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Another 12B4 Beginner's Build

Ok, I spoke with AES and he seemed somewhat bewildered that I would want a matched set of 12B4s. They are all NOS. Should I wait until I can find a matched pair, or just go ahead and order assuming all parameters to be the same?
 
The Reverend said:
Ok, I spoke with AES and he seemed somewhat bewildered that I would want a matched set of 12B4s. They are all NOS. Should I wait until I can find a matched pair, or just go ahead and order assuming all parameters to be the same?
Click to expand...


hey-Hey!!!,
I'd say that no match is needed. There isn't that much operational difference. These are SE voltage amps running side-by-side, not a circuit that depends on the performance of the element it is combined with.
cheers,
Douglas
 
PakProtector said:
hey-Hey!!!,
I'd say that no match is needed. There isn't that much operational difference. These are SE voltage amps running side-by-side, not a circuit that depends on the performance of the element it is combined with.
cheers,
Douglas
Click to expand...

ok, sounds good.:thmbsp: Reverend, I wasn't too sure of it, and since you were on a budget, I didn't want you to build it and then find out you needed more tubes. Douglas has the "been there, done that" advantage:D. This project is on my ever long 'to do' list.
 
Awesome, I will add those to my growing BOM. I will post it again for further refinement/review. It will probably be a few weeks until I order all the parts, and I will probably wait until I finish refining my SOHA project to start building this one (I will have to buy the parts or I will never build this!).

Thanks for the advice you all have given me so far!
 
I want to put this all on a somewhat compact chassis, perhaps similar to the Bottlehead Foreplay but shallower. I can build the wood panels, but how much real estate should I pay for in terms of aluminum?
 
Hello all,

I have a few salvaged parts I want to ask about. First off are some large enclosed power transformers that seem like they are nice, but I have no clue what the specs are at all. I don't know how to even begin to measure them without frying myself, so I figured I would ask here. They have no brand markings but they do have numbers of them, which I googled to no avail.

Next are some really large and pretty old tru-ohm wirewound resistors. The 500R would fit nicely into my PS, though at about 5 inches long it is a bit physically large! I am not sure if they are good to use, but at the size they are I am assuming they will be able to dissipate more than enough heat.

Thoughts?
 
The Reverend said:
I want to put this all on a somewhat compact chassis, perhaps similar to the Bottlehead Foreplay but shallower. I can build the wood panels, but how much real estate should I pay for in terms of aluminum?
Click to expand...

hey-Hey!!!,
One square foot at minimum. You're building a far better PS than the penny-pinched Foreplay, and you will find elbow room useful. My last pre went 10 x 18" and I used most of it...:) For the base, 1 x 4 should do quuite well. I have used Poplar from HD and Lowes. Sand and apply some linseed oil an' yer done.
cheers,
Douglas
 
OK, I will definitely keep that in mind. I guess I will wait until I get all of the parts and make a cardboard prototype of the layout and go from there. I still haven't ordered anything yet, but I am working on building up my headphone amp. I did build myself a nice little passive switchbox over the weekend, so that will help with this project. I also am planning to build a Hagerman bugle or something similar because I am currently without a phono stage since I am parting with the NAD I am using as my preamp.
 
Since this is about beginners asking questions about 12B4 circuits, can somebody please help me also?
I found this circuit,
12B4pre.gif


but am using a 300V B+ and a 10k resistor instead of the 8.5k and 0.47uF instead of 0.33uF on output (all I got for now)
I measure 40V on the anode (pin9) and 4.2V on the cathode (pin1).
The amp works very good, but I want to know if these voltages I am getting are correct (is it O.K. to be like that) and also, what is the anode current now (how do I calculate it?)
What is a better R value for my 10k, if I want to keep the 300V B+ ?
Thanx for all advice.

My PSU is from this circuit, exactly the same. I actually 1st build this amp, but was not happy with the sound:
6072%20copy.gif
 
jdev said:
Since this is about beginners asking questions about 12B4 circuits, can somebody please help me also?
I found this circuit,
12B4pre.gif


but am using a 300V B+ and a 10k resistor instead of the 8.5k and 0.47uF instead of 0.33uF on output (all I got for now)
I measure 40V on the anode (pin9) and 4.2V on the cathode (pin1).
The amp works very good, but I want to know if these voltages I am getting are correct (is it O.K. to be like that) and also, what is the anode current now (how do I calculate it?)
What is a better R value for my 10k, if I want to keep the 300V B+ ?
Thanx for all advice.

My PSU is from this circuit, exactly the same. I actually 1st build this amp, but was not happy with the sound:
6072%20copy.gif
Click to expand...

hey-Hey!!!,
To determine current, we use Ohm's Lay V=i*R, or i=V/R. You have 260V across a 10k resistor, looks like 26 mA to me...:) however, 4.2 V across a 500R cathode resistor is more like 8.4 mA...a serious difference. Can you confirm your measurements?

Your circuit is fine as it is, if the plate load resistor can stand the heat, run it. You get operation in the zone with minimum plate resistance.
cheers,
Douglas
 
Just an update on this project:

I found a nice old McIntosh C28 that is currently serving as my preamp, so I am just using that for now. Unfortunately the glass is broken (along with the MR73 I found), so I am going to put my money towards restoring these first. I am also finishing up my 12au7 headphone amplifier upgrade, so maybe in the not too distant future I can start the 12B4 amp and figure out which sounds nicer.
 
Hello,

I have a renewed interest in this project after digging up this thread! I was over at diyaudio.com and started to get the itch...

Anyway, maybe I will acquire some parts over the summer. I haven't had much cash lately, but I have been working hard (right now- hardly working). Anyway, I saw some designs with amps built inside of baking pans and I thought they looked surprisingly nice! If I actually get around to this I am going to do that for the sake of ease (I hate building enclosures but I also hate ugly ones).
 
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