Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Jul Sun 21, 2019 9:01 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 46 posts ]  Go to page 1, 2, 3  Next
Author Message
 Post subject: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Wed 03, 2014 12:49 am 
Member

Joined: Jun Thu 30, 2011 9:03 pm
Posts: 280
Location: Pennsville, NJ 08070
I bought a lot of tubes off eBay for cheap, one of which was a 60FX5. Comparing the data sheets, it appears to be close enough in its specs that I am thinking I might be able to use it in place of a 50C5 with a resistor across the heater pins (3 & 4) to shunt enough current to the heaters of the other tubes (50C5 is a 150 miliamp heater tube and 60FX5 has a 100 miliamp heater).

I have a copy of the book "Aids to Wartime Servicing," which describes how to shunt using resistors when using different current heater tubes in series string sets, and using the formula in the book, I believe a 1.2K resistor will work to allow the other tubes downstream to see the proper voltages with a 60FX5 in series with them.

Here's the formula, just want to check that this is correct:

R1 = voltage of heater / current to be shunted

R1 = 60 / .05 = 1,200 ohms (1.2K resistor).


Does that sound right? It should be easy enough to tack a small 1.2K resistor right to the heater pins so I don't permanently modify any set I try this tube in. Opinions?



Thanks,
Joe


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Wed 03, 2014 1:29 am 
Member
User avatar

Joined: Nov Sat 26, 2011 4:09 am
Posts: 9518
Location: Texas. USA
jdivito wrote:
....Here's the formula, just want to check that this is correct:

R1 = voltage of heater / current to be shunted

R1 = 60 / .05 = 1,200 ohms (1.2K resistor).


Does that sound right? It should be easy enough to tack a small 1.2K resistor right to the heater pins so I don't permanently modify any set I try this tube in. Opinions?
You're going to have problems with the pin tacking idea because that 'small' 1.2k has to dissipate 3 Watt (and doubling the power rating is a good idea).


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Wed 03, 2014 1:29 am 
Member

Joined: Jun Tue 02, 2009 3:38 am
Posts: 1271
Location: Albuquerque, NM
Is this for a project or repair?

If you've got a couple I'd be willing to make a trade for couple 50c5s if you want to avoid shunting.

Shunting is common in some sets. Battery tube sets do it a lot because of low cathode current maximums but heater shunting makes a lot of heat, so be aware of that.

_________________
-Kyle


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Wed 03, 2014 1:42 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13829
Not much space in most AA5 that use miniatures to mount a resistor, plus a 50C5 won't operate with the mod, otherwise it would be a reasonable sub...


Last edited by 35Z5 on Dec Wed 03, 2014 1:47 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Wed 03, 2014 1:44 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 27719
Location: Detroit, MI USA
The other problem is characteristics of the two types are enough different that it could affect operation. You would also need to change the cathode resistor to get the correct bias.

_________________
Dennis

Experience is what you gain when the results aren't what you were expecting.


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Wed 03, 2014 1:45 am 
Member
User avatar

Joined: Nov Sat 26, 2011 4:09 am
Posts: 9518
Location: Texas. USA
35Z5 wrote:
That's a no go Houston...

A 60FX5 has a 100ma heater vs 50C5 150ma, otherwise it would be a reasonable sub...

That's why he's shunting the heater with 1.2k.


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Wed 03, 2014 1:48 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13829
Flipperhome wrote:
35Z5 wrote:
That's a no go Houston...

A 60FX5 has a 100ma heater vs 50C5 150ma, otherwise it would be a reasonable sub...

That's why he's shunting the heater with 1.2k.


Yeah I already edited my orig...


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Sat 06, 2014 3:52 am 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8540
Location: Long Island
The math doesn't work. If you want the rest of the tubes in the set to run right, the heater current in the string has to remain 150 mA and you'll end up with 50 volts across the 60-volt heater in the 60FX5. At 5/6 of normal voltage, it will probably draw about 5/6 of normal current, say about 90 mA. So a shunt resistor to get you back to 150 mA would be 50 V/.06 A = 833 ohms. Power dissipation in it would be 3 watts.

Ohm's Law aside, a 60-volt heater on 50 volts is likely to perform poorly, and premature failure of the cathode is likely. There's nothing rare or scarce about 50C5 tubes, while the 60FX5 is not so common. I'd hang onto it for a set that really needs it.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Sat 06, 2014 4:44 am 
Member

Joined: Nov Sat 27, 2010 6:15 pm
Posts: 5449
Agree, get a 50C5.


