other 833-builders).
There are 2 varieties of sockets:
- the Johnson. Altough a rather simple clamping-system the mounting can be swiffeled 90 degrees ! And that is very handy indeed. The ceramic base can be fixed to a wall or base (horizontal or vertical) and the tube can be how YOU want it ! Which is in almost all designs standing proudly vertical. I'm going to post a picture some post from now which is absolutely NOT good. And that's even a commercial item.
- The RCA and ITT. Their clamping system is more sophisticated, but the whole tube socket is fixed....so less flexible in your design.

Enclosed is a picture of a ITT (=fixed) socket and a Johnson with one of the filament clamps 90-degrees swiffeled as an example.


Where does one find these? I can't find them in America
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Old 18th January 2016, 09:24 AM   #287
pre65 is offline pre65  United Kingdom
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I use the Chinese ceramic type.

Available on Ebay.


1pc 2pin Ceramic Tube Socket For 833 833A GU48 FU33 PL833A Valve,21

Or, if you are wealthy,

833A GU48 TEFLON SOCKET, Pair of sockets for Power tube 833A GU48, valve,vacuum | eBay
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Old 18th January 2016, 05:26 PM   #288
hpeter is offline hpeter  Slovakia
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Damn good question, where are they ??
Even 300b would feel shame
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File Type: png Screen Shot 12-15-15 at 08.53 PM.PNG (97.4 KB, 160 views)
PAST: TASCAM US200 > JJ ECC803/6L6 > Beyerdynamic DT990pro 250Ω . . BLOG
NOW: XMOS_U8/PCM5102A > LL1544A > 12AX7WB+µfoll > 2A3_SOV/JJ > LL1660 > STAX SR207//STAX SR007 _ LL2748 > 394A > LCLC 4H/100µ
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Old 18th January 2016, 10:39 PM   #289
JBLman is offline JBLman  United States
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well I was looking for the ef johnson mounts lampizator does make some extremely nice mount just tooooo much money fir my taste.
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Old 19th January 2016, 05:59 PM   #290
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Im so glad this thread came back to life. Once of my all-time favorites
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