I would consider using two separate power supplies on one chassis, or mono blocks if you've got two chassis. That'll give you 300V+ at 140ma, certainly enough for many SE designs, with excellent channel separation.
Stick to SS rectification with 250-0-250 secondaries, as tube rectification will drop too many volts. SS rectification is also cheaper and easier and yields a lower output impedance supply which is a good thing.
Stick to SS rectification with 250-0-250 secondaries, as tube rectification will drop too many volts. SS rectification is also cheaper and easier and yields a lower output impedance supply which is a good thing.
Good news and bad news.
Good - found some nice caps
(2) - 90uF 500WV
(2) - 40uF 450WV
Bad - lower current rating on transformers
They are really 250-0-250 CT@40mA and 6.3V@2A
I also found a military 20H 50mA 425Ohm Choke.
I also found (2) OT's - Primary: C, 2.5W, 1.25W, .0625W, 5W, 10W. Secondary: C, 4Ohm, 8Ohm.
Not sure what the primaries mean by wattages..
Good - found some nice caps
(2) - 90uF 500WV
(2) - 40uF 450WV
Bad - lower current rating on transformers
They are really 250-0-250 CT@40mA and 6.3V@2A
I also found a military 20H 50mA 425Ohm Choke.
An externally hosted image should be here but it was not working when we last tested it.
I also found (2) OT's - Primary: C, 2.5W, 1.25W, .0625W, 5W, 10W. Secondary: C, 4Ohm, 8Ohm.
Not sure what the primaries mean by wattages..
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I've done some research and some math.
Heaters:
(2) EL34s take 1.5A
(1) ECC81 takes 300mA
=1.8A, which is less than the 4A available.
Plate:
The nominal plate current for class A was said to be:
(2) EL34s take 200mA
(1) ECC81 take .5mA
=200.5mA, which is a lot more than the 80mA that my two transformers can put out.
Is this accurate? If it is; will this work at all?
Heaters:
(2) EL34s take 1.5A
(1) ECC81 takes 300mA
=1.8A, which is less than the 4A available.
Plate:
The nominal plate current for class A was said to be:
(2) EL34s take 200mA
(1) ECC81 take .5mA
=200.5mA, which is a lot more than the 80mA that my two transformers can put out.
Is this accurate? If it is; will this work at all?
Can't think of a push pull circuit that only needs 40ma. Would vote for single ended.
RH84 would have been nice but think 40ma isn't enough. Perhaps a spud amp based around the ECL86 ( maybe there is an ecl86 based RH84 out there ) or perhaps an ECL82.
Single ended output transformers shouldn't be hard to get.
RH84 would have been nice but think 40ma isn't enough. Perhaps a spud amp based around the ECL86 ( maybe there is an ecl86 based RH84 out there ) or perhaps an ECL82.
Single ended output transformers shouldn't be hard to get.
Here is an interesting build of a PCL86 spud amp which would be within your 40ma per channel power range. The PCL86 would be substituted with the 6.3 volt ECL86.
Has a choke and LOTS of caps in the power supplies......
http://www.iol.ie/~waltonaudio/pcl86.html
Has a choke and LOTS of caps in the power supplies......
http://www.iol.ie/~waltonaudio/pcl86.html
I think they are... but nothing wrong trying them out as SE OPT
I actually ordered a couple of these just to see how they would sound in SE Just a little bit of work needed to determine the Pri:Sec ratio and then getting the Pri impedance from that. Run a 3V AC signal across sec and measure the voltage, then measure the voltage on the primary... get the turns ratio, square that then multiply by the secondary load being applied.
Refer to my post above re the OPT.
As for the power trannies... bad news... but i have a suggestion,
since you have 20+ of the power trannies, you could use 3 transformers, rectify with solid state rectifiers, then parallel the rectified output of all three transformers, then pass that through the CLCLC.
This should give you 120mA total capacity (and it is better as the ESR would be much lower), way above that needed for the RH84, if you use 4, you could run the RH807, 5 and you could use the EL34s But it does mean that you will need lots of real estate on you chassis or better yet, make a separate power unit, then connect to your amplifier monoblocs through some umbilicals
PP can be Class A or AB depending on the bias and operating point. (Load line). Yes, they are 180 deg out of phase and share the work and are more efficient. Technically , class B is possible (bias voltage negative enough so no idle current flows), but has too much distortion for audio.
Based on the fact that your power transformers are only rated for 40ma, you could entertain CLCLC given sufficient voltage and current from another power transformer.
I would use SS rectification. It results in lower power supply output impedance, and is cheaper and easier. It also does not drop voltage like a tube. The only downsides are SS diodes aren't as sexy looking and don't provide a slow warm up B+ voltage like tube rectifiers do.
