HoSo56 amp project...design input sought

[Geezer]

There has got to be a simple solution to toning down the treble when you throw your boost switch!!???

Yes, and I think I've found it! (Thanks for the encouragement to keep looking for a solution.)
What I ended up doing was "draining" some of the highs off at the treble cap with a .001 cap to ground.
I haven't been able to crank it up to performance levels (kids sleeping) but I think I'm at least close.
See the attached schem.....

I tried the last idea you posted (bypass the treble cap with another cap) but it just gave too much mids....this amp is already "mid heavy". The cap to ground seems to drop a bit of highs without shifting the mids too much....we'll see, once I get to turn it up....

[tubenit]

WOW !!!!

DaGeezer, you have come up with another VERY cool sounding amp!  It does sound similar to those video/audio clips. It is a pretty diverse amp. Engage the NFB and leave the other two boost switches off and it has a nice clean tone. Disengage the NFB and engage one of the boost switch, it sustains and overdrives very nicely.

Super touch sensitve and really really nice harmonics with a pretty smooth sounding overdrive.  The amp does not have any more hiss than the Little Wing or the Carolina Blues Rocket at the same volumes. I like a quiet amp and the hiss is not a problem for me at the levels that I will play it at with a band.

I view the NFB switch a must on this amp for me. It offers another very very nice tone and the NFB completely eliminated the hiss making it super quiet even at reasonably loud volumes. It still left the amp very touch sensitive with nice harmonics.

I like the PAB switch with a paralleled .001 on the treble pot cap. That works perfect for me!  Without the .001 it was waaayyy too trebly. The .001 leaves it with about the same balanced tone (as with the tone controls) but boosted.

I choose a 2.2uf instead of a 25uf to be switched in on V2-3 cathode. Sounds smoother/better to me with less grit for my taste. 

I actually like it better without the crossline master volume engaged. But the mstr volume does give it another sound which makes it more compressed sounding and you can control the volume.  I'm using one of Hoffman's 1M pots with the spst. I suspect that I will probably play it not engaged more than with mstr volume.

DaGeezer's Little Wing is a great amp.  I am more wow'd by this HoSo 56T than even the Little Wing. I prefer the tone of this amp more than the other great EL84 amps that I've had a chance to really play on for a while.

More later ...........     I took some voltages with a 5Y3 which I probably will continue to use. It put about 300v on the plates. My preamp volts are pretty similar to DaGeezers but I used different power rail values.

Thanks Geezer !!!!!   With respect, Tubenit

[Geezer]

See....told 'ya!

I view the NFB switch a must on this amp for me.

I'll have to try that, although I just don't see how this amp could sound any better! I've been playin' it all day!

I choose a 2.2uf instead of a 25uf to be switched in on V2-3 cathode

Oops....I just went & checked mine....it's 1uf! I had it labeled wrong all the time, sorry... :-[
The 25u is def too much....

I actually like it better without the crossline master volume engaged.

Me too....I'm going to put a switch on mine. Like Peter says, it definately "opens it up".

On the "cap to ground" thing mentioned in an earlier post, I settled on a 390p. It gave the best balance of hi-cut to boost. If the cap is too large in value, it actually negates the boost, cutting volume & tone. I have updated the schem of my version to reflect what I have now.

IMO, everyone should build one of these (a pentode front-end). Every slight twist of either the gain or trim pots gives a new tone that is very useable......I feel that I don't even need OD pedals anymore....this amp is better than ANY OD I've ever tried.

My next project is to try one of the 5654 pentodes (that Sluckey graciously sent me) in a 2xEL34 Plexi-type amp, and also in one my Super SE amps using the same basic preamp as the HoSo.......

Havin' more fun than a human being should be allowed to have!  ;D

Geez'r

[bigdaddy]

Do you think the preamp will work driving a single EL-34?

I have some EF-86 tubes and even a spring mounted socket.

Would a 12AT7/5751/12AY7 tube work better than a 12AX7? Less gain to have to deal with only driving the one power tube.

Any ideas on how to make this work for a 10 watt SE amp.

