Power supply problem

  • Thread starter Thread starter PhilGood
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OK! I've got my power supply together as well as the mic "clone", but before I connect them together I wanted a little more advice.

The filament voltage for the mic tube (6AU6) is at around 7.03v @ 3.36 mA with NO load, and the B+ voltage is around 303.2v @ 11mA with NO load.

All the resistors are the same as listed in the schematic and the caps are 22uF 450v on the B+ supply and ends for the B-, and 4700uF 35v for the filament.

Should I change the 10k resistor string to 15k's (or higher?) and the 45 ohm resistor to like an 80 ohm, or do you think I'm OK?

When I did my Royers, I noticed the outputs were much higher than the specs with no load and they are fine.

Whaddaya think?
 
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Well, I changed the 10k string to all 22k's and now my B+ voltage is at 241.3v under load. That should be about right. However the filament voltage is at 7.03v with NO load, but when I connect the mic, it drops to 1 volt. I think that's because I'm using a 6.3-0-6.3 center tapped and I'm using the tap and an end. I'm going to try using both ends to get 12.6 and see what that does under load.

When I test my royer PS without load, the filament output is a 35v. The 5840 tube uses the same juice as the 6AU6, but then it's got a bias resistor.

I know Marik isn't back yet, so this is more of a journal. I call it: "Adventures in Microphoning".
 
PhilGood said:
Well, I changed the 10k string to all 22k's and now my B+ voltage is at 241.3v under load. That should be about right. However the filament voltage is at 7.03v with NO load, but when I connect the mic, it drops to 1 volt. I think that's because I'm using a 6.3-0-6.3 center tapped and I'm using the tap and an end. I'm going to try using both ends to get 12.6 and see what that does under load.

When I test my royer PS without load, the filament output is a 35v. The 5840 tube uses the same juice as the 6AU6, but then it's got a bias resistor.

I know Marik isn't back yet, so this is more of a journal. I call it: "Adventures in Microphoning".
Click to expand...

Is the voltage dropping to at the transformer too?

couple of suggestions:
maybe you don't have enough current available in transformer,
maybe the filament is shorted (check with ohmmeter)
maybe resistor is 4.5ohms (long shot :) )

You could always stick a regulator in there for the heater:
http://www.gyraf.dk/gy_pd/g7/gic_s.gif
 
paddyponchero said:
Is the voltage dropping to at the transformer too?

couple of suggestions:
maybe you don't have enough current available in transformer,
maybe the filament is shorted (check with ohmmeter)
maybe resistor is 4.5ohms (long shot :) )

You could always stick a regulator in there for the heater:
http://www.gyraf.dk/gy_pd/g7/gic_s.gif
Click to expand...

I did a couple of things. First I went with both ends of the transformer instead of using the center tap, so I was outing 12.6. That was OK and I was at 13.6 or something before attaching the mic. When I attached the mic I dropped to 3.6 volts. Then I thought, well I've got a 12-0-12 so I attached that instead of the 6.3-0-6.3. I changed the resistor to an 82 Ohm @ 5W. Then I was about right. 5.6-6 volts. Then I noticed a funny smell and went sniffing around the power supply. I touched the resistor and burned my thumb.

I said "This is stupid, what if I went back to the 6.3 trafo running ONLY 6.3 and removed the resistor completely?" Well, it's great! I'm at 6.9 volts at about 5mA WITH the load. If I add a small resistor (maybe 10 ohm) I should be where I want, right?

The plate side is good. I must have an older 6X4 tube (I accidently broke the first one.) Right now I'm at just under 200v (194v) WITH load. I also noticed a buzz coming from the audio side without the mic attached and I'm sure its a sheilding problem. I just need to get my voltages set, work out the sheiding and I'll be ready to start my tests. I don't know what I can compare it to besides my Royers mods. I have an Apex 460. If it's sounds as good or better than either I'll be happy.

Thanks again!
 
PhilGood said:
Have you built this one? This is the G7, right? This looks to be in the ballpark of what I want PSU-wise.

Maybe I'll try this if I keep having trouble.
Click to expand...

