G'day guys,
I'm tuning a Glassware audio 12vac Aikido board.
https://glass-ware.stores.yahoo.net/aikido12vac.html
I'm doing the 12AU7 implementation.
My heaters are currently running at 12.85vdc.
Is this within an acceptable range of 12.6v or is this likely to shorten tube life?
Is it worth performing pcb to lower the heater voltage or just leave well enough alone?
I'm tuning a Glassware audio 12vac Aikido board.
https://glass-ware.stores.yahoo.net/aikido12vac.html
I'm doing the 12AU7 implementation.
My heaters are currently running at 12.85vdc.
Is this within an acceptable range of 12.6v or is this likely to shorten tube life?
Is it worth performing pcb to lower the heater voltage or just leave well enough alone?
I'd say leave it alone. It's within the tube tolerance. Also, form what I saw on the link it's probably a regulated DC heater supply, therefore is not going to change with mains voltage.
Yes, about 2%. Your mains voltage will vary more and a 12AU7 running at sec. AC will vary with it, but not the reg DC output.
How do you make the 12.6VDC regulator? Schematic?
Maybe you can finesse the reg to exactly 12.6 if you're worrying.
Jan
How do you make the 12.6VDC regulator? Schematic?
Maybe you can finesse the reg to exactly 12.6 if you're worrying.
Jan
Non regulated dc.
It's a function of the b+.
The voltage can be lowered by changing r15. Currently it's 10R.
A change to 16R would put me ptetty much bang on 12.6v.
20R would put me slightly under at 12.45v.
It's a function of the b+.
The voltage can be lowered by changing r15. Currently it's 10R.
A change to 16R would put me ptetty much bang on 12.6v.
20R would put me slightly under at 12.45v.
So any variation of B+ would change the heater voltage?
Or are the two zeners Z1 and Z2 supposed to eat any variation?
What's the value of R12?
Are D1, D2, D3, D4 the right way around?
I don't see any path from B+ through R2 to the heater string, only caps and upside down diodes?
Supplying the heaters from (100-s of volts) B+ must be the mother of all wastes?
It also places the heaters quite a high voltage above the cathodes, hopefully not exceeding the max allowed.
It's a weird circuit.
Jan
Or are the two zeners Z1 and Z2 supposed to eat any variation?
What's the value of R12?
Are D1, D2, D3, D4 the right way around?
I don't see any path from B+ through R2 to the heater string, only caps and upside down diodes?
Supplying the heaters from (100-s of volts) B+ must be the mother of all wastes?
It also places the heaters quite a high voltage above the cathodes, hopefully not exceeding the max allowed.
It's a weird circuit.
Jan
Here is a higher resolution schematic sorry.
The heaters come off the voltage doubler form by d3 and d4.
B+ come from the sextupler of d1-d6.
Saying heater voltage is a function of b+ was not quite the right way to put it.
I have not installed z1 and z2 as people have had issues with these elsewhere.
Everything is installed properly. This amp has previously worked flawlessly in a test rig for several years. Now it's going into a proper chassis with a different power transformer of higher VA which sags less.
Hence the need to re-tune the heaters.
B+ is also up 4v on the old implementation which I'm not worried about.
My concern is essentially whether giving a 12.6v heater 12.85v amounts to an over voltage of concern or could be considered within an acceptable range that won't affect tube life.
It is an weird circuit. But it's pretty cool too.
The heaters come off the voltage doubler form by d3 and d4.
B+ come from the sextupler of d1-d6.
Saying heater voltage is a function of b+ was not quite the right way to put it.
I have not installed z1 and z2 as people have had issues with these elsewhere.
Everything is installed properly. This amp has previously worked flawlessly in a test rig for several years. Now it's going into a proper chassis with a different power transformer of higher VA which sags less.
Hence the need to re-tune the heaters.
B+ is also up 4v on the old implementation which I'm not worried about.
My concern is essentially whether giving a 12.6v heater 12.85v amounts to an over voltage of concern or could be considered within an acceptable range that won't affect tube life.
It is an weird circuit. But it's pretty cool too.
If we can compare with lightbulbs then using the right voltage may increase filament life. They don't mention 12.6V (yes with a capital V) without a reason.
