The official G9 help thread

[Gustav]

Step 1. Hooked the 12V/1.5A rated  secondary up to the heater voltage, tubes lighting up, regulator showing ca. 12V.

Step 2. Hooked the 12V/1.5A rated secondary up to the 12V input fo r48V. Adjustment went fine.

Step 3. Hooked both heater and 48+  up to the 12V secondary, D15 burned again.

Step 4. Replaced D15.

Step 5. Hooked up an alternative transformer secondary with a 15V/2A secondary  to just the heater.

Step 6. D15 burned again.


Scratching my head a little here, and would like to know if changing the diode to a 1N540x is a possible fix or it would just be a band aid.

230V secondary giving fine HV for both the first and second trafo.

I tried checking if any of the tubes were doing anything funky in pairs of two. Didn't seem like it.

Gustav

(edited for a little clarity)

 

[Harpo]

.. Hooked them both up to the 12V secondary, D15 burned again...

There is a reason, the schematic shows a mains transformer with dual secondary windings.

 

[Gustav]

.. Hooked them both up to the 12V secondary, D15 burned again...

There is a reason, the schematic shows a mains transformer with dual secondary windings.

First scenario.

The first transformer has two secondaries,, 1 x 230 and 1 x 12. I split the 12V to the two 12V inputs on the board. I didn't realise this was not possible and will examine the schematic for this.

In this case, your information makes sense in accordance with my findings, and I was too dumb to see I could not split the 12V to the two inputs on the board.

BUT

------------
Second scenario.

The second transformer I tried has 3 x split 12V secondaries as well as a 230V secondary. (1 x 12V 2/A and 2 x 12V 100mA).

I put the 230V to the HV input on the board, and the 12V/2A (measured the correct voltage before attaching them) and nothing to the 12V going to the phantom part.

Still getting a stack of smoke on D15 and a shaking transformer.

Ill swap D15 again and try with the second transformer again.

Thanks!

Gustav

 

[Gustav]

Just tugged in the kids and gave it another try.

I fear it may have been a Schödingers cat type of situation, as in measurement influencing the result  :-[ Will check again monday. Too tired or high voltages

I just made some new, small retractable clip probes for my meters, and I fear they may have shorted when attached to adjacent legs of the 12V regulator. Not 100% sure yet. I just tried powering it on with no measurement on it, and I got no smoke.

I DID disconnect the transformer and measure for shorts after the first incident, so I was sure I was not looking for a short circuit...  :-X

Gustav

 

[Gustav]

I just made some new, small retractable clip probes for my meters, and I fear they may have shorted when attached to adjacent legs of the 12V regulator.

Yep, that was the final issue.

Thanks for pointing out the two trafo set-up Harpo. I have built a few units before without even noticing the two 12V inputs are not just split for layout purposes.  Just had a trafo with both HV and 12V secondary, so I thought I could just split the 12V

Thanks!

Gustav

 

[Kari.M]

Hello. Is this the normal spectrum when using OEP:s on input and output?
(Pink noise RTA using 1/24 oct and infinite averaging)

 

[Spencerleehorton]

Hi Everyone,

I have had my G9 running for sometime now and i'm finding that it is weak on the low end. I have had a little experience now with other units using the OEP txf and find they lack bottom end.
I have had many successes with Sowter transformers and continue to use them as they are made only a few miles up the road in ipswich.
after having some hum issues with the G9 i have altered it somewhat by changing some of the caps, the unit is still somewhat noisy if i'm going to be really critical (which we all need to be i suppose).
Im thinking of rebuilding the power supply on another pcb and changing the OEP output txf for sowter 4062 on output?
the sowter is 1:3.23 ratio.
Anyone else having issues with lack of bottom end and have any thoughts?

regards

Spence.

 

[Kari.M]

I think this is a common spectrum with Lundahl trafos

 

[Spencerleehorton]

Ah seems your losing bottom end as well with the Lundahls!!!!!
Im gonna try and find both Sowter txf for input and output to improve bottom end loss!!

regards

Spence.

 

[Kari.M]

I think that its all about  character vs lack of bottom. That lack of bottom is about 3 dB at 31 Hz...

 

[Spencerleehorton]

Hi,

The lack of bottom end would be a good thing to discuss if someone could explain it in more detail and other options. I don't just believe it's just a character thing, I'm sure there are other options.

Regards

Spence,

 

[Spencerleehorton]

Hi,

I think now I would like to put both transformers in and switch between them, is there an easy way to do this?
Cutting track, running cable to DPDT 2 way switch?
Any ideas?

Also using 1:3.23 ratio on output ok? How would the same txf fair on the input?

Regards

S

 

[audiophreak]

Hi

  There was a lot of research / testing done on this subject in this thread - http://groupdiy.com/index.php?topic=9813.0 -  I have built 3 G9's and mod'd one of them with different LL's on the output with ECC88's on the out put ( have to mod heater circuit )  and got a flat response down to 14Hz ... with that said , I actually prefer the sound of my other two G9's with LL's on INP and OutP ... has a certain something I like , just my preference though.

  That thread has a LOT of interesting info and those guys did a lot of work.

  Cheers,
                    Chip

 

[Spencerleehorton]

Hi,

On investigating the lack of bottom end, I have now discovered it's not both channels!
Just the left channel.
Going to swap cables, valves etc to see if left channel plays ball a bit more and read through the stuff you have just posted.
The right hand channel doesn't sound that far off now when I a/b to my ears.

Regards

Spence.

 

[Spencerleehorton]

HI All,

all sorted now, another patch bay issue, bit of solder on some joints hey presto, all working fine!!
bottom end now all correct!!

still might put in some sowter txf though!

regards

Spence.

 

[Spencerleehorton]

Hi,
Wanting to put  another pair of transformers on the output, is it ok to put txf on a dpdt switch opr is this not the done thing?
Is it better to put them on another pair of xlr?
Pros and cons?

Regards

Spence.

 

[gyraf]

you can switch between primaries, no problem.

Jakob E.

 

[Spencerleehorton]

Hi,
Am I right in thinking that switching between the output transformers would have more influence than switching between the input transformers?
Also what influence would the ratio being 1:3.23 have on the output, would I gain volume or loose volume?

Regards

Spence.

 

[Spencerleehorton]

have wired in DPDT switch for switching TXF but have some discrepancies, output control right channel no longer operates?, when on mic when i power off the volume jumps right up? Low cut on right channel doesnt work?
not entirely sure i've wired it up correctly! will investigate.

regards

Spence.

 

[lens42]

I got hold of of some nice 115-12V toriods for about $7 ea. at a surplus place. They are these:
http://www.digikey.com/product-detail/en/70042K/1295-1042-ND/3881435

see the attachment (I couldn't figure out how to embed an image)

There are three 10VA toroids: One feeds the 12V heaters only. Two more connect so that only one 115V primary on each are driven in parallel by the AC line. The other 115V primary windings are then used as secondaries and connect in series for 230VAC. Then finally, the four remaining 12V secondaries are hooked in series for 48 VAC without needing a tripler.

Besides being cheap by using what's available (to me), I think think it has advantages over the original design, that might be worthwhile even if you're paying Digikey for transformers.
1) No power has to pass through two transformers, about 5% more efficient
2) No tripler needed for the 48V output