karloff70

G7 alive and beautiful!!!
« on: July 23, 2008, 02:07:08 PM »
Hi everyone,

Got my G7 put together but there is no sound whatsoever so I was hoping there might be a couple of pointers towards the problem, as I'm a bit lost....even after searching the meta.....

I'm using Dale's M7, a PF86, Gustav's board and a Sowter 3678 transformer, all inside a lenghtened former Nady 1050. At the moment my readings under load on the pins are:

Pin 2: 168V
Pin 5: 56V
Pin 6: 4.5V

These are ok from what I can tell (from other peoples in the meta). The tube lights up, but only slightly. Had someone help me mod the PSU (ex Nady 1050) with a variable heatervoltage pot on the outside. In the process I did tell him to change the 200mA to 300mA for the PF86, but somehow I can't get a measurement to verify this on pin 6...??

The other thing is the Sowter 3678. Talked with someone at Sowter and he reckoned to wire it up how I have it now:

In:

 Yellow from pin 5
 blue    from pin 6

Out:

 pink    to pin 4  (200 Ohm out)
 brown to pin 3  (common)

Pin numbers here relating to the 1-6 pins for the Lundahl on Gustav's PCB.

I was thinking this would give me the 200 Ohm output......(50 and 600 optional). Don't know how to put the Sowter pin diagram on here unfortunately.

And finally, the voltages before and after the 100K resistor are 157V and 67V.

I hope all this points someone's more informed brain towards a likely simple idiocy commited by yours truly. Any help would be greatly appreciated!

Boris


karloff70

G7 alive and beautiful!!!
« Reply #1 on: July 23, 2008, 02:13:11 PM »
Oh yeah, and I connected both pin 1 and 7 to the chassis for grounding, as on my PCB they don't meet at the capsule end. Hope this is right?

rodabod

G7 alive and beautiful!!!
« Reply #2 on: July 23, 2008, 03:32:26 PM »
Is pin1 not grid2? I think that should be connected to the anode for triode operation.

Check the voltage at the filament pin (4.5V?).  Should be either pin4 or 5 depending on which one you gronded.
Quote from: tv
punchy fat bastard chip

karloff70

G7 alive and beautiful!!!
« Reply #3 on: July 23, 2008, 05:46:17 PM »
I think I have everything wired right. Pin 2 is anode. Pin 6 is heater voltage (4.5V). Pin 4 read 0V and 5 reads 56V........ :?:

seavote

G7 alive and beautiful!!!
« Reply #4 on: July 23, 2008, 10:19:34 PM »
pin 6 is the plate. 4 and 5 are heater. see this data sheet:
http://tubedata.itchurch.org/sheets/020/p/PF86.pdf
 i dont recall if the pf 86 is the same pinout as the ef86. i believe that it is. search for the data sheet to be sure.

Quote
I connected both pin 1 and 7 to the chassis for grounding

this may seem silly but you are talking about pins 1 and 7 on the 7 pin xlr connecter are'nt you? you skipped from talking about tube pins right to this.
Everyday is a gift. Thats why it's called the present

karloff70

G7 alive and beautiful!!!
« Reply #5 on: July 24, 2008, 03:39:01 AM »
Actually, I was only talking about the xlr/end-of-PCB pins all along, not tube pins. Pins 1 and 7 to chassis is how I understood some of Jakob's grounding advice in the meta. Seem right?

 PF is like EF, just 300mA instead of 200mA and 4.5V instead of 6.3V.
Trying to verify that I've got 300mA on my heaterpin (pin 6/xlr), but can't get a measurement....tube glows though.

Might I have the transformer wrongly wired? Anyone use a Sowter 3678 in this context before?

karloff70

G7 alive and beautiful!!!
« Reply #6 on: July 24, 2008, 09:22:15 AM »
Got output now and the polar patterns are all working, but the output is VERY low, thin and possibly hissy. I say possibly because I'm running into a friends Soundcraft Delta and to get output I have to crank both gain and fader to the max at which point the Delta gets hissy anyway....

But VERY quiet and thin.

Tried swapping the input side of the transformer, with no difference noticable. Same thing.

Have repeatedly cleaned with 100% isopropyl.......

Any ideas? Please....? Pretty please........ :roll:

rodabod

G7 alive and beautiful!!!
« Reply #7 on: July 24, 2008, 12:22:44 PM »
Transformer wiring looks good, and you have it wired the correct way round.




Can you confirm you are getting ~80V (84V) in between the two 470K resistors? Also, measure the heater voltage. Don't measure the current, just measure the voltage between the heater pin and ground.

Make sure you haven't shorted the capsule backplate to ground (or have created a relatively "low" resistance to ground. How are you mounting?

If you are still stuck after a while, I'll be in London next week if you are still getting nowhere.

