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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6V6 Output?

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triode SE will probably be around 3 watts.
ultra-linear SE will probably be around 4 watts.
pentode SE will probably be around 5 watts.
triode PP will probably be around 6 watts.
ultra-linear PP will probably be around 12 watts.
pentode PP will probably be around 15 watts.

also depends on things like bias point, OPT primary impedance, etc. etc.
Dont put the 3.5K resistor in series with the transformer. Yes, the tube will see something like 8.5K, but thats not the point. The 3.5K resistor is going to drop over 100 volts due to plate current and completely change the operating point. It will also dissipate about 40% of whatever ac output ower is produced, so considering power reduction due to 5k ac load line vs 8.5K, different operating point, and 40% loss in the resistor, you might only get 1 or 2 watts out. (guesstimate, precise numbers would need to be calculated)

You would be better off just using the 5K transformer.

Best of all of course is the 8.5K transformer.
I recently built a 6V6GT Single Ended amp that sounds very good. I have compared it to other single ended amps of known wattage and it has to have about 5 watts output. The guys on this forum helped me tweek the curcuit and it sounds great with absolutely no hum. I would highly recommend it. The output transformers are very inexpensive (Edcors). The schematic is below.


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    6v6gtse final.jpg
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Tom Bavis said:
A 5K transformer will work nicely at a different operating point, say about 250V / 50 mA...

Is that a general rule of thumb? If the OPT offers a lower impedance load than you want, lower the voltage and raise the current? Does it work for push-pull as well? I guess I should be able to deduce the answer for myself by drawing load lines, but...

I ask because I have a set of 6.6K OPT (Hammond 1620) which I'm using with 6BQ5 tubes. My B+ is rather high (nearly 385V, K to A), so I run them at a lower current to keep the overall dissipation within limits. But, at low frequencies (20~50 Hz) they distort at relatively low power levels (3~4 watts out). I suspect it's probably just a limitation of these inexpensive OPTs, but if I thought they would perform better at a lower voltage & higher current, it might be worth the trouble to try.
I think you'll like the 6V6 triode strapped SE sound. When you get it up and running, you can also play around with popping in other tubes, like 6L6, or even 6550.

Yes, they'll run at a low operating point, but sometimes the sound can be surprising. I really liked 6550s running this way.:)
The circuit of Kraznik would make a nice stereo 2 x monobloc amplifier.

The obsession with power is an indicator of being prepared to have noise and distortion rather than quality music. When you drive tubes into distortion and like it it is an indicator of the distorted prefrontal cortex you own. 6V6 in Class "A" can be rated to as much as 4.5 W but plate voltage should not exceed 250 V with screen no more than 250 also. Driving 6V6's at over 300V or in one audio fantasist forum I read, approaching 500V is lunatic. There's always a type who thinks it knows better than equipment and component drivers and they come onto forums beating their chests and then indicating they don't have a clue. Design limits are there to provide good service at intended design outcomes. You will not do better.

When I was more involved with military gear we had good contacts with designers. I could (and paid-for) selected "%" components... but it might cost me a weeks wages. One 'Hi Fi mad' mate had his power transformers and output transformers designed and hand made to provide the finest reproduction and avoiding saturation.

This is what one has to do to get quality results however in practice socket types, the quality of soldering, total value deviation in entire circuitry, size of wire used and its routing, earthing philosophy are a few of the factors producing top results. Overdriving tubes does not. In class AB2, in which the 6V6 which can be driven to max 14watts the 6V6 should not have more than 285volts applied to plate or screen and an 8000 ohm load is recommended. The operating cycle in AB2 allows heat dissipation enabling periodic 'peak input' as opposed to the continuous cycle of class "A".

In other words, I guess, the maximum continuous power the 6V6 can handle is 4.5Watts input, to some degree also depending on the environment but 4.5W is 'it' .

Something else ..don't mistake 500V across a transformer feeding a pair of 6V6's as being suited to 500v across a 6V6...that sort of voltage will be split to feed each 6V6 at no more than 250V in class 'A'...at 8% distortion. Why not operate even more conservatively? Use more sensitive speakers. Get off bass addiction as well...its there that the power people think they need...or do need depending on degree of addiction of the bass addicts... is used in driving today's commonly highly inefficient and largely 'junk' speakers. The more you drive your bass the less you will enjoy your other frequencies...one might experiment with bass with such as "Mars"...the god of war in Gustav Holst's 'The Planets" for example but it's likely you'll realise you are fragmenting the experience of the whole....perhaps this has some useful thoughts.

