Jump to content

Weston AcousticsTempest and Shuguang Treasure KT88Z


Recommended Posts

Hi all,

 

I recently acquired a 2nd hand Weston Tempest amplifier.  As testified by many members here before, it is indeed a beautiful (visually and sonically) piece of gear.

The GL KT88 that came with the amp look well used, they feel a bit loose on the socket, and one of them even has a broken central locating pin.  I decided to look for a set of new valves.

 

After seeing lots of raving reviews on the net, I gave the Treasure Series KT88Z a go, in spite of the price. They are costlier than most other new production valves, but much more affordable than any NOS stuff.  I ordered a matched quad set from AA-Acoustics in the UK through e-bay.

 

It all went well for the first 8 hours of use.  The bias was set at 100mA as per the instruction manual.  However, when I turned the amp on last evening, after about 5 minutes, one of the four vlaves turned all bright red from top to bottom and there was a low hum form the speakers even though the volume was at zero position.  I of course turned off the amp immediately and contacted the seller.  Quite reasonably, he asked for some more info and some proof of the fault.  I swapped the valves with the old GL and all was fine, I suppose that means the amp is in good condition. 

 

I (very, very anxiously) powered up the amp tonight again just for the sake of quickly taking a picture, or a video.  To my surprise, it all works fine!  My problem is that it is now very difficult for me to provide any proof that there is a fault.  It probably made me sound like an idiot and/or an unreasonable trouble maker.  This is only my second valve amp, I rolled the valves of a Jolida before and there was no problem what so ever.

 

Would any member be kind enough to advise if it is still safe to keep using this set of valves?  Is it a 'normal' for new valves to behave strangely initially?  Finally, has anyone have much experience with the Shuguang Treasure Series valves and what were their experience like?  Would I be better off just sticking to GL, TS or EH etc etc?

 

Many thanks.

Edited by The Kel form Hell
Link to comment
Share on other sites

I had one new kt66 out of a quad glow red red, emailed the seller http://www.thetubestore.com/ and they sent me out a replacement no charge no question's asked, great people to deal with.Swapped it over with no damage to the amp.Sorry I've no experience with the Shuguang Treasure Series.

 

Ask Earle if a dud tube may have caused any problems .

Edited by MC240
Link to comment
Share on other sites

yep, if all is working well, it would just be the valve that was the issue.

 

Unfortunately with Valves, like a light globe, you just never know how much life there is in it.

 

When i had a valve pre amp, i just stocked up on plenty of spare valves for such situations

Link to comment
Share on other sites

I had a similar situation occur when I had just finished building my valve amp kit and had started running it in.

 

It had been playing at low volume for a number of hours driving a pair of old Realistic speakers ... when I decided to turn the volume up slowly and all was going well until the volume level started getting up a bit then all of a sudden one of the Gold Lion KT88's "flashed over" and produced a bright light and then a loud hum through the speaker of that channel ...

Needless to say I crapped myself and quickly shut the amp off.

 

I let everything cool down ... inspected the valve for any physical damage internally ... it looked OK.

So I tentatively turned the amp back on with my finger on the power switch should another flashover occur ... the amp powered up as normal this time.

 

So out came the multimeter and I checked all the bias voltages ... the bias on the "faulty" valve way above spec so re-adjusted all the voltages and everything seemed fine again.

Then I swapped the "faulty" valve to another socket on the amp ... just to see if the fault would follow the valve ... re-checked all bias voltages again and the amp again worked as normal.

 

I contacted the designer and described what had happened ... and he said it that it could be a faulty valve and what I described was not uncommon in a valve amp and sometimes tubes prematurely fail.

 

With that I bought another pair of GL KT88's as spares in case of future problems.

 

Subsequently I kept running the amp in and put more hours on it without any further problems.

Moved it into my main system and have been running it ever since without any more issues and listening to it at all sorts of volume levels.

I check the bias voltages from time to time and they have remained steady and within spec.

 

The bottom line of this tale is the valve that I thought was faulty has been fine ever since and is faulty no more.

 

 

Did you re-check the bias at all during those first 8 hours use?

 

Perhaps your Shuguang Treasures need to have some hours put on them (while keeping tabs on bias voltage) before becomming stable or perhaps that one valve really is faulty.

 

Time will tell I guess.

 

Good luck :)

 

 

 

 

Link to comment
Share on other sites

Thanks guys for all the advice. 

 

Sierra, my experience is almost identical to yours. I have now powered up the valves about five or six times to try to take a photo of the 'Great Big Glow' to show the seller. Yet all the valves, including the initially faulty one behave normally.  Initially, there were still some intermittent hum from the speakers. After a few more hours of running in, the hum has now disappeared.  I have started playing some music with them and the sound was actually quite nice!  The initially faulty valve is now in a different position, but remains in the same channel.

 

I did check the bias setting after installing the valves.  The Tempest has a built in meter and it was a breeze to monitor the bias on the go.  I set it to 100mA as per instruction.  For the first few hours, the bias fluctuated a lot and I had to constantly adjust.  Unfortunately, on the Tempest, the bias is adjusted and checked for each channel, but not for each individual valve.  As only one valve went wild, I have no idea if that valve was on a different bias as compare to the good valve on the same channel.  The flucuation of the bias reading seems to have lessened significantly now.  When it went red, I did the same thing as you did,  'crapped myselsf and shut the amp off', I did not think of checking the bias right then, nor taking a photo immediately.

