Author Topic: Slow To Turn On  (Read 666 times)

JohnAZ

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Slow To Turn On
« on: March 06, 2018, 08:23:12 AM »
My '63 Custom Electra VI takes close to 40 seconds to start up cold. The manual states 30 seconds. When I first got this stereo, I tested each tube and one took a long time to register anything on the meter. I forgot which one it was now and am wondering if this is normal to take so long to start up or if I should identify that tube and replace it.

electra225

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Re: Slow To Turn On
« Reply #1 on: March 06, 2018, 09:22:25 AM »
I wouldn't worry about it.  If there is a tube getting weak, it will eventually fail completely.  Lots easier to troubleshoot a dead instrument than chasing your tail looking for a ghost. 
I'm great at multi-tasking.  I can listen, ignore, and forget all at the same time.

Harbourmaster

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Re: Slow To Turn On
« Reply #2 on: March 06, 2018, 06:20:20 PM »
that is not an exceptionally long startup time for a tube console.
-- Aloha, Ken

No Console Left Behind!

JohnAZ

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Re: Slow To Turn On
« Reply #3 on: March 06, 2018, 09:01:46 PM »
Thanks for the replies. I used to have several amateur AM receivers and none of them took this long. I'll leave her be and just enjoy it.

TC Chris

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Re: Slow To Turn On
« Reply #4 on: March 06, 2018, 11:58:59 PM »
You mentioned that one tube was slower to warm up on the tester.  Was it the rectifier?  If so, what does it use?  I have a vague recollection reading that the 5AR4 was designed to have a slow warm-up.  I have an old Heath AA-100 and when it was last in service many years ago the 5AR4 had died so I took the cover off (better cooling anyway) and popped in a 5U4 that I had on hand.  Later I read something about controlled warm-up.  I looked for info tonight and found nothing in a brief search. 

Chris Campbell

JohnAZ

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Re: Slow To Turn On
« Reply #5 on: March 07, 2018, 12:48:21 AM »
You mentioned that one tube was slower to warm up on the tester.  Was it the rectifier?  If so, what does it use?  I have a vague recollection reading that the 5AR4 was designed to have a slow warm-up.  I have an old Heath AA-100 and when it was last in service many years ago the 5AR4 had died so I took the cover off (better cooling anyway) and popped in a 5U4 that I had on hand.  Later I read something about controlled warm-up.  I looked for info tonight and found nothing in a brief search. 

Chris Campbell
I tested the tubes tonight and the 6AU6 and 6HS6 were the slowest to come up. I failed to mention that the audio is the only thing to takes a while to start. I've attached a picture of the tube layout. This site says the 6AU6 and 6HS6 has controlled warm-up times http://www.r-type.org/exhib/aaa1400.htm    http://www.r-type.org/exhib/abv0049.htm

