Hmmmm, I had not thought of that. Thank you so much, that is definitely what I’ll do.
Dan
If you do get higher voltage caps buy them from known good sources of name branded caps. Chinese knock offs are famous for being labeled well beyond their real limits. They might work at first but will soon barf their guts all over the place. As was said, you can always series two caps with balance resistors to get what you need. The value of two caps in series is half so two 100uf make a 50uf. Voltages add.
Be safe & not sorry...I had an old fifties tube radio a co-worker had....the "dried out" buzz was there...A suitable 630V version required a little shuffling for space inside, but I knew the old 450V rated version would only be suitable for another fifty years....now, where is that formula for increased longevity with "rated voltage over actual seen voltage" ratio ..I recall it giving you extra hundreds of years of lifetimes.
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------Rick...
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------Rick...
Quick question - I have a 16V rated capacitor in my filament reg. When no tube is inserted the voltage is around 16V - starts at 16.2V and goes down to 15.7V. In this mode there is no current going through the capacitor. On load with tube in, voltage is 12.6V.
Is this safe or should I worry? I've tried replacing the capacitor with a higher voltage one but it's a bit hard to extract from the pcb.
Is this safe or should I worry? I've tried replacing the capacitor with a higher voltage one but it's a bit hard to extract from the pcb.
Interesting schematic. The audio is no-feedback PP pentode amplifier driving a field coil speaker. The speaker is a 12" Magnavox, countermodulation coil in series with VC. The 600 Ohm field coil serves as power supply choke. Voltage amplifier is conventional high mu triode, but phase inverter is funny. It is another same triode whose input is fed from the output of the first triode through voltage divider to equalize triodes' outputs.
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Connect a scope and observe the filament voltage start up with normal loading.
Probably it will not overshoot. Even so, I would not worry about it.
I bit the bullet and yanked out the 16V caps and replaced them with 35V caps. I hate changing stuff on pcbs - tiny and fiddly to work with and unsolder.
I'm strictly point to point in my builds.
I'm strictly point to point in my builds.
Rayma. It is true that the voltage balance will not be maintained. It is also true that the voltage balance will be such that the overall leakage is minimised. The less leakage the less stress the overall system will experience. The higher leakage cap will naturally operate a a lower voltage and lower its leakage in turn. This will put more voltage on the lower leakage cap and increase its leakage until the leakage finds a minimum balance. This will most likely not be the operating point where the voltages are equal.
Just remember to check the voltage rating of any resistor used for balancing, as the resistor has to cope with the initial surge voltage as well (and resistors typically have just an absolute max, not some 10 second surge rating). A series connection of caps can quickly degrade if one of the balancing resistors goes open circuit, and not all resistors are rated for 500V or 750Vdc. It is not uncommon when restoring vintage equipment to have to replace the resistors when reforming or replacing the caps, as one of the resistors has gone open.
sser2,
The phase splitter you are describing is one version of a Paraphase phase splitter.
There is nothing unusual about that. Tens if not hundreds of vacuum tube amplifier designs used that kind of a Paraphase phase splitter.
At least once, I used a Paraphase phase splitter for a push pull amplifier I designed. It worked fairly well.
It is not my favorite phase splitter.
Then I used a Concertina phase splitter on more than one of my push pull amplifiers. It worked fairly well.
It is not my favorite phase splitter.
When I need a phase splitter, I use a CCS (Constant Current Source) in the parallel cathodes of a LTP phase splitter.
I have used LM317 (no longer use), Bipolar transistor and surrounding circuitry, and now LM334.
I am sure there are better CCS, but those worked for me.
With all its tradeoffs, this is my favorite phase splitter.
The phase splitter you are describing is one version of a Paraphase phase splitter.
There is nothing unusual about that. Tens if not hundreds of vacuum tube amplifier designs used that kind of a Paraphase phase splitter.
At least once, I used a Paraphase phase splitter for a push pull amplifier I designed. It worked fairly well.
It is not my favorite phase splitter.
Then I used a Concertina phase splitter on more than one of my push pull amplifiers. It worked fairly well.
It is not my favorite phase splitter.
When I need a phase splitter, I use a CCS (Constant Current Source) in the parallel cathodes of a LTP phase splitter.
I have used LM317 (no longer use), Bipolar transistor and surrounding circuitry, and now LM334.
I am sure there are better CCS, but those worked for me.
