Tonestack Bassmaster

[Mats]

Hi
Im looking, trying to understand, one Traynor Bassmaster YBA-1 40 Watt.
There seem to be different schematics of this amp.
The one that I look at have:
the stage before LTPI is set set up like a concertina splitter.
(68K at Anode and 2k2 and 68K at Cathode)
Tonestack is connected to the Anode, in this amp.
What if connect the EQ to the cathode ?
Is it possible ?

[HotBluePlates]

Please link to the schematic you're looking at. Perhaps it is this one?

[Mats]

This
Page 9

[sluckey]

(68K at Anode and 2k2 and 68K at Cathode)

I see 6.8K (6800Ω) at the cathode, not 68K.

[Mats]

I first looked in KOC Vol 3-book
and there it is 68k 2k2 and 68k
and in text its written, "configured like a concertina splitter"

[HotBluePlates]

That's a poor choice of words on KOC's part, unless he elaborates further. And it should be 68k, 2.2k, 6.8k.

The 6.8kΩ resistor doesn't contribute to bias, because there is a grid reference resistor returned to the bottom of the 2.2kΩ. There will be some reduction of gain for that stage due to local negative feedback because there is a large (9kΩ total) unbypassed cathode resistance.

It is only "configured like a concertina splitter" because there is a self-bias arrangement similar to the bootstrapping of a self-biased concertina splitter. But a concertina has a gain less than 1 to each output, and this stage will provide some gain more than 1 to its plate output.

[Mats]

Thanks
My mistake
Thanks once again

[HotBluePlates]

Tonestack is connected to the Anode, in this amp.
What if connect the EQ to the cathode ?
Is it possible ?

Look closely at the version you have. Do you see the 0.01uF caps, 100kΩ and 3.3MΩ resistors between V2A and V2B? Those are a bridged-T filter and will create a mid-scoop. Subjectively, signal strength is also lost. So Traynor configured V2B for some gain (but not a lot), then has the tone controls. So that's 2 stages of tone-shaping, one fixed and one variable.

The other versions in the set of schematics you posted do not include the bridged-T filter of fixed tone shaping. I presume Traynor felt there was less signal loss in those versions. So Traynor configured V2B as a cathode follower to drive the tone controls. No loss means you don't need the make-up gain.

Could you take your version and move the output to the cathode? Yes, but you'd have to actually put in a 68kΩ resistor in place of that 6.8kΩ, because output signal level would be too tiny to drive the output stage otherwise. You'd also no longer have the make-up gain from V2B and still have the bridged-T filter, so even after conversion of V2B your amp would likely seem to have lost gain.

[sluckey]

I first looked in KOC Vol 3-book
and there it is 68k 2k2 and 68k
and in text its written, "configured like a concertina splitter"

That may be, but page 9 of the schematics you posted shows a 6.8K. Or someone has a leaky pen!   

[Mats]

Yes
6k8 it is, page 9
"leaky pen "  

[jbrew73]

i believe Ampeg used a similar arrangement   on the V4BH.