z original prescription schematic or info

[Darkbluemurder]

Although I am familiar with snubber caps and cut controls I have never seen a combination like the 1200pf cap in parallel with the 150k resistor. How does this work - is it like a conjunctive filter but before the power tubes?

Very interesting design combining lots of elements of different amps.

Cheers Stephan

[M Fowler]

Is the original Rx also parallel V1?

Also it appears to have split load bias for the EL84's but one resistor is 50R and the other is 500R or am I way off on this point?

Mark

[DR.Z]

[quote="M Fowler"]Is the original Rx also parallel V1?

Also it appears to have split load bias for the EL84's but one resistor is 50R and the other is 50R or am I way off on this point?

Mark[/quote]

No Mark I used a single 50 ohm cathode bias res. on the original RX.
You know to get that great "CLASS A TYPE TONE"........

Z

[M Fowler]

Thanks for the information Doc.

[Darkbluemurder]

I am terrible at this visio but thought I would show what I am working up.

Thanks for putting this together.

I believe the ground connection before the second stage should not go to the junction of the two 220k resistors but to the junction of the second 220k resistors with the 1.5k and 56k cathode resistors of the second stage. The way it is drawn now it would shunt all the signal to ground.

Cheers Stephan

[M Fowler]

I was looking at that Friday and it didn't seem right. I haven't got back to this amp for a while so I will make corrections and show what I have drawn so far.

I was hoping the more technically inclined would have kick me off to the side and taken over.

Perhaps a more talented person would take over the visio, I suck at these visio or any graphic drawings.

If not I promise I will forge ahead.


Notice: the drawing is not a working amp.

[M Fowler]

Here is version 2 ready for people to review for errors.

Uses shielded wire from V1 to 68k on jacks and from V2a to 220k junction shield goes to bottom of 220k on left which goes off to ground.

Not finished but getting closer.

Mark

[JamesHealey]

why is the HT connected to the volume pot?

[Darkbluemurder]

why is the HT connected to the volume pot?

Probably a drawing error - the HT should be connected to the plate resistor coming off V1.

Otherwise the layout looks good to me.

Mark, thanks a lot for your effort.

Cheers Stephan

[M Fowler]

Hope Doc doesn't get mad at me for this but here is the original Rx I have using to base this drawing off of.

[Gee]

I am not familiar with this amp,but what is the 150K and 1200pF doing across the PA grids? Is that a fixed attenuator and top cut?

NB Also there is a ground missing off the first pair of caps on the left.

[Darkbluemurder]

why is the HT connected to the volume pot?

Probably a drawing error - the HT should be connected to the plate resistor coming off V1.

Otherwise the layout looks good to me.

Mark, thanks a lot for your effort.

Cheers Stephan

The photos confirm that - look at the red wire going to the plate resistor of V1 - that is the HT connection. It is a bit difficult to see since it is partly hidden by the grey shielded cable.

Cheers Stephan

[M Fowler]

So your saying I have it right or do I need changes? Hard to figure out where all those red wires going under board end up at.

[Darkbluemurder]

So your saying I have it right or do I need changes? Hard to figure out where all those red wires going under board end up at.

There is only one thing that needs to be corrected: in your layout there is a dotted line going from the small resistor right beside the big blue 40uf e-cap to the eyelet/turret which is connected to the blue wire coming from the volume pot wiper. The B+ should not be connected there but to the plate resistor of the first gain stage. You need to move the dotted line so that it goes to the next eyelet which is connected to the 47k plate resistor belonging to the first gain stage. That's all.

Cheers Stephan

[Gee]

And the first 2 caps on left need joining at the +ve end and a ground connection at the -ve end. Actually other photos show a single 40uF for the first cap.