[prs_matt]

I have been thinking of trying an EF86 amp for a while now as well and have been very intrigued by this thread. The last few days I have been puzzling over the bump channel and Master questions discussed.

Tonight I went over to the 65amps site and read everything I could about the SOHO.

Says "20 WATT (2xEL84), Tube rectified, EF86-12AX7 Cathode Follower with BumpTM circuit and Defeatable Master VoltageTM"

I was puzzled by the term "Master Voltage"... Turns out they scale the B+ with that knob to get lower volume without destroying tone. It is not a master VOLUME in the traditional sense.

As for the bump control, I wonder if it has more in common with the Hammond Organ swell circuit than a Fender tone control. It is a variable capacitor control that allows more mids to pass through as the level is increased. As it reaches max level, the bass and highs roll off a bit giving a tight compressed mid-heavy scream. I have not looked at the pics of the guts of the SOHO yet but I will soon and see if I can learn anything.

I am even more interested in pursuing this project than before and am so impressed at the skill of all of you in coming up with schematics and prototypes in such a short time.

Keep it up!
-Matt

[macula56]

This project is looking pretty good. I am trying to round up the parts I need to build mine. You guys rock, as always. Jmac

[prs_matt]

In another video on YouTube, Peter Stroud mentions a 6-position rotary tone control. I have a rough schematic put together that I need some help with. I have no idea how to switch between the two "channels" if you will. and I am not sure of the values everywere but it is a start.

[tubenit]

PRS_Matt,

Can you post your schematic in a GIF or Bitmap format?  Also, did you read all of the thread on this amp?  We may have possibly already covered some of the ground that you're referring to??


Macula56,   If you don't have the trannies yet, I think Hoffman's 18w trannies with a 5Y3 would be excellent. You can change the B+ rail closer to what I used to get the same preamp volts range.

With respect, Tubenit

[macula56]

thanks Tubenit. I want to build something with 4 EL84's. I started another thread about that as I was looking for info on OT's for that project.

[prs_matt]

Tubenit, I put up an image of my draft.

I did/have been reading through this thread for several days now. Not so say I have not overlooked something or forgotten some details. I have spent the last several minutes re-reading some of the early posts and realize that a lot of this has been covered. Sorry :-[

[tubenit]

PRS-Matt,

Looke at where you have the B+ hooked up on the EF86.  It needs to be at the juncture of the 330k & 2.2M resistor.

You're asking the right questions!

And it looks like you're retracing some of the ground we covered. I can't remember for sure but I posted several schematics early in the thread that I later deleted & I think one of them was pretty similar to what you've drawn?  I think Heinz ruled it out because it created way too much gain?  Not sure about that though.

With respect, Tubenit

[prs_matt]

Thanks tubenit. I just stumbled on one of your schematics from somewhere early on in this discussion and found nearly the same design.

Too much gain from the CF or from the gain stage after the TS?

I will adjust the V1 B+ connection. Thanks!

[Geezer]

Well, looks like I'll probably be building another HoSo56 real soon.
I took the prototype up to my friend who owns one of my "Little Wing" amps, the same guy who did the sound clips for me. He played the HoSo about 30 seconds and a big grin came across his face!  ;D
We only had a few minutes...he tried it with a Strat. I told him it really screams with Humbuckers & P-90's....and after we unplugged it, I remembered that he didn't even turn on the "boost", so he has something more to look forward to!

I'm going to finish all the "final touches" on the HoSo Proto & take it back to him to use for a week or so. If he likes it as much after that as he did today, he's going to order one. I think he will  ;)

Also, I'm getting ready to try one of the 5654 pentodes tonite....hope it goes as well as I expect.....G

[Geezer]

Various "other" pentodes tested tonite & here are the results:

Note: all tubes were tested with the exact same circuit values as the "original" 5879 pentode.

**5654(AKA 6AK5 / EF95) - http://tubedata.itchurch.org/sheets/084/5/5654.pdf
More hi-end & seemingly more gain than the 5879. Also seemed to be more sensitive to variations of input signal gain. I think some tweaks of the circuit values will be needed to get the absolute best tone out this little tube. That said, it sounded excellent! Just rolled off the treble a bit &  backed down the gain & it sweetened right up. Also, ZERO microphonics, which would be a big plus if used in a combo. Tapping on the tube yielded complete silence! Another "plus"...they are ~$5 each just about anywhere on the net!
A Big "THANKS" to Sluckey for providing the test units of the 5654's!

