scout keeps blowing fuses help pleazzzz !!!!!

[radioreddz]

got a scout 2 x 6 amp. on the high side i have it on a dead key of 350 watts swinging to 1050 exactly. on the low side it dead keys 125 watts and swing to 300. the problem i am having is that on the high side if i key up more than 5 seconds it will blow the fuse in the amp which i have at 8 amps slow blow. also if i am on the computer it will cause my curser when i key up to stop and i have to turn my computer on and off to get it to work again. but on the low side i have no problems at all. could it be reflect of mayber a tube. i have been using the 8 amp fuse for years with no problems before. also did not have the problem with the computer before this problem. also it sems like the tubes are glowing more than before. help pleazzzzzzzzzzzz miss my amp !!!!!!!!!!!!!!

 

[Mr Clean]

I have a 4 driving 4. I love how it said on the case not for use on 11 meters

 

[radioreddz]

got a scout 2 x 6 amp. on the high side i have it on a dead key of 350 watts swinging to 1050 exactly. on the low side it dead keys 125 watts and swing to 300. the problem i am having is that on the high side if i key up more than 5 seconds it will blow the fuse in the amp which i have at 8 amps slow blow. also if i am on the computer it will cause my curser when i key up to stop and i have to turn my computer on and off to get it to work again. but on the low side i have no problems at all. could it be reflect of mayber a tube. i have been using the 8 amp fuse for years with no problems before. also did not have the problem with the computer before this problem. also it sems like the tubes are glowing more than before. help pleazzzzzzzzzzzz miss my amp !!!!!!!!!!!!!!

help !!!!!!!!!!!!!!!

 

[nomadradio]

Umm, a "Scout", eh?

Never have seen one that I remember.

But I think there's one unintended clue in your description:

also it sems like the tubes are glowing more than before

If you mean that the outer gray or black structure inside the tubes is showing color, that's a sign of two possible things:

1) You have already overheated the tubes enough to damage them.

-- OR --

2) You will, if you keep it up.

Big, "transmitting"-type tubes like 3-500Z, 572B and 811A will all show some "cherry" on that plate structure when running full bore. Those types are built from materials meant for a higher operating temperature than small tubes adapted from color TV circuits.

I'm assuming your Scout has eight 'sweep'-type tubes, meant for use in color TV receivers. The plate on these is NOT supposed to show color. How long you key it will affect this, as well as how hard you drive it.

Either way, if the plates on those tubes "cherry" AT ALL, the life is (or was) draining out of those tubes by the second.

I'll predict that some small (soldered-in) part that controls bias voltage on the driver tubes has failed. Typically a 20 or 30 year-old electrolytic capacitor will wear out and short. This blows out the black plastic rectifier diode that feeds it. Now the tubes have NO fixed bias voltage on them. This causes the tubes to pull more current from the power supply than they should. The extra heat just gets dumped onto the tubes' plates. Enough excess heat and they'll glow. First a dull red, then brighter. Before they can get to orange, the fuse should already have blown.

I'll give you credit for one thing. You skipped the next step in this process. What usually comes next is the owner will cuss the last "correct"-size fuse he had, and puts in a larger size.

When that one blows out, larger fuses get put in, until eventually the circuit breaker for the building's outlet circuit trips out.

By then, so much smoke has been let out of it that the repair estimate gets out of hand.

Even if all you've damaged is tubes, that won't be cheap. Unless it was made with "orphan" tubes with high heater-voltage ratings, like 30KD6, 31LQ6, and such types. Some of those are still cheap.

If it uses the more common 6-Volt heater tubes like 6MJ6, 6KD6, 6LF6 or such there will be sticker shock, if you haven't shopped for those in a decade or three.

And if it was made with the, er, "industrial" 4-digit tubes like 8950, 2057 or 8098 tubes, the sky's the limit.

Maybe the tubes are still okay, but it doesn't sound like it.

And if you install new ones, don't let them "cherry". But if they do, it would prove that there are other faults remaining in the amplifier besides just failed tubes.

73

 

[radioreddz]

Umm, a "Scout", eh?

Never have seen one that I remember.

