The official G9 help thread

[gyraf]

You'll still need three of the five pins of the molex: Gnd-Gain-Att for the gain switch..

Only the two first pins are now redundant/disconnected (to/from jack)

Jakob E.

 

[gareth33]

Thanks Jakob and Rodney, with your info and looking at the schematic it's all coming together. And thanks Jakob for this project, it's the most fun I've had with a soldering iron ever!

It's coming together nicely, though it's been a lot of work wiring up. Could someone give some advice on how I've hooked up my power transformers? It's according to http://www.groupdiy.com/index.php?topic=16168.0 skylars diagram, my transformers are coloured the same.

I have basically taken the 15v orange off to the PCB but also looped in to the red and yellow of the secondary on the other toroid. Repeat with the loop mechanism in to black and orange.

To me it seems good, but I may be wrong?!

Many thanks in advance

Gareth

 

[gareth33]

Hey everyone....

I took the silence as to mean the wiring was ok.. It made sense to me, though a touch eccentric I thought, but I powered it up and it was C17 that exploded not the transformers. Had the heater cap the wrong way round so it started boiling.

I swapped that out and double checked everything again powered up, but nothing. The valves don't seem to heat up. I didn't try and pass any audio.

I have 265VAC from the secondary of the second toroid, going out to the main board. I have 390V on the C14/C15 caps (they're 100uf rated 385V).

Around 17V on the 15V secondary and 245V entering the main board after the step up. 

What else could have been damaged from the C17 melt down? The TL783? Everything else looks good, no burning smell or burnt components that I see. I was very careful stuffing the boards, soldering was very neat and no shorts as far as I could see.

Any advices on where to start debugging would be appreciated. I checked a lot of the voltages on places I had easy access to but not sure where else to check safely.

Gareth

 

[gyraf]

The most likely casualty from shorting the G9 +245V HT line to ground is the TL783 - it's not short circuit proof when used like this...

Jakob E

 

[Jamie1234]

Hi. G9 going well so far, I just have one question. On the layout PDF the phase switch is listed as 3 position. Is this supposed to say 2 position or am I missing something obvious? Thanks

 

[gyraf]

Overlay error - phase switch is off course two-position...

Jakob E.

 

[Jamie1234]

thanks

 

[gareth33]

Hi all...

I'm sitting down to go through the schematic, as something is awry.

I have 345V on the 245V HT resistors R31 and R131.

23V on the 78S12. This doesn't look right. The input from the toroid at this point in the circuit is around 16.9V.

Could the 78S12 have been fried with the 1000uf C17 meltdown as well? Or the diodes.

Aprox. 345V going to C14/15 and also on the R31's. That is about 100V over what it should be, I'm going to hazard a guess that maybe it could be a wrong value on one on the 2W power supply resistors, R33, R34, R37. Hence the voltage jump.

Or, looking at the schem, I'm seeing C17 closest to the, 78S12, I'm thinking this may have been shorted not the TL783?

I appreciate any tips on where else to look.

Gareth

 

[MHBuur]

Hello everyone

I'm a few steps from completing my first G9 build. As expected I ran into the usual problems: hum and oscillation, but besides from that, things worked seemingly ok (I did only measure 211V at the 245V HT test spot though, but that is hardly related to hum or oscillation issues).

Here are the (somewhat scary) test numbers before applying any hum/osc. fixes (i.e. plain unshielded molex connections):

CH1:
Hum
  Input @ step 6, Out @ Max 
  Btwn. Gnd and Hot/Cold = 350mV @ 50Hz
  Btwn Hot and Cold = 9mV @ 50Hz

Oscillation (step 9-11)
  9: 25V @ 4.6 kHz
  10: 15.8V @ 7.1 kHz
  11: 7.4V @ 6.0 kHz

CH2:
Hum
  Input @ step 6, Out @ Max 
  Btwn. Gnd and Hot/Cold = 190mV @ 50Hz
  Btwn. Hot and Cold = 11mV @ 50Hz

Oscillation (step 8-11)
  8: 20.5V @ 3.8 kHz
  9: 7.4V @ 2.2 kHz
  10: 3.9V @ 1.0 kHz
  11: 3.6V @ 0.5 kHz

I have the trafos mounted side by side (not on top of each other) on the side of the chassis (to get better heat dissipation) - as far away as possible, and plan to shield them better later on.

I cut the pcb lanes as instructed in the gif posted earlier (http://www.gyraf.dk/gy_pd/g9/G9-EDIT.GIF) and rewired with shielded cables and did a test - silent as h***, no oscillation etc. almost too good to be true, so I tested with a mic (still only hooked up to the scope). There was signal, though weak.

Then the smell came. The sour smell of fried semiconductor :-/ It was D15 in the rectifier block near the hot as hell regulator (which do in fact have a cooling profile attached, but I fear its too small). The main trafo also started getting warm and humming directly from the box. Time to turn it off and head in here...

What killed D15?

