• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

mono block amps with 2 x 833C overkill ? even possible to DIY?

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
 
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.
 
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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
 
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.....
 
okay . you will need equiptment . variac high voltage insulated test leads .voltage and current meters capable of handling the voltage .

oh well . a blast shield like george uses is also a good precaution . invest in a Proper galvanic isolation before even commencing work on anything !

think about this first . how are you going to power two 10V 10A heaters ?

Ok DC heating is required this will mean lineair or switchmode . oh well if you go lineair transformer has to be rated at 14-15 volts AC at 16 amps or so to keep a fair bit of headroom to regulate .

15 volts AC gives about 12.5-13 under load . needing a minimum of 22,000 u of smoothing
imagine 20 % line sag . your regulator will fall out of regulaton! resulting in ripple .
so we add 20% to our 15 volts =18vac this will give us about 15 volts DC under load wich means the regulator is likely regulating about 50 watts ! under normal line conditions .

Imagine high line you will have 21.6 Vac unloaded yet giving 18VDC you guess your reg. is now regulating a whopping 80 watts !

v4lve
 
A 833 SET is a great project, why lose time and money with Pentodes and PushPull!!
Safety procedures are many>: use rubber gloves, not put both hands on the amp, not use a wrist watch or rings, Static discharge in transformers can happen above 500V, so transformers may need cover or insulation.
Good Luck.
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-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

If you like big tubes, there is a bigger tube than the 833C available. Its called a TB3-2000 and apparently it should be good for about 500 watt of pure class A musical pleasure :)

If the budget is not a problem for you then I suggest you take a look at this website: http://home.tiscali.nl/fishbowl.amping/

The owner of the site build it, according to him it sucks up about 5.5KW without even playing a single note :D

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An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.
 
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Joined 2009
I am building a PP AB2 GU81m amplifier. 12.6v @44A Had all the transformers made custom. the thread is in the section if you want to take a look. waiting for the power trasformer. The high voltage transformer alone weighs 12-14kg. The low voltage (650va core) weighs 6kg the transformers for the ercury rectifiers weigh as much.

:)

go for it.
 
Yes, it is possible to DIY an 833 type amp. See this thread for some examples:

http://www.diyaudio.com/forums/tubes-valves/24424-where-833-amps.html?highlight=833A+amps

I must say that the 833A or 833C amp should not be anyones choice for a first time tube amp build. Let's just say that you understand all the safety stuff, and you read everything ever written about vacuum tubes until you fully understand them. Most builders have some difficulties with their first amp expecially if is is built using point to point wiring just chasing the hum out of it. More than a few builders blow up a few parts. At the power and voltage level needed for an amp like this stuff gets expensive quick. Custom parts are usually needed, like transformers, and the transformer winder may not even know how to make them.

I have been building tube amps for nearly 50 years. I can generally make whatever amp I want, but I abandoned my attempt at making an 833A SE amp because I couldn't get a suitable OPT. The 833A has a fairly high plate resistance and the OPT design is rather difficult.

My experiments are here:

The 833A SE Amp Prototype
 
I think you should abandon the idea of using any of the bigger transmitter triodes for a first build. I've got a few lower power transmitter tubes, including a quartet of HF100's with graphite anodes, and I'm not yet ready to make amps with such voltages. 500V B+ is actually quite easy; just understand the basics, keep in mind that some wires have insulations rated for only 300V or some even less, and make a nice clean build (avoid messy wiring).

But when the voltage jumps up to the kilovolt range these tubes need to work, you'll have to take the voltage into account in almost every part! Plus output transformers for low powers are hard enough to be made decent, so with voltage and power ratings going up, it get's even more difficult. I've seen pictures of a Philips amplifier, that gave a kilowatt of class B power out of 2 TB3/350's. It's OPT was immersed in oil. And it needed 3-phase power...

My second question is, actually how much power do you need? 20W of class A power is actually quite much in most circumstances. Having played around with some circuits and concepts for some years now in tube amplification, I would even go as far as to suggest a single watt spud amp as your first build. It would probably not satisfy all your needs, but would give some perspective as to what really is necessary. I did build one, with an E55L, and got quite amazed.

In my main system I run KT88's in triode, class A push-pull. They put out around 20 watts of mostly clean power. They have no feedback loops. And their sound have amazed most that have listened to them. You could raise the power output for example by doubling the amount of output tubes, but then you'd run into other problems. And with more than 90 dB/W/m sensitivity, it's not really necessary. Even this amount of power can make my ears hurt. So 200W of Class A sounds quite extravagant... Plus you'd be idling at around a kilowatt per channel... Half a kilowatt if you got it right and used push-pull pentodes. And that doesn't include the heaters...