Hi Phil,

Havn't built one but it a fine and simple design, I would probably add a 100nF cap at the output of that regulator as they can be noisy.

5mA is much too small for the heater current - if you're supposed to drop 3.7V on the 45ohm resistor the current should be 82mA - check with the ohmeter if the output is going to pins 3 and 4 on the 6AU6.

Maybe your 6au6 has had it - luckily theres a plethora of them on ebay. You could just buy a cheap one until your happy with the circuit, then consider upgrading it.
 
Well, the first rule--if you don't want to kill your tube, never ever connect B+ before you make sure you have a proper filament voltage.
As I wrote before, with different current and voltage rating x-former you must adjust 45 Ohm resistor. It just sucks too much voltage. I'd use 12.6V connection and go from there. It is very hard to calculate exact value of the resistor because of tolerances in the resistors themselves and current of the filament and x-former, so start with higher values, and then go down until you get the voltage between 5.8--6.3V.

Then (only after your filament works properly) connect B+. 245V sounds way too high for a cathode follower circuit. Looking at the schematics, my guess, it should be somewhere around 120-150V.

Of course, you should not connect the capsule until all the circuit is properly adjusted, and you have a right bias there. Instead of capsule uses dummy capacitor of about 50pf.
 
BTW, after building many regulators, finally I desided to drop the idea itself. As a rule, they are very unreliable. A simple resistor works pretty well, and I never had a problem of hum.
 
Marik said:
Well, the first rule--if you don't want to kill your tube, never ever connect B+ before you make sure you have a proper filament voltage.
As I wrote before, with different current and voltage rating x-former you must adjust 45 Ohm resistor. It just sucks too much voltage. I'd use 12.6V connection and go from there. It is very hard to calculate exact value of the resistor because of tolerances in the resistors themselves and current of the filament and x-former, so start with higher values, and then go down until you get the voltage between 5.8--6.3V.

Then (only after your filament works properly) connect B+. 245V sounds way too high for a cathode follower circuit. Looking at the schematics, my guess, it should be somewhere around 120-150V.

Of course, you should not connect the capsule until all the circuit is properly adjusted, and you have a right bias there. Instead of capsule uses dummy capacitor of about 50pf.
Click to expand...


Got it! Glad you're back!

OK, I'll try changing the string to 47k's or higher. I've got extra tubes. I would, however, like to dump the 6X4. Any suggestions/drawings? Could I just use a couple of 1N4007s? Royers power supply would be ideal if I could get the B+ *UP* to 120-150.

I'll disconnect the capsule and put a 50pF there. I had the 6X4 disconnected while I was adjusting the filament voltage.
 
paddyponchero said:
Hi Phil,

Havn't built one but it a fine and simple design, I would probably add a 100nF cap at the output of that regulator as they can be noisy.

5mA is much too small for the heater current - if you're supposed to drop 3.7V on the 45ohm resistor the current should be 82mA - check with the ohmeter if the output is going to pins 3 and 4 on the 6AU6.

Maybe your 6au6 has had it - luckily theres a plethora of them on ebay. You could just buy a cheap one until your happy with the circuit, then consider upgrading it.
Click to expand...

Whew! I was worried my filament amps might be too high. Glad you chimed in there! Like I just posted, I've got extra 6AU6s. 4 used ones and 2 new Sylvania's for the final product.

I thought the 6AU6 filament was rated at .3mA? That's what the sheet I printed out says.

http://hereford.ampr.org/cgi-bin/tube?tube=6AU6

Once again, if I'm reading it wrong tell me and make me wiser, oh great ones!
 
PhilGood said:
I would, however, like to dump the 6X4.
Click to expand...

Why?
A tube rectifier sounds different from SS, and also ensures slow B+ startup. If you want to use SS rectification, then I'd go for Hexfred diodes--to my ears they sound much better than 4007, but are much more expensive.
 
HA! That's what I need! A good smack to the back of the head!

So you're saying a tube rectifier can affect the sound that much eh? Me like! The 6X4 is not a readily available tube, though, is it?

I know the world currently has one less...
 
For my next trick...

