Taking a little break from debugging my simple 12b4 linestage, coffeedj helped me to discover noise from the dc heater supply, i switched to ac and the noise went, not totally quiet though.
I grounded one leg of the 6.3ac in the psu through a 100R resistor. This worked, but i was in search of total silence. I then grounded both legs through 50R resistors to the single 100R and then to ground, a small amount of noise and hum came back....
So i just lived with it, desperate for an evening of listening to music. I think I'll go back to looking at the dc heater method, maybe later in the week.
In the meantime i would like some advice on where to purchase the rubber 'O' rings to reduce microphoics. I have an elma stepped attenuator, that is quite stiff and causes microphonis when turned....
I live in the UK, do i buy normal O rings? which size will fit snuggly?
cheers stuart
I grounded one leg of the 6.3ac in the psu through a 100R resistor. This worked, but i was in search of total silence. I then grounded both legs through 50R resistors to the single 100R and then to ground, a small amount of noise and hum came back....
So i just lived with it, desperate for an evening of listening to music. I think I'll go back to looking at the dc heater method, maybe later in the week.
In the meantime i would like some advice on where to purchase the rubber 'O' rings to reduce microphoics. I have an elma stepped attenuator, that is quite stiff and causes microphonis when turned....
I live in the UK, do i buy normal O rings? which size will fit snuggly?
cheers stuart
surfstu said:
look at post No.151
use LM 317 as CCS and elevate heater PSU ( right after Graetz) to ~50V above cathode potential
each tube own CCS for heating .
Salas said:
Teresonics claim is 103dB (not 104--my mistake) with the DX4 driver. I know that their speaker is quite a bit more sensitive than my Medallion II w/ Lowther PM2As, which rate at about 101db. Anyway I accepted their claim as reasonable, although I haven't actually measured it myself.
I still wonder why I have no hiss at all. Hiss is fairly broadband above a certain point, so I should hear it if there was a problem. Also, my Sennheiser HD 650's are rated to 39KHz, so they should definately reveal any hiss.
A little later this week I'm going to go through different 12B4's to see what the results are. I have a few hundred, so I should get a fairly representative sampling.
Good tubes, layout, well starved heaters, it looks like you got it nailed.
DX4 is 99.5dB nominal again. There is a bump at around 10kHz where it gets hotter. Maybe they swell the midbass with the horn also and they quote the peak level bands.
DX4 is 99.5dB nominal again. There is a bump at around 10kHz where it gets hotter. Maybe they swell the midbass with the horn also and they quote the peak level bands.
Hi,
it is very painful building a line amp with 12B4A's :-(
I think i solved the problem; it was/is the 12B4a itself.
I own 40 NOS pieces 12B4A.
10* JAN made by GE
20* Sylvania red and yellow label
10* KR's, RCA's; GE's
Out of this bunch 80% have problems with mircophonic and hissing like hell (most likely both!) ; 20% are O.K, but out of them there is a huge variation in terms of operating point
(i build up a matching device, with CCS which gives 90V @ anode and 500 Ohm @ cathode; matching can be done with Ucathode and scope)
So; this means that out of 40 pieces; i could maximal use one or two pairs 🙂
...i should go for a 6H30 (2 triode systems in parallel) anode choke loaded 🙂
KR
Hauke
it is very painful building a line amp with 12B4A's :-(
I think i solved the problem; it was/is the 12B4a itself.
I own 40 NOS pieces 12B4A.
10* JAN made by GE
20* Sylvania red and yellow label
10* KR's, RCA's; GE's
Out of this bunch 80% have problems with mircophonic and hissing like hell (most likely both!) ; 20% are O.K, but out of them there is a huge variation in terms of operating point
(i build up a matching device, with CCS which gives 90V @ anode and 500 Ohm @ cathode; matching can be done with Ucathode and scope)
So; this means that out of 40 pieces; i could maximal use one or two pairs 🙂
...i should go for a 6H30 (2 triode systems in parallel) anode choke loaded 🙂
KR
Hauke
barossi said:Hi,
it is very painful building a line amp with 12B4A's :-(
I think i solved the problem; it was/is the 12B4a itself.
I own 40 NOS pieces 12B4A.
10* JAN made by GE
20* Sylvania red and yellow label
10* KR's, RCA's; GE's
Out of this bunch 80% have problems with mircophonic and hissing like hell (most likely both!) ; 20% are O.K, but out of them there is a huge variation in terms of operating point
(i build up a matching device, with CCS which gives 90V @ anode and 500 Ohm @ cathode; matching can be done with Ucathode and scope)
So; this means that out of 40 pieces; i could maximal use one or two pairs 🙂
...i should go for a 6H30 (2 triode systems in parallel) anode choke loaded 🙂
KR
Hauke
WOW. I'm going to check my stash and report as well. Makes me think the 6CG7 might be a better choice--except you lose the low impedance output and direct headphone connection.
