Gremlin 2 !! Please Help

[David Mccallum]

Hi folk's,i would be most greatfull for some help with a recurring problem.I've had problems since i built my kel84 with the right ecf80 resonating,it produces a whineing noise which stops if i tap the glass side of the valve.I thought i'd cured it with a change of mains tx and some mullard valves,however on swapping these for two telefunken ecf80s the whine returned not good.I opened it up again and looked over everything,all seems fine.I went through the measuring procedure again and i have a couple of readings outside the 15 percent allowed.
Valve-1 pin-3 =97volts. valve-2 pin-3 =86volts. rated at -110volts.

Valve-1 pin-6 =90volts. valve-2 pin-6 =87volts. rated at -75 volts.

Valve-1 pin-9 =87volts. valve-2 pin-9 =89volts. rated at -75 volts.

Valve-3 pin-2 =.07volt valve-4 pin-2 =0.3volt. rated at -0 volts.

Valve-5 pin-2 = 0 volt valve-6 pin-2 =0.2volt. rated at-0 volts.

Do these reading's set off alarm bells.could they be responsable for the ressonance in the right ecf80?
Despite this problem the amp sounds great,so i'm thinking that there cant be that much wrong with it.
The mains voltage at the time of testing read 248volt so quite high but reasonable.
I like this amp very much so i'd especially like to sort it if possible.

[David Mccallum]

I've refitted the Mullard ecf80's, no more whine.. Either there is an awful lot of dodgy versions of this valve around, or i've still got a slight problem which is masked somehow by the Mullards. At present it sounds fine so i am just going to continue using it, unless someone has other advice.

[Greg.]

Bumping this to the top again because Dave hasn't had a response and I'm not familiar with KeL84. It seems to me that the first three readings listed are ok, but I wonder about the measured voltage (although small) on pins that should read zero. Can anyone help out?

Best wishes,

Greg

[hooger]

I have the same problem with my KEL84. It only happens once in a while, and it seems to be happening less and less (i've only had it built for a couple of months). There was a suggestion in response to my post (see KEL84 Whistle) that it could be due to the speaker cables or zobel network, though I didn't find a solution. So any help would be doubly appreciated. Incidently, what is the impedance of your loudspeakers? Mine are 4 Ohm, dont know if that will make a difference.

[David Mccallum]

Hi Hooger,im using speakers rated at 6 ohm.I've found that the noise(in mine) is coming from the fillament of the right ecf80 it seems to resonate though not all the time.I tried different make's and the least affected seem's to be mullard's version(£5) each from langrex supplies.It still does it though not as badly.I blew 60 odd quid on some cryo treated telefunken versions and they,after a brief run in screeched horribly so im .I've calmed down a bit now (these were marketed as being free from such pish) im now feeling a bit Leonard Cohen,to say the least.I've had few sugestions for help so im scunnered with it now and i've ordered a icon audio stereo 40i so i hope to be whine free real soon.Some people seem to be happier arguing about the right's and wrong's of forum protocol while pointing out that the purpose of this forum is to support Worid Audio's product's.Ive waited three month's to try to resolve this while tryin to maintain my temper!.The most annoying thing is that when it work's correctly it's one of the best amp's i've heard regardless (almost) of cost. I'd like to thank Greg for his support with my diy
effort,your a star,the cables are great by the way.

[Richard]

David

The guys on here will mostly help if your problem rings bells with them. This is a self-help forum and there have been fewer people building WAD/WD amps recently due to the lull before Peter took over. It's also tricky to diagnose problems at a distance.

Have you asked Peter for help? There used to be a help service available.

Alternatively if you get over this way, Nottm, and can leave it with me I'll fix it.

Rich

[Mike G]

Hi David,

I too had a problem (although not the same as your's) with my KEL84 a few years back. At the time I didn't know this forum existed, and after several weeks of frustration, I discovered via Nick Lucas who was with WAD at that time, that John Caswell maybe able to help, and he did! Ok some of the satisfaction of building the amp and getting it to work yourself was lost, but as soon as I admitted defeat, having the amp fixed and working correctly, far outweighed this, and I learn't a little in the process. Like Richard said, this is a self help forum with many people offering suggestions based on their own experience. I post very infrequently, as I don't have a wealth of valve amp knowledge, I tweak my WAD kit following suggestions, and comments made here, and have learn't much, sometimes I feel I seem to take rather than give positively to this BB, personally I find this BB inspiring, and a gold mine of idea's and information.

Following on from Graeme's recent "Newbie builds KEL84" thread, I've rebuilt mine, new internal cable, heater mod, shunt mod on vol control, new phono inputs, and speaker posts, to go with the black gates, and Alps pot already fitted. Just after some chrome transformer caps now.

IMHO, i'd certainly pursue the KEL84, I'm sure a trip to the good Dr John, would be a cheaper option than buying another amp!

Regards

Mike.

[David Mccallum]

Originally Posted by Richard

David

The guys on here will mostly help if your problem rings bells with them. This is a self-help forum and there have been fewer people building WAD/WD amps recently due to the lull before Peter took over. It's also tricky to diagnose problems at a distance.

Have you asked Peter for help? There used to be a help service available.

Alternatively if you get over this way, Nottm, and can leave it with me I'll fix it.

Rich

Thank's Richard,a kind offer indead. I have traded an amp im not using in for an icon audio (i recon that it's better than the tripath digital im trading in).
I would still however like to somehow resolve my problem with the kel84,for mine and possibly other's benefit.I've discussed the problem with John C and he made a couple of sugestions but as was rightly pointed out it is difficult in the extreme to diagnose problems over the phone,i;ve tried what he suggested to no avail so im left thinking ,i dont want to continually be pestering him on the phone about this. And i dont want to stretch his patience any further.Thanks for the repair offer thou i think that im at a bit of a geographical disadvantage.Unless you fancy a short break with an oscilloscope in the west highlands of scotland .I could however send it by white van man . Thanks again.

[Greg.]

I acknowledge the wisdom of Richards and Mikes post above, but I do think David is being a bit let down here. He's posted a set of voltage measurements and apart from me (commenting in ignorance) no one has expressed an opinion. In particular,pins with voltage on them that should read 0v. What is that all about? It might be shorts in the circuit.....I don't know, but I do think he deserves a more constructive reply of the kind that has sorted me out in the past.

Best wishes,

Greg

[NickG]

I would suspect non zero voltages where it should be zero would make me suspect there was a higher resistance in the 0v line somewhere thjan there should be.

The other (less easy to find) possibility is that there is some VHF oscillation going on, and its just upsetting the meter. I have found that if I push a pentode into instability a nearby unconnected DVM start to show a reading. 12E1's seem to love to sing at 1mhz given a chance.

Maybe not much help as it stands, but I agree the non zero voltages seem like they should be looked at.