18Watt.com

Just a little more on pentodes .... We’ve had excellent results (Thanks to ZP ! ) with the “ 6SJ7 Pentode 18 watt Lite...Formerly the ABSOLUTE Minimum , and had no troubles with microphonics ... Nice Sweet Tone , loves pedals , LOUD !!!
Also have had Great success with the 6U8 , triode pentode tube in the “Croaker “ series at Wattkins.com ... Again chime and sweetness of Tone .... been called “ Jimi in a box” ...

Lots of alternative pentodes to choose from ... just sayin’ ... and we gig with ours , so it’s been well tested ...

I have used EF83 tubes, they are cheap, pin compatible with EF86 and can be got quite cheaply. They can be found in some Grundig reel to reel recorders where they were used used for automatic level control.

Yes, there is some evidence that the degree of microphony is dependent on the type of tube, with EF86s possibly being more sensitive to microphony than other types. I've also had reports that Amperex Bugle Boy EF86s are pretty good with microphony, and shouldn't normally need shock mounting.

I have recently got a bunch of 5725 (6AS6W) pentodes, which are 7 pin valves used in military airborne applications and are stated as able to withstand severe mechanical vibration.

Has anyone tried these as a preamp?

http://www.r-type.org/pdfs/5725.pdf" onclick="window.open(this.href);return false;

Dave , that’s Very Interesting !!! Thanks !!!

I came across this link about the little dot headphone amp which uses the 5725 as a preamp tube, so I guess they must be OK for audio applications.

http://www.littledot.net/forum/viewtopic.php?f=9&t=815" onclick="window.open(this.href);return false;

DaveW wrote:I came across this link about the little dot headphone amp which uses the 5725 as a preamp tube, so I guess they must be OK for audio applications.

http://www.littledot.net/forum/viewtopic.php?f=9&t=815" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

Found a brief mention on AX84, a few more others to try as well.

Lots of pentode Fun going on at Wattkins ... http://www.wattkins.com/node/18704" onclick="window.open(this.href);return false;

Lots of people talk about pentode problems in preamp and microphonics, but can anyone advise on building a ef86 preamp (ac15 amp actually), into a head. Many of the posts I have read are in regard to noise problems from speakers etc. but I'm building a head, so any ideas?

You will have less microphonic tube problems with a head style amp build. The speaker will not be beating the snot out of the tiny little innards in those tubes so the ones that start out not microphonic will usually stay that way. One downside is you will need two hands instead of one to transport the amp. There used to be a couple of 18 watt layouts with an EF86 in the download section. No Vox layouts though.

It'll only weigh maybe 18-20lbs, but do you mean two hands for stability, or they don't like shaking, or what? I assumed it would be better in a head, as I have read a bunch of the posts here on ef86's, and everyone seems to build them into combos and they get insanely beat up by speakers. I have a AC30/4 schematic I'm using. And I searched the AC15 schematic several times on the internet, they are so close it was fine.
Thanks,

Maybe he means a speaker cab in one hand and head in the other?

Dd

+1
When you set up the head at a gig or a session, be sure to put it on something that doesn't vibrate (i.e. on or in front of a speaker cab) or get bumped around. Set it on top of a layer or two of padding on a chair or a small parsons table (I love my $7.99 Ikea "Lack" table for my home rig) or atop an effects rack. The pad attenuates and damps vibration and the "remote" location avoids vibration due to direct contact.

BTW the leg spacing of that Ikea "Lack" table http://www.ikea.com/us/en/catalog/products/20011413/" onclick="window.open(this.href);return false; is just right for a poor man's rack. 19" rack equipment fits nicely and you can use sheet metal screws to mount things (just be sure to pilot drill the holes in the legs so they don't crumble when you drive the screws).

KennyO

If you're worried about vibration, you could probably also use speaker isolation foam, like the stuff they use under studio monitors.

I did mean amp head in one hand and speaker cabinet in the other. Usually means one more trip back to the car to get the guitar. A lot of times those microphonic tubesthat rattled and howled in a combo work fine in a head in the v2 or v3 spot.

I think you also get better tone out of a dedicated tone cabinet, combo cabs are just for convenience imho.

Finished mine yesterday. Sounds great, except need to reduce the el84 cathode cap from 18watt value (500uf) to 250uf like in a ac15, and a couple small tweaks, but it sound great, maybe the fact that I used original Celestion Blue (Vox Silver Bulldogs) speakers for playing, in a 2x12 cab... Guess that helps, but sound really great though.
Anyway, Yea in a head cabinet it sounds pretty good. I had to take the tube shield off of it as it rattled, and it really only is as Microphonic as a bad 12ax7, so its pretty reasonable. And no problems with it right on top of the cabinet. I played it through a little 1x12 with a WGS reaper in it and that was great too. It squeals with my tele, when you dime it, so I gotta try some other guitars too, as It's just that that guitar is a little microphonic itself, as the pickups arent potted. but they are pretty good.

The 5879 pentode is a nice alternative to the EF86. We've used this in V1 in numerous builds including the HoSo56 which originally had EL84's.

http://www.el34world.com/Forum/index.php?topic=6176.0" onclick="window.open(this.href);return false;

and in overdrive sections of amps like this one:

http://www.el34world.com/Forum/index.php?topic=9636.0" onclick="window.open(this.href);return false;

With respect, Tubenit

I've got the AC15 EF86 preamp as a second channel in my 18 Watt head. Works fine except for the EF86 in there at the moment has gone noisy (it crackles) and needs replacing. I've never had microphonic issues with it.

Hello

another very good option is to use a used EF804 from Telefunken. The differences to the EF86 are very small and it is a really very stable tube with less micro phonics than the today available 12AX7A, even selected. I have build some custom amps with that tube and the sound is really wonderful.

Best regards
Ingo