Off Topic - Heater Power Supply
If this is too far off topic, it would be cool to move this to a tube power supply thread, but I thought it wasn't too bad since SY referenced a heater supply in his LA article.
I admit it. I'm a Tubie Newbie. So I've been doing lots of background reading, most especially on power supplies as the tube world is some different from solid state land.
One thing that I ran across for DC heater supplies is the discussion of regulated voltage .vs. regulated current. The advantage stated for the constant current regulation is that it acts like a soft start and reduces the cold start current on the heaters.
From my inexperienced point of view, it looks like you could do something like SY referenced in the LA article using the "His Masters Noise" heater supply concept, but reconfigure the regulators as constant current regulators. The regulators themselves would lose the direct voltage reference to the floating ground, but it seems like it would still work.
Any thoughts from you experienced tube guys on regulated DC voltage or current? How do you guys prefer to avoid cold start heater shock?
Thanks.
Jac
If this is too far off topic, it would be cool to move this to a tube power supply thread, but I thought it wasn't too bad since SY referenced a heater supply in his LA article.
I admit it. I'm a Tubie Newbie. So I've been doing lots of background reading, most especially on power supplies as the tube world is some different from solid state land.
One thing that I ran across for DC heater supplies is the discussion of regulated voltage .vs. regulated current. The advantage stated for the constant current regulation is that it acts like a soft start and reduces the cold start current on the heaters.
From my inexperienced point of view, it looks like you could do something like SY referenced in the LA article using the "His Masters Noise" heater supply concept, but reconfigure the regulators as constant current regulators. The regulators themselves would lose the direct voltage reference to the floating ground, but it seems like it would still work.
Any thoughts from you experienced tube guys on regulated DC voltage or current? How do you guys prefer to avoid cold start heater shock?
Thanks.
Jac
You absolutely need a DC reference to ground. Constant current is better for series heaters, e.g., tubes like the 12SN7. IME, and the other old-time tube guys as well, is that heater burnout is exceptionally rare in indirectly heated triodes. For what it's worth, my line stage has tubes in it going on 10 years of service, and they're still running perfectly.
Are PCC-88 tubes suitable for this phono preamp? I once bought a dozen of good quality NOS Ei brand PCC-88 tubes at very good price.Different heater voltage?
The intention was to fill the gap for folks who want to build now or who want to use Jan's layout. I believe Jack intends to have a different layout done towards the end of the year.
In order to not turn this in to a group buy thread, e-mail me via the forum if you're interested. Priority goes to those who expressed interest in this thread first, and then anyone else until I run out. Cost is $5.35 per board, so that's the sale price + PP fees + shipping. You need two boards per channel. Anything left over will go in swap meet.
In order to not turn this in to a group buy thread, e-mail me via the forum if you're interested. Priority goes to those who expressed interest in this thread first, and then anyone else until I run out. Cost is $5.35 per board, so that's the sale price + PP fees + shipping. You need two boards per channel. Anything left over will go in swap meet.
I'm in a holding pattern for jackinnj's boards, but great job on your part to get rolling.
A great job indeed. JP is both doing the work of getting and shipping the boards and saving us money by using his sunk tooling costs for the new boards. Thank you very much, JP.
Jac
Optimum Current for Low Noise - Other tubes
SY,
I've been reading about choices in tubes for this project. The 7 volt tubes caught my interest because they seem to have a good quality/price ratio.
In your Linear Audio article, you talk about 4mA being the optimum low noise current for the ECC88 family of tubes. Based on the Blencowe article, was there any difference with the PCC88/7DJ8 tubes, if they were even tested? My assumption is that the 7 volt tubes are close enough to the ECC88 family that 4mA would still be the target, but it would be nice to know what Blencowe had to say on the subject.
Also, since the PCC88 family are said to work at 6.3V, if you were using PCC88 tubes and building the Equal Opportunity MM, would you design your heater for 6.3 or 7 volts?
Thanks in advance.
Jac
SY,
I've been reading about choices in tubes for this project. The 7 volt tubes caught my interest because they seem to have a good quality/price ratio.
