Just connected up an old friend, Radford STA25 III

[walpurgis]

SS rectifiers will last indefinitely whereas valve ones predictably wear out and also have high series resistance. Thorn were not exactly known for over engineering...
Random (or not so random) blowing of diodes etc is entirely due to bad design practice.

Many swear a valve rectifier allows the amp to sound better. Not sure how that can be though. It just rectifies.

[Arkless Electronics]

Many swear a valve rectifier allows the amp to sound better. Not sure how that can be though. It just rectifies.

As you would no doubt expect, I completely disagree.... Indeed it just rectifies and with vastly less losses than a valve rectifier.

[mik_rik]

Hi Jez the Thorn set was just an example,every type of tv was just the same .In theory ,ss devices should not go wrong but they do - changed thousands in my time -and in all sections of tv's etc-from s/c ,o/c and leaky/noisy In tech college in the 70's I remember the lecturer saying [and the older tech's at work] transistors etc would never need replacing as they wouldn,t go wrong.Just think valve recs can take more stick if something goes wrong somewhere else in circuit.If they sound better is another can of worms discussion to get into -myself ,I like the thought of valves Mick

[spendorman]

Yes, solid state transistors, rectifiers can fail at any time although there is no other fault in the circuitry. It's a rare occurrence, but does happen. Probably some latent fault in manufacture.

A lot of Germanium transistors have failed decades on due to tin whiskers.

Fairly recently one of my Quad 303's (of 1967 vintage) had a failure of one of the output transistors, strange as it had not been maltreated and nothing else was found to be faulty. The faulty transistor was replaced and all is fine again.

DSCF2277 by A60man, on Flickr

[struth]

Transistors failed in tvs, as did valves..valves failed more i guess. Old tvs were not a great envioron for valves especially.. hot and dusty, valve bases always got dirty. Many homes were damp so arcing caused probs... big smoothing caps blowingwith messy results... hell youve no idea what you used to see inside some of those things.

[Arkless Electronics]

Hi Jez the Thorn set was just an example,every type of tv was just the same .In theory ,ss devices should not go wrong but they do - changed thousands in my time -and in all sections of tv's etc-from s/c ,o/c and leaky/noisy In tech college in the 70's I remember the lecturer saying [and the older tech's at work] transistors etc would never need replacing as they wouldn,t go wrong.Just think valve recs can take more stick if something goes wrong somewhere else in circuit.If they sound better is another can of worms discussion to get into -myself ,I like the thought of valves Mick

Hi Mick,
As you would expect I've changed thousands of faulty semiconductors myself also... Valves will take vastly more stick electrically than SS devices but the downside is they wear out... In consumer gear such as TV's the bottom line is pretty much all that matters for most makers! High voltage rectifiers have come on a bit since back in the day but it was always recommended to specify for many times the maximum voltage that could occur even in a fault situation. Best practice is to use strings of say 3 x 1N4007 1000V rectifiers for 240V mains, each with a resistor of around 220K and a capacitor of around 0.01uF across it. Two such strings replace a standard bi-phase valve rectifier used with a transformer with grounded centre tap. Done properly like this it should outlast the amplifier....
Similar strings with many more rectifiers are commonly used in valve RF power amps where they routinely work with 2500V for decades without trouble.

Obviously nothing is 100% reliable and just as with valves there will be the odd rogue failure... but usually far less often than with valves!

[mik_rik]

I agree about the bottom line, British electronics industry would have lasted longer if they had used better than bog standard components in the main[Hunts caps anyone].Also agree with valves wearing with use as in "the tubes gone" in the tv! crt's are only a type of valve.As I said ,I like the idea of valves just as some people like E-Types or Bonnevilles against modern cars /bikes [hands on fettling included

[mik_rik]

On about heat in tv's with valves,back in the 70's one model of Pye colour tv,-CT205 I think had an all valve line o/p stage.A common fult was a 100k resistor and a.1uf cap which went s/c.The pict would be lost and a few times the customer would sometimes wait for it to come back on ,all the time the PL509 was drawing more current and getting hotter and hotter.End result was the glass envelope melted leaving a sucked in hole in it."Oh no ,the picture went off and we switched it straight off" Now that is a room heater!

[Arkless Electronics]

On about heat in tv's with valves,back in the 70's one model of Pye colour tv,-CT205 I think had an all valve line o/p stage.A common fult was a 100k resistor and a.1uf cap which went s/c.The pict would be lost and a few times the customer would sometimes wait for it to come back on ,all the time the PL509 was drawing more current and getting hotter and hotter.End result was the glass envelope melted leaving a sucked in hole in it."Oh no ,the picture went off and we switched it straight off" Now that is a room heater!

I've only seen this happen the once personally.... A JJ EL34 fitted to a guitar amp...

[spendorman]

I've only seen this happen the once personally.... A JJ EL34 fitted to a guitar amp...

From what I read a while back, early JJ EL34's were not terribly reliable, they soon improved the situation. I have used JJ KT77's and EL34's in several amps, not had a failure, yet!