Rangemaster Bias issue

[andrew4566]

I have scratch-built three amps, but this is my first FX project. I thought that it would be quite simple.

I etched  my own board from the tonepad layout with the millenium bypass.

I tested about a doz 2n404a's and found 3 that measured in the eighties after subtracting for leakage. Most were very low leakage but at 35-40.

My issue is that my collector voltage is around 3.5ish vdc and I am at the extreme limits of acceptable adjustment according the the tech of rangemaster article. When I measure the base and emitter they are both at 8.6v?

I have searched the board for bridged traces and triple checked all other component values.

Aside note the millenium bypass lights all the time... this may be a FET issue as it's not socketed in this layout and I may have damaged it.

-Andy

[barret77]

Hi Andrew

I'm the least experienced one around here, but I've been through similar problems;

- check the pinout of the transistor. I had transistors which were magically inverted (everywhere suggesting a pinout, and they had the opposite) that yelded 8.6 voltages for bias and almost drove me nuts.
- check all the grounds. Also, I had ground problems that resulted in >8v in the transistor. Check with magnifier for small traces, shorts and the input/output ground connections...

good luck!

[petemoore]

my own board from the tonepad layout with the millenium bypass.

I tested about a doz 2n404a's and found 3 that measured in the eighties after subtracting for leakage. Most were very low leakage but at 35-40.
  ? These are PNP, and the RM circuit is Pos Gnd?

My issue is that my collector voltage is around 3.5ish vdc and I am at the extreme limits of acceptable adjustment according the the tech of rangemaster article. When I measure the base and emitter they are both at 8.6v? [miswire?/transistor orientation]?

I have searched the board for bridged traces and triple checked all other component values.
  After close in high intensity light/magnifying glass inspections, I've found miswires and misconnects using the DMM, mostly beep mode testing actual connection from say pin to resistor lead, not pin to solder on R lead, I'll find a place has a buncha connections, clip on one and test all the others as made/not made.
  Testing resistors in circuit DMMing in R Ranges, figureing there may be an alternate path for current when the resistor is attached to a circuit, mathing that out, or pulling one end to test it only.
  At near top of threads is "What to do when it doesn't work", using stated methods in there is the best approach for effective debugging.
  The emitter should be near ground rail.
  The base needs a difference of .6v or more from emittter
  Collector ITCase of the RM is ~7/9ths of power supply, near top rail, set to taste.
  An Exploration into the Rangemaster circuit, excellent read, is available at GEO. I think it's called 'Dallas' though...in the 'technology of' section.

Aside note the millenium bypass lights all the time... this may be a FET issue as it's not socketed in this layout and I may have damaged it.