In your Linear Audio article, you talk about 4mA being the optimum low noise current for the ECC88 family of tubes. Based on the Blencowe article, was there any difference with the PCC88/7DJ8 tubes, if they were even tested? My assumption is that the 7 volt tubes are close enough to the ECC88 family that 4mA would still be the target, but it would be nice to know what Blencowe had to say on the subject.
Also, since the PCC88 family are said to work at 6.3V, if you were using PCC88 tubes and building the Equal Opportunity MM, would you design your heater for 6.3 or 7 volts?
Thanks in advance.
Jac
I'd run them where the datasheet specs them. Merlin's data showed the noise vs. current to be reasonably shallow, so I'd have no hesitation of sticking to 4mA. After all, I used 12V versions...
Rookie Question
I'm sure that I am missing something simple here. Hopefully, one of you more experience tubers will take the time to lift the fog from my eyes.
In the L.A., Equal Opportunity article, SY proposed the balanced heater circuit from "His Master's Noise". I like the idea because of the benefits to common mode noise.
What has me stumped is the balanced heater connection to the ECC88 tube family. By all of the datasheets that I have looked at, the ECC88 family of tubes doesn't have a heater center tap connection. Rather, the only connections to the heater are at pins 4 and 5. It seems that you need a center tap to drain the current from each side of the heater in order to actually use the circuit from "His Master's Noise". Am I missing something?
Jac
I'm sure that I am missing something simple here. Hopefully, one of you more experience tubers will take the time to lift the fog from my eyes.
In the L.A., Equal Opportunity article, SY proposed the balanced heater circuit from "His Master's Noise". I like the idea because of the benefits to common mode noise.
What has me stumped is the balanced heater connection to the ECC88 tube family. By all of the datasheets that I have looked at, the ECC88 family of tubes doesn't have a heater center tap connection. Rather, the only connections to the heater are at pins 4 and 5. It seems that you need a center tap to drain the current from each side of the heater in order to actually use the circuit from "His Master's Noise". Am I missing something?
Jac
Warning: Pathetic Fallacy Ahead
You don't need (nor do you particularly want) CT heaters. All the heater "cares" about is that there's 6.3V between pin 4 and pin 5 (for ECC88). So if you have a reference point voltage (in this case, from a voltage divider string bypassed to ground) and one regulator is 3.15V above that and the other is 3.15V below that, the heater will be "happy."
You don't need (nor do you particularly want) CT heaters. All the heater "cares" about is that there's 6.3V between pin 4 and pin 5 (for ECC88). So if you have a reference point voltage (in this case, from a voltage divider string bypassed to ground) and one regulator is 3.15V above that and the other is 3.15V below that, the heater will be "happy."
Just a quick note that everyone who committed to buying boards has paid, and they are all awaiting USPS pick-up to go out today. I'll list the remainder in Swap Meet.
A big thanks to all for being so prompt in communication and payment - it was a pleasure.
Now, let's see some builds! 😀
A big thanks to all for being so prompt in communication and payment - it was a pleasure.
Now, let's see some builds! 😀
I'll give it my best shot, but I do have a solid state system build to finish first. It's a house warming gift and already late.
Slightly off topic.
My plan is to build the B+ regulator just like SY designed it. But looking around, I ran into the TL783 high voltage regulator that looked pretty useful for a tube regulator. It has 125 V regulation, 76 dB ripple rejection, and short circuit protection. The biggest issue is the minimum current output which at 15 mA is probably too close to the 16 mA of these boards on B+. Does anyone have any experience or comments on this little IC?
You can always add a bleeder resistor at the output by adding as many mAmps as you need to the total. But you may not be happy with the TL783 preformance...? it`s slow and a sluggish regulator.
Slow and sluggish is a GOOD thing in a regulator. The ideal is so slow and sluggish that it doesn't move.
In any case, the circuit has high PSR and, being differential, a constant current draw. The regulator is pretty non-critical. Just use a decent bypass and try to keep the noise reasonably low.
In any case, the circuit has high PSR and, being differential, a constant current draw. The regulator is pretty non-critical. Just use a decent bypass and try to keep the noise reasonably low.