**6AU6(A) - http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6AU6A.pdf
Note that this tube has the same basic pinout as the 5654 (see above)....just connect pins 2 & 7 on the socket & you can pop in either one!
This was the best sounding of the (3) tubes I tested. I had the same basic tone as the 5879, but in the smaller 7-pin format. No circuit changes are needed, it has great tone with the same values. Only darwback seems to be microphonics.....several of the 6AU6 examples I have were noisey if tapped, but I found a 6AU6-A that was almost silent, so good examples are possible. ~$10 each.

**6SJ7 - http://www.pmillett.com/tubedata/HB-3/Receiving_Tubes_Part_2/6SJ7_6SJ7-GT.PDF
Octal pentode with metal jacket....high on the "cool factor".
Tone was the "weakest" of all (3) tested, but still an excellent sounding tube with seemingly less gain than the others tested. I think with some circuit changes it would sound excellent....seemed to have more "chime" when the treble was boosted. Microphonics were again kind-of high on the several examples I tried, but some were better than others. There is a MilSpec version that is "Red" in color out there (5693) that has better results on the microphonics, but are $35 each! Ouch! http://thetubestore.com/nos-5693.html

The 5879 is still the hands-down winner in this particular amp, but as I said, I think all of these can be tweaked to give super tone.....as has been said, the effort is well worth the time!

Geez'r

[tubenit]

DaGeezer,

Had a chance to play my 56T again tonight. Cool amp!  I really like it alot. Playing it, I'm not sure what I could tweak that would make it sound any "better"?  It is remarkably expressive. Very nice tone for playing slide too.

If the 250p cap across V2-1 were removed ...... would that remove some treble?  I won't have a chance to experiment for a few days with it, so I thought I'd go ahead and ask. That's the only thing I can think of that I might try at this point?

Thanks for the additional info you provided about your friend's response & also about the other tubes. .  I'd love to hear your friend record "Spanky Blues" (or something comparable) with the HoSo 56 for a comparison to the Little Wing.

I am dialing my amp with volume on 7, treble 3, mid 7-8, bass 6-7, trim about 5-7 and mstr vol around 4-5 to get my favorite tone/s so far. Switching the 2.2uf cathode cap on & no NFB.  Guitar about 8. Very little hiss at all. Less than the Princeton Reverb I used to own with those settings. I also like the NFB engaged with the guitar on 9-10 quite a bit.

What are you using mostly?

With respect, Tubenit

[Geezer]

If the 250p cap across V2-1 were removed ...... would that remove some treble?

No, that would add treble. Try a 470/500p.

What [settings] are you using mostly?

I really vary it alot (there's so many cool tones in there!), but I suspect fav would approx be:
Gain-5, Treb-3, Mid-3, Bass-4, Trim-8, MV-6

On the MV, I had a 2Meg pot that I put in there & it works great without having to switch it out circuit. I can turn it up all the way, then disconnect it from the circuit & there is no difference. It still has a good, smooth "sweep" also, so that's what I'm going to try for a while.

[drew]

On the schematic, do you have a "B" where you should have a "C" on the lower part of the 12AX7?

[harryk]

Geeze! I got very interested in this amp you have designed. I have never met a EF86 amp which I liked. This could be the one. Today I went to my component supplier and  by chance he had four 5879 NOS tubes in his stash. I bought all of them with to my mind reasonable price (some 12 USD/tube). Now my question is: Can you put that tube to V1 instead of EF86 without modifying anything in your schem? Harry

[tubenit]

Harry,

Now my question is: Can you put that tube to V1 instead of EF86 without modifying anything in your schem?

If you're asking if DaGeezer's schematic can be used for a 5879 in V1. That is what he is using in V1. He is not using an EF86. Hope that helps.

http://www.el34world.com/Forum/index.php?topic=6176.0

With respect, Tubenit

[macula56]

hows about a 6SJ7? does that require and extra's or is it interchangeable?

