Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: LooseChange on September 21, 2010, 12:10:24 pm
-
Here is another Desktop Series amp.
-
Inside...
-
Man, I sure like how your amps turn out! Cool stuff.
Any chance of sharing a schematic? Seems like in a previous thread there was a problem getting a 6L6 to overdrive well in a SE design? And if you have found a solution to that, I'd love to see it. If I ever do a single ended amp, I might want to try something similar.
With respect, Tubenit
-
Very nice amp!!! inside and out!!!
Any chance of sharing a schematic?
+1. :wink:
Best Regards
Rzenc
-
I spent a lot of time with a few design people to come up with the look. I've had six sets of plates made up and chose the one I like.
I don't have a schematic. I used the tweaked Dumble preamp schematic and married it with a fixed bias single ended power tube.
I think you need to play with the controls a bit. I find the Master volume to be really useless with this design. I usually max it out, set my clean level and balance the dirty level in after that. I bias the power tube on the hot side.
-
Nicely done, pretty iron there too! Is it fixed bias? Was looking for a VVR MV chip & are you using a pot to control B+ on preamp?
-
Do you have some 'desktop' speaker too? :laugh:
-
:laugh: every time I go to submit the post, someone's already posted.
I see it now. I bet the VVR MV would work better or be more useful than the voltage divider MV?
Where's the faucette and handles? (kitchen sink) :wink:
-
VVR is not really needed. It's a low power amp and the distortion comes from the overdrive channel.
Thanks for the fun comments... Desktop speakers and hot/cold water coming out with the next version.
-
Since I'm going to do a SE 6L6/EL34 fairly soon, is there a reason you went w/ the former over the latter?
(don't forget the Easy Bake oven, you can mount the 6L6 horizontal w/ an oven rack or bowl depending what you're cooking) :laugh:
-
Nice clean build there, inside & out! :grin:
I'd think a fixed bias, single-ended 6L6 would provide a lot of clean headroom.
Is the on-board fuse for the AC? Don't see that too often on botique amps.
Cheers,
Chip
-
Well, the reason I was asking about a schematic is DaGeezer and I were going to try to build Mat's mini-HRM with a single ended 5881. Geezer built it & it lacked volume to it and there was some talk about the preamp and OD not having enought "oomph" to drive the dual 5881's.
In that thread you mentioned what I thought was a similar issue in this quote from you:
From my experience building one... the preamp (especially the clean) does not have enough drive. It's funny how you jumped it over to a PP EL84 power amp. I did the exact thing when I first powered the amp up and noticed the low output. AND it did sound great.
&
Just add the phase inverter and get it done.
Geezer eventually gave up on it making this statement:
Sorry to say, this project is dead (or at least has taken a major detour). The preamp sounded really good when run into a PP poweramp, but just couldn't generate enough grunt for the big octals SE.
So I guess, I'm wondering was the issue that Geezer's was a dual cathode biased 5881 SE & that a single fixed bias 6L6 works OK?
I am posting the schematic we were using at one point on that failed idea. Can you say whether your schematic is reasonably close to this one, please (except cathode vs. fixed bias)? I'd still like to have a D-style SE 5881 amp at some point?
LC, I am a fan of your projects and your website stuff. The stuff you make always looks superb to me. I am just trying to figure out if there is some resolution to the low volume of the D-style SE 5881? Guess I am hoping you found a answer and/or tone that the mini-HRM project failed in?
With respect, Tubenit
-
Is your fixed bias SE power section on the SE Overdrive anything like what you used on the desktop Jubilee?
http://www.el34world.com/Forum/index.php?topic=8494.msg76271#msg76271
-
Well, the reason I was asking about a schematic is DaGeezer and I were going to try to build Mat's mini-HRM with a single ended 5881. Geezer built it & it lacked volume to it and there was some talk about the preamp and OD not having enought "oomph" to drive the dual 5881's.
I think the reason for the lack of "oomph" is that the 5881 needs a 20 volts signal for full power and especially with effect loop there, you only have something like 3-6 volts driving the 5881, I think.
If I were to build SE 5881 amp, it would look something like this. Add a reverb and you could call it a Tosser. :grin:
-
If I were to build SE 5881 amp, it would look something like this.
Yep, that would do it, I'm sure........
-
I struggled with "is it not loud" and kept comparing it with the Desktop Champ. It is almost as loud as the champ... Looking at the schematics, it should be just as loud. With the PAB engaged it's plenty loud.
As I said before, the Master could be eliminated in this amp.
The OD channel is what its all about. You can get clean and dirty with a twist of a knob and a push on a string. The amp is not designed for performance. There are not foot switches.
Anyway, the tweaked schematic with the preamp I used is below. Yes the power amp is like the Silver SE below.
-
Is the on-board fuse for the AC? Don't see that too often on botique amps.
Yes, the AC fuse is inside because I didn't like the spacing with it on the back panel.
-
Is the on-board fuse for the AC? Don't see that too often on botique amps.
Yes, the AC fuse is inside because I didn't like the spacing with it on the back panel.
You know LC, I was thinking last Sunday "What causes a fuse to open up" in a tube amp that is.
1 somethin real wrong inside
2 somthin real wrong with a tube
3 somethin real wrong with the operator
Remembering that Epiphone Galaxy 10 find last week and finding the aluminium foil wrapped fuse, I might start using those "inline fuses".
2 out of 3 of the above conditions really make you want the least access to the lightning inside.
Ray
OH! awesome amp!
I really do admire your take on tone and how you implement it in such a nice friendly size. You seem to have a new twist on each new amp, but not just like doo dads, practical twists, innovative I think is appropriate here.
How many do you make a year? 52? about one a week? :laugh:
-
LooseChange... how do you drill the chassis holes , with a template ? If you just "free hand " it , how do you get the control knob holes perfectly even with one another ?
-
Ray, good reasoning about the fuse. I wish I made 52 per year.
I use a paper template. All laid out in that .sch program. Print out a template, affix to the chassis, punch, drill, curse a bit, punch holes, use the unibit, curse some more, dremel out the IEC socket, dremel down the burrs, done. See below.
-
LC,
THANKS for sharing your amp builds and the information. I appreciate knowing what preamp & poweramp you're using on the Desktop Series Overdrive.
With respect, Tubenit