Oscillating Liverpool?

[tubejunky]

Hi all.

I have this 18w Liverpool build I'm working with that has what sounds like an oscillation or fizz riding the distortion. My layout is good, shielded grids, twisted leads going to the power tube grids etc. Moving wires, changing preamp tubes etc. doesn't change anything.

Is this just characteristic of this circuit? I admit I don't think I've ever even played through an El84 amp before this, and it sounds good otherwise.

Thanks,

tJ

[HeeBGB]

Can you post a sound clip of the problem? It's hard to find a problem like this with just a verbal description of it.
And some pics of the guts would be nice too!

[tubejunky]

Yeah, here are some clips.

[Doug H]

Wow, it sounds good to me.

What kind of output transformer are you using? I'm prototyping a ~13W Liverpool using a pair of ECL86's and it sounds pretty harsh. I'm thinking it is the 125E xformer I'm experimenting with. I'm going to try a Heyboer next.

Where did you have your volume control set for that clip?

Doug

[Omar]

Couldn't tell from the clips but from the description it sounds like it could be blocking distortion. I had this problem with by clone and putting blocking resistors tamed it down. Just my .02 cents.

Omar

[tubejunky]

Here's a better clip of the problem..

Doug, it's a Heyboer OT. Volume was at about 7.

[Doug H]

Ok I hear it. My guess is it might be oscillation. I have heard this kind of thing before and fixed it by moving the longer grid wires around.

Doug

[tubejunky]

I can't pin it down. Are Sovtek 8L84's decent enough? Any other ideas?

[Doug H]

That's not due to tube brand. I think you have something else going on. Layout, lead dress, grounding etc are places I would look.

Doug

[tubejunky]

I'm not sure that the shielding in my guitar isn't the culprit. I also have a transistor/zerner voltage-dropping network in the PS that I'm a little weary of. The PS is star-grounded at the transistor.

Seems like I've had a similar oscillation in other builds..

[HeeBGB]

Hey TJ...where are you at with this?

Ant headway?

I am having some problems with my Express clone but only with El34 tubes in it. 6V6's run fine.

Anyway....see if you can get some pics up so we can see what we're dealing with!

Greg

[tubejunky]

I finally figured this thing out.. It was the attenuator I was using (weber mass)! That explains why my other amps have had the same oscillation. Instead of having sustain and feedback, the amp would go into harsh oscillation. I do know that this amp is LOUD.

Thoughts?

[HeeBGB]

SO it was the MASS all along?!!!

Note to self:don't buy a MASS!

[Doug H]

I hate using an attenuator, which is why I'm building a 13W Liverpool.

Doug

[Aharon]

Wow, it sounds good to me.

What kind of output transformer are you using? I'm prototyping a ~13W Liverpool using a pair of ECL86's and it sounds pretty harsh. I'm thinking it is the 125E xformer I'm experimenting with. I'm going to try a Heyboer next.

Where did you have your volume control set for that clip?

Doug

Doug...what voltage are you running your ECLs at?
Thanks