Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tubenit on February 13, 2018, 09:14:53 pm
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Starting on a new build. I am hoping this will turn out to be a reasonably light weight "grab & go" practice amp. Planning on a small 16" x18" x 9.5" cab for it with a 10 inch speaker. Will be a tweed style chassis with controls on top.
It will have 6BM8 power pentodes for maybe 7-9 watts of power. I am using a few used and mostly left over parts from previous builds to complete this one. It will also have an active FX. This amp will have only 4 tubes using solid state rectification.
I've always like the 5879 V1 preamp tone and touch sensitivity. Will keep you guys posted as I slowly get this thing done.
With respect, Tubenit
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Like it. Have you tried a 12at7 with these tubes?
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No, I haven't tried a 12AT7 with those tubes, but that's not a bad idea! I presume you're meaning in the V2a & V2b position? 5879 12AT7 6BM8 triodes into 6BM8 pentodes
With respect, Tubenit
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Exactly! I have been messing around with 6Bm8's some and just thought about it while looking at you new version. If you get a chance to check let me know the results.
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Hi everyone. I am new to this forum. I usually hang out at Ampgarage . This is a great forum with so many interesting ideas! I especially like the cathode follower with a IRF820.
I was building a tweed deluxe cabinet for another 5e3 type build when I heard how this amp sounds with 6BM8 tubes.I am now interested in building an amp like this instead and placing it in my 5e3 cabinet. I have a lot of el84 tubes lying around and wondered if this would sound good with el84 as opposed to 6BM8 tubes or should I sell my el84 tubes and buy 6BM8 tubes instead. I mainly play around the house and small gigs at friends backyards. Would these amps be friendly with strats and teles? Thank you Tubenit and Geezer and everyone else for the great work on these amps.
Cheers
Guy
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Guy,
I find the 6bm8 tube to have a thicker tone, not saying better. Univox used them in a Bass amp, the U45. Now it was not a real bass amp.
Tubenit I believes prefers a little darker tone. Personally I like both, but I believe they are quite different.
Check out Brad playing a U45.
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should I sell my el84 tubes and buy 6BM8 tubes instead
It's all an issue of personal preference. IF you want 18watts then use El84's. IF you want 7-9 watts, then I suggest 6BM8 tubes. IF you want to use EL84's then look at Geezer's original HoSo56 schematic & you can add the FX IF you want to.
Remember you will need a 12A_7 for the LTPI. The 6BM8 has a triode that I am using in this design.
I think the HoSo56 is a very touch sensitive amp where when you pick lightly, it cleans up and when you pick more firmly it has more overdrive. So, yes I think it would sound good with Tele's or Strats,
With respect, Tubenit
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Tubenit, what OT you use with 6BM8 tubes and what is your usual plate voltage?
Also do you use NOS tubes or the new electro harmonix tubes and do you have matched pair?
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Thank you everyone for the feedback and the video . The 6BM8 tubes sound really good from this video and the fact I can save on having a tube for the LTI already built into the tube I am leaning towards the 6BM8 tubes. Love the nice deep bass in those tubes! May pair it with my G12H65 speaker .
Cheers
Guy
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what OT you use with 6BM8 tubes and what is your usual plate voltage
Look at the schematics below. 5E3 deluxe OT
http://el34world.com/Forum/index.php?topic=6176.0 reply #5 297volts on plates
http://el34world.com/Forum/index.php?topic=562.0 275volts on plates
Univox U45b http://el34world.com/charts/Schematics/files/univox/univox_u45b.pdf 300v on plates
New matched EH 6BM8
Having said that, I installed a VVR in the first HoSo56 with 6BM8's I built. It lowered voltages on power section and LTPI only. It was pretty amazing to me how great the amp would sound with remarkably low voltages on those 6BM8 pentodes/triodes.
This time will probably be around 266 volts or so, I'm thinking? 190-0-190 PT 120ma with solid state rectification
With respect, Tubenit
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Now here is an idea for anyone interested. IF you use a PT with around 270-0-270 and 100ma (or 275-0-275) .......... or so ...........
You can use a 8 pin socket for rectificier tubes & use a GZ34 for 351 volts or a solid state plug in for 378 volts for 6V6 tubes.
And then you can make an adapter for 6V6 to 6BM8 tubes and instead use a 5Y3GT for 297 volts for 6BM8 pentodes.
A few years ago, I built a Tweed BluezMeister for my son with 6V6's using a 275-0-275 PT. The TBM is cathode biased. So what I did was install a switch that would change out the power tube resistor for the power tube to switch between the 6V6's and 6BM8's. I'd switch out a GZ34 for a 5Y3GT & flip the switch for a different cathode resistor & simply plug in the 6BM8 adaptors.