 

While it is great that the dud seems to have come good, yet it presents a dilemma for me.  I now cannot provide a proof to the seller as it does do the big red glow again. It sounds quite good, but I still feel somewhat uncomfortable about it.  After seeing how it looked about to blow up, there is no way I will turn on the am and say, have a shower while it warms up.  Of course, I am also worried about any possibility of damaging the amp and speakers if I continue to use them in the long term. I still have to decide what I should do with them.  I am seriously thinking about just cop the loss of around $385.oo and  buy another set of valves.

 

On that subject, any suggestions on what brand of valves, and which seller?  It is good to hear MC240 relating his experience with the great service and replacement policy of the tube store.  I bought my last set of KT77s to replace the EL34s on a Jolida from them too.  Jon seems to be very nice to deal with.  They are a liitle bit more expensive than some other sellers, but may be I should stick with the reputables, in spite of the slightly higher cost!

 

Your advice is much appreciated.

Link to comment
Share on other sites

Hi Kel.

 

It isn't uncommon for new valves to fault like this. I have heard of one GL doing this (now two), and many Chinese made KT88's, various brands.

I have had three or four Tempest owners with issues using Treasure KT88 valves. Similar to yours where one tube goes into runaway bias.

It sounds as though yours has settled and may have been a partial internal short on the plates that has "fixed" itself. Don't stress too much leaving the amp alone as there are fuses installed to protect the output transformers and amplifier from overload. (check manual and rear panel of your amp, it may even be wise to double check the fuses, they should be no more than 500ma slow blow. If you are worried, replace them with 250ma slow blow, this will fuse them earlier if the fault appears again). The main fuse in the IEC socket should be 2 amp slow blow.

 

It may have shortened the life span of that particular tube a bit, and also may not be perfectly matched to the others. A simple way to check this is to set the bias to 100ma (each channel) let the amp run for a good 20 minutes, check and adjust the bias to 100ma. Turn off your amp, wait for the valves to cool (5 minutes) then swap the suss tube with a tube in the other channel. turn on the amp and monitor the bias reading for the channel with the suss tube. After 20 minutes it should read 100ma or very close, 95 to 105 would be acceptable (+/- 10%).

 

Whilst some may suggest running the output tubes at a lower bias setting, this isn't ideal. Distortion will increase and it will switch to class B at a lower output level. Setting the bias at 100ma (50ma per tube) or 17 watts, is well below the maximum recommended idle plate dissipation for a KT88 output tubes in a class AB design.

 

Cheers, Earle.

Link to comment
Share on other sites

Hey Kel,

 

As Earle has mentioned I wouldn't be too worried about it ... there is a good chance that the valve won't fault again.

 

I was also a bit concerned for the first day or two after my flashover happened but that disapeared the more hours I put on the amp.
Eventually I forgot all about it and havent given it a thought since.

 

Just follow the checks mentioned by Earle and sit back and enjoy your music.

 

My original GL KT88's came with my amp kit (as an upgrade) ... the subsequent pair I bought I got through Jim McShane who was great to deal with and can source most valve types and brands.

Link to comment
Share on other sites

Should you wish to buy another set of valves try Winged C's which have a good reputation. Evatco in Queensland can supply them and Mal has complete valve testing/matching capabilities.

 

A good guy to deal with.

Link to comment
Share on other sites

A sincere thanks to everyone who helped out, especially Earle, there is nothing more reassuring than hearing from the creator of the amp himself.

Just when I thought my communication with the seller was going nowhere, I got an e-mail offering to send me a single replacement Tresure KT88 with the same measurement of 55mA.  I therefore expect a satisfactory ending and lots of musical enjoyment.

As such, I think I also owe Ian Large sales@aliumaudio.com  a positive comment about and his service and replacement policy.
 

Link to comment
Share on other sites

I cannot comment on KT88s, but I had an identical issue with new production "Mullard" EL34 valves a few years ago.  Shockin'.  Pun intended.

 

I have been using new production Genalex Gold Lion KT77s for about 4 years without a blip.  This is not an endorsement, just an observation, as we know production runs vary in their consistency and reliability.

 

It also helps to swap them about every six months or so in the same manner as you rotate tyres.

Link to comment
Share on other sites
  • 10 months later...

Hi all, this thread is old now but someone may pick up on my experience. I have had a Tempest for a while now (signature special if I believe the hype). For a while I fell out of love with it and this was because of the KT series tubes. I know that these are flavour of the month and I have tried many different types...Valve Art, Gold Lions (new issue) etc. The power amp came with TungSol 6550's I think, maybe EH. But then I began rolling into KT's. Big mistake. I put the amp away for a while and played with other things which were ok but I missed my Tempest. So I got it out, dusted it off, fitted a set of 6550's and I was back in audio heaven. I swapped in several KT's to 'just see' and I was right the amp was much better with the 6550's....MUCH. So now i am running a new set of matched Winged C 6550's and it has never sounded better– it is stunning. The message here is that I was a bit thick and thought I knew better than the manufacturer who had designed a 6550 amp. not a KT amp. Now I know these are to some extent interchangeable but don't dis the 6550 if your Tempest was designed around them. The KT's sounded hard/harsh and not noice at all. 

cheers,

Sonic Monster.

Link to comment
Share on other sites
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.




×
×
  • Create New...
To Top