[harryk]

 :)Thanks Tubenit! I am very interested in to hear also your opinions of different tubes in V1 position like DaGeezer described earlier. I do not have any deep experience of using this kind of tubes in preamps. A friend of mine just built a Matchless Clubman and he was suprised how good sounding it turned. It has also EF86 as the first preamp tube. Harry

[tubenit]

harryk,

This is my 1st experience with any kind of tube like this and it's a favorable one. I have used a paralleled 12A_7 on all my scratch amp builds prior to this.

My impression is the Matchless uses a EF86 in the V2 position with a paralleled 12AX7 in V1.

http://www.el34world.com/Forum/index.php?topic=597.0

http://www.schematicheaven.com/newamps/matchless_clubman.pdf

With respect, Tubenit

[harryk]

 ::)Either I have to go to eyedoctor or I have a worse and worse dementia because I do not see anything and do not rememer anything anymore :-[. Luckily we have more fresh people here to guide us loser like me ;). Anyhow I have to build this amp this spring in any case. I also wait some sound clips of your amps. Harry

[Geezer]

hows about a 6SJ7? does that require and extra's or is it interchangeable?

I think that (6SJ7) was covered a little ways back....10 posts up, under "pentodes tested"

Harry, this is also my 1st experience with pentodes @ the input.....so glad I "went for it"!! This amp has the most "fun factor" of any amp I've ever built, or even played....

G

[Geezer]

On the schematic, do you have a "B" where you should have a "C" on the lower part of the 12AX7?

I thought we fixed that!  :-[
It should be "C" on both plates of the PI.....

[macula56]

I think that (6SJ7) was covered a little ways back....10 posts up, under "pentodes tested"


yeah, maybe if i tried reading instead of asking, lol.
thanks Geez, Jmac.

[PRR]

> all tubes were tested with the exact same circuit values as the "original" 5879 pentode.

That's unfair. Like testing my ThunderBird with Honda-size tires. Or trying a fine Gibson acoustic with head-banger rock strings and titanium pick.

With "same" values, one tube may be happy and another may be jammed in a corner (plate voltage way high or low).

That may cover some of your observation about 6J7. It is a good tube but "smaller" than those RF pentodes. It may be starved, barely working right. It sure "can" have as much gain as the others, although you may have to raise all resistances to find it.

Throw the DVM on the plate and adjust cathode resistor so all plate voltages are "similar" within 20%.

[Geezer]

That's unfair. Like testing my ThunderBird with Honda-size tires. Or trying a fine Gibson acoustic with head-banger rock strings and titanium pick.

 ;D Exactly .....that's why I noted that no circuit values were changed.

Throw the DVM on the plate and adjust cathode resistor so all plate voltages are "similar" within 20%.

I will hopefully have time this weekend to try it again with that method....

[imaradiostar]

I love pentodes on the front end but the cap across the Rp makes me wonder if this might be a good place for a cascode- lotsa gain but with less pronounced high-end. Should I volunteer?

jamie

[pullshocks]

Ordered an RCA 5879 today....

[Geezer]

Ordered an RCA 5879 today....

Cool!
I'm making the faceplate for my amp (former Epi VJr head) right now..... ;D

[drew]

Somebody else's take on a 5879-based amp, with youtube demo videos:

http://ampgarage.com/forum/viewtopic.php?t=8138

[tubenit]

HotBluePlates gave me a capacitor substitute box that sure helps when tweaking amps! 

I changed two caps on my 56T.  The paralleled treble cap is now a .002 instead of .001. And the cap going into the phase invertor is now a .01 instead of a .0047. This allowed more mids and more overdrive and a smoother sound to my ears. It will get a pretty decent Billy G type sound with the PAB switch on.

DaGeezer mentioned that he couldn't quit playing his amp. I'm having the same thing happen. It's a great amp and is definitely super touch sensitive and expressive. Probably the most "fun" amp I have played. I'm using a delay in the passive effects loop and the amp sounds huge for a small amp.