Commercial transformers and chokes are not made to 'perfection' as were the ones we designed and had built at several weeks wages. Everything in circuit design is compromise or dismissing of some consideration to produce the average but competitive equipment. In closing, 'watts' is an' input' term not an output term. Speakers are not 4, 8 or 16 ohm, that is a handy dc resistance guide and allows for "%" variations. Electrical gear power specification is based on input power. The only true output power indicator of a transmitter for example is gained through an RF antenna meter...With audio equipment in which power varies across frequency one must measure at the point of application to a speaker but that changes continually with tube socket and other insertion loss. The quality of the speaker ultimately determines what you hear or think you hear (like the difference "between 4W and 5W". The quality or lack of it of one's brain in self educated response to stimulation does the rest. Try less power obsession and more self education in quality rather than 'mind-blowing'. The discovery of self through the great composers may make life much more fulfilling.
kirwanrebel said:
In closing, 'watts' is an' input' term not an output term.
No, watts is a power term. It can apply to input or output or anything in between.

Speakers are not 4, 8 or 16 ohm, that is a handy dc resistance guide and allows for "%" variations.
Not quite. '8 ohms' etc. is a nominal speaker impedance. The DC resistance will probably be a little smaller than this.

Electrical gear power specification is based on input power.
Not always.

Welcome to the forum.
Hi...thanks for your support. In the areas I mentioned measured power is always input, not output and I explained the difference in an RF example. I didn't feel the need to cover every situation however there are occasions similar to a car...HP/BHP/ power at flywheel/power at driveshaft/power at wheels...there are electrical devices which produce measurable mechanical power and torque at output however electrical power is measured, competently, at input. a 40W light bulb is a simple example whereas its 40 W input then is measured in lux/lumens 'output'. Electric motor utilities measured in nett power input and output typically in torque and horsepower output not watts. I think that's adequately covered in electrical theory.

I explained, for electronics, the difference between power in and power out of say 6V6 tube used as an amplifier in class "A" and class A"B2" . A valve data book would confirm what I said. On 'output', electrical power is almost always a different unit measurement and I could discuss impedance matching and the summation of power used in solid state direct coupling...but it still is not 'power out'. Audible levels usually involve 'decibels' for simpler measurement and description of outcome.

In' nuisance' for example the quantum is rather poorly explained and evasively used where sound has to exceed (say) 70dB for 10 seconds...Thus the eardrum- piercing scream of the Macdonald's 'chips ready' machinery evaded prosecution even though over '75dB'. I had to leave the premises owing to the pain which lead to my plaint

Whilst the WHS 'Department' failed to act on the OHS issue for protecting employees owing to that 'duration' argument , Peter Ritchie, Macdonald's Australian founder and a good bloke whom I knew before he began Macdonalds may have listened to me as it has been 'phased-out' not so long after I called him when all else failed.

To measure 'real' audio output power quantitatively would be quite an operation. I' didn't try to be exhaustive, but I am correct. As well as being familiar with average power, I'm also familiar with peak and rms.

I didn't dwell on output transformer or speaker coil dc resistance. There are % variations in design and production. As you commented, and I'm aware, the measurable dc resistance is lower than the nominal dc resistance and may vary even with different meters and producers. It is however a handy guide at 4 8 and16 ohms for the 'general public' rather than say 3.2, 6.5 or 12.9 ohms or in your words "anything in between". The reality is not dc resistance but 'impedance' the inductance, capacitance resistance at f? being "Z" (??? ohms)and that changes continually with frequency.

I don't think more needs to be said other than perhaps that electronics technicians and laboratory technicians and engineers also use the common 4,8,16 ohm identification. I do.

Thanks for the opportunity to explain further what I deliberately avoided....engineering calculation trade-off's. I hope that satisfies the curiosity of other readers whom you may have alerted to the deeper philosophies.
In class AB2, in which the 6V6 which can be driven to max 14watts the 6V6 should not have more than 285volts applied to plate or screen and an 8000 ohm load is recommended.

In other words, I guess, the maximum continuous power the 6V6 can handle is 4.5Watts input, to some degree also depending on the environment but 4.5W is 'it' .
I think you don't understand AB2 class.
The 6V6 operate extremely well in AB2, as it's a transmitting valve.
(As was the 6L6 originally).

If you really want to run them in AB2 you HALVE the A-A load, but the AB2 characteristics are hard to find in literature for this valve (I have them).

They are to be found in the GE book, where they show clearly driving the g1 a good 15V positive with a cathode current of 200m/a, and a g1 current of 6 m/a
(YEP it works!).
For good reasons it's not reckoned to be a good plan to run the screen higher than 250V like this.
You can also use them successfully as a AB2 driven triode, driving the g1 up to +20V..

I was suprised to see how some old 1950s AB2 amps are run.
A pair of 807s in AB2 have a A-A load of 3k3, and they work perfectly like this, making a LOT of power.

If you want to run 6V6 in AB2 you have to drop to well down - typically A-A of 4k5-5K, and run the Anodes at up to 385V, on the upper limit, where most beam tetrodes produce least odd harmonic distortion.

Like this they WILL make as much as 20-25W, but don't expect to find that in many of the text books, and best to use the rare Westinghouse big anode variety.
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