pahstah

new g9 ht problems
« on: November 10, 2005, 06:24:10 PM »
hi,
i just finished my first g9 nd i took some quick measure:

12v and 48v are fine but on ht  i found only 220v (with tubes on).. and i don't have a clue (such a newestbie); what it could be? tl 783 or power caps?

paolo


[email protected]

new g9 ht problems
« Reply #1 on: November 10, 2005, 11:57:44 PM »
Paolo,

I am not an expert by any means on this, but I am having the same problem as you are having. These are some of the possible causes I have gathered/learned:
1. The transformer(s) you are using do not deliver enough current to make the step up from 15V to 230VAC when loaded by the tubes. Make shure you use at least 30VA transformers. (most likely cause)
2. The 100K 2W resistor goes funky when subjected to high voltages. Most resistors are not rated to operate at more than 200V. (more likely the cause)
3. There is a bad zener that clamps the output voltage. Zener are pretty tough though. (unlikely cause)
4. There is too much load caused by a component hanging off the HT rail such as a capacitor dying, but not dead yet.

Tamas

pahstah

new g9 ht problems
« Reply #2 on: November 11, 2005, 02:19:51 PM »
hi Tamas,

i've checked without tubes and i've foun:
ac voltage at transformer 220 v,  voltage at  c14 289v, and at c15 280v.. it seems like tl 783 doesn't  regulate..
when i put tubes in sockets all the voltages drop to 200v ac  and 220v dc...

paolo

[email protected]

new g9 ht problems
« Reply #3 on: November 11, 2005, 06:23:15 PM »
Quote from: "pahstah"
...ac voltage at transformer 220 v,  voltage at  c14 289v, and at c15 280v.. it seems like tl 783 doesn't  regulate..
paolo


Without some load (least a 5ma current draw) the TL783 will not regulate. Put at least two tubes in there when you test.

Jazzy_Pidjay

new g9 ht problems
« Reply #4 on: November 13, 2005, 05:58:21 PM »
i have the same "low" voltage !

HT about 208v when the 4 tubes are pluged in.

The two main trafo are 30VA

 :?:  :?:  :?:

 :roll:

alk509

new g9 ht problems
« Reply #5 on: November 13, 2005, 06:11:55 PM »
Quote from: "[email protected]"
Without some load (least a 5ma current draw) the TL783 will not regulate.


Actually, that's 15mA minimum for the 783.

Peace,
Al.

Lest laziness get the best of you!

Michael_Hartlieb

new g9 ht problems
« Reply #6 on: November 14, 2005, 06:44:14 AM »
Quote from: "Jazzy_Pidjay"
i have the same "low" voltage !

HT about 208v when the 4 tubes are pluged in.

The two main trafo are 30VA

 :?:  :?:  :?:

 :roll:


We have kind of the same problem: For testing purposes we used 12AX7 tubes on our G9 first, which should be at least pin compatible to 12AU7. It worked fine, HT voltage was about 250V.
After putting in the proper 12AU7 tubes, HT voltage dropped to 230V. It´s working fine nevertheless, so we don´t care really, but we´are interested in the background of this drop. Anyone?


Michael & Matthias

Edit: We´re using 30VA transformers also

gyraf

new g9 ht problems
« Reply #7 on: November 14, 2005, 07:48:56 AM »
It's because the 82's draw more current than the '83's.

Too low a supply voltage probably means that you'll have to use a lower-voltage second transformer.. that is, higher transformation ratio..

The reason is that different brand power transformers seems to behave different when used in step-up mode..

Jakob E.
..note to self: don't let Harman run your company..

moamps

new g9 ht problems
« Reply #8 on: November 14, 2005, 08:08:48 AM »
Quote from: "gyraf"

The reason is that different brand power transformers seems to behave different when used in step-up mode..


Yes.
The first aid is connecting the second 15Vcoil to the secondary side in series with two 110Vcoils. Also, if DC voltage on C14 is below 245V when the power supply is loaded, the regulator doesn't work. The good idea is in this case setting regulator (with R34) to smaller output voltage (ca 10V below voltage on C14).

Regards,
Milan

[email protected]

new g9 ht problems
« Reply #9 on: November 14, 2005, 11:13:54 AM »
The most common reason is insufficient AC from the step-up transformers. However, I was getting 270V after the rectifier under 20ma load and the output of the regulator was still only 210V. I found the 100K 2W resistor changing its value about 10% when current was going through it.


Jazzy_Pidjay

new g9 ht problems
« Reply #10 on: November 14, 2005, 12:16:26 PM »
how many current is necessary
for the four heaters of the 12AU7's ??
1A ? 2a ?

the 78s12 can be a possible cause of
the problem ? or definitively not ?

mcs

new g9 ht problems
« Reply #11 on: November 14, 2005, 12:41:24 PM »
The four heaters (or eight actually) need 1.2A. The 78S12 has nothing to do with the low B+ voltage.

[edit]A small correction. The heaters are run on 12V, so they only need 600mA[/edit]

Best regards,

Mikkel C. Simonsen

Jazzy_Pidjay

new g9 ht problems
« Reply #12 on: November 14, 2005, 12:42:31 PM »
ok  :thumb:

Jazzy_Pidjay

new g9 ht problems
« Reply #13 on: November 15, 2005, 03:40:55 PM »
another question...

is this lower voltage affect the overall sound of the pre ?

i have only 208vHT (normally 245v)
and only 11,5v for the heater (ideally 12,6v)

of course my G9 sound beautiful
but maybe it can sound better with proper voltages

thanks  :thumb:

caps

new g9 ht problems
« Reply #14 on: November 15, 2005, 10:30:31 PM »
Quote from: "Jazzy_Pidjay"
another question...

is this lower voltage affect the overall sound of the pre ?

i have only 208vHT (normally 245v)
and only 11,5v for the heater (ideally 12,6v)

of course my G9 sound beautiful
but maybe it can sound better with proper voltages

thanks  :thumb:


Someone please correct me if im wrong....

But I think it would only affect the gain available, not the sonics ?

CJ

new g9 ht problems
« Reply #15 on: November 15, 2005, 10:51:01 PM »
Sometimes the sonics change too. Don't ask me why. If I remember right, the higher the plate supply, the more "trebly". I would not bet on hearing a major diff from 208 to 245, maybe from 150 to 245 would be discearnable.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Jazzy_Pidjay

new g9 ht problems
« Reply #16 on: November 16, 2005, 05:41:48 AM »
ok thanks for the infos  :thumb:

gyraf

new g9 ht problems
« Reply #17 on: November 16, 2005, 05:53:15 AM »
Quote from: "CJ"
I would not bet on hearing a major diff from 208 to 245, maybe from 150 to 245 would be discearnable.


I agree completely..

Jakob E.
..note to self: don't let Harman run your company..

Michael_Hartlieb

new g9 ht problems
« Reply #18 on: November 16, 2005, 06:12:29 AM »
Thanks, too!

This forum is just great...

Michael

Jazzy_Pidjay

new g9 ht problems
« Reply #19 on: November 16, 2005, 06:25:35 AM »
:thumb:

the best place on the web !!


 

Related Topics

  Subject / Started by Replies Last post
10 Replies
1917 Views
Last post October 26, 2004, 12:35:39 PM
by Gus
4 Replies
1582 Views
Last post November 13, 2004, 10:51:40 AM
by Adky
5 Replies
1652 Views
Last post November 16, 2004, 12:00:47 PM
by Gus
5 Replies
1253 Views
Last post April 04, 2011, 03:03:21 AM
by abechap024