motherone said:
Yes. Thanks Motherone. I picked off 4 yesterday.
Does anyone know if these can be mounted horizontally?
Best,
Paul
I also sent for 6 0D3's
Thanks for the link mother1
Fair Radio may have some more JAN 12B4A's.
LLyndy, thanks for the leg work on the transformer from Edcor.
Thanks for the link mother1
Fair Radio may have some more JAN 12B4A's.
LLyndy, thanks for the leg work on the transformer from Edcor.
No problem, Ed.
I am just bummed because UPS ground says they will deliver the custom transformer this coming Wednesday, when my school is closed.
I was hoping to put this all together with Mark's help over the holiday weekend.
Also, give thanks to George (Tubelab.com) who was the original guy trying out the Edcor transformers in various projects.
I can't wait to put this together with that Danish volume remote control. Mark says it is the bee's knees!
Lyndon
I am just bummed because UPS ground says they will deliver the custom transformer this coming Wednesday, when my school is closed.
I was hoping to put this all together with Mark's help over the holiday weekend.
Also, give thanks to George (Tubelab.com) who was the original guy trying out the Edcor transformers in various projects.
I can't wait to put this together with that Danish volume remote control. Mark says it is the bee's knees!
Lyndon
Glad I could help -- I also want to send a thanks to Mark for the project, and Lyndy for the heads up on those Edcor transformers. I'll definitely pick one of those up for the project!
Geek said:
I see what you mean... How many of what types of LEDs did you use?
Anyway, I am currently using plate chokes, and CCS in cathode, bypassed with 470uf. Can I try LEDs in cathode unbypassed? (or bypassed by 50uf as Shoog mentioned in an earlier post?) How many LEDs and which types should I use?
thanks!! 🙂
pengboon said:
A series of 7 parallel pairs (14 total) of generic, 3mm red LED's for 20mA current. For 30mA, use a series of 5 parallel trio's (15 total).
Here's the schematic of the one I used...
pengboon said:
Sure! Just grab a bag of a zillion-for-a-buck from Ebay 😉
If you bypass them with a cap, just use a zener or a resistor, because you've practically made moot the advantage of LED's, which is to eliminate the bypass cap and its inherent distortion.
Geek said:
Thanks Geek! Will try that this weekend. How do you determine how many series LEDs to use? I have 150V as B+ befoe the plate chokes and about 108V on the 12B4 plate (IIRC). Is the main advantage of LED over that of CCS that of eliminating the bypass cap yet still somewhat a constant current?
The post about bypassing with 50uf is here:
http://www.diyaudio.com/forums/showthread.php?s=&postid=980525&highlight=#post980525
Hi Ryssen,
No. But if you bypass a CCS with a cap, you ruin the PSRR. As for the effects of a CCS with a 12B4, see my post here #545.
From the plate curves. Determine the voltage needed for the tube to operate at the specific point, then calculate how many LED's based on the voltage drop of the particular ones you are using. The red ones I use have a voltage drop of 1.75V each with any current above 6mA.
LED's don't give constant current at all, but constant voltage with low internal resistance. The opposite of a CCS. It's like having the cathode tied to ground AC wise, but at proper bias DC wise, without a bypass cap. As long as the tube stays in class A1, no problem (the LED's won't cutoff).
Cheers!
Ryssen said:
No. But if you bypass a CCS with a cap, you ruin the PSRR. As for the effects of a CCS with a 12B4, see my post here #545.
pengboon said:
From the plate curves. Determine the voltage needed for the tube to operate at the specific point, then calculate how many LED's based on the voltage drop of the particular ones you are using. The red ones I use have a voltage drop of 1.75V each with any current above 6mA.
pengboon said:
LED's don't give constant current at all, but constant voltage with low internal resistance. The opposite of a CCS. It's like having the cathode tied to ground AC wise, but at proper bias DC wise, without a bypass cap. As long as the tube stays in class A1, no problem (the LED's won't cutoff).
Cheers!
Geek said:
Geek, thanks for your explaination, I think I understand now.
From the curves, for 30mA, and 5x1.75 negative grid voltage, I get about 90V plate-cathode. So actual plate voltage will be ~99V. So perhaps I need 6 series trio instead for my ~110V to maintain 30mA?
Hi Pengboon,
Give it a try. Have an analog current meter inline and see what it gives you.
I experimented with a sleeve of 5 12B4's, three different manufacturers, NOS and used mix - each were different slightly, but within 20%.
Give it a try. Have an analog current meter inline and see what it gives you.
I experimented with a sleeve of 5 12B4's, three different manufacturers, NOS and used mix - each were different slightly, but within 20%.
OK thanks Geek,
one more question if you don't mind. I've shortlisted 3 LEDs from Farnell (1045471 and 1045472), can you help to assess the suitability of them before I order? They look the same to me, except for clear vs red tint and brightness? 🙂
one more question if you don't mind. I've shortlisted 3 LEDs from Farnell (1045471 and 1045472), can you help to assess the suitability of them before I order? They look the same to me, except for clear vs red tint and brightness? 🙂
Hi Pengboon,
Your 5 stacks of LED pairs will give you roughly < 9V. That's the same thing I am doing (I idolize SY's red light, I want a mini one) on a small PCB which will replace the 317 CCS I currently have which yields approximately 9V.
However, prior experience tells me that it's not really 1.75 but more like 1.5 so I have a stack of 6. My GE 12B4 pair are close in bias fortunately.
It's cool looking when everything's lighting up. 😀
But why Farnell? They're expensive for an LED. I buy mine from a local electronics store and they're at less than half in price compared to that of Farnell or RS Components.
Your 5 stacks of LED pairs will give you roughly < 9V. That's the same thing I am doing (I idolize SY's red light, I want a mini one) on a small PCB which will replace the 317 CCS I currently have which yields approximately 9V.
However, prior experience tells me that it's not really 1.75 but more like 1.5 so I have a stack of 6. My GE 12B4 pair are close in bias fortunately.
It's cool looking when everything's lighting up. 😀
But why Farnell? They're expensive for an LED. I buy mine from a local electronics store and they're at less than half in price compared to that of Farnell or RS Components.
Hi Arnoldc,
OK, will try the local electronics store first! 🙂 on my way to lighting up for Christmas!
OK, will try the local electronics store first! 🙂 on my way to lighting up for Christmas!
Just a heads up for those of you who bought the OD3's on Ebay. Mine arrived today, and they're mint NOS just as was stated, so hopefully everyone else's will arrive safely!
Can't wait to get these suckers lit up and regulatin' 😀
Can't wait to get these suckers lit up and regulatin' 😀
Hi Arnold,
They're all going to be slightly different, even from lot to lot within same mfr. and part #.
Best to test each set individually 🙂
arnoldc said:
They're all going to be slightly different, even from lot to lot within same mfr. and part #.
Best to test each set individually 🙂
