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COULD TUBES BE FLATTEN OR BAD OR SOMETHING ELSE?

C

countrycousin

Member
Jul 22, 2009
9
0
11
I HAVE PURCHASED A AMPLIFIER THAT USES 2 813 TUBES. WHEN I TURNED THE AMP ON IT SHOWED 349 MILLIAMPRES I HAVE A SMALL RM KL 500 THAT I AM USING DEAD KEY SET AT 50 WATTS. WHEN TRYING TO TUNE THE AMP AND LOAD IT AT FIRST IT SEEMED TO BE GOING OK AT LEAST I THOUGHT. THE WATT METER READS 50 WATTS FROM MY SMALL DRIVING AMP AND WHEN I PUSH THE FOOT PEDAL I HEAR THE BOX CLICK LIKE IT ENGAGES BUT TUNE AND LOAD ONLY MOVES JUST ABOUT 10 TO 20 MORE WATTS BEFORE IT
RETRACTS TO A LOW READING. I HAVE TRIED AGAIN AND AGAIN BUT IT DOES THE SAME THING AND WHEN I LOOKED THROUGH THE LITTLE HOLES IN
THE SIDE BY THE TUBES THEY ARENT EVEN GLOWING AT ALL NOT RED NOT BLUE NOT NOTHING. THERE IS AN EXPLANATION FOR THIS EITHER I'VE BEEN
HAD BY A PERSON THATS ADVERTISING ON THE WEB "THE BEST AMP I HAVE
EVER OWNED" AND PUSHING CRAP OFF ON SOMEONE ELSE OR THE TUBES ARE NO GOOD BUT THEY DONT LIGHT UP AT ALL WHEN THE KEY IS DOWN. SOMEONE TELL ME THAT I JUST NEED SOMEMORE TUBES OR THIS PROBLEM IS NOTHING SERIOUS. OH THIS AMP IS A WELL PUT TOGETHER HOMEMADE I GUESS WITH B&W PARTS. HELP!:angry:
 

The relay could possibly have bad contacts causing this. Usually you can hear it arcing if so. Does the amp have a HV meter on it? If so does the reading drop when the wattage drops? It sounds like something is getting hot and it is losing drive maybe.
 
NO THE TUBES OR FILAMENTS ARE NOT LIGHTING UP WHEN FOOT PEDAL IS BEING ENGAGED. THE MILLIAMPERES READ ABOUT 345-350 SOMEWHERE BETWEEN THERE AND WHEN ENGAGED THE FOOT PEDAL IT DROPS TO 300 MILLIAMPRES. ON MY WATT METER WITH MY DRIVER ON I DEAD KEY ABOUT 50 WATTS AND SWING. WHEN THE FOOT PEDAL ON THE BIG BOX IS ENGAGED THE METER MOVES TO ABOUT 90 -100 AND SWING WHEN I MOVE TUNE KNOB IT FALLS ALSO THE LOAD KNOB IT FALLS BACK. WHEN I LOOK IN THE HOLES IN THE COVER I SEE THE THE TUBES ARE LIT BUT NO PLATE INSIDE THE TUBE LITES WHEN THE PEDAL IS PRESSED. I DO HEAR A CLICK IN THE AMP BUT NO SIGNIFICANT CHANGE IN WATTAGE. THANKS FOR REPLY HOPE YOU CAN SHINE SOME LIGHT.
 
Bionic Chicken said:
The relay could possibly have bad contacts causing this. Usually you can hear it arcing if so. Does the amp have a HV meter on it? If so does the reading drop when the wattage drops? It sounds like something is getting hot and it is losing drive maybe.
Click to expand...
YES IT HAS A HV METER AND IT READS 345-350 ON THE METER WHILE THE AMP IS JUST ON. WHEN I ENGAGE THE FOOT PEDAL IT DROPS TO 300 MILLIAMPRES. I HEAR CLICK BUT NOT A LOT OF CHANGE IN WATTAGE ON MY WATT METER.
 
