kt88 amp

dear all
i,m a newbie here ,and was wondering if somebody can help me.iv,e had a
wdkt88 for about 2years now,it has been extensively modified with a whole
load of classy bits & has 2 sowter uo82 trannies,it play,s very well indeed.
now can anybody tell me anything about it ,also how often have these to
be checked and serviced.
many thanks
willfal60
dundee.

[david]

Hi Will,
It depends on how much and what use it's had. The small signal tubes have a very long life but the KT88 output tubes have a life of around 2,000 hours or less-depending on brand according to some.

I just had a pair of WAD300b monoblocs I built back for a service. These are now 9 years old, and the output tubes-300bs-were 5 years old. The amp is used most days for 8 hours.

The only thing that needed doing was replacing the output tubes. Although these still sounded OK, the new tubes gave the amp back its sparkle.

All the signal tubes and rectifiers were still fine but were replaced simply because we wanted to set the amp fair for another 5 years. We also replaced the psu caps.

So, after two years you might be nearing the end of life for the output tubes depending on use. That and a good contact clean valve and input sockets would probably set you fair for another few years.
David

hello david
this amp has 4genelex gold lion kt88.approx 10months
2mullardcv4003 approx 1year
2gec6au6wc, new fitted this morning.
the amp gets about 4to5 hours a day,the reason i asked is i thought it was
running a bit hot,i,m maybe dreaming ,because it still sounds great.
i also run a mf a100 class a amp and boy does that get hot.as i said i,m
pretty new to valve amps and don,t want anything to go wrong.
i,m greatful for all the help i can get.
regards
will

[david]

Hi Will,
It all sounds fine then. Valve amps do run fairly hot.
David

[Greg.]

Originally Posted by david

Valve amps do run fairly hot.
David

That is not necessarily the case. It depends on the engineering of the individual components in the build. You, David will know that the mains Tx of the 300B PP only gets warm when it has been on for several hours.

Will, the WD88 mains transformer does get fairly hot over several hours but you should still be able to place a finger on the cover for several seconds before you need to remove it. Modern valve amps are built with finer tolerances in their components compared to older units that over engineered, so things can get hot, but that does not mean they are overheating. I have run a WD88 amp continuously for over 8 hours a day and although the mains Tx gets hot to the touch, the amp as a whole is not stressed at all and performance remained as expected. I don't think you have a problem here.

Greg

[Ali Tait]

Hi Will,

If you are happy you can do so safely, use the build instructions and check all voltages are in spec. Should ease your mind that the amp is running as it should.

hello all
regarding amp yesterday it was on for about 10 hours ,it played faultlessly
and it was ok heatwise ,well i was able to put my hand on it and hold it there.
now,ive been offered a mint pair of castle stirling3 speakers and was
wondering if any of your learned gentlemen have any thoughts on them.
iv,e read that they go great with valve amps.at the moment i use
kefiq5se & revolver music3 speakers,not the best but not the worst either.
i value all the advice i get.
many thanks
cheers
will.:

[Richard]

Hi Will,

Was it my old amp last seen heading to Scotland a good few years ago?
If so it's WAD Kit88 with those Sowters on in place of the original op txs.
The mains tx is inside and the amp does run warm but should be fine.

In this pic it has Svet 6550C valves,

[Black Stuart]

If amp designers could get their heads out of the 1950s and start out with the idea of creating chassis that allowed for heat conduction this would go a long way to lengthening the life of components. Both our WAD amps had components fail due to excessive heat when we lived behind the Snowy Mountains in Spain.

That's why I use a slate box which has a partially open rear and a Noctua fan to constantly shift the heat produced - this means that all components are running much cooler.

I've just finished working on the chassis top plate to create an even better airflow for the 7806 regs, mosfets, power resistors etc.

A very simple and effective mod is too cut off the bottom 4 mm from the heatsinks on regs etc. this allows the heat to be constantly removed due to conduction and even better when you use a quiet computer fan as I do.

Most heatsinks have fins but this is pointless if the heatsink sits directly onto the PCB.