ed from Baltimore

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Re: Slow To Turn On
« Reply #6 on: March 09, 2018, 01:36:19 AM »
    The "controlled warmup" time is talked about in a lot of the fifties-sixties RCA tube manuals. There is something about 11 seconds mentioned, such as it reaches a certain percentage of its final filament temperature in 11 seconds. Tubes  drawing the same filament  currents, such as 600 milliamps (tv sets) or 150 milliamps (table radios) were placed in series like 12BE6 12BA6 12AV6 50C5 and 35W4  directly across the 120 volts AC line with the assurance that they all had the correct voltage on their filaments throughout the initial warmup cycle just as if they were connected to a power transformer filament winding.
     If you have ever seen a series filament circuit where the tubes are not all controlled warmup type tubes when the power is first turned on, you won't soon forget the experience. One or more of the tubes will  suddenly light up its filament like a flashlight bulb for the initial second, then will settle down to a dull red glow as the other tubes slowly become dull red than orange. The tube will not last nearly as long in a series string circuit as it would when connected to a transformer filament winding.
      Tubes designed for series string television sets always were controlled warmup time. They have odd filament voltages like 17, 21, 9, 5 etc. depending on the power needed for the tube cathode. These tubes always had 6 or 12 volt equivalents for tv sets with power transformers.
         I'm not sure if battery radio tubes were controlled warmup such as 1L6, 1R5, 3V4, but they had a huge voltage dropping resistor to drop 120 volts DC to 9 volts for the series filaments anyway which would swamp out the variations in resistance of an  individual tubes filament resistance. Those tubes would be 50 milliamps or so, some of the subminiatures were I think 40 milliamps,
       Also, low signal level audio preamp tubes would have their filaments in series powered by a DC filtered power source to eliminate the audible hum  from nearby 6.3 volt wires at the tube socket. 12AX7, 12AU7, 7025, 12AY7 and others had a 150 milliamp current draw in series hookup. There would either be a 48 or 36 volt or maybe 24 volt power supply that would double as a bias supply for the output tubes, or sometimes the cathode current through the output tubes such as 6L6GC would be adjusted to 150 milliamps and the 12AX7 preamp tubes filaments would be part of the cathode resistor circuit, and those tubes really did take forever to warm up because they didn't even have filament voltage applied to them until the output tubes warmed up enough to draw their full cathode current.
          For several years, my daily listener was an HH Scott mono integrated amp with a 5U4 and 6L6GCs that warmed up as fast as normal, but you didn't get sound for another minute or two because the 24 volts DC from the 6L6GCs cathode current powered the 2 12AX7s filaments. I kept forgetting about the cathode circuit each time I turned it on and would always wonder if I had a burned out tube each time I didn't get sound when I expected to. 
 

JohnAZ

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Re: Slow To Turn On
« Reply #7 on: March 09, 2018, 08:43:08 PM »
    The "controlled warmup" time is talked about in a lot of the fifties-sixties RCA tube manuals. There is something about 11 seconds mentioned, such as it reaches a certain percentage of its final filament temperature in 11 seconds. Tubes  drawing the same filament  currents, such as 600 milliamps (tv sets) or 150 milliamps (table radios) were placed in series like 12BE6 12BA6 12AV6 50C5 and 35W4  directly across the 120 volts AC line with the assurance that they all had the correct voltage on their filaments throughout the initial warmup cycle just as if they were connected to a power transformer filament winding.
     If you have ever seen a series filament circuit where the tubes are not all controlled warmup type tubes when the power is first turned on, you won't soon forget the experience. One or more of the tubes will  suddenly light up its filament like a flashlight bulb for the initial second, then will settle down to a dull red glow as the other tubes slowly become dull red than orange. The tube will not last nearly as long in a series string circuit as it would when connected to a transformer filament winding.
      Tubes designed for series string television sets always were controlled warmup time. They have odd filament voltages like 17, 21, 9, 5 etc. depending on the power needed for the tube cathode. These tubes always had 6 or 12 volt equivalents for tv sets with power transformers.
         I'm not sure if battery radio tubes were controlled warmup such as 1L6, 1R5, 3V4, but they had a huge voltage dropping resistor to drop 120 volts DC to 9 volts for the series filaments anyway which would swamp out the variations in resistance of an  individual tubes filament resistance. Those tubes would be 50 milliamps or so, some of the subminiatures were I think 40 milliamps,
       Also, low signal level audio preamp tubes would have their filaments in series powered by a DC filtered power source to eliminate the audible hum  from nearby 6.3 volt wires at the tube socket. 12AX7, 12AU7, 7025, 12AY7 and others had a 150 milliamp current draw in series hookup. There would either be a 48 or 36 volt or maybe 24 volt power supply that would double as a bias supply for the output tubes, or sometimes the cathode current through the output tubes such as 6L6GC would be adjusted to 150 milliamps and the 12AX7 preamp tubes filaments would be part of the cathode resistor circuit, and those tubes really did take forever to warm up because they didn't even have filament voltage applied to them until the output tubes warmed up enough to draw their full cathode current.
          For several years, my daily listener was an HH Scott mono integrated amp with a 5U4 and 6L6GCs that warmed up as fast as normal, but you didn't get sound for another minute or two because the 24 volts DC from the 6L6GCs cathode current powered the 2 12AX7s filaments. I kept forgetting about the cathode circuit each time I turned it on and would always wonder if I had a burned out tube each time I didn't get sound when I expected to. 
 