Could it be the testing period it self - I had the oscillating steps going at full output for some time (maybe 15 mins or so)?

and while I'm here, a few other questions:
- I'm supplying 230V - why is the additional step trafo needed at all? Why not take the fused main supply directly?
- I'm using two 100 uF / 400V filter caps - but I've seen other recommendations, any point in going up in capacity here?
- Is the side by side mounted ring trafos a bad idea (increased inference issues), if so why?

Regards

Michael - (long time lurker in here)

 

[MHBuur]

Okay - the unit is up running again and things seem to work well. I changed the rectifier diodes to 1N4005 (I dont have any spare 1N4004), any problems with that substitution?

It must have been the test with the extreme oscillation that blew the D15 diode. All of the diodes in the rectifier block got hot during the test (I could tell from the solder pads).

I tested it in a real setup and I now only have some 50Hz hum issues to solve. Besides trafo shielding and repositioning, are there any other places to rework to minimize the 50Hz hum?

 

[gareth33]

Hi everyone

I wonder if someone could offer some advice on the situation.

All components look good. I had an LM970 (?!?) in place of the 78S12, must have been very tired when I did that.

Centre pin of the 78S12 is showing 23v, does that sound right?

Still getting around 345V on R31 and R131

I'm not sure where to go with it now, do those voltages seem too high? All the wiring looks good but any advice on how to proceed or where to check voltages, tube pins etc. would be appreciated. Perhaps I blew the tubes filaments with the 78S12 confusion or the C17 short?

Many thanks

Gareth

 

[MeToo2]

and while I'm here, a few other questions:
- I'm supplying 230V - why is the additional step trafo needed at all? Why not take the fused main supply directly?

Regards

Michael - (long time lurker in here)

Because that could be downright ^%&$&! dangerous or at very best leave you with earthing problems. Don't do it.

 

[gyraf]

Centre pin of the 78S12 is showing 23v, does that sound right?

No - centre pin of 78S12 is definitely grounded. Look at PCB overlay and schematic.

Jakob E.

 

[MHBuur]

and while I'm here, a few other questions:
- I'm supplying 230V - why is the additional step trafo needed at all? Why not take the fused main supply directly?

Regards

Michael - (long time lurker in here)

Because that could be downright ^%&$&! dangerous or at very best leave you with earthing problems. Don't do it.

Alright, so it is basically to maintain galvanic separation, which could be done with a 1:1 trafo alone then?

 

[gyraf]

Yes - but such a transformer is not trivial to find most places in the world. 12V or 15V secondary is.

Jakob E.

 

[MHBuur]

Ok thanks, that makes good sense then

Should I worry about the low voltage at the 245V HT test spot?  I get around 211V there..
I'm mounting a metal shield btwn the trafos and the print right now - is it crucial on which side of the shield I put the filter caps (50 Hz hum in mind)?

EDIT:
Shield done. I left the capacitors inside the shielded area with the trafos, didn't seem to make any difference.

Channel 1 is now very silent, I hear some hiss at high gain, but I guess thats expected?
Channel 2 is still suffering from a little hum. I'm already using shielded cables everywhere, and even the molex wires have been wrapped in shielding foil (connected to common gnd). Is there something else that could improve this hum reduction on ch2?

Both of the instrument inputs are dysfunctional (I rechecked the wiring, seems ok) - I only hear loud hum and no signal passes through (I tested with a guitar). I did the DI mod. Any clues here?

 

[whomper]

Hi,

Starting to assemble parts of this build.
Short question for the power trafos. Will those work:

50VA, 15v - http://www.mouser.com/ProductDetail/Triad-Magnetics/VPT24-2080/?qs=%2fha2pyFadugmtBQK5%252bC3b4pnRZ%252beRIAEgSomuwbPAFk0JsUE29sIzw%3d%3d

50VA 12v - http://www.mouser.com/ProductDetail/Triad-Magnetics/VPT30-1670/?qs=%2fha2pyFaduiy1%252bXH2FTKPEjjTbIjqPEfSIO4FyKEH8KgD19OROh4YA%3d%3d

Have been using Triad Magnetics for all my builds and have noticed (reading the now 73 pages of this great topic) that no one had mentioned them.

 

[gyraf]

Yep, my guess is that they'd work fine. Power transformer type is quite non-critical, that's why they're left unspecified but for the voltage- and VA-rating.

Try and let us know?

Jakob E.

 

[whomper]

Yup, will do.

Another one, have seen in tubedepot.com additional services while selecting tubes. have enclosed a screen capture.
Should I go about choosing additional service, or just purchase tested tubes as is?

 

[MeToo2]

Yup, will do.

Another one, have seen in tubedepot.com additional services while selecting tubes. have enclosed a screen capture.
Should I go about choosing additional service, or just purchase tested tubes as is?

Some people spend a fortune on special tubes with all sorts of special characteristics, including cryo treatment, pair matching, long getters, named manufacturers, special date codes, NOS etc. etc.

Only you can tell whether it's worth the money. Me? I just buy plain vanilla stock of the correct type of a known brand that has reasonable quality control.