G7 alive and beautiful!!!

[mich]

i would check the transformer offboard to see that it passes the signal as it should.-just inject a signal to the 200 ohm side and expect it to come the other side 6 times bigger(or whatever the ratio is)

i had a similar problem conecting an oep in my G7 until i found out i conected it wrong...

 

[karloff70]

I've grounded XLR pin 1 and 7 to the chassis at the mic end. Correct?

The PSU was done for me by a pro (very good..) guy, so I think it'll be unlikely to find a problem there. I'll have a look inside though. He put a pot on the outside for me which adjusts heater voltage from about 3 V to 7 V, so I can underheat the PF86 easily once run in. I did mention to him that the current needs to be 300mA for the PF86 as opposed to 200mA. Not a hundred about this being the case.

As far as the transformer, there are only two options connectionwise and I've tried both + its new straight from Sowter.

I've been trying to determine the current on the heater voltage, so I disconnected pin6 (xlr) and put the meter across it under load. Got no current reading. Voltage is 4.5 V (as set by my pot). Can't get a reliable resistance measurement though. It seems the only stable (repeatable) one is a reading of about 75 when the meter is set to a 200k scale...???resistance. This, with Ohms law results in some miniscule current....or am I being six-toed about this..??? Long time ago these things entered and left my brain at school......

Thanks a lot for everyone chiming in with help by the way !!!!

 

[rodabod]

[quote author="karloff70"]I did mention to him that the current needs to be 300mA for the PF86 as opposed to 200mA. Not a hundred about this being the case.[/quote]

You can either specify the heater current or the heater voltage in this case. The filament in the valve has a fixed resistance (well, once heated) and so if the voltage across it is correct, then so is the current. Alternatively, if you feed it with the correct amount of current, the voltage across it will also be correct. This is because the different values have to obey V=IR or I=V/R.

As far as the transformer, there are only two options connectionwise and I've tried both + its new straight from Sowter.

Looked ok to me.

I've been trying to determine the current on the heater voltage, so I disconnected pin6 (xlr) and put the meter across it under load. Got no current reading.

Meter should be in series with the heater circuit. Eg. path would be 4.5V -> DMM -> heater pin -> ground. I wouldn't bother.

We don't care to much about the pot resistance assuming it has been wired correctly. Sounds like your tech gave you adjustable voltage. This should be set to no more than 4.5V.

 

[ioaudio]

are you sure that the signal output from the transformer + and - reaches to output´s xlr pin 2&3 (i ask this because you didnt make the psu yourself)
edit: and that it doesnt short to ground (e.g.in the mic cable´s connectors)

 

[karloff70]

So my current should be fine then, as I've put my adjustable pot to putting out 4.5 V.

The (old chinese at the moment) mic lead DID have a problem before, as one of the pins ( I think 4) was to ground on both ends, which had me getting no sound at all. It's since I removed that I get very faint sound. As I am getting faint sound I'm guessing the pins in the PSU are correct, but more so because I gave the tech the schematic for the G7 so I'd be very surprised if it was wrong. Again, I'll open the little bugger right now and have a look.

 

[karloff70]

Just checked the inside of the psu and, yes, the transformers output (mic end pin 3 and 4) goes to psu xlr out pin 2 and 3 as it should.

I'm starting to feel blinder and blinder......no doubt when the solution occurs it will be a case of 'OOOH, THAT SIMPLE THING....' Can't for the life of me see what I haven't tried yet.

Maybe recheck the capsulemount to make sure the screw into the bottom of the base doesn't touch the chassis inside the hole? But this wouldn't make any difference as long as the rubbermount is not leaky, and I measured nothing, silch, across it........

:roll:

 

[burdij]

It may be that you are leaking your polarizing voltage to ground. You should try lifting the base of your capsule mount off the surface its mounted on with an good insulator. Even though you don't measure any leakage with a meter, to a 1G resistor just about everything is a conductor.

 

[karloff70]

Cool, I'll go for the mount. The screw that goes in the bottom has nylon washers on both sides of the chassis plate it goes through, but MAY be touching inside the hole....maybe I need to widen the hole to make sure this can't be the case and then see.....

 

[karloff70]

OK, now I took the whole mount off, drilled the hole for the screw bigger, lapped the screw stem with electrical tape so it CAN'T touch the side of the hole, put it all together again and........AAAAAAAARGH

It's the same! No, wait, it now also has some dirty crackle on top of the TINY signal it passes (probably dirt somewhere, although I did rub the whole board with isopropyl again....)

I'm starting to get seriously tempted to give the whole thing to the tech, except I haven't really got funds to do so. Breathing very slooooowly and deeeeeply .........help.....please........pretty please.....

 

[craigmorris74]

Maybe post a couple of good pictures?

 

[rodabod]

It will most likely be something simple.

Made sure the resistor values are correct? Double check. Photos of the various areas would help (including the PSU with the top off).

If you are still stuck after the weekend, I am in West London and coud help.

 

[karloff70]

Resistor values are definitely correct. Don't know how to put pics up in posts...?

Probably something stupidly simple indeed.....noob disease.....

If you can tell me how to put pics up, I will.....

 

[rodabod]

Take photos, then go to www.imageshack.us which will "host" them for you.

It will then provide several links wich you can copy and paste. Copy the "direct link to image" link and paste it in your reply. You need to repeat this for each photo.

 

[karloff70]

Cheers!! I will have to eat and play tennis first though, as my nervous system is getting a bit frail......

Pics coming this evening!

Again thanks to everyone for chiming in to help!!!

 

[Mr. Snoid]

I had a similar problem with mine. Turns out I put in a 220K resistor where the 220R is called for. I could hear faint output if cranked full on.
I pissed with it for a week until I stopped and double-checked everything I had "double-checked".

tOD

 

[karloff70]

Thanks for the tip Mr Snoid. Just 'double-checked' again, but unfortunately I got it right....220R.

Knackered now, pics will have to wait until tomorrow morning......

 

[karloff70]

Having until now discounted the idea that my resistors could be the problem I have to point out that my values are not entirely kept strict because the old Holco H4 resistors I used don't come in the spec'ed values.

My 100K is in fact a 97K6....(0.5%)

My 1K6 is 1K65

My 220R is 218R (150R+68R)

My 470K's are 464K

I figured since the tolerance is so low on these, it would come out in the wash, but then I am a total noob so who am I to know.......maybe not?

I'll put some pics up in a bit...

 

[rodabod]

Resistors should be fine.

 

[karloff70]

Right, here goes....hope I'm doing this right....

















Here we are.....

The capsulemount has nylon washers (loads of them) on both sides of the chassis plate and electrical tape around the screwstem to avoid the screw touching inside the hole.......

The 220R is actually two resistors in series.

The light blue resistor on a lead is a 10K I replaced to see if the original was a problem. It wasn't, but I lifted the traces getting him out, so leads........

The two bananas on the PSU are to put the meter on when adjusting heater voltage with extra front pot.

Pictures bring anything stupid to light, invisible to my noob eye?

Oh, yeah, the pcb is loose at the mo, as I was messing about. Will get strapped back in......

 

[plumsolly]

Hey Karloff - sorry, no help for you here. I was just wondering where you got your mci body. Thanks, Ben