But I think there's one unintended clue in your description:

also it sems like the tubes are glowing more than before

If you mean that the outer gray or black structure inside the tubes is showing color, that's a sign of two possible things:

1) You have already overheated the tubes enough to damage them.

-- OR --

2) You will, if you keep it up.

Big, "transmitting"-type tubes like 3-500Z, 572B and 811A will all show some "cherry" on that plate structure when running full bore. Those types are built from materials meant for a higher operating temperature than small tubes adapted from color TV circuits.

I'm assuming your Scout has eight 'sweep'-type tubes, meant for use in color TV receivers. The plate on these is NOT supposed to show color. How long you key it will affect this, as well as how hard you drive it.

Either way, if the plates on those tubes "cherry" AT ALL, the life is (or was) draining out of those tubes by the second.

I'll predict that some small (soldered-in) part that controls bias voltage on the driver tubes has failed. Typically a 20 or 30 year-old electrolytic capacitor will wear out and short. This blows out the black plastic rectifier diode that feeds it. Now the tubes have NO fixed bias voltage on them. This causes the tubes to pull more current from the power supply than they should. The extra heat just gets dumped onto the tubes' plates. Enough excess heat and they'll glow. First a dull red, then brighter. Before they can get to orange, the fuse should already have blown.

I'll give you credit for one thing. You skipped the next step in this process. What usually comes next is the owner will cuss the last "correct"-size fuse he had, and puts in a larger size.

When that one blows out, larger fuses get put in, until eventually the circuit breaker for the building's outlet circuit trips out.

By then, so much smoke has been let out of it that the repair estimate gets out of hand.

Even if all you've damaged is tubes, that won't be cheap. Unless it was made with "orphan" tubes with high heater-voltage ratings, like 30KD6, 31LQ6, and such types. Some of those are still cheap.

If it uses the more common 6-Volt heater tubes like 6MJ6, 6KD6, 6LF6 or such there will be sticker shock, if you haven't shopped for those in a decade or three.

And if it was made with the, er, "industrial" 4-digit tubes like 8950, 2057 or 8098 tubes, the sky's the limit.

Maybe the tubes are still okay, but it doesn't sound like it.

And if you install new ones, don't let them "cherry". But if they do, it would prove that there are other faults remaining in the amplifier besides just failed tubes.

73

hey mr. nomad just the guy i was hoping to answer thanks for your reply. i think i might have found out the problem hopefuly before i have done any serious damage to the tubes. i did a little playing with my load and tune knobs, it seems like the swrs were a little high around 1.4 higher that normal. i used the load to bring them down then retuned the tune and the driver. i don't know what sequence or anything just got crazy and started turning knobs in desperation. but any way the tubes aren't getting cherry and it seems like i don't have the reflect with it screwing with my computer cuasing me to have to reboot it. on the low side it will dead key 175 to 200 watts and swing to 450 and on the high side it will dead key 350 and swing a little over 1000 i will keep my finger crossed and maybe i did not hurt the tubes to much i have had this box for over 25 years or more with the same tubes been a good ol'e box it's like a old friend. but thanks again Mr. Nomad for your very informative reply.

 

[nomadradio]

Glad to hear it turned out to be simple. No small children in the house who like to twist knobs?

Makes me wonder if you didn't accidentally turn the Load control too close to its minimum position. Sometimes this will produce a "false" peak on the wattmeter, a quarter-turn or half away from the "real" peak position. The false peak will always be a much lower reading on the meter than normal. Also tends to make the SWR read higher than it really is.

Didn't think of that. This happens more often with smaller amplifiers, with no more than three tubes. Frustrates the tar out of the user, until that Load knob gets put where it belongs.

If you've gotten this many years from one set of tubes, it's clear that you have been treating them well. No other way to make them last that long. Eventually, the glue holding a chrome-plated cap onto the top of the tube gives way. This puts stress on the tiny wire that actually goes through the glass to the inside. Removing the clip on the cap of that tube will fatigue that wire and the cap falls off when the wire severs. Just be nice to those plate caps atop the tubes.

Only tubes with a "black" pate cap are immune to this.

Good luck with your old friend. Eventually it will blow a head gasket, drop a valve or a ring. Enjoy it until it does. The bill for a 100,000-mile tuneup could prove to be a real heart-attack risk.

73