I changed the 22ks to 47ks and got the B+ to 118v (under load) which seemed low to me since Marik said it should be between 120-150v. So now I have the first 2 as 47ks and the last as a 22k and now my B+ is at 140v. Is that OK?

I tried the 12.6v with a 10ohm and the voltage was at 9.6v. With a 47ohm I think it was at 3.6 and I don't have anything in between right now.

I put it back at 6.3 with a 4.7 ohm (cause I had one) and now it's at 5.4v. I think I was wrong before with the amps 'cause now my meter says it's at .86! I have a one ohm. BTW, the 6.3-0-6.3 trafo is a 1 amp.

How far off am I?

It seems to me if i have to make this many changes that deviate from the schematic, the hand written notes were probably wrong.

Have I thanked you again yet today?
 
PhilGood said:
For my next trick...

I changed the 22ks to 47ks and got the B+ to 118v (under load) which seemed low to me since Marik said it should be between 120-150v. So now I have the first 2 as 47ks and the last as a 22k and now my B+ is at 140v. Is that OK?

I tried the 12.6v with a 10ohm and the voltage was at 9.6v. With a 47ohm I think it was at 3.6 and I don't have anything in between right now.

I put it back at 6.3 with a 4.7 ohm (cause I had one) and now it's at 5.4v. I think I was wrong before with the amps 'cause now my meter says it's at .86! I have a one ohm. BTW, the 6.3-0-6.3 trafo is a 1 amp.

How far off am I?

It seems to me if i have to make this many changes that deviate from the schematic, the hand written notes were probably wrong.

Have I thanked you again yet today?
Click to expand...

The hand written notes may well be wrong.

.3A is indeed the current recommended in the data sheet however it would be impossible to get this current with a 45ohm resistor and 10V transformer. The original design must have been underheated. With a 10V transformer and 45 ohm resistor we need 82mA to give 6.3V heater voltage.

You can't really set the voltages without a load - do as marik says and substitute a cap for the capsule. If you still have to deviate that much from the schematic something is definitely amiss.
 
I've got the dummy load cap in there now, and I'm pulling the leads from the big trafo until I get the filament right. How much damage coud I have done to the capsule? It looks alright. Didn't melt or anything. I think I even measured the voltage going to it and it was pretty low.


I think I'll go back to what Marik suggested and run the 12.6v but with 2 10ohms in series. I may have to go get something like a 22 or whatever the next one up is. These are 5W flameproofs BTW. Should I go back to the 47ohm with a new tube?
 
PhilGood said:
So now I have the first 2 as 47ks and the last as a 22k and now my B+ is at 140v. Is that OK?
Click to expand...

It is hard to know its exact voltage value. The best is to find the factory specs. Something to think about: since a bias for a capsule is taken from a tube bias the B+ will affect it. Check the voltage on 100K-3K-100M junction--that's the capsule bias. If you cannot find specs, use your ears to adjust the voltage, which sounds right to you.
 
PhilGood said:
I've got the dummy load cap in there now, and I'm pulling the leads from the big trafo until I get the filament right. How much damage coud I have done to the capsule? It looks alright. Didn't melt or anything. I think I even measured the voltage going to it and it was pretty low.


I think I'll go back to what Marik suggested and run the 12.6v but with 2 10ohms in series. I may have to go get something like a 22 or whatever the next one up is. These are 5W flameproofs BTW. Should I go back to the 47ohm with a new tube?
Click to expand...

Your capsule should be fine. To disconnect from B+ just pull 6X4 out. If you did not put B+ with way underheated tube for a long time your tube should be fine, as well.
 
Marik said:
Your capsule should be fine. To disconnect from B+ just pull 6X4 out. If you did not put B+ with way underheated tube for a long time your tube should be fine, as well.
Click to expand...

Uh, that's how I broke the tip off the last tube. I'm not doing THAT again! this is my last one of those.
 
I put in a 33ohm for the filament running off the 12.6v. Now my filament is at 5v @ .66 A.

With the B+ I have the following:

141.3v B+ @ 25mA
Bias area is 70.1v
'capsule' is getting 1.1v

How am I doing?

I've searched the web for original specs on the B+ and came up with squat!
 
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