A triode wired EL86 is very very close to the same specs as the 12B4,
they will run at the same parameters as the 12B4, also quite a few of
the pins are the same, if you've allready built a 12B4 pre and are having
noise/matching problems before going batty may just want to give EL86
a listen, they are quite nice sounding tubes and relatively inexpensive... 🙂
Cheers!
they will run at the same parameters as the 12B4, also quite a few of
the pins are the same, if you've allready built a 12B4 pre and are having
noise/matching problems before going batty may just want to give EL86
a listen, they are quite nice sounding tubes and relatively inexpensive... 🙂
Cheers!
120v on the plates and 25ma of current they will run just fine in a preamp.
I've used them at those settings quite a few times for drivers, even swap
them back an forth in the same stage with a 12B4..
There is nothing that says you can't run them lower then they can take. 🙂
I've used them at those settings quite a few times for drivers, even swap
them back an forth in the same stage with a 12B4..
There is nothing that says you can't run them lower then they can take. 🙂
triode strapped pentodes
I notice the 6AK5 listed here. This is the basic dumpster tube--millions of them out there and no one wants to buy it.
Has anyone tried the 6AK5? Specs look good.
I notice the 6AK5 listed here. This is the basic dumpster tube--millions of them out there and no one wants to buy it.
Has anyone tried the 6AK5? Specs look good.
coffeedj,
Not triode strapped, but I love them as a pentode driver. Yamamoto use them in pentode mode in their CA-4 linestage.
http://www.positive-feedback.com/Issue17/yamamotoca04.htm
Not triode strapped, but I love them as a pentode driver. Yamamoto use them in pentode mode in their CA-4 linestage.
http://www.positive-feedback.com/Issue17/yamamotoca04.htm
ok, i have not given up on this linestage yet but I have ordered some ecl86 valves, one is mullard yellow print, and the other is mullard white print. I bought these as i was unable to find 12b4 in the the UK and i just want to test my linestage for hiss. I have two 12b4's in the linestage at present and both channels have hiss, I am using ac heaters as dc heater produced more hiss..... so i have finally decided to swap valves to see if hiss is still present, can i just swap the 12b4's for ecl86?
my linestage can be found here
http://www.diyaudio.com/forums/showthread.php?postid=1825602#post1825602
cheers stuart
my linestage can be found here
http://www.diyaudio.com/forums/showthread.php?postid=1825602#post1825602
cheers stuart
12B4 Hiss
I want to figure out why I have absolutely no hiss so I'm going to check my stash and report to the group. It has been a little slow for me since I'm still recovering from a fairly serious head injury and broken ribs, but I hope to get it done this week. I have about 200 12B4's, so I should be able to get a representative sample.
I want to figure out why I have absolutely no hiss so I'm going to check my stash and report to the group. It has been a little slow for me since I'm still recovering from a fairly serious head injury and broken ribs, but I hope to get it done this week. I have about 200 12B4's, so I should be able to get a representative sample.
Me too.No hiss at all,but I have to admit it's a difficult tube to work with.IMHO it's worth the effort.
yes, i can hear that it is worth the effort, maybe i have dirty mains supply hear in the UK. The hiss i get is low volume but i can hear it from anywhere in the room and it is constant. And every now and again i get an even louder hiss for a minute or so, it reminds me of a gentle breeze that blows every 10 minutes or so on an otherwise relatively calm day!
wishing you a speedy recovery coffeedj.
stu
wishing you a speedy recovery coffeedj.
stu
Hi, I'm very new to tube DIY, although I have finished a 6SN7 SRPP preamp but it's a kit using PCB, very easy.
Now I just want to build 12B4 pre by myself, start with the simplest, my first question is, the transformer I have (came with 6SN7 kit) has 0-100-200 60MA, 0-6.3-12.6 2A, is it sufficient?
If the answer is yes, can someone suggest me a PSU? again I want to keep it simple, just CRC or CRCRC, but I have no idea how to calculate those Rs.
Thanks
Now I just want to build 12B4 pre by myself, start with the simplest, my first question is, the transformer I have (came with 6SN7 kit) has 0-100-200 60MA, 0-6.3-12.6 2A, is it sufficient?
If the answer is yes, can someone suggest me a PSU? again I want to keep it simple, just CRC or CRCRC, but I have no idea how to calculate those Rs.
