Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ToneJunkie on September 18, 2016, 11:26:56 pm
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I've got the money for another build and I want to do a similar style build to the last AB763 Lite (Pictured below). I'm have been using two AB763 style amps in stereo both into 1x12 cabinets and I want to try a different circuit. I play mostly clean and get my overdrive from pedals... Zendrive, AC Booster, Timmy, Eternity Burst are the flavors I have (all diy). What I'm looking for is something that is a little more compressed and some more midrange... I don't really want it to crunch up though. So the circuits I'm choosing between an Hoffman AC30, AC15, JTM45, or 5F6 Bassman.
I have always played through blackface type circuits... even the Dumble clone I played through for a long while sounds very blackface. Some concerns I have are I don't think the AC15 would have enough headroom although I'm playing with a jazz drummer and upright bass for the most part so I don't get that loud, I'm concerned a JTM or Bassman would not compress much more than my AB763's so an idea i had was to use cathode bias.
Ok I know this forum is for circuit help but the crew here has helped me so much and I trust everyone to give me some good advice. I will change the thread title as I purchase my parts and build this amp just like I usually do. Any opinions are welcome. Thanks guys!
P.S. If you guys are interested in what kinds of things I'm playing check out www.brookgannon.com (http://www.brookgannon.com) and under the music tab I have a stereo Tascam DR-05 recording of our show last week.
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Check out my Dual Lite.
http://sluckeyamps.com/dual_lite/dual_lite.htm (http://sluckeyamps.com/dual_lite/dual_lite.htm)
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I'm looking for is something that is a little more compressed
I don't have any advice regarding which amp you should build. I will say that I find using 2.2k screen resistors on power tubes along with cathode biased does help with more of a compressed tone. Just something to consider.
With respect, Tubenit
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I thought of another thing as far as getting a more compressed tone. The Alnico speakers I've tried tended to the more compressed. Not sure if they are all that way though?
Tubenit
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Thanks guys... OK I have a couple of specific questions...
1. Does an AC15 have more or less headroom than a Deluxe reverb?
2. How does the compression order of these amps go. My guess is from least to greatest AC15, AC30, Bassman, JTM45, Pro Reverb (I'm thinking of this given the same speaker cabinet)?
3. Would the headroom order of these amps be the same?
4. How would you compare the midrange between the AC30, Bassman, and JTM45 w/ KT66... my reference is a Pro Reverb.
Thanks for you time guys!
Slucky that amp looks cool that may be the ticket but I have more questions... Tubenit I will be sticking with my 1x12 cabs as seen in the picture with either Celestion G12-65 or Eminence GB128.
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I suggested the dual lite mainly because you can build it in that same chassis and have a very similar look but a different sound. You could cover quite a variety of sounds with your AB673 and the dual lite.
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Thanks guys... OK I have a couple of specific questions...
1. Does an AC15 have more or less headroom than a Deluxe reverb?
2. How does the compression order of these amps go. My guess is from least to greatest AC15, AC30, Bassman, JTM45, Pro Reverb (I'm thinking of this given the same speaker cabinet)?
3. Would the headroom order of these amps be the same?
4. How would you compare the midrange between the AC30, Bassman, and JTM45 w/ KT66... my reference is a Pro Reverb.
I would say the AC15 is relatively similar to a Deluxe Reverb. The AC30, Bassman, JTM, and Pro are also kinda in the same ballpark as one another. I'd look at it more like the different 'flavors' of amp. The AC style amps have a very unique treble character with a more unique touch sensitivity and compression due to the Class A operation. The Bassman and JTM45 are pretty much the same amp. More low end and midrange cut. Saggier attack and a spongier feel. More of an iconic rock and roll tone. The Blackface sound is smoother and has more mid scoop, keeping things cleaner.
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My AC-15 sounds very different from my Deluxe Reverb.
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Ok... I'm going JTM45. It looks like the width of the Gold Lion KT66 tubes are 2" which if I use the Stout Chassis like I would like to there would be a little under 1/4" distance from the tube to the power transformer. Does anyone see an issue with that?
I will eventually build a AC30...