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Sat 06, 2014 1:26 pm 
Member

Joined: Jun Sat 09, 2007 8:14 am
Posts: 3683
Location: Florida
If you can get the 60FX5 to act like a 150 ma tube by adding a parallel resistor, the overall result would be similar to using a 45Z5 for a 35Z5 in an octal AA5. The "extra" 10 volts distributes across the entire string. This reduces the voltage to each tube to 92.4% of the nominal (121/131=0.924). This is only a little different from running on 110 volts, which used to be common (110/121=0.91).

I'd still use a 50C5 since the gains are different (can you say oscillation and/or hum pickup?) as well as the plate resistances and bias.

RRM


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Sat 06, 2014 2:35 pm 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 22902
Location: Somers, CT
I'm glad you pointed that out, RRM... (voltage sharing) I was getting ready to make a similar comment.

Pete

_________________
Just because it can be done doesn't mean it should be done.


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Sat 06, 2014 5:19 pm 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8540
Location: Long Island
If you were to fully light the 60FX5 at 100 mA, with a 50-mA shunt to take up the slack, the series string would require 60 + 35 + 12 + 12 + 12 = 131 volts. That's a bit more than the line voltages in most houses, even today.

Now if one were to plug the set into 120-volt power, each tube heater would be running 8% below normal. That's the point at which tube life could be shortened due to inadequate cathode temperature, so I would not endorse that. Plugged into 110-volt power, the heaters would be 16% below normal--i.e. the the 35W4 would be seeing about 29 volts, and the 12BE6 would have about 10 volts on its heater. The set might play or maybe not, depending on a whole lot of factors like which way the wind is blowing.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Sun 07, 2014 5:59 am 
Member

Joined: Jun Sat 09, 2007 8:14 am
Posts: 3683
Location: Florida
There was no mention of trying to use the 60 volt tube with 110 volts in, only that it is workable if the line voltage is about 120 or maybe a little less. Common sense says that things may get unhappy if the line voltage is much lower. As for 8% low being a potential problem, I have an AA5 that is labeled 105 to 120 volts. This would be 105/121=0.87, or about 13% low. That doesn't seem so good to me but that's what the set's label says.

The radio that used to reside in the kitchen of the house I grew up in was happy on 110 volts and never had a tube replaced in over 30 years of daily use. That would be 110/121=0.91, or about 9% lower than nominal.

As for acceptable filament voltage variations, I've seen very little real data on this, only that tubes are happier at the nominal voltages. Some writings say +/- 5% others +/- 10%. The only agreement seems to be that higher is bad, too low is bad, and nominal is always better. Good thing we're not going to the moon here.

RRM


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Sun 07, 2014 9:32 am 
Member

Joined: Dec Sun 14, 2008 3:33 pm
Posts: 843
Location: Tokyo
The line here in Tokyo is 100VAC. A number of old timers have told me most people never bothered to get a step-up transformer for their US made receivers, at least the simple ones, without VR tubes. Just touch up the alignment, if necessary, and run them on 100 volts. They claimed near zero tube failure. One S38E is apparently still going strong on its original tubes, which would make them about 45 or 50 years old. I've got a couple of AA5 radios and they seem to work fine on 100VAC. This may not be, technically, good practice, but if you get a couple of decades of use from a tube, why worry about it?

Rob


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Sun 07, 2014 3:14 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13829
This is so funny, one month the virtues of increasing total heater string voltage is in vogue, the next it's a Cardinal sin...

It's no doubt as Rob's example, other than a slower warm up 10, 15, even 20v isn't likely to create any noticeable issue...

After two NOS 35Z5 failures in approx 24 months(9 & 14mo), and three well used that lasted maybe 12 months total, I stuck a 45Z5 in the little Admiral daily player that's only turned off maybe five or six hours a day(and sometimes never)... After approx six months, if there's any difference in performance I can't tell it, even warm up occurs within what would be considered a normal amount of time...

I'll update in a year or so...

Tom


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Sun 07, 2014 4:54 pm 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8540
Location: Long Island
Look, all I am saying is that it is best to run tube heaters at their rated voltages. What's so bad about that?

You want an anecdote where lower heater voltages result in documented, demonstrably shorter tube life? It's in the numerous HP 410B VTVMs I've repaired over the years. HP intentionally ran the first amplifier tube, a 12AU7, with 4.5 volts on the heater instead of the nominal 6-V to cut down on noise. In nearly all the 410Bs that came across my bench, that tube is dead. Not due to open heaters, but due to absolutely no detectable cathode emission. The other 12AU7s in these instruments, which are often the same age and manufacturer, run with normal heater voltage, and are usually still good. HP even mentions in the manual that the first preamp tube may need to be replaced more often because of the low heater voltage. But back then new 12AU7s cost less than a buck, and the meters were so much better than anything else at the time, that the tube was just treated as a "consumable."

