• 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.

Circlotron questions

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#181
fumbling with component values 😛
 

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#183
oh, ok, thanks

when constructing, I will do all I can to make it fairly easy to change bias resistors
and preferably be able to connect meter and adjust from outside amp
 

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#185
nazaroo said:
I kept back for most of this.

But I just can't let this go:

Especially with a Circlotron style circuit,
where voltage references to ground may be ambiguous,
you absolutely must avoid an auto-transformer.

This is a death-trap,
just waiting for some child to tug a speaker-cable.

D.C. voltages stored in powersupply are just looking to empty themselves through some unforeseen or accidental connection.
The windings in the autotransformer will simply conduct DC.
Click to expand...

As you can see from the schematic the center tap of the auto-transformer is grounded. I fail to see how you could generate any significant DC on the speaker terminals just by tugging the speaker cables.
 
#187
Revintage ( Lars )

Since we slowly abandoned diff.amp (LTP) at input tube ,what do you think about two separate Ecc99 cathode ,each one with Rk as trimpot and with bypass 100uF elkos , and each one in series with small value resistor of 47ohm to ground , this two connection nodes to use for applying of low percent GNFB ? similar as is done in my schematic from post #133 at input Ecc81 tube ?
Best Regards !
 
#188
bohrok2610 said:
As you can see from the schematic the center tap of the auto-transformer is grounded. I fail to see how you could generate any significant DC on the speaker terminals just by tugging the speaker cables.
Click to expand...

For starters, suppose someone reverses a two-prong AC plug at the other end. Now 120 (or 240) volts is on the chassis, and through the few windings of the secondary will be on the speaker wire.

Thats why good practice says speaker lines be isolated by an output transformer,
and feedback loops should be done on a separate winding.

But why list all the possible things that could go wrong?
We all know they do.
And when they do, circuits designed with safety in mind
can save lives rather than destroy them.
 
#189
nazaroo said:
For starters, suppose someone reverses a two-prong AC plug at the other end. Now 120 (or 240) volts is on the chassis, and through the few windings of the secondary will be on the speaker wire.
Click to expand...

Maybe you have misread the schematic? The mains voltage is isolated from the chassis in the usual way. The autotransformer under discussion is handling the audio signal, not the mains supply. And it is grounded at the centre.

Chris
 
#192
jane said:
And I would not be too concerned to use an autotransformer in a circlotron configuration like this.
Click to expand...

other highly skilled members have told me the same thing
properly wired, grounded, etc etc, and theres not much to worry about
just the same issues like with any other 'normal' moderatly volatged tube
amp

thank you for this support
very appreciated

but, I still like the new schematic, with trafo wired like normal tube OPT 😉 especiall now I hear the lower impedance works even better
 
#193
I think we can 'safely' leave the safety issues

and maybe ask nazaroo to cool it a bit more
thanks

100% safe tube amps ?
I guess not
no reason to expect this to be any better than others

I hope we can get on with it now, please
 
#197
tinitus
I was think to be something simple like this :

Still I need others member opinion and sugestion related to this schematic !!!

BTW , this yours tube amp project missing something very important !!!
The project Name !!!
 

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#198
Here is my cirlotron circuit from some year ago: 6SL7 input, ECC99 driver and 6P45S final into a 600R OPT.
An externally hosted image should be here but it was not working when we last tested it.

(I have to redraw that non-figurative art into some sort of a proper schematic..)

Think I got 50W+ out of it without questions. It's one of my frequently used amplifiers.

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