Thanks
hi albrerta,
i probably know less about valves than anyone else here, but i think that you may need a slightly more powerful transformer, i used 100mA, however my 12b4 is drawing 21mA per channel but i beleive the heaters are drawing some too
please take my advice with a pinch of salt,
coffedj:
how is the recovery going? hope you're well, still waiting to here about the tube rolling tests,
stuart
i probably know less about valves than anyone else here, but i think that you may need a slightly more powerful transformer, i used 100mA, however my 12b4 is drawing 21mA per channel but i beleive the heaters are drawing some too
please take my advice with a pinch of salt,
coffedj:
how is the recovery going? hope you're well, still waiting to here about the tube rolling tests,
stuart
surfstu said:
Thanks for asking--slowly getting better. It was a serious concussion and will take up to 6 mo to heal since I bruised my brain. My advice--don't do that!
I did get a chance to do some tube rolling, and discovered some interesting things. Before I started rolling the tubes I decided to fix my B+, which was just everso slightly low for the OD3's to strike reliably. I did this by replacing one of my chokes with a lower DCR choke, changing from a 5U4GB to a 5V4G, and adding an extra dropping resistor to set the OD3 current at 20ma.
All of a sudden I had a little hiss!! (and a tiny bit of hum). Not much, but enough hiss to notice in an ultra-quiet room. First I replaced the carbon comp 470 dropper with with a metal film--that helped a little, but I could still hear the hiss. Then I started playing with swapping 0D3's--other than finding an occasional noisy one, this didn't make much difference.
Next I started rolling 12B4's. What I found may be a little different than others, but mainly there is good agreement with what others have experienced. There is definately a difference in hiss levels between 12B4's, but the difference was not huge in my test--only a few dB. This was generally true except for the occasional very noisy 12B4--those tubes went to the dumpster. Microphonics on the other hand is a persistant problem. Some of the tubes sing, some ring, and about 1/2 are quiet enough that tube dampers do the job.
With respect to hiss and microphonics I found that my 50's vintage Sylvanias seemed to be the best, and the Raytheons seemed to be the worst. RCA and GE could be good, but generally had a little higher hiss that the Sylvania's. Unfortunately, I didn't have enough of the vintage Sly's to make a definate finding here--just noticed a trend. Bottom line--rolling tubes makes a difference, and there is a fair degree of variation in the 12B4 line. But, as was said--the effort is worth it. The only other thing I noticed is that the 12B4's take a fair length of time to warm up and quiet down. I had to wait up to 10 minutes sometimes for the 12B4 to stabilize.
That done I decided to go back and fix the slight hum I picked up from reducing my second stage choke. I had a small choke that replaced the 470ohm dropper nicely, so I put it in and went back for a listen. Hum was completely gone, but hiss was reduced back to my previous level as well! I could not hear it at all except for putting my ear in the speaker.
The conclusion is that some hiss is coming through the power supply. It appears that a LC stage just before the last dropper to the regulator tubes makes a difference. My final dropper between the regulator and LC stage is 470ohms--fairly small and thus the LC stage will definately have an effect on the AC bypass as well. This could also be part of the equation.
Finally, I pulled the LC stage, put the resistor dropper back in and started rolling rectifier tubes. Yep, it makes a difference--not huge, but it is there. Put the LC stage back in and verified that if did help reduce hiss.
I'd be interested in hearing from others that can verify or clarify these findings.
well, must say that i'm very pleased with the sound of the 12b4 linestage. I'm enjoying listening to it very much. However, I am ready to make improvements, and maybe finally try to rid myself of the hum and hiss ghost. Thanks for the comments as usual coffeedj, I have checked my tubes, they are Sylvanias, but how do i know if they are from the good stock? Mine come in a yellow and black box, which has 5Z printed inside, the tube has cf, and jcv printed on it.
But from reading your post i feel it may not definatley be the tubes. I have posted my linestage and psu schems on this thread often enough and wandered if you'd check them again with your new findings and maybe assertain if I may benefit from the regulator tubes or even a new choke in the psu or even a choke loaded plate?
All suggestions welcome as usual and maybe if you'd be happy to send some parts i'd be happy to pay,
cheers stuart
But from reading your post i feel it may not definatley be the tubes. I have posted my linestage and psu schems on this thread often enough and wandered if you'd check them again with your new findings and maybe assertain if I may benefit from the regulator tubes or even a new choke in the psu or even a choke loaded plate?
All suggestions welcome as usual and maybe if you'd be happy to send some parts i'd be happy to pay,
cheers stuart
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