Roddy
Quote from: tv
punchy fat bastard chip

karloff70

G7 alive and beautiful!!!
« Reply #8 on: July 24, 2008, 01:59:31 PM »
Hi Rod,

Getting about 67V between the two 470K (they're actually 464K's).

The heater voltage at tube socket pin 5 (heater) is 4.57 V(good for PF86, still looks hardly fired up though). Pin4 (second heater pin) reads 0.02V. Pin 6 (anode) reads 67 V.

Mounting with a rubbermount as a foot ( I believe I posted you the details on where it came from when you were looking for an M7 mount) onto which I araldited a brassring at the top. Screwing into it from the bottom with nylon washers both between rubber and metal plate and metal plate and screwtop. Might have to measure the rubberfoot for leakage.....in case the screw is touching inside the hole.

Another thing that just occured to me is the 10K resistor first in line from XLR pin 5 seems to not, or almost not pass current. Went round the board checking continuity and everything else 'beeps' but not him....no more here at the mo...I'll get one to try. Might have cooked him. XLR pin 5 reads 57 V in cardioid.

Thanks for trying to help! Does it bring on any more ideas, or should I just try a new 10K...?

Boris

karloff70

G7 alive and beautiful!!!
« Reply #9 on: July 24, 2008, 02:01:31 PM »
Hi Rod,

Getting about 67V between the two 470K (they're actually 464K's).

The heater voltage at tube socket pin 5 (heater) is 4.57 V(good for PF86, still looks hardly fired up though). Pin4 (second heater pin) reads 0.02V. Pin 6 (anode) reads 67 V.

Mounting with a rubbermount as a foot ( I believe I posted you the details on where it came from when you were looking for an M7 mount) onto which I araldited a brassring at the top. Screwing into it from the bottom with nylon washers both between rubber and metal plate and metal plate and screwtop. Might have to measure the rubberfoot for leakage.....in case the screw is touching inside the hole.

Another thing that just occured to me is the 10K resistor first in line from XLR pin 5 seems to not, or almost not pass current. Went round the board checking continuity and everything else 'beeps' but not him....no more here at the mo...I'll get one to try. Might have cooked him. XLR pin 5 reads 57 V in cardioid.

Thanks for trying to help! Does it bring on any more ideas, or should I just try a new 10K...?

Boris


craigmorris74

G7 alive and beautiful!!!
« Reply #10 on: July 24, 2008, 02:32:26 PM »
What is the brass ring connected to?

karloff70

G7 alive and beautiful!!!
« Reply #11 on: July 24, 2008, 03:53:14 PM »
Tried another 10K. No different....

The brass ring is a U shape, closed at the top with a screw and glued with metal epoxy at the bottom to a rubber mount footing. Just measured the rubber. NOT leaky. On the outside of the ring I have soldered the backplate lead going to the pcb.

rodabod

G7 alive and beautiful!!!
« Reply #12 on: July 24, 2008, 03:59:49 PM »
Quote from: "karloff70"

Another thing that just occured to me is the 10K resistor first in line from XLR pin 5 seems to not, or almost not pass current.


There should be pretty much no current flowing through that resistor. There aren't many places it could go.

I'd make sure the capsule backplate is well insulated first and then look elsewhere.
Quote from: tv
punchy fat bastard chip

craigmorris74

G7 alive and beautiful!!!
« Reply #13 on: July 24, 2008, 04:34:50 PM »
Actually, what I was implying was, shouldn't the brass ring be connected to the "capsule center" pad on the PCB?

karloff70

G7 alive and beautiful!!!
« Reply #14 on: July 24, 2008, 04:50:34 PM »
Sorry, it is connected to the center pad. All three leads (front, back, center from the brassring) are definitely in the right place and the rubbermount is not leaky......



 :?:

craigmorris74

G7 alive and beautiful!!!
« Reply #15 on: July 24, 2008, 04:57:21 PM »
Is the tube good?

karloff70

G7 alive and beautiful!!!
« Reply #16 on: July 24, 2008, 06:14:27 PM »
Likely. Bought 2 Siemens NOS. Supposedly read 3,2 and 3,5 (as new)......tried both, no difference.

ioaudio

G7 alive and beautiful!!!
« Reply #17 on: July 25, 2008, 03:42:19 AM »
check out how to measure current (though i dont think thats the problem)

i think your problem is somewhere between the tube, plate to transformer cap, transformer itself or the wiring to the output xlr.

karloff70

G7 alive and beautiful!!!
« Reply #18 on: July 25, 2008, 05:27:33 AM »
G2 to blocking cap to transformer and all 7 XLR pins seem ok ??? Transformer is wired correctly I'm told....?? I'll search for current measuring info....

rodabod

G7 alive and beautiful!!!
« Reply #19 on: July 25, 2008, 06:43:09 AM »
Also check if the earthing is all correct - look in the PSU too.
Quote from: tv
punchy fat bastard chip


 

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