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IF you're wanting to cram everything into a Stout chassis ................
Here are some ways to save space and perhaps still get the JTM tone (more or less) with your KT66's (which would change the tone anyway compared to 6L6 or 5881).
Not sure what the fixed bias circuit should look like? Maybe Sluckey or someone can help give you the correct values for the bias circuit using KT66 tubes?
I like the idea of the cathode biased version with PPIMV and using a solid state rectifier. The DPDT switch would allow a crunch tone or a brighter/cleaner tone with the flip of a switch.
I think the cathode biased version with 2.2k screen resistors would have a smooth compressed mid tone. Might be a really nice amp?!
With respect, Tubenit
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:icon_biggrin:
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So I plan on using the 6V6 plexi layout with the appropriate parts. Debating on what transformers to use. And still kind of debating on KT66, 6L6, or EL34s... I have been reading that primary impedance is not all that important for tube amps. So I'm thinking Ill just get a British style OT with 3.4K primary. At least that is where I'm leaning right now. If I used KT66's I would think of it as a 6.8K primary and use the appropriate speakers. I will order the parts this weekend.
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> KT66, 6L6, or EL34s...
For equivalently beefy tubes...
At the same B+ voltage and general power zone....
All tubes will favor about the same loading.
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I am using the stout chassis which is 2.5 x 3.125 mounting centers for the PT... I have two transformers to choose from that fit
#1 Classic tone... Fender Style Laydown, 120V, 60hz to 650VCT@180mA, 50V Bias, 6.3@4.5A and 5V@3A
or
#2 Heyboer Fender Vobrolux Laydown, 120V, 60hz to 710VCT@300mA, 50V Bias, 6.3@3.75A and 5V@3A
So I'm thinking I need the Classic tone due to the heater current rating... For my amp with 2 KT66's and 3 12AX7 I need 3.6A with is pretty dang close to limit of the Heyboer. When you guys get transformer are you comfortable with going right up to the limit? Will it make the transformer run hot?
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Got my parts and started the build... PT is in and first stage of filtering is in. I think choke and OT is next :-)
I was wondering about the Plexi 6V6 input... So its basically always jumped to both channels right? So if I wanted to just use the "normal" channel do you just turn down the Bass channel and it has no effect or do I need to put a couple of switches in to pick between Normal channel and bass channel or jumpered? Thanks guys
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That's as good a job as I recall ever seeing here on laying in the heater wiring.
:bravo1:
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So its basically always jumped to both channels right? So if I wanted to just use the "normal" channel do you just turn down the Bass channel and it has no effect
Yes, permanently jumped. Just turn down the dark channel if you want to only use the bright channel. Or vice versa.
IMO both of those channels are useless when only one channel is used. But when the two channels are blended together you can get some very nice sounds.
That OT is HUGE! And it's right on top of the most sensitive stage in the amp. I hope you will move it as far away from those preamp tubes as possible before you bolt it down.
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Thanks for the compliments... Willabe. Its the Mojo version of the JTM45 OT. The picture is a little misleading so I will take some better pictures tomorrow and see if you think I am shooting myself in the foot here. I may have to just get the same transformer I got for my AB763 Lite build. Hmmm.
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The OT looks to be an appropriate size for the circuit you are building. But you're putting 10lbs of stuff in a 5lb box! Things will be tight.
I would swap places with the OT and the choke. OT will work fine next to the PT. And the primary leads will be closer to the power tubes.
PS... Have you actually plugged tubes into those sockets next to the PT?
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I would swap places with the OT and the choke. OT will work fine next to the PT
Do that. My D'Mars has the PT & OT very close and the choke on the other side of them.
Here is another example of a build I did: http://s28.photobucket.com/user/tubenit/media/TxRaptorfront.jpg.html?sort=3&o=22 (http://s28.photobucket.com/user/tubenit/media/TxRaptorfront.jpg.html?sort=3&o=22)
With respect, Tubenit
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Thats what I will do... I 'm going to try the headphone trick to see if I can find a good spot for the OT (never tried it before). Slucky,I did fit the KT66 tubes in the sockets and they fit... with about 1/4 inch to spare :icon_biggrin: Tubenit... Nice cabinets and amps!
