Valves....what % of new values is still ok?

[philv]

Curious about old power valves.

If a valve is measured at 80.% of new book values, is it still considered ok?
Will a valve at 80% typically underperform one measuring with new book values?
Or is it that it just has a reduced life?

At what % will a power valve typically be considered not usable?

The 80% is just for example.

Thanks

[anthonyTD]

Hi Philip,
It will depend greatly on the aplication, but safe to say, as long as there are no other aparent issues ie; low heater to cathode insulation, or other internal faults, then I see no reason why it cant be used indefinitely, or untill its emision drops low enough to apreciate a considerable diffrence in sonics, or output etc.
Hope this helps.
A...
Curious about old power valves.

If a valve is measured at 80.% of new book values, is it still considered ok?
Will a valve at 80% typically underperform one measuring with new book values?
Or is it that it just has a reduced life?

At what % will a power valve typically be considered not usable?

The 80% is just for example.

Thanks

[philv]

Yes..thank you.

I do remember my first valve amp,an aud ioinnovations s700.
It had a mxture of mullards and other power valves.
It sounded gorgeous, though tne valve amp tech said they measured badly
Mismatched, knackered and sounding luvly.

Hi Philip,
It will depend greatly on the aplication, but safe to say, as long as there are no other aparent issues ie; low heater to cathode insulation, or other internal faults, then I see no reason why it cant be used indefinitely, or untill its emision drops low enough to apreciate a considerable diffrence in sonics, or output etc.
Hope this helps.
A...

[anthonyTD]

In push-pull output stages, just remember; without individual bias adjustment for each valve; it is important to use matched pairs, as there will be an imbalance of current draw, withing the output transformer primary winding, which can cause hum! :)
Yes..thank you.

I do remember my first valve amp,an aud ioinnovations s700.
It had a mxture of mullards and other power valves.
It sounded gorgeous, though tne valve amp tech said they measured badly
Mismatched, knackered and sounding luvly.

[philv]

Thanks for the info.
The primaluna prologue 2 luckily doesn’t need matched valves.
Makes buying a quad of mullards much easier.


In push-pull output stages, just remember; without individual bias adjustment for each valve; it is important to use matched pairs, as there will be an imbalance of current draw, withing the output transformer primary winding, which can cause hum! :)

[philv]

One quesion.
If i’m looking at mullard e34 for eample, does it matter if i mix sngle halo wth twin halo?
Or for that matter wekded and staped plates?
Thanks



In push-pull output stages, just remember; without individual bias adjustment for each valve; it is important to use matched pairs, as there will be an imbalance of current draw, withing the output transformer primary winding, which can cause hum! :)

[anthonyTD]

Not really, as long as they test within their correct parameters, then no worries!
One quesion.
If i’m looking at mullard e34 for eample, does it matter if i mix sngle halo wth twin halo?
Or for that matter wekded and staped plates?
Thanks

[philv]

Thanks again.

[anthonyTD]

:)
Thanks again.

[oceanobsession]

The power valves I have had in the past the bias starts to drift a lot when they get past there best , a good example the bias is stable . the valve tester could also be out . phil

[goraman]

If out put valves are rated to last at 2,000 hrs, and your at the 1,000 hour mark and they test 70 to 80%.Why change them if they sound good /unless you are an ebay seller. A shady ebay seller would simply silk screen Telefunken on them, put them in a white box and sell them for several times more than they paid for them! Then buy new again.:cool: