The official G9 help thread

Hi! I have a question regarding the toroid transformers. My apologies if this question has been raised before. My Google-fu could not find any trace of it

From  Jakob's official site, it says:

You need two 220:15+15V 1A (30VA or larger) toroid transformers, the first converting 220v to 15v - for the heater and through the tripler to P48 - and the other one converting the 15V also used by the tripler back to 220v for the HT

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and from the BOM from the same site it says:

POWER TRANSFORMERS, for 220V-Countries:
First:    220V:15+15V /30VA TOROID      PSU 220V mains to 15VAC
Second:    220V:12+12V /30VA TOROID      PSU 15VAC to 220VAC *note:updated!

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I rushed my order of the toroid transformers, and ended up ordering two 220V:15+15V 30VA transformers, instead of one 12V and one 15V.

Will this be a problem? From what I can decipher from the schematic,  the input to the HT transformer is 15 VAC.

Thanks to Jakob for putting out this project. I can't wait to get it finished

You can probably use the two 15V transformers - the step to the 12V-version was just because a few people had too low a HT supply voltage.

So if you build it and it works (mine did), don't worry about it.

Jakob E.

Ok, thanks a lot for the quick reply!

Hi there,
Did anyone tried replace the two big HT capacitors with smaller values
like this : https://fr.rs-online.com/web/p/condensateurs-polypropylene/3779131/
Will it work ?
Can find a decent 100uF on RS or Mouser that's less than 30€ 

Yuy dont want polypropylene capacitors threre, but electrolytics. Expect prices in thr 2-euro range...

Jakob E.

Hi

Something happens on one channel of my G9,

The input signal seems to pass through the volume pot on which I have no control and sometimes the problem disapears if I  power off and on.

It doesn't seem to be a short circuit.

defaulting tube ?

Pierre

I recently tried running mixdowns through the line input of my G9 and really liked what it does to my mixes. One thing that bothers me however is the lack of low end. I know that it wouldn't be perfectly flat down to 20Hz, especially after reading this thread:
https://groupdiy.com/index.php?topic=9813.0
But just for reference I measured the frequency response and accidentally discovered something strange: the lower cut off frequency rises if the unit is on for some time!
In the attached image you can see measurements I made over a period of three hours, the corner frequency has gone up one octave!
Any idea what might be causing this?

Tube loosing emission?

Does heater voltage remain constant (12V), then it indicates a tube is bad. Probably output driver tube?

Jakob E.

gyraf said:

Tube loosing emission?

Does heater voltage remain constant (12V), then it indicates a tube is bad. Probably output driver tube?

Jakob E.

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Thanks for your reply!
I haven't checked voltages yet (I'm on vacation) but heater voltage might be a good hint. The second channel behaves more or less the same...

Using input transformer Lundahl 1538XL wired as 1:5

I cant see any hints, am i thinking right ?

https://drive.google.com/file/d/1SBRuhBfjInE3bXqZmKlyY6o9n6fjrl_7/view?usp=sharing

Looks good to me...

Jakob E.

Tack för att du tog dig tid Jakob !
Gott Nytt År !

Hi Mike.

I'm not sure what is happening but I didn't get your original email, or the one that you resent. It doesn't appear to be going to junk, so I'm not sure what is happening.  Can we try for the repair address again?  Is there a way to send a direct message to me or you to get the repair address?  Or a phone call?

Erik

Erik,

Shouldn't this have been in a PM (private message) perhaps?

Jakob E.

My mistake.  This went to the entirely wrong location.

hello do you remember what Lorlin switches you used ??  Thank you

Hi everyone!

Just finished the build, and i have a very noticeable difference between the two phases positions (on each channel), is that normal?

I would expect no difference as the source is mono and listened in solo...

Thanks!!

Hi all,

I'm working on a G9-alike pre (same preamp circuit), but the output is really weak. With both gains maxed, I'm getting about 43 dBv gain (~48mv in / ~6v out) from the first grid of V1 (input secondary) to the plate of V2 (output primary) . Is this low or in the ballpark?

--mark

Here is a sample, you can hear the difference between the two phases positions.

https://drive.google.com/file/d/1CUJUt4KjLNOJkN14U3IHjwOVNnr56aBy/view?usp=sharing

If you have any remarks or comments...

Thank you all!

I usually see some 55-58dB of gain in a G9, mic in to line out, all at max.

Jakob E.

mhuss said:

Hi all,

I'm working on a G9-alike pre (same preamp circuit), but the output is really weak. With both gains maxed, I'm getting about 43 dBv gain (~48mv in / ~6v out) from the first grid of V1 (input secondary) to the plate of V2 (output primary) . Is this low or in the ballpark?

--mark

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