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Another 12B4 Beginner's Build

Here is my BOM so far. How does it look? I want to use better power resistors with a lower tolerance but from either mouser or tubesandmore (to cut shipping costs).
 

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Looks good. Power supply resistors don't need to be exact. You can just use the 500ohm 10watt ones they have available instead of seriesing two to get 470.

Don't forget the DN2540N5 (689-DN2540N5-G) and the DN3545N3 (689-DN3545N3-G) from mouser, as well as trimmer potentiometers for fine tuning. ...And any low power resistors and a volume pot if you need one too.
 
Cool, I am still working on the BOM, I just wanted to be sure I was on the right track. Are there any other wattage requirements on the other unmarked resistors?
 
Looks like your almost ready to order.:thmbsp:

For the 100ohm resistors that go from heater to ground, they only need to be 1/2watt, and you can get them from mouser.

I'm assuming you want stereo, so for everything below "12B4 Circuit" and "mouser.com," you'll need to double in qty, except for the dual potentiometer.

Good to get spare DN2540 and DN3545 if you can too.

Mouser also has cheaper 100uF, 450V electrolytic capacitors if you don't mind the radial lead variety (like this one: 140-LS101M2W-2235-RC).

You'll probably also need to get some of these (P-0401H03 from AES), one or two packs should do. They will help immensely in point to point wiring.
 
OK, great. I will update further my BOM and document this whole process, perhaps leading up to a webpage detailing the entire thing so that other beginners can learn from my mistakes and have at it themselves!
 
How does one determine the value required for the coupling cap? I just picked 4.7uF arbitrarily since I figure it is a bit larger and its sole purpose is to block DC. I assume this will just require me to wait a couple of extra minutes before powering up the power amp (or flipping the standby switch off, depending on how I build this).

One other question, should I worry about bypassing any of the caps?
 
The Reverend said:
How does one determine the value required for the coupling cap? I just picked 4.7uF arbitrarily since I figure it is a bit larger and its sole purpose is to block DC. I assume this will just require me to wait a couple of extra minutes before powering up the power amp (or flipping the standby switch off, depending on how I build this).

One other question, should I worry about bypassing any of the caps?
Click to expand...

hey-Hey!!!,
There is a simple sol'n to the pop issue. A SPDT switch. Close it for mute, and open it( 'OFF' position ), to run. It shorts the outputs during start up. No pop is going to get through one of those.

A 330VAC/5 uF oil cap is a *FINE* coupling cap. Do take care to insulate its case from signal/chassis ground. There is capacitance from both terminals to the case. Putting what amounts to another cap in series with it( the insulation ), makes it smaller and bleeds less music.

I have also used high-current dry caps, the Vishay 735P for one works well, and with no metal case offers no cap to ground.
cheers,
Douglas
 
The Reverend said:
How does one determine the value required for the coupling cap? I just picked 4.7uF arbitrarily since I figure it is a bit larger and its sole purpose is to block DC. I assume this will just require me to wait a couple of extra minutes before powering up the power amp (or flipping the standby switch off, depending on how I build this).

One other question, should I worry about bypassing any of the caps?
Click to expand...

For quick and dirty determination of output caps, use a standard RC filter high-pass equation: Coutput = 1/(2*pi*fc*Rload). Use a standard fc of 5-10Hz or so and find out what your lowest load you'll ever drive is. Standard SS gear is typically 10k at the lowest. Tube gear is much higher. With a load of 10k and fc=5Hz, Coutput = 3.2uF, so 4.7uF will work.

For this circuit, you probably won't have to worry much about bypassing caps, might be something to try later, but probly wont have much of an impact here.

edit: whoops, just saw you posted Douglas, all good stuff
 
PakProtector said:
hey-Hey!!!,
There is a simple sol'n to the pop issue. A SPDT switch. Close it for mute, and open it( 'OFF' position ), to run. It shorts the outputs during start up. No pop is going to get through one of those.

A 330VAC/5 uF oil cap is a *FINE* coupling cap. Do take care to insulate its case from signal/chassis ground. There is capacitance from both terminals to the case. Putting what amounts to another cap in series with it( the insulation ), makes it smaller and bleeds less music.

I have also used high-current dry caps, the Vishay 735P for one works well, and with no metal case offers no cap to ground.
cheers,
Douglas
Click to expand...

About the SPDT switch, I am not really clear on how to wire it like this. It has three terminals, but I never really have understood exactly how to use all three.

Will the cheap Solens do the trick for coupling caps now?

Finally, is e-bay the best source for the 12B4?
 
The Reverend said:
About the SPDT switch, I am not really clear on how to wire it like this. It has three terminals, but I never really have understood exactly how to use all three.

Will the cheap Solens do the trick for coupling caps now?

Finally, is e-bay the best source for the 12B4?
Click to expand...

OOOOOPS, damn, I meant DPST, two sets of switches, ON or OFF for both.

