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General repair of a HI watt HI gain 50w valve head.

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Tann-44

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This one came in with no sound fault!


So let's get on with it....remove chassis and connect to test speaker and power up...next check front panel to ensure all indications are working/lighting up. A quick signal in and turn the gains up...mmmm no sound...to cut a long repair story short, it turned out to be dry joints on all valve bases due to the crappy lead free solder..a reflow with 60/40 solder and she burst back to life working fully. that darn lead free solder has a lot to answer for!


Never power up a valve amplifier with out a speaker load or damage may happen!!
 
yeah, that stuff is loads of fun...... i'm seeing lots of IC failures from tin whiskers. but i have noticed that you can't tell a bad solder joint from a good one with lead free solder because both have the same frosted appearance.
 
Despite what it was doing to the gear, I got a big kick out of loading up tube types to the point that the plates glowed red. And if it was a push-pull circuit, even better. I just knew I could see the electrons flowing (or so I convinced myself)...
 
Despite what it was doing to the gear, I got a big kick out of loading up tube types to the point that the plates glowed red. And if it was a push-pull circuit, even better. I just knew I could see the electrons flowing (or so I convinced myself)...

well you might not have actually seen the electrons, but you can see their effects:
Code:
FLUORESCENCE (Photo 1)- this type of glow is usually violet in color and most noticeable 
around the inside surface of the glass bulb. It is most pronounced on power tubes and is the product 
of electron bombardment of the glass taking place within the tube. It generally has no adverse affect 
upon receiver performance, and in fact, tubes displaying this phenomenon are particularly good with
respect to low gas content.

the problem with running tubes with enough current to turn red, is they don't last very long in that condition. you strip the cathode material and can also melt the glass (letting air in). i once replaced a horizontal output tube in a TV that had sucked the glass into a funnel shape and eventually vented air in at the tip of the funnel.

there are tubes made to run red, but these are very large transmitter tubes with graphite plates and envelopes large enough that the glass is far enough away from the plate that it doesn't melt.
 
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That too. The ionizing effect was present often. But I'm referring to the plates. I've actually seen them with holes burned through the plate material. Little incandescent sparks be emitted from the edges of the hole(s) during the process.

Course, back then, tubes were considerably cheaper, and wasting one or two was no big deal.
 
had an amp in for repair with a separated grid wire in a 6550 (ampeg svt) and the cathode resistor was showing 1.5V across it (and IIRC the cathode resistors in an SVT are 1Ω, so the tube was drawing 1.5A before the protection circuit kicked in). the customer had just tested all the tubes, probably on an emission tester, so this is one good reason to use a Gm tester.
 
I've had two more HiWATT 50's this week...fault report by the sound guy... 'These amps have no reverb' and he said 'Ive removed the chassis looked in side them and could not see any thing a miss... So after inspection of the main tank the simple problem was both fine wires had came away from the connection to one side of the transformer coil and needed a quick solder up and back in action:):)
 
that's very common in reverb tanks...
 
It's been a few months now from the last hi watt... Yesterday just finish 1 more this time round a replacement valve job... sounds sweet happy days.:D
 
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