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Old 15th March 2012, 08:56 AM   #1
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Default mono block amps with 2 x 833C overkill ? even possible to DIY?

Hi everyone,

I was wondering if it is possible to build a pair of mono blocks wit 2 x 833C tube ?

Is this overkill ? And is it even possible to DIY ?

Are there people on the forum who has done this ?

Thanks Matthias
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Old 16th March 2012, 08:48 AM   #2
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nobody who can help me ?
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Old 16th March 2012, 09:26 AM   #3
lechuck is offline lechuck  Netherlands
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Hi Thesoundmen,

Sure, it is possible to build a pair of mono blocks utilizing the 833C triode. However, if this will be your first tube amp to build I would suggest to begin with different tubes because of the high voltages and high heater current needed for a 833 to operate.

George from Tubelab.com has been working with the 833C in Single Ended operation mode driven by his powerdrive circuit which allows for class A2 operation of the output valve.

More information can be found here: The 833A SE Amp Prototype

Best regards,
Anthonie
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Old 16th March 2012, 10:20 AM   #4
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The efficiency and tube life would certainly improve dramatically having two tubes per channel in low bias class AB2 push pull. But even 20 mA bias per tube at 3 kV is still 60 Watts; adding the four filaments puts you at 640 Watts into the bottles at no signal. Use it only in winter? A pair could certainly deliver 700 Watts or so (per channel) with suitable output transformers and a 2.5 - 3 kV plate supply since they routinely did that as modulators in a.m. broadcast transmitters. With some air blown across them and filaments running 5 -10 % below rated value, the version with graphite anodes holds up far better than the earlier types. Single ended service is pretty hard on them as they were never meant for the continuous maximum heating of class A. If doing that, I'd suggest using one of those hand-held IR temperature guns to see that the bottle and pin/seal temperatures stay below 200 C. The getters release gases back into the tube beyond that point and life becomes very poor. If you want to run single-ended glowing bottles, use tubes like the 3-500Z or 4-400A that are made to (actually must at least periodically) run that way for proper getter action of the zirconium anode material. 833A getter deposits should be large dark or silvered areas without any brown/white on the edges. Many of the broadcast discards from several decades ago or longer are in very poor condition. The most common transmitter that used them had marginal airflow. I believe it's fairly easy to build good 833As. Thorium cathodes are very simple and the radiation exposure shouldn't be significant as long as you don't break the bottles. If buying surplus tubes/ components from ham estates etc. be aware that many of the h.v. caps removed from old transmitters contained PCBs. I do think these would be overkill, and potentially very dangerous if not in a cage with safety interlock switches and something that automatically shorts the plate supply when the cage is removed. One can''t trust power supply bleeder resistors to work when the charge left on caps could be lethal if they fail. Those issues aside, the custom output transformers would no doubt be very costly. The usual vendors may not be accustomed to providing insulation ratings of 7.5 kV or so. <br><br>

I think for a DIY project, something like class 2 driven paralleled EL34's or sweep tubes at 750 V, or quad triode pulse regulators running at perhaps 1200 V could put out at least 200 W at far lower cost and energy use, and you could use tubes that don't have the dangers of plate caps. But those, too, really could use a fan. The big tubes do look great though.<br><br>

From a sonic and efficiency standpoint I think it would be far more practical to bi or tri-amp with mosfets for the bass and valves for the rest. The effective power is much greater than the sum of the parts when it is broken into bands, the low end damping/phase can be outstanding without imposing feedback requirements on the other bands, distortion from one band doesn't go into the drivers for the others, and there's no longer a performance/cost struggle with huge output transformers.

Last edited by riccoryder; 16th March 2012 at 10:50 AM.
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Old 16th March 2012, 10:35 AM   #5
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thanks for the replies ,

Are there some good plans to build just monoblocks with one 833c ?
I saw there are amplifiers with just one 833c but no mono blockcs

is that more doable ?
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Old 16th March 2012, 02:51 PM   #6
lechuck is offline lechuck  Netherlands
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Quote:
Originally Posted by Thesoundmen View Post
thanks for the replies ,

Are there some good plans to build just monoblocks with one 833c ?
I saw there are amplifiers with just one 833c but no mono blockcs

is that more doable ?
Before I answer your question, please answer these first :

- Have you build a tube amp yourself before?
- Why are you focussing on the 833C triode?
- What speakers are you using?
- What are the requirements for your build in terms of budget, amplifier topology and output power?
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Old 17th March 2012, 09:39 AM   #7
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Quote:
Originally Posted by lechuck View Post
Before I answer your question, please answer these first :

- Have you build a tube amp yourself before?
- Why are you focussing on the 833C triode?
- What speakers are you using?
- What are the requirements for your build in terms of budget, amplifier topology and output power?
-I haven't build a tube amp yet but I builded some others thing like DAC and phono and ect. I have a degree in electric en electronics so I'm not new with electricity
- one reason I love the big old tubes
- For the moment I have a pair of B&W 802N
-budget is no fator , Topology I would like Class A, power output somewhere between 50 -200 I think
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Old 17th March 2012, 09:14 PM   #8
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Send a message via Skype™ to v4lve lover
prepare for a storm of safety advice from people who know .

heres mine: a degree has no use if your dead . building a DAC is like learning to walk compared to running olympics .

v4lve
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Old 17th March 2012, 09:51 PM   #9
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Originally Posted by v4lve lover View Post
prepare for a storm of safety advice from people who know .

heres mine: a degree has no use if your dead . building a DAC is like learning to walk compared to running olympics .

v4lve
ofcourse , I really understand the fact that these are high voltages and it is dangerous if you don't take it serious
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Old 17th March 2012, 10:01 PM   #10
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OK...If you know the risks & all, go for it! You will be the toast of the town, so to speak if you pull this off without any major hitches..It's just that way HV has some peculiarities...things we take for granted ....like bleeder resistors....series out a half dozen or so, voltage dividers , so you don't just zap them into smoke. Insulation values of EVERYTHING in sight must be considered, re-evaluated...keeping your 2 1/2X safety margin..... EG Working voltage at 1500VDC, insulations at 5KV...etc, etc!

__________________________________________________ ____Rick.....
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