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Old 15th March 2012, 03:04 AM   #1
MelB is offline MelB  Canada
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Default Taming the 83

I switched my parallel 300B's from a 5AR4 over to an 83. There were a lot of sparks at first!! Here's the circuit: Transformer is a Hammond 272JX 300-0-300 51 ohm secondary => 83 => 20uF => 5H Hammond 193H 65 ohms => 680uF => 2 x 300B. I'm getting 388 volts and set the tubes at 70 mA each with fixed bias. I get ~50mA per 300B at about the 2-3 second mark.

What I ended up doing to stop the arcing was installing an inrush current limiter and 150uH choke on each secondary lead. The current limiter is a GE CL-140 which is 50 ohm @ 25C rated 1.1 amp max. It's what I had on hand. I'm going to try tweaking the limiter using no arcing and max voltage as my reference.

Yes, I just turn it all on. From what I have read the 83 is classified as a receiving tube by RCA and you just turn them on. I know 680uF never existed back then but neither did in rush current limiters.
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Last edited by MelB; 15th March 2012 at 03:26 AM.
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Old 15th March 2012, 06:56 AM   #2
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Goodness. You should be arrested for abuse.
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Old 15th March 2012, 09:16 AM   #3
316a is offline 316a  England
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Originally Posted by MelB View Post
I switched my parallel 300B's from a 5AR4 over to an 83. There were a lot of sparks at first!! Here's the circuit: Transformer is a Hammond 272JX 300-0-300 51 ohm secondary => 83 => 20uF => 5H Hammond 193H 65 ohms => 680uF => 2 x 300B. I'm getting 388 volts and set the tubes at 70 mA each with fixed bias. I get ~50mA per 300B at about the 2-3 second mark.

What I ended up doing to stop the arcing was installing an inrush current limiter and 150uH choke on each secondary lead. The current limiter is a GE CL-140 which is 50 ohm @ 25C rated 1.1 amp max. It's what I had on hand. I'm going to try tweaking the limiter using no arcing and max voltage as my reference.

Yes, I just turn it all on. From what I have read the 83 is classified as a receiving tube by RCA and you just turn them on. I know 680uF never existed back then but neither did in rush current limiters.
That's not the right way to use a type 83 ! First cap is too large for a start , also I find with MV the filaments have to be hot enough before HT is applied , probably the reason why you are experiencing arcing . I'm well aware some old valve testers used a 83 like you have but I do not recommend it . I use a latching relay to energise the HT manually after about 30 seconds for slow start along with an NTC thermister (surge-gard). You don't seem to mention suppresion chokes have been fitted either . These can either be a common mode choke in the filament supply or separate chokes in each side of the anode circuit . These really do help the top end , without these I find holding an AM radio close to the amp causes excessive interference

For best sound use a small first cap , the 83 seems happiest (to me) running with a cap under 2uF .

316A
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Old 15th March 2012, 05:50 PM   #4
MelB is offline MelB  Canada
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That's not the right way to use a type 83 ! First cap is too large for a start , also I find with MV the filaments have to be hot enough before HT is applied , probably the reason why you are experiencing arcing . I'm well aware some old valve testers used a 83 like you have but I do not recommend it . I use a latching relay to energise the HT manually after about 30 seconds for slow start along with an NTC thermister (surge-gard). You don't seem to mention suppresion chokes have been fitted either . These can either be a common mode choke in the filament supply or separate chokes in each side of the anode circuit . These really do help the top end , without these I find holding an AM radio close to the amp causes excessive interference

For best sound use a small first cap , the 83 seems happiest (to me) running with a cap under 2uF .

316A
Not the right way to use it? But I'm simply following the manufacture's guidelines. If your concern is because of cold cathode stripping, I can't find anywhere that that occurs below 600v. I think this has been discussed to death. Any other reason not to use it the way I am?
First cap is too large? Again RCA data mentions up to 40uF being used in their guidelines. How do you arrive at 2 uF? Is that a personal preference? Just looking for your reasoning. Also as the filament heats in my design is it not essentially a slow turn on? Would not hitting this circuit on a warm filament result in a possibility of more arcing due to immediate high current capability of a warm 83? Again just asking for an understanding of the mercury vapor tube. I have pre-heated these things in my Hickok tube tester and kept them upright while moving then to the amps to make sure the mercury is all pooled at the bottom of the tubes.
Do I not have suppression (150uH) on each side of the anode circuit (see picture and circuit description)? I kinda pulled 150uH out of thin air for a value. Any help with a value here appreciated. Are my chokes not in the right place?

Thanks!
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Old 15th March 2012, 06:36 PM   #5
316a is offline 316a  England
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Originally Posted by MelB View Post
Not the right way to use it? But I'm simply following the manufacture's guidelines. If your concern is because of cold cathode stripping, I can't find anywhere that that occurs below 600v. I think this has been discussed to death. Any other reason not to use it the way I am?
First cap is too large? Again RCA data mentions up to 40uF being used in their guidelines. How do you arrive at 2 uF? Is that a personal preference? Just looking for your reasoning. Also as the filament heats in my design is it not essentially a slow turn on? Would not hitting this circuit on a warm filament result in a possibility of more arcing due to immediate high current capability of a warm 83? Again just asking for an understanding of the mercury vapor tube. I have pre-heated these things in my Hickok tube tester and kept them upright while moving then to the amps to make sure the mercury is all pooled at the bottom of the tubes.
Do I not have suppression (150uH) on each side of the anode circuit (see picture and circuit description)? I kinda pulled 150uH out of thin air for a value. Any help with a value here appreciated. Are my chokes not in the right place?

Thanks!
I believe you should run as close to choke input (small or no input cap) as possible with all MV's and ensure the filament is hot enough . I have tried the 83 as cap input , listened and much preferred the small input cap and a slightly higher voltage HT transformer I'm not sure how to work out the value of suppressor choke as it will depend other factors such as the DCR of your HT transformer , load current etc . You can try a very low DCR common mode choke between the filament and filament supply also if your filament transformer has a centre tap . A tip to check what is going on RF wise is to hold a small radio near to the 83 , put on an AM band and run the the stations . Alternatively hang a choke off a scope probe , wave around the amp as a crude serach coil .

316A
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