Is there any issue using the filaments in parallel with a separate transformer? The circuit seems cool but also too complex and imprecise for the simple task.
Is there any issue using the filaments in parallel with a separate transformer? The circuit seems cool but also too complex and imprecise for the simple task.
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A
Look, most tube heaters are specified +/-10%. Yours is 2% high. No worries.
Jan
Ahhh yes, I see the AC input! But I still think it's weird 😎
Look, most tube heaters are specified +/-10%. Yours is 2% high. No worries.
Jan
I'd be more concerned if the V is too low. a couple of % over is no concern at all IMHO.
It is too high as can be read in post #1. I think many would rather have slightly less than 12.6V like 12.35V instead of 12.85V. Since voltage dropping is a popular art in the tube world it won't hurt to do so and have the "right" voltage. A slightly higher value R15 will have a small extra benefit that inrush current will be slightly lower as well. Win win for a few cents.
How can it be too high if it is way inside the manufacturer's tolerance? With that reasoning even 12.61V is too high.
It was a reaction to stephe and it's 12.85V not 12.61V. Anyway we can debate as much as we like but just one (1) resistor and things are exact with the mentioned small benefit. To some things feel better if things are just right, some feel better by not doing so and then often in more than 1 area. Point being that I see a lot of sloppiness in many areas in DIY tube audio so a little precision would not hurt.
Ciao!
Ciao!
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The output from heater transformer can vary a bit with mains voltage.
It will also be high off load.
I recently bought a 12VAC 1.5 amp transformer and output is 15VAC volts off load.
Even with 150mA to heaters and 50mA to rest of circuit the heater voltage is still a bit high.
I once used 12vdc for a valve amplifier for heaters and B+ (rectified)
I had problems and adjusted 12 volts up a bit forgetting it was driving heaters.
I got up to about 20 volts before realising heater was bright !
Luckily there was no lasting damage.
It will also be high off load.
I recently bought a 12VAC 1.5 amp transformer and output is 15VAC volts off load.
Even with 150mA to heaters and 50mA to rest of circuit the heater voltage is still a bit high.
I once used 12vdc for a valve amplifier for heaters and B+ (rectified)
I had problems and adjusted 12 volts up a bit forgetting it was driving heaters.
I got up to about 20 volts before realising heater was bright !
Luckily there was no lasting damage.
I'm thinking that a useful experiment would be to measure my mains voltage and see if it is higher or lower.
If my mains is on the higher side I'm probably best to leave as is.
If my mains is on spec or on the lower side I'm probably best to adjust R15 accordingly. My thinking being that perhaps I or at least the preamp moves house at some stage. If my current mains low and the future mains is higher then it could end up well out spec.
If my mains is on the higher side I'm probably best to leave as is.
If my mains is on spec or on the lower side I'm probably best to adjust R15 accordingly. My thinking being that perhaps I or at least the preamp moves house at some stage. If my current mains low and the future mains is higher then it could end up well out spec.
That is why voltage regulation has been invented. Takes away such issues. Mains voltage can today be lower and tomorrow higher than usual.
In my circuits as a mater of principle I always want max life possible ... why not change R15 to be just at 12,6V or below ?
Those small tubes would run perfectly at 12V or even below , so low mains is not an isue .
Those small tubes would run perfectly at 12V or even below , so low mains is not an isue .
I think so too. And for maximum lifetime of the valve, the the nominal voltage should not be exceeded.
Data sheets say that ±5% is acceptable, but "acceptable" because that was the reality of the tolerance of mains supply voltages in the 1950s. Recently, here in the UK, and other countries, the tolerance of mains Line voltage has degraded to ±10%.
+10% on heater voltages will severely reduce the lifetime, since the oxide coating's temperature is strongly dependent on power. Remember that the heater current will increase (a little) at higher voltages too, so the power increase is more than 10%.
As heater temperature rises, the speed at which the cathode's subsurface barium evolves increases. At any temperature above the nominal voltage, the rate is faster than necessary to operate the valve, and so the barium is wasted. This is frequently the limiting factor for lifetime.
These are all well-known facts, and can easily be looked-up.
Here's an example from the «Philips Technical Review» 1956, pp185. It explains that ±5% voltage control is vital, but slightly lower-than-nominal voltage is better, and that stabilised to 1% is best: