#26 pre amp - Page 283

Bas Horneman · 21st March 2013, 07:49 PM

Quote:

CSS+shunt or shunt+CSS, thats what SSHV is.

CCS + shunt.

iko · 21st March 2013, 07:54 PM

Lots of them on ebay. I'd use two VR75 in series, because they have a beautiful orange glow.

The VR150 (0D3) has a soft purple glow. Also nice.

merlin el mago · 21st March 2013, 07:57 PM

Yes I see lots of them on ebay but where is a trust seller and what manufacture look for?
I don't have a lot of space just for two tubes rear the OPT so VR150 is my choice.

merlin el mago · 08:17 PM

Tomorrow I will do scope measurements, good night guys and thanks for all your support.

stajo · 21st March 2013, 08:15 PM

Make sure your realated to ground tonight, or you might fly. G'night

merlin el mago · 21st March 2013, 08:17 PM

I hope not dream with grounds

CV6045 · 21st March 2013, 11:49 PM

Try reversing the leads on the Filament to the 26 Tube...this should clear the Hum...if not try taking out the 2 X 22 ohm resistors and placing a (Humdinger) 100 ohms pot across the filament supply with the middle leg connected to the 2.2K Bias Resistor

amandarae · 22nd March 2013, 12:45 AM

Hello guys,

I have some questions if you do not mind.
My raw DC supply out of the filter is 19.4V (same for the other channel). When using umbilical to connect to main preamp, I get 14.4 V at the input of Rod Coleman regs. With the 26 tube and 10 ohm connected (pin 4 is + of the filament regulator, then tube, then pin1 to 10 ohm resistor then negative of the regulator then to 0V system ground), I get 1.15 volts across the filament of the 26 tube(pin 1 and 4), 8.52V across 10 ohm resistor.

At this point, I cannot adjust the filament current anymore using the pot on the board (also true with the other channel). I am wondering why?

I tested the regulators, with the heatsinks of course, and I can adjust the current to about 1.47Amps. Supply is 12 vrms through CLC connected to SUPPLY of RC regulators, then filament reg out connected to a 50W 1.5 ohm resistor.

What could be my problem?

regards,

Abe

iko · 22nd March 2013, 12:56 AM

Most likely the voltage drops under the 2A load. Save everyone time and show us a drawing of your filament supply, with details and measurements on the drawing.

Oh yeah, another possibility is that the regulators are oscillating.

amandarae · 22nd March 2013, 01:19 AM

Iko,

Thanks! I think I figured it out. I tested the regulators with 18 Vrms(24 Vdc) trafo, not 12 Vrms(14Vdc). With ~4Vdc filament board drop, there is no way I will get 10V to the 10 ohm cathode resistor using the 12Vrms trafo.

Let me change the trafo first to what I have on my PSUD schematic. I don't know why I got the 12V trafo in there and I will report back. And if I do, I will have the schematic and measurements included.

regards,
Abe

21st March 2013, 08:13 PM	#2824
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Catalonia new Europe state	Tomorrow I will do scope measurements, good night guys and thanks for all your support. Last edited by merlin el mago; 21st March 2013 at 08:17 PM.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

21st March 2013, 07:54 PM	#2822
iko diyAudio Moderator Join Date: May 2008 Location: Toronto	Lots of them on ebay. I'd use two VR75 in series, because they have a beautiful orange glow. The VR150 (0D3) has a soft purple glow. Also nice.

21st March 2013, 07:57 PM	#2823
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Catalonia new Europe state	Yes I see lots of them on ebay but where is a trust seller and what manufacture look for? I don't have a lot of space just for two tubes rear the OPT so VR150 is my choice.

21st March 2013, 08:15 PM	#2825
stajo diyAudio Member Join Date: Jun 2011 Location: Stockholm	Make sure your realated to ground tonight, or you might fly. G'night

21st March 2013, 08:17 PM	#2826
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Catalonia new Europe state	I hope not dream with grounds

21st March 2013, 11:49 PM	#2827
CV6045 diyAudio Member Join Date: Mar 2013 Location: Portsmouth	Try reversing the leads on the Filament to the 26 Tube...this should clear the Hum...if not try taking out the 2 X 22 ohm resistors and placing a (Humdinger) 100 ohms pot across the filament supply with the middle leg connected to the 2.2K Bias Resistor

22nd March 2013, 12:45 AM	#2828
amandarae diyAudio Member Join Date: Oct 2004 Location: Diamond Bar, CA	Hello guys, I have some questions if you do not mind. My raw DC supply out of the filter is 19.4V (same for the other channel). When using umbilical to connect to main preamp, I get 14.4 V at the input of Rod Coleman regs. With the 26 tube and 10 ohm connected (pin 4 is + of the filament regulator, then tube, then pin1 to 10 ohm resistor then negative of the regulator then to 0V system ground), I get 1.15 volts across the filament of the 26 tube(pin 1 and 4), 8.52V across 10 ohm resistor. At this point, I cannot adjust the filament current anymore using the pot on the board (also true with the other channel). I am wondering why? I tested the regulators, with the heatsinks of course, and I can adjust the current to about 1.47Amps. Supply is 12 vrms through CLC connected to SUPPLY of RC regulators, then filament reg out connected to a 50W 1.5 ohm resistor. What could be my problem? regards, Abe

22nd March 2013, 12:56 AM	#2829
iko diyAudio Moderator Join Date: May 2008 Location: Toronto	Most likely the voltage drops under the 2A load. Save everyone time and show us a drawing of your filament supply, with details and measurements on the drawing. Oh yeah, another possibility is that the regulators are oscillating.

22nd March 2013, 01:19 AM	#2830
amandarae diyAudio Member Join Date: Oct 2004 Location: Diamond Bar, CA	Iko, Thanks! I think I figured it out. I tested the regulators with 18 Vrms(24 Vdc) trafo, not 12 Vrms(14Vdc). With ~4Vdc filament board drop, there is no way I will get 10V to the 10 ohm cathode resistor using the 12Vrms trafo. Let me change the trafo first to what I have on my PSUD schematic. I don't know why I got the 12V trafo in there and I will report back. And if I do, I will have the schematic and measurements included. regards, Abe