With all its tradeoffs, this is my favorite phase splitter.
For folk living in the Land of Milk and Honey, and possibly elsewhere, who need replacement can caps, I and my building partner itishifi.com can both enthusiastically recommend an outfit called Hayseed Hamfest, who can make you up some beautiful (looks like stainless steel cans) custom multi-section can caps using Nichican 105C caps up to 500VDC at very reasonable (think Ham radio, not audiophile) prices. Been very happy customers for years.
All good fortune,
Chris
All good fortune,
Chris
I made a calculation error and an not-so-new Nichicon cap of 450 V got 490 V for 2 years.
Wihout problems.
It was at room temperature with low current.
Wihout problems.
It was at room temperature with low current.
In your circuit above there would have been no load after switching on the radio. If you were to add bleeder resistors, a safety feature anyway, then perhaps the small load would reduce the overshoot of the secondary voltage, until tubes are warm and conduct.
"I am sure there are better CCS, but those worked for me. with all its tradeoffs, this is my favorite phase splitter"
rJ
Question; What do you see as a tradeoff, is it number of components, gain, or other ?
rJ
benchbaron,
My statement is at the start of your post.
The text that is "boxed in", is not from me, even though my moniker is also in the box.
You are quoting someone else in your Post # 34, or inserting other additional text into the quote.
I did not say that text as you have quoted it.
I often make mistakes, but whether I am right or wrong, I hate being misquoted.
Thanks!
Phase splitter Tradeoffs? Yes!
My favorite phase splitter, the LTP with a CCS at the parallel cathodes is because I consider it to be the most intrinsically linear circuit,
and one of the most intrinsically balanced signal swings (the concertina has that too, IF all the parasitics and filament cathode problems have been addressed).
Reasonable simplicity is good too.
It needs good tubes, they do not have to be super matched but they can not be badly dissimilar (good tubes are easy to get).
I know how good the phase splitter is, not just at mid frequencies, but at high frequencies and low frequencies . . . I measure them
with matched probes and scope channels (you need to know how to verify your probes and scope channel match; that is another subject).
The concertina could be next, but certain parasitics, such as filament to cathode resistive leakage, requirement to elevate the filament voltage, filament to cathode capacitance, and less than unity gain of the two output phases; make it not for me. Except for needing the elevated filaments, it is the simplest circuit. I have seen very poorly matched in-phase and out-of-phase signal levels, because some forgot to elevate the heaters (over time the match gets worse and worse). More 7199 triode section concertinas have been 'destoyed' because there was no elevation of the filament.
AC filaments can couple to the cathode, and cause hum.
Elevated filaments is a compromise for 7199 since the pentode section cathode voltage is near ground.
A typical concertina gets its signal from a triode's or pentode's plate that is DC coupled (important to calculate the proper DC level to make both the voltage amplifier work properly, and the concertina work properly.
The only thing I like about the Paraphase splitter is it has lots of gain. It is also the most complex circuitry.
All of those phase splitters can work very well, if they are designed properly and implemented properly.
I hope that answers your questions.
6A3sUMMER.
My statement is at the start of your post.
The text that is "boxed in", is not from me, even though my moniker is also in the box.
You are quoting someone else in your Post # 34, or inserting other additional text into the quote.
I did not say that text as you have quoted it.
I often make mistakes, but whether I am right or wrong, I hate being misquoted.
Thanks!
Phase splitter Tradeoffs? Yes!
My favorite phase splitter, the LTP with a CCS at the parallel cathodes is because I consider it to be the most intrinsically linear circuit,
and one of the most intrinsically balanced signal swings (the concertina has that too, IF all the parasitics and filament cathode problems have been addressed).
Reasonable simplicity is good too.
It needs good tubes, they do not have to be super matched but they can not be badly dissimilar (good tubes are easy to get).
I know how good the phase splitter is, not just at mid frequencies, but at high frequencies and low frequencies . . . I measure them
with matched probes and scope channels (you need to know how to verify your probes and scope channel match; that is another subject).
The concertina could be next, but certain parasitics, such as filament to cathode resistive leakage, requirement to elevate the filament voltage, filament to cathode capacitance, and less than unity gain of the two output phases; make it not for me. Except for needing the elevated filaments, it is the simplest circuit. I have seen very poorly matched in-phase and out-of-phase signal levels, because some forgot to elevate the heaters (over time the match gets worse and worse). More 7199 triode section concertinas have been 'destoyed' because there was no elevation of the filament.
