6BM8 Tube

[FunkyE9th]

I may have a lead on amp using 6BM8s. The amp has a 5Y3, a 12ax7, and 2 6BM8. I haven't seen the amp in person yet. I'm thinking of converting it to use EL84s or 6V6s. Are the socket chassis holes needed for 6BM8s the same for EL84s or 6V6s?

Thanks,

-FunkyE9th

[p90freak]

http://www.nj7p.org/Tube4.php?tube=6bm8

According to the above, it has the same base as an el84.

(edit: meant to say socket )

[Firestorm]

The 6BM8 uses the same nine-pin socket as an EL 84, but it's NOT the same base. 6BM8 = 9EX; el84 = 9CV. The sockets will have to be mostly rewired (only the heaters are the same).

The 6BM8 has a triode and a sharp cutoff pentode in the same envelope; the el84 is just a pentode. If you convert to to el84s, you will lose two preamp triodes (I'd guess in the original amp, the triode sections of the 6BM8 would be used as the phase inverter). To use el84s, you'll need to add a tube somewhere.

You'll pick up a few watts, but it will a bit or a chore. Plate-to-plate load resistanmce for the two tubes is a little different, too.

[FunkyE9th]

Thanks guys!

For what I'm thinking of doing to the amp (i..e. convert it to a dual SE), I only need one preamp tube. So I don't need the triodes in the 6BM8. The amp already has a slot for a 12AX7.

BTW, the amp is currently using one of the 6BM8 triodes in the tremolo circuit.

-FunkyE9th

[Firestorm]

Ahah. Is the amp currently push-pull? Some of those relatively low-power amps have output transformers even smaller than a decent reverb transformer! You planning on replacing the OT? (Or is the amp SE already?)

What's the tone stack look like? With just one 12AX7, if the tone and volume controls are in between the triodes, you'll get a pretty significant insertion loss (think of non-reverb Fenders). Just for jollies, you could try a Baxandall/James design. These tend to have lower losses and will pump a little more signal into the power amp.

[Andy Le Blanc]

had a guild amp once that used 6BM8's
good sound......

[FunkyE9th]

The amp is a Gibson GA8T... http://www.freeinfosociety.com/electron ... onga8t.pdf. Push-pull.

If I do get the amp, I will replace the OT...probably with a hammond 125ESE. The seller did not respond to my email and has up'd the price on the listing.

[Firestorm]

Yeah, not one of Gibson's better efforts. The tweedish tone stack in that one isn't very lossy, so okay as is (plus you only have one knob). You could rig a switch to bypass it completely a get a real raw sound. Those Hammond 125 OTs are great. If you do get the amp and want to go silly, pick several tap combinations with moderately different primary impedances and wire 'em to selector switch for a broader palette. Did that to a Champ once and now it goes from Champ to Plexi.

[10thTx]

You will need ExpressSCH to open the files but there are a number of 6BM8 concept amps here:

http://www.el34world.com/Forum/yabb2/Ya ... 1195825729

http://www.el34world.com/Forum/yabb2/Ya ... 1194702099


Having said that, I have built 14 amps and the Little Wing Reverb (mini-
Bassman with 6BM8) has gotten more positive compliments than any amp I have built. It has a Marshall/Bassman type typology.

The sustain is phenomenol. With humbuckers I can hold a note until it feedbacks. Amp is a LOUD 7 watts. The picture is of the Little Wing Reverb.

http://www.el34world.com/Forum/yabb2/Ya ... 1163435923

There is a great soundbit of the original non-reverb Little Wing amp here:
http://www.el34world.com/Forum/yabb2/Ya ... 1176300997

I personally have owned some EL84 amps and did not care for the tone they had and sold them. I don't think the 6BM8 sounds like an EL84.
I think it sounds much better, IMO.

With respect, 10thtx

[FunkyE9th]

The amp sounds good. By the way the guy is playing it, it sounds like a very touch sensitive amp.

[Doug H]

Here's a 6bm8 amp I built:

http://www.aronnelson.com/gallery/main. ... attWonder/