EF-86 issue

[sixstringer]

I've recently completed a AC-30/4 - Stangray style combo with a EF-86 as V1. The amp sounds great except for one thing. I've tried a couple of new JJ EF806-S tubes and every one seem to have the same issue. When I play a an F#7#9 on the 9th fret, the amp goes nuts. Because it happens with both of the EF806-S tubes, at first I thought it must be some other issue with the amp. I went through the amp, pulled the component board, checked and checked but could find no other problems. I put it back together and still had the same issue. Then I added a couple of O-rings as harmonic suppressors on the EF806-S and the problem was gone. I played it a bunch with no issues, and it was used on a medium volume gig for 3 hours with no problems.

So...the question is, is it really the tube, are there other things I should do to prevent this from happening again? The EF806-S does not seem to get very warm at all so are nitrile o-rings ok to use as suppressors? I have read that silicon is better, but where do you find those? I've also have read about the problems with EF-86 tubes in combo amps but Dr Z, Matchless and others seem to make it work so there must be a way.
Thanks for your help and advice

[212Mavguy]

ef86's are prone to microphonics. Nature resulting of design of the little pentode-y buggers. Gotta damp the bottle or isolate them from speaker vibrations.

[wsaraceni]

ef86's are prone to microphonics. Nature resulting of design of the little pentode-y buggers. Gotta damp the bottle or isolate them from speaker vibrations.

this is interesting to me. my next amp will probably be ef86 on the front end. What do you guys use for damers?

[tubeswell]

Vibration damping is best in all its guises. The more the better. I use o-rings and also the little nylon grommets in the chassis where the socket attaches (as well as an o-ring around the tube).

[img:925:1024]http://farm6.staticflickr.com/5234/7099 ... 9bc8_b.jpg[/img]

[M Fowler]

That is a very nice looking build.

I use o-rings from Sandyphoto on ebay they do the job.

Mark

[212Mavguy]

You guys are gonna laugh at this one...I had a problem with a microphonic pre tube in my silverface Fender Champ that I waaaaay hopped up, playing out, I stuck the amp upside down onto it's top, kept playing, and the problem went away enough to not interfere anymore.

Then I remembered that the old school octal preamp tubes in the old school guitar amps were worse than the smaller bottle stuff. The old school amp builders always put the amp's power section with tubes upright in the bottom of the cab next to the floor, better damping for the chassis by far and what is plugged into it in addition to tending to better tube cooling and longer life from their upright operating postion...

[sixstringer]

Thanks everyone. I'll isolate the socket. Mark, I just ordered up some of those silicon o-rings, thanks for the tip.

[212Mavguy]

Look into getting some tube coolers for your power tubes at least, the reason that small bottle hot running power tubes like 6aq5 and 6bq5 can die quickly if mistreated is that when tube glass envolopes, get very hot, they become enough more porous to the passage of outside air into the vacuum for the tube to be fatally poisoned over time at a much more rapid rate than if the glass was not allowed to overheat. And they aid in reducing microponics as well as RF shielding. The long out of production cold war tech IERC tube shields are great for el84's if you can get them. for my pair of el34 RFT/Siemens I use black corrugated thin aluminum tube coolers, as well as on my 12ax7 types, I use the el84 sized cooler for them because of the increased inertia from more length and increased mass's lowering the bottle resonance or "sympathetic vibration" frequency, the note present in a ringing type of microphonic behavior. For what it costs for the amp and effort in getting nice glass these are very worthwhile accessories that will overcome the significant buying resistance as well as percieved dollar cost. I thought I was a complete stupid cork sniffing tube dork for buyint them until after I had them and had used them for a few hundred hours, after noting initial benefits from the get go.

I still am a complete stupid cork sniffing tube dork tidiot...

But the power tube grid rattling present in those 50-60 year old el34's within my 50w D-clone is pretty much gone if I put the head on the right place on the cab..

The bias current at just under 70% draw has not changed at all for those power tubes after at least a couple hundred hours. The preamp is dead quiet and sounds gorgeous.

[Structo]

That is a very nice looking build.

I use o-rings from Sandyphoto on ebay they do the job.

Mark

Yes I use those O-rings on preamp tubes as well.

Mavguy, I hadn't heard that about the tube glass becoming more porous as they heat up.

Makes sense.

Do you have a link for the tube coolers you mention?

Edit:
http://www.partsconnexion.com/tube_cool_pearl.html

Make your own:
http://www.diyguitarist.com/GuitarAmps/Tubecool.htm

If you are really serious, water cooling! (more appropriate for transmitter tubes)
http://www.realhamradio.com/liquid-cooling.htm

[tubeswell]

That is a very nice looking build.

I use o-rings from Sandyphoto on ebay they do the job.

Mark

Yes I use those O-rings on preamp tubes as well.

Mavguy, I hadn't heard that about the tube glass becoming more porous as they heat up.

Makes sense.

Do you have a link for the tube coolers you mention?

I wonder if there is some kind of special heat-resistant, electricity-and-idiot-proof expanding gunk that you can rub on the outside of the tube to block the pores in the glass as it heats up? Maybe prolong the life of the tube. A great idea for oil made from snake hides maybe?

[Structo]

I'll get right on that.

[Reeltarded]

I wonder if there is some kind of special heat-resistant, electricity-and-idiot-proof expanding gunk that you can rub on the outside of the tube to block the pores in the glass as it heats up? Maybe prolong the life of the tube. A great idea for oil made from snake hides maybe?

I like the way you think. I made some from GoJo and Tabasco, but it won't work until I brand it, so don't even try.

i branded it. Willy Mathers' Tube Lather. It's official now. It works.

[212Mavguy]

Yup, for preamp tubes in 12ax7 size it's called 1 inch heat shrink tubing cut to length, two thicknesses quiets microphonics a decent amount, especially after the bottle heats up. But I still prefer the coolers. I just googled those words to find them years ago, they are out of canada and market to the HIFI crew.

[tubeswell]

I wonder if there is some kind of special heat-resistant, electricity-and-idiot-proof expanding gunk that you can rub on the outside of the tube to block the pores in the glass as it heats up? Maybe prolong the life of the tube. A great idea for oil made from snake hides maybe?

I like the way you think. I made some from GoJo and Tabasco, but it won't work until I brand it, so don't even try.

i branded it. Willy Mathers' Tube Lather. It's official now. It works.

flea-bay somewhere?