I have a couple of questions...
- What bias range resistor should I use for KT66 do you think? Should I just try the 47k as shown in the Plexi layout or...?
- I want to use a pot for the negative feedback resistor... do I need to have a resistor in there to put a cap on how much negative feedback is available like a blackface 820ohm value or is that not needed? Also what pot value would you use? 100K? I like the way I can use the "soul control" negative feedback pot to change how an amp feels.
Oh... I made the board this evening...
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Looking great! Will look forward to your tone review.
With respect, Tubenit
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Board looks good!
I "think" the KT66s will need a higher bias voltage than the EL34s. The bias range resistor for Hoffman's 6V6 Plexi is R38, a 220K/3W resistor. Decrease the value to increase the bias voltage, or increase the value to decrease the bias voltage.
Look at the "meat" control on Hoffman's Blues Jr. conversion. It may be similar to the "soul" control.
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Here it is... one small circuit issue but when I found it the amp fired right up and sounded great. I will have to adjust the bias range as Sluckey suggested but its close enough for jazz at this point and I think I'm going to like this amp. I usually play a AB763 style circuit with some tweaks and this will compliment that well. Here is the style of music I play... funky jazz stuff. I've been playing a bunch thats why it took me so long to build this thing :-)
https://www.youtube.com/watch?v=YdMhQtbLj5o (https://www.youtube.com/watch?v=YdMhQtbLj5o)
https://www.youtube.com/watch?v=-fWJaXR3HuA (https://www.youtube.com/watch?v=-fWJaXR3HuA)
Thanks for all the help guys!
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ToneJunkie,
That is some VERY beautiful guitar playing! Especially loved the 2nd tune. Great stuff. Thanks for sharing it. Enjoyed it a lot.
Amp and guitar sound good. With respect, Tubenit
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Guys,
Check out ToneJunkie on this YouTube:
Tubenit
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nice workmanship! you are a very, very talented individual!
--pete
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Amp looks great and the playing sounds fantastic. :thumbsup:
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Thanks for the kind words guys! That made my day :-)
Sometime in the future I will post another you tube video of some sounds from the new amp and I think from some tweaking I did today I will be playing a wet dry rig with my Sluckey AB763 and my Sluckey JTM 45 ! So cool :-)
Oh and I have been playing the AB763 like the one you see in the first post for around a year with exposed tubes. Its really cool looking on stage but I'm starting to play more gigs again (I used to play almost 100 shows a year) and I have to be super careful during transport so that is starting to get cumbersome which leaves me no choice but to make head cabinets for these two machines. I think I want to try to use plexi glass so you can still see the tubes but alas the cool exposed build is going to go by the way side.
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I've had thoughts about building a type of head cab that's really just an "Amplifier Head Use In Base Flight Case". The amp chassis would be bolted to the bottom of the case and then the top of the case would drop over the chassis and latch to the bottom of the case. Handle on top. Walk in, pop the top, and show off your glowing tubes. Latch the top back on and just walk away when done.
Something based on this case...
https://www.ebay.com/itm/Laney-L20H-Amplifier-Head-Use-In-Base-Swan-Flight-Case-Hex/201921653892?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D41451%26meid%3D902b3ce7c047400cbbe6c387478398b9%26pid%3D100005%26rk%3D2%26rkt%3D2%26sd%3D172670244660&_trksid=p2047675.c100005.m1851
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Thats a great idea Sluckey... I as I look at my head pictured below that I already have built with a 1/4" aluminum plate on the bottom your idea sparked this idea... Just use the plate on the bottom as a lid to an open top box. The side flanges would sit on the lip of that box and I would put a handle on the bottom of the amp on that plate. So when you carry the amp the amp would be "upside down" with the tubes facing down in the box... I'm going to build one today and see what I think :-)
Thanks for the idea! Sluckey for the win!
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Please post pics.