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Sun 07, 2014 11:24 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13829
Chris108 wrote:
Look, all I am saying is that it is best to run tube heaters at their rated voltages. What's so bad about that?

You want an anecdote where lower heater voltages result in documented, demonstrably shorter tube life? It's in the numerous HP 410B VTVMs I've repaired over the years. HP intentionally ran the first amplifier tube, a 12AU7, with 4.5 volts on the heater instead of the nominal 6-V to cut down on noise. In nearly all the 410Bs that came across my bench, that tube is dead. Not due to open heaters, but due to absolutely no detectable cathode emission.


Nothing wrong with operating tubes at their rated voltage, which for most receiving tubes is + /- 10%...

When one is comparing a tube operating at 71.4% of rated voltage vs an additional 10v added to a 122v string that's now operating at 92.4% of rated voltage, not a very good comparison...

I don't think anyone would recommend operating a AA5 at 87v which is 71.3% of normal AC at 122v(what voltage is into this house)...


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Mon 08, 2014 12:27 am 
Member

Joined: Jun Sat 09, 2007 8:14 am
Posts: 3683
Location: Florida
Chris108 wrote:
............. the first preamp tube may need to be replaced more often because of the low heater voltage.......


4.5 volts is only 71.4% of nominal and way lower than I would have thought was a good idea but then HP wasn't exactly a garage shop. How much do you suppose the lifetime was affected? Was it the difference in the tube lasting 10 years instead of 20 or 2 years instead of 20?

All the tubes in my 410B were good when I got it and none were new but I have no information on the history of the meter.

As for the original topic, we're talking about a klooge here.

RRM


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Mon 08, 2014 4:20 pm 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8540
Location: Long Island
Most of the 410Bs I've worked on were older than I am, or at least contemporaries, so I did not know their whole histories. But very rarely have I ever found an original HP branded tube in one, suggesting that most were already on their second or third re-tubing by the time they found their way to my bench. Based on comparisons of the dead or dying tubes to the ones which still worked, I'd have to say that the first preamp tube only lasts about 50% as long as the rest. How many years that takes would of course depend on how the meter is treated: if left powered on all the time, one would probably be changing that tube about once a year. If the meter was only turned on occasionally, the tube would last a lot longer.

When J. Presper Eckert designed the WW-2 ENIAC computer, he found it necessary to reduce the heater voltages of most of the tubes so they could make it through one day of work without something breaking down. But he also reduced all the other voltages on the tubes in similar proportion, which appears to be a key insight. Thus, an AA-5 going 40 years without a tube change on 100-volt power in Japan, or 30 years in parts of the US which had 110-volt power seems perfectly logical. The B+ voltages in those radios would be lower too, and the tubes might last nearly forever. Presumably the performance would not be as good as when full voltages were applied, but in an AA-5 tuned to a local station, who would ever notice the difference?

But in situations like the HP 410B, where full B+ is applied to tubes with low heater voltages, the cathodes seem to suffer greatly. HP had a rationale for it which made sense at the time (lower noise), but I just don't think the OP's idea of using a 60FX5 and a shunt resistor in place of a 50C5 is really advisable. Especially considering that while neither tube is scarce or hard to get, on average the 60FX5 sells for about twice the price of the 50C5 on eBay!

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
 Post subject: Re: Question on subbing a 60FX5 for a 50C5.
PostPosted: Dec Mon 08, 2014 4:26 pm 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 22902
Location: Somers, CT
As an academic exercise, it is an interesting discussion.

There are other examples of tubes being run at reduced filament voltages, most notably diodes used in noise limiters (effective contact potential.) Here is a discussion relating to a Collins receiver, but Hallicrafters and others used the same technique:
http://amfone.net/Amforum/index.php?topic=15898.0;wap2

Hallicrafters and others used the same technique for the same reason.

But, perhaps the OP has a few sleeves of the 60fx5 tubes, and may have found a useful application, at least for his needs.

Pete

_________________
Just because it can be done doesn't mean it should be done.


Top
 Profile  
 
Post New Topic Post Reply  [ 46 posts ]  Go to page 1, 2, 3  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: Eddy and 1 guest



Search for:
Jump to:  


























Privacy Policy :: Powered by phpBB