Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Archives of favorite topics => Topic started by: tubenit on March 08, 2014, 05:55:38 am
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I have done this with one of my amps to switch between a 6V6 to a 6BM8. I simply plug in the adaptor with the 6BM8 tube and then flip a mini-toggle spdt to change between a 270R/10w & 70uf (6V6) .............. to a 430R/10w & 10uf (6BM8).
IF you were doing this between a 6V6 and EL84, then the mini-toggle might switch to a 130R/10w to 170R/10w range resistor and then whatever value cap you would want. I would mount the mini-toggle in a fashion to make sure the toggle switch isn't accidently bumped into the "wrong" position. OR ...... you could install something that would interfere with it being moved into the "wrong" position.
With respect, Tubenit
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I use bear claws to hold the adaptor in place and a wire holder to hold the 6BM8's in place. I eventually used JB Weld to epoxy/weld the
turret/terminal board material in place. I would suggest having maybe 1/8" overage on the size of the board material to make it easier to epoxy it in place. The JB Weld works quite.
I drew a pattern around the board material using the perimeter of the 8 pin socket base & then cut around it with a dremel cut off tool. I then rounded and smoothed the edges of the board material with a belt sander. Took less than 5 min to do this.
Because the bolts that hold the 9 pin socket down bumped the edge of the 8 pin socket base, I used a dremel cut off wheel to simply notch the edge of the 8 pin socket base.
Gently pull wire thru until the board material is flush or close to flush with the top of the socket base.
CHECK for shorts and for wires touching before plugging in to your amp! CHECK the illustrations I posted to make sure they are correct and be careful to note the orientation in the illustrations.
With respect, Tubenit
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8 pin to 6AQ5.
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Al Pacino (tubenit), "I don't need no stinking yellow jackets. Say hello to my little friend!" :laugh:
Love this T!
Would you say that the 6BM8s are about half as loud as the 6V6s? Also, have you tried 6K6s for lower volume?
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I'd say the 6BM8's are about 2/3 as loud as 6V6. The main thing is they sound very Marshall in tone to me and not Fendery. The 6BM8's
have remarkably good bass tone.
Yes, I've used 6K6's quite a bit and like them. The 6BM8's and 6K6's are about the same volume, IMO.
With respect, Tubenit
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Way back when geezer first came out with his original Little Wing design, back then you, me & maybe a few others first began messing around with 6bm8s. But we also first started using the 5879 pentodes in place of the 12ax7. Anyway, mine had various value or set-up differences to the 5879, power supply, OT, pi, nfb, tone stack, & biasing but the overall basic design "flowchart" was similar to the original. Needless to say all those things added up to make a big difference from being an easily overdriven yet tonally harmonically rich amp to a very versatile fendery clean AB763-ish to a nicely overdriven beast. Playing it clean & punchy is one of my favorites to this day paired with a 10" alnico Weber blue pup but it sounds great with any speaker cab (and guitar) I pair it with. This is when I know I've hit the bulls-eye in the design. It's just right for playing at home levels too and really like those tubes as well. I think they're similar to the lower powered JJ EL844s. If you haven't tried those yet I think it would be a good idea for you and yet another option? They're a little different sounding to their bigger brother EL84.