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I've had thoughts about building a type of head cab that's really just an "Amplifier Head Use In Base Flight Case". The amp chassis would be bolted to the bottom of the case and then the top of the case would drop over the chassis and latch to the bottom of the case. Handle on top. Walk in, pop the top, and show off your glowing tubes. Latch the top back on and just walk away when done.
Something based on this case...
https://www.ebay.com/itm/Laney-L20H-Amplifier-Head-Use-In-Base-Swan-Flight-Case-Hex/201921653892?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D41451%26meid%3D902b3ce7c047400cbbe6c387478398b9%26pid%3D100005%26rk%3D2%26rkt%3D2%26sd%3D172670244660&_trksid=p2047675.c100005.m1851 (https://www.ebay.com/itm/Laney-L20H-Amplifier-Head-Use-In-Base-Swan-Flight-Case-Hex/201921653892?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D41451%26meid%3D902b3ce7c047400cbbe6c387478398b9%26pid%3D100005%26rk%3D2%26rkt%3D2%26sd%3D172670244660&_trksid=p2047675.c100005.m1851)
i had a similar idea. built it a few years ago. inspiration was a tube tester i was working on.
--pete
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Dummy Load... That looks awesome! I really like the natural wood.
Here is that idea in action. A open toped box with rails on each side to support the amp. A fender blackface style handle will go on the bottom plate of the amp and I'm thinking I will drill a couple holes in the aluminum plate on each side to allow a couple of thumb bolts like the piggyback bolts on fender amps will go into threaded inserts into the rails. I think this would make transport easy and safe. You may wonder why I'm putting the handle on the Aluminum or bottom of the amp instead of on the wood box... the reason is I think with just attaching the amp with a couple of thumb screws and using those to support the weight of the amp would not make me feel confident while carrying it. This way I'm holding onto the actual amp. What do you guys think any ideas would be welcome.
Also I just weighed it and its still only 21.6 lbs so the head with no box is 16 lbs.
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Hey guys... I'm still working on getting the final design of the top so the amp will be easily transportable which I will post the end result when I do. Here is a video shot this weekend of the AB763 and JTM45 in action... I'm really liking the combo!
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Got my parts and started the build... PT is in and first stage of filtering is in. I think choke and OT is next :-)
I was wondering about the Plexi 6V6 input... So its basically always jumped to both channels right? So if I wanted to just use the "normal" channel do you just turn down the Bass channel and it has no effect or do I need to put a couple of switches in to pick between Normal channel and bass channel or jumpered? Thanks guys
what schematic did you end up using and what gauge wire are you using for the filaments? excellent wiring job btw.
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I used a JTM45 / Fender Bassman schematic combination. One change I made was to make the negative feedback variable with the soul control... I really like that on all my amps now. 20 guage solid core teflon coated for the 12ax7 and 18 guage for the power tubes. Hope that helps. Thanks
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I like that! Y'all are having fun too.
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I used a JTM45 / Fender Bassman schematic combination. One change I made was to make the negative feedback variable with the soul control... I really like that on all my amps now. 20 guage solid core teflon coated for the 12ax7 and 18 guage for the power tubes. Hope that helps. Thanks
Indeed. Thanks.
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Here is the final design for my transport box for the amp. I've gigged with is several times and it works great. It took me a couple of iterations to get a design I was happy with and worked well. There is also one of my videos in the next post with the amp featured at 0:48 in the video. Kind of geeky but it was fun to put together. So its a simple topless box with rails inside with 1/4 x 20 T-nuts attached in a little dado. I attached a spring loaded handle to the bottom aluminum plate on the amp. Works like a charm. Thanks for everyones help!
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Here is the video
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Fantastic! :thumbsup: Made me want to be there with you guys. :headbang:
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That was very cool!
Nice work, loved seeing that amp in the video
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Hey guys I have one of the the prototype bottom plates for this chassis... I was wondering if someone wants it. My final design called for a plate a little bigger than this one. If you will pay for shipping its yours... and if you want to donate some scratch to my music fund that would be cool too :-) I usually finish them by sanding and they look great after a little work and it already has the holes drilled for the attachment to the chassis as well as where the feet go. Oh I'm in Washington State so if you want to calculate shipping.