AC filaments can couple to the cathode, and cause hum.
Elevated filaments is a compromise for 7199 since the pentode section cathode voltage is near ground.
A typical concertina gets its signal from a triode's or pentode's plate that is DC coupled (important to calculate the proper DC level to make both the voltage amplifier work properly, and the concertina work properly.
The only thing I like about the Paraphase splitter is it has lots of gain. It is also the most complex circuitry.
All of those phase splitters can work very well, if they are designed properly and implemented properly.
I hope that answers your questions.
6A3sUMMER.
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Apologies, my post was completely "mashed up" by a system error, (Firefox ?) exactly the same time I posted.
Agreed on comments.
I have always disputed whether a direct coupled concertina, as per 7199 or sim config as you mention is treated in many amps as a 4th stage, but for stability I look at this as 3 stages as the pentode is DC coupled with no phase shift.
In progress is a 110W 3 stage beast using LTP and powerful diff drivers. This amp will be the 3rd heaviest amp 65kg (143Lbs) I have built. All can be used in bridge mode. The B+ common to all is PFC (power factor controlled) for excellent stability.
More anon !
rJ
Agreed on comments.
I have always disputed whether a direct coupled concertina, as per 7199 or sim config as you mention is treated in many amps as a 4th stage, but for stability I look at this as 3 stages as the pentode is DC coupled with no phase shift.
In progress is a 110W 3 stage beast using LTP and powerful diff drivers. This amp will be the 3rd heaviest amp 65kg (143Lbs) I have built. All can be used in bridge mode. The B+ common to all is PFC (power factor controlled) for excellent stability.
More anon !
rJ
Voltage rating - Voltage DC or Voltage AC?
It's interesting that Wima caps are rated with a DC and an AC voltage. Thus a 600V wima is typically 600Vdc but not AC, which is typically rated for less AC such as 400Vac -- at 85degC. The temperature also derates the voltages too. So a high temp 600V may actually require a 1000V or 1250V to maintain the required AC rating. I don't see any difference with electrolytics in this regard.
Also vintage caps were built way over their indicated ratings. This allowed for the inexact voltages from tubes etc.
Personally I would rate way above the surge voltage as the over voltage is promoting an unknown mode of break down over time.
Only my view but considering electrolytics have the shortest life (except tubes) of any component in/under the chassis, I would be wary of pushing today´s generation caps over peak voltages quoted on spec sheets. I did this once and heard the typical stress "tick-tick" discharge from inside, so tells me peak ratings do mean what is written.
The question of self healing an internal discharge wound with electrolytics, I am not so sure on this but any dielectric puncture should be avoided as capacitor life is bound to degrade. Do not compare with some metalized film types which can mention "self healing".
Over decades, dielectrics and materials have got purer, resulting in thinner films and reduced can sizes and the time temperature ratings have gone up. However, there is still the previous reliability steep sided graph that for every 10°C rise the life is cut by half.
In the late 1950´s it was common practice that electrolytic capacitor placements were often quite close to tubes, a wholly reckless physical placement.
Play safe with electrolytics. I got "stung" by one even though I thought it was discharged. The Nichicon regained it´s joules over 1/2 year in the junk box.. Such is the quality of today´s electrolyte and materials.
rJ
The question of self healing an internal discharge wound with electrolytics, I am not so sure on this but any dielectric puncture should be avoided as capacitor life is bound to degrade. Do not compare with some metalized film types which can mention "self healing".
Over decades, dielectrics and materials have got purer, resulting in thinner films and reduced can sizes and the time temperature ratings have gone up. However, there is still the previous reliability steep sided graph that for every 10°C rise the life is cut by half.
In the late 1950´s it was common practice that electrolytic capacitor placements were often quite close to tubes, a wholly reckless physical placement.
Play safe with electrolytics. I got "stung" by one even though I thought it was discharged. The Nichicon regained it´s joules over 1/2 year in the junk box.. Such is the quality of today´s electrolyte and materials.
rJ
benchbaron,
It is OK, no problem.
. . . I think most vacuum tube amplifiers are more reliable than computer software, etc.
It is OK, no problem.
. . . I think most vacuum tube amplifiers are more reliable than computer software, etc.