With respect, Tubenit

[jojokeo]

Hi guys,
My eyes are all blurry from trying to read all of this thread over last night and today as I have great interest since I have made three EF86 amps over the last 6 months.
This has sounded very close to my second amp which I ended up using the EF86 switchable into a 12A_7 (X,T,U) cathode follower stage or input directly into a single EL84.
The EF86 has a pentode/triode switch option going into TB stack which is also bypassable. This yields more control of the EF86 as well when you don't want so much gain for jazz/country playing. The difference in my amp is that I made the tone stack and switching ability between the cathode follower so that I had control of the pentode tone when not going through the 12A_7 (which does give instant levels of more gain) for versatility and my own experimentation. After the 12A_7 CF stage it has a volume and treble cut similar to the Vox AC Heritage amp (this is what inspired this design in the first place) and also a bright switch on the volume pot which helps when using a Les Paul / warmer guitars. Overall I think it's pretty similar to what's going on here w/ great designing at work by DeGeezer and Tubenit. Great job you two (and others)!

Great thread everyone!!! I'm really stoked to see this. BTW for those worried or thinking EF86's have too many issues, in my last amp I double up on using two EF86's - one driving the switchable tone stack and another used as a driver stage both w/ their own volume pots - a truely fun and totally simple but effective little practice amp. Depending which tube you drive more it's really got a great vibe. It could be a great higher powered amp IMHO but that's another thread/story.
Cheers, Joe G  :)

[Geezer]

in my last amp I double up on using two EF86's - one driving the switchable tone stack and another used as a driver stage both w/ their own volume pots - a truely fun and totally simple but effective little practice amp. Depending which tube you drive more it's really got a great vibe. It could be a great higher powered amp IMHO but that's another thread/story.

Welcome Joe!

Do have a schematic for that amp?(or any of the other amps you referred to?)

Thx, Geez'r

[jojokeo]

Sure can but I don't want to mess up this thread since I'm new and I don't want to step on anyone's "guitar chord" err toes.  Let me know what's appropriate and also what file format should I scan with to be able to post?
Thanks for the welcome  :)

[bigdaddy]

I would love to see any SE amps you have made especially with an EF86.

[tubenit]

Joe,

We're interested!  Post in a GIF, JPEG, etc.....   

When you try to post it, it will show the type files and size allowed.

Thanks for sharing and welcome aboard the forum!

With respect, Tubenit

[jojokeo]

Sorry for the delay as I hadn't drawn up a corrected version from when I finished this. It's as close as I remember and w/ a little picture help I think it's pretty accurate? I wanted to show the amp I was telling Doug H about when I was ordering parts and never got around to doing it and visiting the forum until now (and also 2 more amps later  :-[). I've learned so much in the last couple of days from you guys, it's been eye opening. But, when I was involved w/ this there wasn't any info that I could find really except some version I remember that had a "squishy" control for the EF86. I tried it originally but it was like a compression effect and I didn't end up using it. I started out having that, a tremolo circuit, and a pentode/triode switch for the EL84 w/ this but aborted that all as well and ended up w/ this instead. As I'm sure you all know, funny how things don't end up where your intentions usually begin?!? Anyways, I hope this can add a little bit to the forum amp fun?
Quick description: EF86 w/ pentode/triode switch going to TB or bypass (w/ a little low end filtering here for this at higher levels) going directly to EL84 output OR switch this output into CF stage (this sounds great w/ 12AX7 or 12AT7) to kick things into higher gear then this output has a treble bleed and volume control going into EL84. Any constructive criticism is welcome. Thanks.

[bigdaddy]

Thanks that's exactly what I have been looking for as a start to an SE project using the EF86.

[jojokeo]

I hope it will work out well for you. The name is a bit lame but it was basically built w/ the AC-4 circuit in mind originally. I didn't want to call it a JC-4 because it might make someone think of the Roland JC-120 or whatever and I didn't want to conjure up any thoughts of a solid state amp  :o
Please email me when you're done, I'd like to see another and what you came up with. Thanks.

[Geezer]

Well, that's it!.....this thread is "officially" the largest thread ever on the Hoffman Forum (more posts & views than any other!) THANKS to all who have contributed!