Hate to tell you this, but your amplifier is not working at all. No filaments, nothing going into the tube, certainly nothing coming out. No idea why.
- 'Doc
 
W5LZ said:
Hate to tell you this, but your amplifier is not working at all. No filaments, nothing going into the tube, certainly nothing coming out. No idea why.
- 'Doc
Click to expand...
THANK YOU FOR YOUR REPLY.! I TOOK THE TIME TO UNSCREW ALL OF THE SCREWS IN THE COVER OF THE AMP AND FOUND THAT ONE OF THE TUBES IS NOT LIGHTING UP AT ALL SO I SWITCHED THEM TO SEE IF IT WAS THE PLUG AND FOUND THAT IT IS THE TUBE NOT THE PLUG AND I GOT A SIGH OF RELIEF WITH THAT THANKS AGAIN. COUNTRY COUSIN.
 
Mr Clean said:
Man that sounds like a ton of drive. Do you know what kind of DK that amp likes?
Click to expand...

I was just looking that up on an Amperex datasheet but what do they know about tubes. ;) On their sheet they spec never more than 2 watts per tube for class B RF amplifier service. The 813 is a pentode and as such has a crap load of gain.


http://www.basenjes.de/tubes/data/813.pdf
 
QRN said:
So you're saying that even the filaments are not lighting up? A pair of 813's make a nice amp of about 500-600 watts.
Click to expand...

Really?
the datasheet you link to shows 100 watt plate dissipation rating.
But it does show that you get 200 watts out with a 2kv plate voltage.
It shows half watt drive to get that.
So if you hit a pair of those with 50 watts, its hasta lavista baby.
 
I should have stated that power rating a bit better. That 5-600 watts is NOT in AB service running AM on CB.:D It is pep rating for an SSB signal or the oldtimers would run a pair of 813's in class C on CW.It was not unusual to see a plate input of 700-800 watts when running under those conditions but of course the duty cycle is fairly low. The 813 is a tough tube but it needs to be driven fairly lightly. Typical homebrew transmitters using them were often driven by a simple oscillator/buffer circuit that only provided a couple watts and would deliver several hundred watts out. With a pentode you need very little drive.
 
They could also be configured as triodes and cathode driven. That would account for more drive level.
 
HiDef said:
They could also be configured as triodes and cathode driven. That would account for more drive level.
Click to expand...


Yes that is quite true. Often tetrodes or pentodes are run as triodes in grounded grid service and the drive level requirement does become much higher.Sometimes I tend to forget the obvious. :headbang All my career I dealt with grid driven amplifier systems and still think in terms of that.Oddly however, whenever I think of building an amp for myself I think GG. :D GG amps are more stable and simpler to build but the grid driven amps have much more gain and will often provide more power output for a given circuit. Oddly most amateur amps on the market today are GG while homebrew amps of decades ago tended to be grid driven.
 
QRN said:
Yes that is quite true. Often tetrodes or pentodes are run as triodes in grounded grid service and the drive level requirement does become much higher.Sometimes I tend to forget the obvious. :headbang All my career I dealt with grid driven amplifier systems and still think in terms of that.Oddly however, whenever I think of building an amp for myself I think GG. :D GG amps are more stable and simpler to build but the grid driven amps have much more gain and will often provide more power output for a given circuit. Oddly most amateur amps on the market today are GG while homebrew amps of decades ago tended to be grid driven.
Click to expand...

As you said with a few more points. Given power levels of common transceivers cathode driven amps are a natural. They are also easier to deal with as opposed to grid driven with it's requirement for neutralization, regulated screen supply and extra bias supply. Don't bang your head. The know-it-alls on QRZ don't get it even after being spoon fed.

Cathode drive doesn't waste the extra drive power either. Most of it shows up at the RF out pipe. The RF will also have lower IMD with the same tOObs used in GG.
 

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