Lots of good info here. Thank you!

ed from Baltimore

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Re: Slow To Turn On
« Reply #8 on: March 09, 2018, 10:42:17 PM »
     I'm glad you liked it but it was definitely "TMI---too much information" as the kids say today.
     Looking at your tube layout chart, which I should have done in the first place, I am wondering if the unit has a separate rectifier and filter to put 12 volts DC on the two 12AX7s pre-amp tubes (not the 3 12AX7s in the FM multiplex ). If  so, that could be the cause of the longer than usual warmup time for two reasons. 1) they usually put less than 12 volts on the filaments instead of the full 12.6 (6.3 parallel) because the full emission capability is not needed in a low current pre-amp circuit, and the tube is less noisy at the slightly reduced cathode temperature, and other types of stray noises like heater to cathode leakage are much lower. With only 11 volts on the filaments, however, it takes longer to reach operating temperature.  2) With RC filtering of the DC power supply, the voltage takes some seconds to build up to the 11 volts instead of the large initial current from a transformer AC winding that gives the cold low resistance filaments a spurt of high current until they reach operating temperature. I have noticed that certain stereo preamps I used regularly with DC on the filaments seem to take a certain extra amount of time for sound  to come through.Their final filament voltage is always less than 12. Sometimes the selenium rectifiers lose efficiency and only 10 volts is on the filaments.
          5AR4s take longer to warm up than most audio tubes because they have a very large cathode cylinder and thick ceramic sleeve between the filament wires and cathode. . The plates are also cylindrical and the small spacing gives it a low conducting forward resistance unlike the wide spaced 5U4 somehow without sacrificing reverse voltage rating. 5AR4s put the highest continuous stress on the filter capacitors compared to 5U4s  (but not compared to silicon rectifiers)  , because of the high pulse currents through the low forward resistance. However...... their long warmup time ensures that the caps charge up slowly and no high voltage goes to the filter capacitors until the audio power tubes are all warmed up and ready to draw current. With 5U4s, the filter caps might have 500 volts on them after turn-on until the output tubes warm up and voltage goes down to normal , say 420. They used to rate electolytic capacitors WV or working voltage and surge meaning voltage it can withstand for so many seconds or so for that reason----  5U4G rectifier tubes warm up much faster than   6L6GC output tubes.
      If you turn off a 5AR4 powered amplifier and turn it back on after 3 or 4 seconds you will see a frightening flash inside the tube because its cathode will still be hot enough to allow a huge charging current into the caps which will have discharged to near zero thanks to the output tubes cathodes staying hot and discharging the caps in that same 3 seconds. This wont happen with 5U4Gs as their filaments cool off fast and it's probably good that Magnavoxs use 5U4s for their big amps as a lot of record playing users turn the stereo back on right after the record changer shuts off to put more records on the turntable. .
      This info can all be found in various years of the RCA tube manual under 5AR4, 5U4, 3DG4, 6AU4, 5V3 and other various indirectly and directly heated rectifiers tubes. Each one seemed to have a special explanation                       

TC Chris

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Re: Slow To Turn On
« Reply #9 on: March 09, 2018, 11:14:44 PM »
     I'm glad you liked it but it was definitely "TMI---too much information" as the kids say today.
                   

No, no--not TMI at all.  The wonderful thing about reading text is that the eye can scan and edit--skipping stuff that's not of current interest.  Better too much than too little info.  You confirmed what I vaguely remembered about the 5AR4, except that I thought the 5U4 had lower resistance, so I've always felt a bit guilty about popping it into the old Heath.

And I had never heard about running preamp tubes at lower filament voltage to get less thermal noise.

The whole purpose of a group like this is to learn and share information.  Life is more fun when you hang out with people who know more than you do.

