Help with Ram's Head big muff

[eightsevenzero]

I just built a RH big muff based on the schematic below. I used NOS BC239C's with hFE just at 600 each. Everything works just fine but I'm getting some gating out of it. My voltages are listed above in the schematic. I saw the Q3 collector voltage (labeled Q2 in this schematic) is a bit high for some reason. I tried increasing the resistor value which did bring down the voltage a bit but the gating still remained. At this point, I'd just like to know the source of the gating in a circuit like this.

Also, I checked the DC on all the caps, for example, C6 and C7, and it looks like they are passing DC, about .66v. Is that normal?

[antonis]

Also, I checked the DC on all the caps, for example, C6 and C7, and it looks like they are passing DC, about .66v. Is that normal?

It's quite normal 'cause they don't pass any DC at all..
What you measure actually is the diode(s) pair forward voltage drop..

[idy]

You could share those voltages....

[eightsevenzero]

You could share those voltages....

They are pictured above in the schematic photo.

[GibsonGM]

Yes, and notice that the schematic shows "B: .67V" etc...the drop Antonis described.

So - what are YOUR voltages? Don't be shy      They may well indicate where the gating is occurring, and why.   Also, your high Q2 voltage - what was it, and what did you change the R to?    An off value resistor in there somewhere could cause similar effects...

An audio probe might show which stage is gating faster than us talking about it!  Check each collector if you have a probe.

[eightsevenzero]

I put those voltages in the pic. they are mine. I changed the resistor on the high CV from 15k to 30k and reduced to around 5V. Gating was maybe a slight bit less but still present. Ive double checked all my resistors and they are all correct. In theory if older BC239C's were lower hFE would that lower or raise collector voltage much?

[GibsonGM]

Sorry bud, misunderstood, thought the voltages were from an as-built, not your own   I don't see anything remarkably different from what I just ran thru my simulator.  Could it be the usual, check the pinouts, component values...anything going on in the tone stack, etc?       

I'd audio probe it to confirm where the gating starts, it's my hunch that it would be a fast way to find the problem stage and narrow it down...

[eightsevenzero]

Sorry bud, misunderstood, thought the voltages were from an as-built, not your own   I don't see anything remarkably different from what I just ran thru my simulator.  Could it be the usual, check the pinouts, component values...anything going on in the tone stack, etc?       

I'd audio probe it to confirm where the gating starts, it's my hunch that it would be a fast way to find the problem stage and narrow it down...

Sounds good, thanks!

[duck_arse]

In theory if older BC239C's were lower hFE would that lower or raise collector voltage much?

if older BCxxxC's were lower hFE, they would be BCxxxB's or A's. that's how the BC markings work, old or new BC's. 600 hFE's on your parts? how much higher would you expect them?

lower hFE means the base needs more current to reach the same biasing, so more current thru Rcollector means a greater voltage drop, and lower Vcc. I think.