Turner Audio

[TIMBO]

index
Has long passed and was considered to be the GUY here in Australia
I thought I would post his site for anyone to have look as it maybe be useful to someone


I found this guitar-amps-2016
It was a good read but way over my head in some of the aspects
I'd be tempted to do a build but 40/20w is a bit too much power.
El84/6v6 is but my speed, would it perform in the same way with smaller output valves?

[glass54]

Hi Timbo,
He spent his last years in Canberra (interesting chap  ) You needed many cups of coffee if you had a conversation with him.
I would use 6V6, 300Vac Secondary on HT (with Diode Bridge Rect) Probably 120VA or so.
O/P Tx 6k6 primary Z. You'd end up with 20W+ rms (Clean)
So basically your heading down the AB763 B/F Deluxe Rev Power amp design (proven and reliable)
You could play with Patrick's preamp to achieve you goal/taste.
Kind Regards
Mirek

[TIMBO]

hey mate, Thanks for that.
I become very interested in a circuit when I can see a noted person has taken the time the add his spin on an already proven circuit


food for though

[tubeswell]

If you want high gain with 6V6s, try it. But methinks way too much unusable gain for 6V6s (and definitely way to much for EL84s). YMMV

[TIMBO]

Thanks for the input mate

[tubeswell]

All good. 


I dunno - call it a hunch.  I brought a Ceriatone Son of Yeti a while back - which is a plexi 'inspired' 20W amp for 6V6s. It has a similar number of actual preamp gain stages to the Turner amp (albeit in a different order, and also doesn't have a 12AU7 driving the FX loop), (and the SOY has some horrible clipping diodes which I never use) but I can never get anything anywhere near fully cranked (even without the clipping diodes switched in) because it just goes to mush.


I suspect the Turner amp would work fantastic with bigger output tubes (that have 40-50V grid voltage) but just dunno about the 6V6s - which might have like 18 or 20V grid voltage, or EL84s with 11-12 volts grid voltage.

[TIMBO]

I suspected the smaller valves may not handle the heavy load, my reason for asking.




I have a variety of valves, PTs and OTs, so I'll see what's in the stash to play with.


Thanks

[kagliostro]

..... and definitely way to much for EL84s

Ciao Tubeswell

Why do you say that ?

Despite all EL84 and EL34 has both a gm of 11 or 11.5mA/V

Franco

[Helmholtz]

The Turner schematic is missing a (10k) PI tail resistor.
I assume a drawing error.

[tubeswell]

..... and definitely way to much for EL84s

Ciao Tubeswell

Why do you say that ?

Despite all EL84 and EL34 has both a gm of 11 or 11.5mA/V

Franco

gm is a measure of grid voltage change and plate current change. Once you hit clean peak grid voltage there’s no more change in grid voltage - only a longer time in peak voltage (as the area under the square wave function gets bigger - until it reaches peak square, and then its peak mush).  EL84 grid (bias) voltage is around 11 to 12 volts (negative volts), so doesn’t take much drive from the PI to clip. Of course, one might like this effect - it’s a matter of personal preference (That’s my story and I’m sticking to it. :-)

[tubeswell]

Oops - And so Post removed by post author

[kagliostro]

OK Tubeswell, I understand what you mean.

So, if we want to keep the sound of that exact preamp, but the output swing of the PI is too large, why not use a pair of voltage dividers to tame the output level of the PI and allow the use of tubes that require less drive?

This way, it should be possible to use EL84s or 6V6 tubes.

To find the optimum voltage-divider resistor values, a dual-gang linear pot could initially be used, and then replaced with the appropriate fixed resistors.

Franco

[tubeswell]

Yeah YMMV  = 'You Make Master Volume' LoL

[kagliostro]

Ciao TIMBO


It may seem but it is not supposed to be there forever


Franco

[TIMBO]

Hey Franco, thanks for the input.
Going through my stuff and this is what I found
Valves - 6L6gc EL34 Kt66 6V6gt EL84
PT - 300-0-300 with bias tap and plenty mA's to power the lineup.
OT - I think I've got a few to choose from all around 50-60w - 4K with multiple secondary taps
                                                                                        - around 3.4k single secondary 8ohm tap
                                                                                        - 6k6 single secondary 8ohm tap
3H choke
I'll use the bigger valves (cause otherwise I'll never use them) and insert a PPIMV
It's a start anyway

[sluckey]

The Turner schematic is missing a (10k) PI tail resistor.
I assume a drawing error.

Looks like Turner is relying on the presence pot to be the tail.

[Helmholtz]

]Looks like Turner is relying on the presence pot to be the tail.

Yes, that would be the consequence, resulting in very poor PI balance.

[Helmholtz]

]Looks like Turner is relying on the presence pot to be the tail.

Yes, that would be the consequence, likely resulting in poor PI balance.
Also means that a significantly larger fraction of the NFB signal will be fed to both cathodes, where it acts a common mode input signal and lowers the NFB.