It looks fine except the EL34 current. 100ma/tube is a lot. Of course it depends on your B+ voltage. Check out the table in Duncan Amps TDSL pages for typical PP and SE operating conditions. 50-60ma per tube is typical.
EL34's are rated for 24W max dissispation. Exceed this and bad things can happen (red plate/melt/etc). Some tubes remain happy when their power rating is exceeded others do not. The harder you run the tube, the shorter it's useful life. So multiply your B+ times the current to get an idea of the dissipation. I run my EL34's at 400V and 60ma =24W.
The ECC81/12AT7 filaments can be wired for 6V@300ma or 12V@150ma.
TDSL Tube data [ECC81]
TDSL Tube data [EL34]
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Hi guys. I was thinking of the paralleled power supply idea. Are there phase issues that I need to deal with? I need to make sure that both transformers have the same phase angle... right?
Basically, what is being said is that I can rectify each transformer and put them in parallel before the CLCLC section for more current capabilities?
Will I be safe doing this, or will the transformers kill eachother?
I don't mind using 2-3 transformers, but 5 is a little ridiculous?
Basically, what is being said is that I can rectify each transformer and put them in parallel before the CLCLC section for more current capabilities?
Will I be safe doing this, or will the transformers kill eachother?
I don't mind using 2-3 transformers, but 5 is a little ridiculous?
if you do that without rectifying first, then yes, you will have phase issues to deal with and possibility of killing the trannies..
if you rectify them first, then no problem. I am doing the same thing with my RH (GU-50)
Thank you very much Quikie. That's good to know! Do you use bridge rectifiers? and connect the + and - terminals of each bridge?
Sorry for the multiple posts, but I have a picture of the transformers you may want to see.
When I can get to a meter, I'll check the resistance of the 10W primary.
An externally hosted image should be here but it was not working when we last tested it.
When I can get to a meter, I'll check the resistance of the 10W primary.
Fingerboy: Measuring the primary resistance won't tell you much, as an output transformer "reflects" the secondary impedance to the primary. You need to attach a load resistor to the secondary (like 8 ohms) and test, possibly with AC, measuring voltages, etc. I've never done it, but the search button is your friend. Or perhaps one of the experts around here can comment on the primary side labeling as they are pretty clearly marked.
Edit: Those look like 70V transformers...possibly for PA applications? I don't think they will work as tube output transformers.....
Edit: Those look like 70V transformers...possibly for PA applications? I don't think they will work as tube output transformers.....
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run them at 50mA and you should be ok. You can use whatever you want, ready made bridges, 1N4007 bridges if you are on a budget, UF4007 bridges if you want better sounding diodes. but since these are centre tapped, you should connect all the CT together, then put a diode in each limb of the trans...as per the original RH84, that should give you the + voltage, which you can parallel together.
as boywonder said, it's not the resistance you are interested in, its the reflected impedance. calculate it as I described earlier.
yup, they are 70V line trans, no harm trying them though, since he already has them, but needs a little work to find the impedance. Don't expect first class performance though. Once he has been bitten by the bug, he will certainly start looking for better OPTs...
You said: "Run a 3V AC signal across sec and measure the voltage, then measure the voltage on the primary... get the turns ratio, square that then multiply by the secondary load being applied."
Just to be sure, that means to connect the 3VAC supply across the common and 8Ohm taps on the secondary and measure that voltage. Then, measure the voltage induced into the 10W to common of the primary. I know the ratio will give me the turns ratio between those two pairs. That's all I need since I am not interested in 5W or lower?
(Vpri/Vsec)^2 * 8Ohms = Rpri?
I'll do this in the lab tomorrow and get back to you guys.
I found a pair of SE OPTs online for about $80. That seems to be pretty inexpensive compared to the others I've seen. Should 15W transformers be appropriate to run a SE outputted EL34?
This is getting expensive fast even when I had a lot of the parts... Ugh haha
Just to be sure, that means to connect the 3VAC supply across the common and 8Ohm taps on the secondary and measure that voltage. Then, measure the voltage induced into the 10W to common of the primary. I know the ratio will give me the turns ratio between those two pairs. That's all I need since I am not interested in 5W or lower?
(Vpri/Vsec)^2 * 8Ohms = Rpri?
I'll do this in the lab tomorrow and get back to you guys.
I found a pair of SE OPTs online for about $80. That seems to be pretty inexpensive compared to the others I've seen. Should 15W transformers be appropriate to run a SE outputted EL34?
This is getting expensive fast even when I had a lot of the parts... Ugh haha
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