It works great! And it was relatively easy to do. There is a thread here on how to do this: http://el34world.com/Forum/index.php?topic=16786.0
You could actually install 8 pin sockets for 6V6's and adapt to EL84's OR 6BM8's.
With respect, Tubenit
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I think the best 2 sounding samples of 6BM8 tubes are DaGeezer's mini-bassman:
http://www.musicwebtown.com/jallenshaw/46763
Here is the HoSo56 with 6bM8's that I built with VVR on and volts dialed down super low for a more overdriven tone. There was NO pedal used at all in this demo. I added a little delay in the mix but otherwise it was just 10" Ragin Cajun speaker mic'd.
https://www.soundclick.com/html5/v3/player.cfm?type=single&songid=7988948&q=hi&newref=1
With respect, Tubenit
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I have a pair running 300vdc I changed over from el84 and used a 10k to 8 ohm Baldwin transformer. Fairly heavy 20 watt iron and the nice low is there.
However, I am not running a LTPI. I favor cathodyne then use the triode as gain stages. Similar to a Major or SSSDumble in that you gain up after the PI.
I do not care for the triode tone in the 6bm8 when used as PI.
Considering this build, but want to add triode after a 12at7 LTPI. I am thinking, don't know, the current push may get push as much headroom. I currently am using a 6sn7 in the cathodyne and get have a bit more filtering than the Univox.
It sounds a LOT like Carr Rambled with breakup beginning at about 5 watts and seriously bent at 8 watts. Volume clean is similar to a champ with a single 10 gold, but the tubes have a much wider window of overdrive and overdrive and still gain volume.
This is the touch of the amp. Problems dealing with cathodyne is simply balance, and I do not use a pot, I use resistors. Tedious, but I prefer certain tubes and try different ones. Maybe using a pot would help, but after I decide on the tubes they stay.
Sylvania from the 70s last and are very durable. This is the only RCA tube I don't care for and not even sure they made it. The EI are by far th he best in tone and not getting splatty sounding. They will not rum long with screens running heard.
Good thing is even the NOS are cheap, but careful of the older Mullards, and I cannot believe I just wrote that. I am not sure who made them, but if it was Mullard they are not smooth at all.
The Eh are mid focused to me.
I am actually considering dual output, switchable. Add just 2 more 9 pin for el84 or the lower output JJ. This design with the versatility of changing wattage, a real change, not just a triode switch or choking off the tubes with lower voltage interests me.
Funny thing is it has become difficult for me to use a LTPI when having the added tweakability of the small gain stage prior to the output tubes. This is easy to make adjustable gain as well.
I assume you could do the same with a LTPI, but it may take more twiddling. This is why I am interested in a 12at7 or maybe even a 6sn7.
Thanks for the info. Keep it coming. I would love to get a versatile clubbing amp design as an alternative to a champ or princeton.
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I think the best 2 sounding samples of 6BM8 tubes are DaGeezer's mini-bassman:
http://www.musicwebtown.com/jallenshaw/46763 (http://www.musicwebtown.com/jallenshaw/46763)
Here is the HoSo56 with 6bM8's that I built with VVR on and volts dialed down super low for a more overdriven tone. There was NO pedal used at all in this demo. I added a little delay in the mix but otherwise it was just 10" Ragin Cajun speaker mic'd.
https://www.soundclick.com/html5/v3/player.cfm?type=single&songid=7988948&q=hi&newref=1 (https://www.soundclick.com/html5/v3/player.cfm?type=single&songid=7988948&q=hi&newref=1)
With respect, Tubenit
Thanks for sharing your tunes. The first soundcliick has a remarkable ripping compressed lead tone.
There amp have the 5e3 OT new sensor like Doug sells? I have 4 of these stashed.
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There amp have the 5e3 OT new sensor like Doug sells?
I don't know for sure but I don't think so? I don't see any reason why Doug's 5E3 OT wouldn't be a great match for the design though.
Ah, I think I am understanding what you are saying now. My son's TBM with 6BM8's installed just used the 6BM8 pentode only and the triode was a 12A_7 ( I left the triode unwired and not grounded) . I don't remember if I tried a 12AT7 but I do think that would be a good choice.
With respect, Tubenit
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Thanks T. I really like the Heybour OT Doug has, it is nice iron. I also like the New Sensor.
Play time.
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Would these be reasonable values to experiment with on this amp for negative feedback? 100R/4.7k ?
Wiring up this amp is going reasonable well. Pretty tight fit in a small chassis.
With respect, Tubenit
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Fender liked a 820Ω where you plan the 4.7K. There is no right or wrong. Maybe plan to experiment with that value and let your ears be the judge. I would probably start with the 820Ω because that will give more NFB, so if you have the phase wrong it will be more obvious. :wink:
Once your are sure the phase is correct, then experiment with different resistors.