Chris Campbell

ed from Baltimore

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Re: Slow To Turn On
« Reply #10 on: March 10, 2018, 12:33:18 AM »
      Well, until this answer-to-all-my-prayers website came to my notice a few months ago, I hadn't thought about these things for over thirty years (I'm 63 yrs old) and I feel like I should be ending every sentance with "I think" or "maybe"  cuz I'm just not sure about any of this, which is why I had to mention the various years of the RCA tube manual as the possible source.
      Here's what I remember about the 5U4-----large space between filament and plate, (even more in the 5R4 which has even higher peak inverse voltage and always seems to be used in high powered PA amplifiers supplying 750 volts DC onto class B biased 807s  ) The 5U4s filament is a tungstan ribbon with what looks like a small area compared to the large diameter 5AR4 cylinder. I think the large spacing combined with small area give it 50 ?? ohms or more forward resistance.
      Here's what I remember about 5AR4 -----large cylinder cathode with ceramic sleeve heated by thin looking tungstan inside the sleeve. The cathode cylinder takes forever to get red compared to the filament wire and I think this was deliberate so that even large cathode audio output tubes like EL34s would be warmed up before the filter caps would get their DC voltage from the 5AR4. The plate is a cylinder very closely spaced to the cathode which, along with the large cathode area gives it a lower voltage drop than a 5U4 at the same pulse current (capacitor input filter) which might not be expressed as ohms resistance......that part I forget.......Less voltage drop at same current is less power heating the plates and is why these tubes can be 6V6 size instead of 6L6 size.
        Something......and this part I forget also.......about the very close spacing, maybe combined with the uniformity of spacing due to using two concentric cylinders............gives the 5AR4 as high an inverse voltage rating as the 5U4 super large spacing. Space-charge effect ??   or virtual cloud cathode ???.....or maybe that explains why 6L6 and 6V6 beam tubes don't need suppressor grids or maybe why tiny cathode area FM tuner RF tubes have enormous transconductance...........Even if I could remember the words, I wouldn't know what they meant. Tubes really are magic !! 
        Either the RCA tube handbook explains it or maybe something like "Radio Engineering" by Frederick Terman of Stanford U or maybe F Langford-Smith's "Radiotron Designers Handbook". BTW,  don't pick up either book unless you want to stay awake for a week, they are that well written and that engrossing, and take it from me....... no......math......required !!!!!!  That's how down-to-earth the explanations are.
        The "original" close spaced cylinder plate high voltage rectifier was I think 5V3 (used in those beautiful Fisher amps in the President, I think, so there might be an explanation under that tube type in the RCA manual.
         Well......did it again, sorry about the TMI,  especially cuz I'm so uncertain about it all.

SeniorSteve

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Re: Slow To Turn On
« Reply #11 on: March 10, 2018, 11:35:27 AM »
Ed had a very good overview on the different reasons for controlled warmup on the tubes.  I took a sneak peek on the fisher consoles website and looked up the schematic on your 1963 Custom Electra.  There are three tubes in series which are the two phono preamp tubes and the 1st audio tube on the tuner chassis.  They are powered by the cathode current of the output tubes.  Your delay in sound is a natural thing.  First the output tubes have to warm up and start conducting in order for the preamp tubes to get filament power.  Then you have to wait for the preamp tube filaments to heat up.  With that in mind, if you have a bad output tube it may increase the warmup time even more as there won't be as much power for the filaments (if my thinking is correct).

Very good information in this thread, Thanks Ed.
Great site here.

Steve

JohnAZ

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Re: Slow To Turn On
« Reply #12 on: March 10, 2018, 12:52:43 PM »
Ed had a very good overview on the different reasons for controlled warmup on the tubes.  I took a sneak peek on the fisher consoles website and looked up the schematic on your 1963 Custom Electra.  There are three tubes in series which are the two phono preamp tubes and the 1st audio tube on the tuner chassis.  They are powered by the cathode current of the output tubes.  Your delay in sound is a natural thing.  First the output tubes have to warm up and start conducting in order for the preamp tubes to get filament power.  Then you have to wait for the preamp tube filaments to heat up.  With that in mind, if you have a bad output tube it may increase the warmup time even more as there won't be as much power for the filaments (if my thinking is correct).

Very good information in this thread, Thanks Ed.
Great site here.

Steve
Thank you! My knowledge of electronic theory is limited, but this makes sense to me.