10,000 M Ohm resistor !! ??

[MartyMart]

"Brown- Black- White- Gold"      is this correct, a 10,000 M ohm value !
( finding 10M Ohm resistors is hard enough !!.... Brown - Black -Blue- Gold )

Just ordering some 1 watt and 5 watt resistors to fix my mic-pre and came
across one of these ....

HELP !

MM.

[Ge_Whiz]

Nah. Gold either means 5% tolerance (now obsolete), or x0.1. So brown/black/white/gold is 10.9 ohms by my reckoning.

[Mark Hammer]

Shouldn't it be brown-black-blue?

[theundeadelvis]

Using this calculator (http://www.electrician.com/resist_calc/resist_calc.htm) it would be 10,000 Mohms +-%5 tolerance. WOW!

[MartyMart]

Using this calculator (http://www.electrician.com/resist_calc/resist_calc.htm) it would be 10,000 Mohms +-%5 tolerance. WOW!

That's the one i have  !!

All the others on the board "make sense" using "gold" as the tolerance and this one
is the same "type" ( others are 1k5 15k 82k and 22 Ohm )
a straight 10M is brown black blue ... this is positively brown black white !!

SHIT ... I need to order these now !!

MM.

[Johan]

what is it for?..10GOhm inside modern equipment just doesnt sound very likely...even if its for biasing the capsule of a condensermic it's BIG...if its for that valvepreamp, couldnt it be a fried 100k and with the collors shifted/faded with heat?..

johan

[MartyMart]

what is it for?..10GOhm inside modern equipment just doesnt sound very likely...even if its for biasing the capsule of a condensermic it's BIG...if its for that valvepreamp, couldnt it be a fried 100k and with the collors shifted/faded with heat?..

johan

It is indeed, however its not "fried" it's fine, just found out about a "known" problem with these
Mindprint mic-pre's and several of the 1/2 watt resistors need to be 1 watt !
( also two 2 watt are becoming 4 watt )
It looks wierd, I know ... perhaps I'll leave that one as is, its connected to pin 1 of the tube !

[Ge_Whiz]

A cheaper replacement for a 10 Gohm resistor would be - AIR. What's the point of buying one? How do you propose to test it? Your DMM will tell you it's an open circuit!

[zachary vex]

10Gohms is only useful in million-volt applications, like physics experiments... i've seen 100Mohm as bleeders on diode/capacitor voltage multipliers before but 10G is just plain silly.  at that resistance range, you're starting to see competition from the circuit board material!

it's not 10Gohms.  it's something else.  what function does it perform in the circuit?

[Johan]

A cheaper replacement for a 10 Gohm resistor would be - AIR.

..or the greace left from your fingers touching the pcb
johan

[Ge_Whiz]

Nah, finger grease contains water and salt. It would be a much lower resistance than that, even in trace amounts.

[gez]

Is it damaged?  If not, use it. 

Out of interest, why don't you pull it and measure it...

[MartyMart]

10Gohms is only useful in million-volt applications, like physics experiments... i've seen 100Mohm as bleeders on diode/capacitor voltage multipliers before but 10G is just plain silly.  at that resistance range, you're starting to see competition from the circuit board material!

it's not 10Gohms.  it's something else.  what function does it perform in the circuit?

Yeah I know !!
If the first designator were "grey" then it would be 80,000 M  !!
Its part of the connection to pin 1 of a 12AX7 in a mic pre ... comes from
the power bypass caps via a small network and off to a 150n 400v cap ...

MM

[gez]

It'll be a plate resistor then.  No way is it the value you think it is.  The bands on some resistors discolour with time.  I still say measure it...

[gez]

Its part of the connection to pin 1

When you say 'part', is anything else connected to pin 1?

[gez]

An awful lot of valve amps use 100k plate resistors for 12AX7 input stages...

[MartyMart]

Its part of the connection to pin 1

When you say 'part', is anything else connected to pin 1?

OK, dont have the schem yet ( on its way ) so bare with me ... and there's lots of current floating
around in here .. !
Pin one and pin six share a connection via several caps/resistors from a pair of 15uf 450volt caps
with a 82k 1 watt resistor across them
Pin 1 then goes off through a 150n 400v cap to the main section of the board ... I dont know anymore
from just flipping it over ... when i have the schem I'll probably know less

MM

[Sir H C]

All resistors that I have seen in the 100MEG and larger catagory have been encased in glass so that you can keep them clean and high impedance.  I agree, that is not 10 gig.

[MartyMart]

Bang on Gez .... it is a 100k plate resistor
PROBLEM :
This should have 300volts across it ... it has less than 1 volt !!

As the transformer is supplying 13 volts to pin 4 and +15/-15 to the ic's etc
and ...48v phantom power works, transformer must be good .. right ?
So I presume that this network of caps/resistors and diodes stepping up to 300v
is dead and needs replacing .... any other suggestions ? ... Ton/Doug ..

Cheers,
Marty.

[A.S.P.]

where does HV come from?
voltage on both sides of the 82k towards ground?
raw HV? (probably small blue xfmr...)