I am currently working on a version using 6BM8's for the PI & output tubes (ala Little Wing), so it will be the "HoSo" preamp into the LW poweramp. I'm hoping for good poweramp overdrive without the need for a Master Volume.
It will also have the ability (via a "parallel" wired 7-pin V1 socket) to run the 5654 & 6AU6 pentode tubes.....
I'll post results in several days.

Once again, just to make it clear (for those of you considering building this amp) that this is absolutely the best amp I've ever played....either current production/vintage/modern/boutique/younameit!
I simply can't stop playin' it...it's THAT good!

G

[jojokeo]

The EF86 tubes in the amps that I've built are little tone bottles of pleasure. My recent posted amp and current newest double EF86 amp has me feeling the same way as yours does for you. In fact while I was reading this thread originally, I was doing so plugged in at the same time,  ;D  To see what you and the others were doing and conjuring up was like a shot of adrenaline as I've spent a lot of the last year messing around w/ this tube.
What was your latest/last final schematic? I think I DL'd  appx. 20 of them between you and tubenit getting neat ideas along the way. It sure is a great design idea and would be a fun build & nice amp to own.

[bigdaddy]

I actually amp going to use an 18 watt chassis I got on ebay cheap and see if a champ type PT fits.

From right to left will be input-multi position switch-tonestack. Some of the holes for input jacks could be used for mini switches.

I was think of having 2 preamps to choose from the EF86 and a 12AX7 with different inputs.

I'm going with an EL34 and all handmade SOZO caps.

[prs_matt]

Tubenit and DG, I have a couple quick questions as I put together a parts order to get started on a pentode preamp project of my own...

Where are you sourcing 2.2uF caps for the cathode bypass caps on V1 and V2? The only ones I can find so far are $20+ Hovland MusicCaps and $30+ Audience Auricaps. There has to be an affordable option somewhere.

Tubenit, are you using a SPST switch and a DPDT switch right next to each other in the PAB part of your circuit?

I am excited to get going on this!
Thanks,
-Matt

[jojokeo]

Bigdaddy - all sounds good!

Matt - these caps are non-critical. You can go to Radio Shack or any local electronics supply if you want and get polarized or non-polarized for a dollar - maybe get two in a pkg?

[Dynaflow]

 Ahem, Doug has em for .75 cents a piece. I heard he sells parts..  ;)

Regards,

Dyna

[jojokeo]

My bad, thought that would be looked at first.  :-[

Hey Mo! I can't see, I can't see...
Why not!?!
I got my eye's closed - nyuk nyuk  ;)

[Geezer]

Where are you sourcing 2.2uF caps for the cathode bypass caps on V1 and V2?

Look near the bottom this (linked) page, under "More caps not listed above" >> http://www.hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&thispage=parts4.htm&ORDER_ID=!ORDERID!

If you don't already have some, go ahead & order a few 1uf & 4.7uf also.....your "taste" may want a little more or less gain in those positions & it's easy to just "clip" different caps in to see the differences. Don't be afraid to experiment w/ different values. Even a 25uf is not out of the question to try.....

My bad, thought that would be looked at first.  :-[

No Prob! We just like to keep reminding folks that "our sponsor" has a great selection of parts & the absolute best service anywhere around!  ;)

[tubenit]

The latest (& I anticipate final) version of my amp is right here:

http://www.el34world.com/Forum/index.php?topic=6176.0

I got my 2.2uf caps from Hoffman.

PRS-Matt, I am not sure exactly what you mean by the spst and dpdt right next to each other? If you mean literally the answer is no they're not but having them next to each other would be fine. I use the PAB playing quite a bit. I tend to leave the 2.2uf (spst) on most of the time.

As a side note, because my amps all have the passive effects loop ........ I can experiment with the preamp of one going into the power amp of another.  After experimenting, I plan to change the preamp of my Carolina Blues Rocket into the 56T preamp. The 56T (5879) had a fatter sound & was more touch sensitive to playing, but not as much overdrive as the CBR preamp.

With respect, Tubenit