Gremlin 2 !! Please Help

[Richard]

Hi Davy, All,

Well done Davy I felt you tried everything we could think of and really expected you to throw the thing out of the window sometimes. Thank heaven the Gremlin's dead!

Davy sent it here on carriers and really I couldn't fault it. It sounded great in my system and tested spot on. £15 each way, but at least it didn't get damaged and we knew it wasn't a build fault.

When he plugged it in at home again it was just the same, very disappointing. He tried rewiring with/without fb etc and re-routing various parts but still no joy.

I sent a couple of 100pF caps to go g1 to ground. With the new 10K first valve gridstoppers they made a 160KHz roll off in case hf oscillation was the issue. Still no cure.

Last ditch was the mains filter which we hoped might lower or stop what must be local noise at his end. Well, we still don't know for sure as the filter went in at the same time as the supply company upgraded the mains so it could be local RF noise, which the filter has now stopped, or it could have been the mains all along.

This really has been a nightmare situation for any amp supplier or builder but it's great it's fixed.

Upgrade path for me Davy would now be a couple of 47K Maplin metalfilms used with that 50K pot to convert it to a shunt volume control. This gives much greater clarity and will bring a little more life to the top end which I felt was the main weakness. Certainly it would come before any silver wire or fancy bits.

Rich

[David Mccallum]

Thank's Richard,
the backup and assistance that yourself and others have given me on this forum has been invaluable,many thank's to all of you.
Regard's the volume pot/resistor upgrade,it sounds well worth trying.I came across it before but was more interested in getting my amp working properly before modifing it further.
Trouble is i can't remember where i'd seen it,can you please refresh my memory as to how the resistors were connected?.


Cheers

[Richard]

Hi Davy

There's a long write up in the FAQ Tweaks but, simply, you just add the 2 resistors and reconnect the pot pins like this,

[David Mccallum]

Thank's again Richard,i'll let you know how i get on with this interesting looking mod.I'll need to spend more time going through the FAQ'section in future.

Cheers