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You could also try the values from little wing amp
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Great suggestions and this gives me a good starting place for the NFB.
Thanks guys! With respect, Tubenit
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Had a chance to play this amp today for a while and it sounds absolutely terrific. Very sweet tone. Great bass for a small tube. Very touch sensitive with the 5879 V1. I think it sounds warmer then my original HoSo56 with 6BM8 tubes.
The goal was a inexpensive "grab and go" small "practice" amp. So, I used ALOT of left over parts from other builds. It has some Orange Drop PS caps and some Vishay Dale RN65 resistors on plates.
I did NOT do a good job with the layout. Sections got waaaay too cramped and wiring was a challenge. IF I were competing for a "crammage award for low floor noise" this would be the amp. I was expecting it to be noisey at idle and having all kinds of problems. It is super quiet. This could be the kind of amp where you'd accidently leave it on because you couldn't hear it. I'm stunned by the low noise level. Completely surprised me and I don't understand why it's so quiet with so many wires running so close to one another between the turret board and the tube sockets.
The amp doesn't need NFB in my opinion. It has plenty of headroom and the balance of bass mid treble is great on this amp.
With respect, Tubenit
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I am VERY excited about the small cab I built for it. The chassis is only 16" x 2.5" x 6"
The cab is 18" x 16" x 9.25". I typically used "hardwoods" like sapele, mahoganey or figured maple ............ but I wanted a cabinet that is super light and so I wanted a lighter wood, but I wanted a pretty cabinet. It's all wood, no tolex & I ended up with something that is reasonably creative to meet the looks and weight requirements. Will share the photo when it's all assembled. Still putting on clear coats right now.
I ended up coming up with something that looks terrific from my perspective and is very light weight and small. It will have an Emminence Legend 1058 (10" speaker).
Check out how not neat and cramped the wiring is. I have NO idea why the amp sounds so good and is so remarkably quiet. The original Princeton Reverb I owned yrs ago was much louder floor noise at the same levels. Ironically, given how cramped stuff is, it was a good thing to use so many different color wires. Still pretty easy to trace where things go. :thumbsup:
With respect, Tubenit
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Very nice! Pretty grass too. All of my green is just winter weeds!
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> just winter weeds!
Inch of solid ice over all my "lawn". It's weathered enough that I broke-off a small patch today. Under the ice is more ice.
Did prune the pear, and the buds show life.
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Cabinet is done! VERY light weight! Figured maple top and trim on front edge. The lighting makes it difficult to see in the photo. The rest (sides and bottom) is plain ordinary pine.
I had enough "left over" stuff from previous builds to only need around $32 to make the cabinet.
Very happy with it. Nice sounding amp.
With respect, Tubenit
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As always your cabinets are fantastic :thumbsup:
Franco
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Just beautiful!
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AWESOME mate! :thumbsup:
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I think the best 2 sounding samples of 6BM8 tubes are DaGeezer's mini-bassman:
http://www.musicwebtown.com/jallenshaw/46763
Here is the HoSo56 with 6bM8's that I built with VVR on and volts dialed down super low for a more overdriven tone. There was NO pedal used at all in this demo. I added a little delay in the mix but otherwise it was just 10" Ragin Cajun speaker mic'd.
https://www.soundclick.com/html5/v3/player.cfm?type=single&songid=7988948&q=hi&newref=1
With respect, Tubenit
Great slide work Mr. Tubenit, that tune on Soundcloud was cool, great tone as well
{EDIT- untangled quote}
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I've a reasonable amount of play time on the amp now. I think it's a fantastic amp and definitely in my top 5 that I've built. Easily the best of a
"grab and go" small amp tone I've heard. It has an amazingly "full tone" with nice bass response around reasonably low "conversational" volumes. It sounds good to me and not thin at volumes much less then TV volume.
I've only made two small tweaks. Mid-boost switch and a 121p smoothing cap on the FX return.
The Legend 1058 10" speaker seems to be a great choice for this amp.
I've played it with my Tele's trying the humbuckers and the single coils thru it. And I've played it thru my semi-hollow body 335 type guitar. Everything sounds good with it, IMO.
100R/4.7k added for negative feedback NFB
I've tried a Moen Pretty Dolly delay and a Digitech RV-7 reverb pedal in the effects loop. I like the tone of both of them.
With respect, Tubenit
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There is a demo of the amp being played clean on two tunes here:
http://el34world.com/Forum/index.php?topic=23477.0
I think for a low wattage amp, it has an amazingly good bass tone to it.
With respect, Tubenit