The Solen will work just fine, but there are better caps at comparable price. get it running, then play with it. Just be careful with the soldering iron, a slight brush can be quite damaging.

I'd go to Radio Electric Supply for the 12B4's. GE's are quite nice, and have given me good service.
cheers,
Douglas
 
PakProtector said:
OOOOOPS, damn, I meant DPST, two sets of switches, ON or OFF for both.

The Solen will work just fine, but there are better caps at comparable price. get it running, then play with it. Just be careful with the soldering iron, a slight brush can be quite damaging.

I'd go to Radio Electric Supply for the 12B4's. GE's are quite nice, and have given me good service.
cheers,
Douglas
Click to expand...

OK, so now I understand. If I use the DPST, I hook the hot to one pole and the output to the other, so that when it is open it is muted and off, and when it closes it is unmuted and on. That seems like it would only mute the output when the amp is off. I guess this isn't really what your description says, but for some reason it just doesn't make sense to me, but when I read yours it sounded like it was saying that the inputs will be muted while the hot is connected and unmuted when the hot is disconnected, and that seems like it means that if the amp is on the outputs are off, so I am a little bit confused about it.

If that was too confusing what I mean is that when the switch is set to 1, the hot will be 1 and the out will be 1. When the switch is 0, the hot will be 0 and the out will be 0. Your scheme sounds like it is saying that when the switch is 1, the hot is 1 and the out is 0. When the switch is 0, the hot is 0 and the out is 1. Thinking about it now, I am not sure that is even possible with a DPST, maybe with two of them or some sort of DPDT... hmmmm.

Perhaps I should save a few more pennies for caps, or maybe I will just hold off until later. I looked at the Vishay caps you recommended but they were pretty expensive! Where should I look for oil caps?

I will look at Radio Electric Supply, sounds like a great plan.

Thanks!
 
The Reverend said:
OK, so now I understand. If I use the DPST, I hook the hot to one pole and the output to the other, so that when it is open it is muted and off, and when it closes it is unmuted and on. That seems like it would only mute the output when the amp is off. I guess this isn't really what your description says, but for some reason it just doesn't make sense to me, but when I read yours it sounded like it was saying that the inputs will be muted while the hot is connected and unmuted when the hot is disconnected, and that seems like it means that if the amp is on the outputs are off, so I am a little bit confused about it.

If that was too confusing what I mean is that when the switch is set to 1, the hot will be 1 and the out will be 1. When the switch is 0, the hot will be 0 and the out will be 0. Your scheme sounds like it is saying that when the switch is 1, the hot is 1 and the out is 0. When the switch is 0, the hot is 0 and the out is 1. Thinking about it now, I am not sure that is even possible with a DPST, maybe with two of them or some sort of DPDT... hmmmm.

Perhaps I should save a few more pennies for caps, or maybe I will just hold off until later. I looked at the Vishay caps you recommended but they were pretty expensive! Where should I look for oil caps?

I will look at Radio Electric Supply, sounds like a great plan.

Thanks!
Click to expand...

The Vishay I got was more 'spnsive than an ASC oiler from Allied. Space was a major issue, and I felt like experimenting. I think the part number starts with X387. 330VAC/5 uF will do well.

For the DPST, look at it this way: with the four contacts facing you and the switch upside down, put the pole pairs horizontaly; one set on top of the other. Vertically tie two together and attach that node to ground. The other two each get a hot, one right and one left. Switch open, and the amp will pass signal. Switch them closed, and you put a short circuit in parallel with the output and the amp won't pass signal.
cheers,
Douglas
 
Oh, I see why I am getting confused, you are talking about having two switches. One for power, one for muting. Right?

So what that is doing is sending the output to ground when the switch is closed, right? Where should I jumper the wire to the switch? Right before the RCA, correct?
 
Nevermind about the switching, it all makes perfect sense to me now.

Douglas, do you ever display the diodes for an additional light show?
 
The Reverend said:
Nevermind about the switching, it all makes perfect sense to me now.

Douglas, do you ever display the diodes for an additional light show?
Click to expand...

hey-Hey!!!,
I usually just hang the strip of perf board I mount them on somewhere underneath. By the time I have cut all the holes needed for the rest of the tubes, I am waaaaay to impatient to get to the wiring and assembly. Not saying it is a bad idea though...:) I may do something like that when next I build. The phono pre I have in mind will run LED bias( single red LED ). One poking through the plate next to the first tube stage would be pretty cool I think.
cheers,
Douglas
 
The Reverend said:
is e-bay the best source for the 12B4?
Click to expand...

AES has them for $6, doesn't have a description though. You can call them to see if they are new, but I'm pretty sure they wouldn't sell bad tubes. Ask about matching, because parameters on the 12B4, from what I've heard and one's I've tested, can vary a lot. Prices for these have been steadily rising on ebay due to the efforts of people like us, so that $6 tag isn't too bad now, and you don't have to pay extra shipping if you get it with your other order. You can sometimes get a bargain on ebay with these though, as it is not a huge buzz tube type.
 
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