KT 88 project request

[Tom Phillips]

Good Grief!

[Justin Thomas]

Graph paper for schems? Brilliant! I'm stealing that.


Justin

[catalin gramada]

Better drawing. Any oppinions regards the circuit.please ?



and the PS again

[catalin gramada]

Hi. The bias circuit (point3)it is grounded together with power cathodes(point2)in the same spot.here represented to easy follow the signal path .The points in red means the ground points for decoupling caps. Each node was linked with one wire to a cooper star washer in the middle of chassis. I will put again a pic with my layout. Thanks. Catalin





The pic have definition enough to can see clearly how return path looks like.
It is nothing fancy. but very classic and think well done enough as time I have not any grounding issues at all. Thanks for asking

[The Dude]

Sorry, catalin. I deleted the post above yours after I figured out your ground indication. I was looking for the "traditional" ground indicator symbol. I then figured out your "slash" indication. All's good.

[catalin gramada]

Hey. No critics. no one? no opinions? c'mon guys. I.m only ears...

[nickb]

Your ears won't be much good to you after you crank that baby up in your room for an hour or so...

[KevinOConnor]

Hi Guys

You haven't noted the signal levels through the circuit although there are some DC voltages that help. It would look like the splitter only has to provide a 12V signal, but maybe it's more? The preceding stages should be able to provide this.

If you move the EQ to the position shown, significant signals must be handled by the EQ, which has a flat-setting loss of 20dB. I would still suggest adding a stage ahead of the splitter to assure that there is more gain than actually needed.

Have fun

[catalin gramada]

Hello gents.
...well I didn't figured cause it is not a closed case yet. Still have to do some homeworks when I'll arrive home, in order - the tone control moving into presented position and maybe little bit tweaking on it. Next have a list of tubes have to buy and try in first position for voicing, tone consideration. You can do an idea about gain. amplification factor by dc data condition. This amp should run clean for a input sensitivity around 100mv. ht voltage ensure a lot of headroom for that. Thanks.
Catalin

[nickb]

Perhaps you could tell us about your ideas behind having an dual EL84 voltage amplifier stage?

[catalin gramada]

Hello.I like it a lot. If you listened an el84 triode connected you know what I.m talking about. Love it. Why not? It's a very potent driver with a very nice sweet sound. It have so low ra I can drive almost everything from its plate. My initial goal was to use an large inductor as load and to can overdrive separately the driver and the power stage using a dual gang pot in between for control. That will be for the future project, I hope. Till then I enjoy the amazing rich tone that el84 at high current can provide. It.s huge. It full worth that extra expense for me. If you like a tube how it sound just use it. The 12at7 it is another tube it sound amazing and worth every cent. It is strange for what reason many people avoid it...I read some about nonlinearities, akward prestation. That.s nonsense...or maybe not, but who cares?it have so nice sound stage presentation you cannot ignore. For the rest of electrical aspects I.m here on this Forum to learn how to not commit horrible mistakes and to optimise it from those tech which have lot experience than me and want to share it. Thanks.Catalin

[catalin gramada]

Hallo. I designed a overvoltage protection circuit for my 500v caps. with zener diodes ,as much I understood.
The circuit should protect 500v capacitors in no load condition.ex tubes swapped or no conduct. In normal condition the voltage over last cap is no more than 420v. I imagined two supply situation with nominal 580v and worst mains condition with supply at 540v. Please let me know if is correct. Thanks. Catalin
I intend to use 4pc. Zener at 110v or 3pc. at 150V depends at what rated current are available.
Do you see any issues if I implement it in that way.please? Thanks

[Enzo]

before you go to that extreme, consider no commercial amps see the need for it. And one reason why is that 500v caps have what is called a "working voltage" rating. In other words, 500v on a 500v cap is fine all day long. Caps also have a surge rating. Look up your caps' data sheet. It should be on there. I have no idea what you have, but if the surge voltage is 575 on your 500v cap, then THAT is what you would protect to.

Also, caps don't just pop when their voltage is exceeded. Your 440v of zener have a 100k in series. The 500v cap node is in the middle of that voltage divider. But any draw off the node will vary the voltage drop across the 18k. I could be wrong, but it would seem to me you might want your zener stack to be a lot closer to your target protection so it doesn;t conduct at all until the threshold is reached.

[catalin gramada]

Your 440v of zener have a 100k in series. The 500v cap node is in the middle of that voltage divider. But any draw off the node will vary the voltage drop across the 18k. I could be wrong, but it would seem to me you might want your zener stack to be a lot closer to your target protection so it doesn;t conduct at all until the threshold is reached.

Hello. Thanks.I already have this concern too. I can top up those 100k resistor to have a reserve for that. But on the other side heard zener diodes need to have a minimal current to be effective and to conduct in reverse....I have no experience about that. For me is more simple to do it and tweak it then
One resistor should be there otherwise too much dangerous power dissipation over zener network could be. On the other side I can leave 100-200k say.permanently connected with the price of some 3-5mA current spent.It will act as a bleeder too. I.m not decided. Please help. Thank you. Catalin

[Enzo]

But remember your purpose here is to limit over volts, not to create a regulated supply. They need some minimal current to conduct, yes, but they need not have it continuously for this purpose. This is really no different from the 9v zener in a Boss effect pedal across the power jack. You only need it to conduct when the voltage exceeds some level.