New HoSo56 Build is Alive!

[darkbluemurder]

Hi,

With the help and information from this forum, in particular da Geezer, Heinz, tubenit and CraigB I was able to build the basic version of the HoSo. I used da Geezers version but omitted the 250pf plate resistor bypass cap on V2a, used Fender values for the tone stack (slope R 100k, treble 250pf/250kA, bass 100nf/500kA, mid 47nf/50kB). No bump circuit yet.

Built the amp on an 18W chassis and used an 18W transformer set from Shinrock. Tubes:

V1: NOS RCA 5879
V2 and V3 JJ ECC83S
V4 and V5 TAD EL84Cz
V6 EZ81

I love the clean tones of the amp - clear, sparkling and with great sustain. It also takes pedals very well. The overdrive tones still need some tweaking.

Thanks again for all the information on this interesting and wonderful amp design.

Greetings
Stephan

[Geezer]

Good job!

The overdrive tones still need some tweaking.

That's why I went with the Marshall values in the tone stack.....I wanted an "overdrive" amp, by design. That was also the reason for the "smoothing" caps @ the plates....they improved the OD tone.
You should be able to tweak it to a "happy medium" to get the best of both worlds.

G

[tubenit]

Very cool!  Keep tweaking it. Your speaker choice and style of playing usually requires fiddling with component values etc..... to get it to be your tone.

I started with the EL84 version (which does have more chime) and then converted it to using just the pentodes of 6BM8 which in my amp was a little smoother sounding (but less chimey) . Conversion only took me about 30 min to try.

Geezer came up with an absolutely amazing design with this amp.
 

With respect, Tubenit

[snoof]

Built the amp on an 18W chassis and used an 18W transformer set from Shinrock.

How long was the wait for the Shinrock trannys??

[CraigB]

Yeah, it is a great design!

I did one with the marshally tonestack per Geezer's schem and one with the fendery values, both EL84 powered.  I prefer the sound of the marshally tonestack for overdrive rhythm and smooth lead playing, especially with single coil p'ups.  the fendery one is really great with the Les Paul, but I also love the cleaner tones and it's great for chicken pickin with the tele.  That was sort of the mission for me, to have two different variations on the theme.

I agree with Geezer and tubenit, there is a happy medium in a single amp, but it might take some tweaking.  Do try the *smoothy* cap, and try different values to see what suits your speaker, your guitar and what your ears want to hear.

CB

[Geezer]

The solution (but would require planning from the start of the build) is to use 2x switchable channels, one with the Fender values (cleaner/brighter) & the other using the Marshall values (darker/tweaked for overdrive). I think that would be a "complete" amp covering all the bases.
Hmmmm, guess I'll have to build one! 

Geez'r

[darkbluemurder]

Thanks!

Here are the voltages:

V1: Pin 1=   0, Pin 2=NC, Pin 3=0,07, Pin 6=NC, Pin 7=  43, Pin 8=146, Pin 9=0,07
V2: Pin 1=143, Pin 2=  0, Pin 3=1,1,  Pin 6=222, Pin 7=143, Pin 8=144
V3: Pin 1=178, Pin 2=28, Pin 3= 39,   Pin 6= 172, Pin 7=26, Pin 8=  39
V4 und V5: Pin 3=11, Pin 7=340, Pin 8=321.

It seems that the screen grid voltage of V1 (5879) is a bit low. I noticed that the 56T schem specifies 56V. With another 5879 I got 37V. The sound was pretty much the same with both tubes. Is this something I should worry about or just a variation in the tubes?

Yesterday I changed the gain pot from 1MA to 500kA. This removed the blocking distortion I experienced when turning up the pot full. It also improved the overall tone of the amp to my ears. I now decided that before I start tweaking the tone stack or other values I will replace the mid control with the bump circuit and add a switchable cathode bypass cap to V2a. Getting more bass should not be a problem since my output coupling caps are 0.01uf. I noticed that tubenit's version uses 0.022uf but maybe higher values would work here, too.

@Craig: yes, two amps would probably be the best of both worlds. Maybe I will convert my 18W Liverpool build.
@snoof: Ingo had the set in stock so the wait was no problem.

I am running the amp through either an 18W small box Bluesbreaker cab with a Celestion Alnico Gold or through a 2x12" Bluesbreaker cab with a Jensen Neo and a Jensen Jet Tornado. It sounds great through either.

Cheers Stephan

[darkbluemurder]

Here is the schematic of the amp. The parts above the treble cap do not exist yet. They will be replaced by the bump circuit.

I added the cut control and the boost switch on V2a. The latter is really good for the OD tones.

Cheers Stephan

[darkbluemurder]

Yesterday I incorporated the Bump circuit. I adapted CraigB's solution. The schem is attached.

The boost offers some brutal sounds. I guess it is normal that the volume jump is more pronounced at lower gain settings. At higher gain settings it increases the gain into the PI.

I still need to tweak the amp for the overdrive tones. Generally I feel that the sound gets muddy in particular with humbucker guitars at higher gain settings, yet the amp sounds a bit "small" when overdriven. Could be the EL84s though. My Chieftain build has more overdrive and is clearer yet fatter at the same time. Of course it has EL34 tubes.

I will reduce the first coupling cap from 0.01uf to 4700pf and increase the PI output caps from 0.01uf to 0.033uf (I don't have TAD 0.022uf anymore). If that does not get me there I will reduce the slope resistor from 100k to 56k and maybe change the tone caps back to 0.022uf. I will also try the 250pf snubber cap at V2a.

Cheers Stephan

[darkbluemurder]

Did some changes as indicated. They helped a lot. Updated schems below.

Just noted that I missed the 250pf snubber cap at V2a but it is there.

I will play this set up for a while and then evaluate.

Thanks for all your help.

Cheers Stephan

[tubenit]

Thanks for experimenting and sharing the results!  PLEASE keep us posted.

With respect, Tubenit

[darkbluemurder]

The HoSo Master Volume (the "Pre Master" in mine) as identified by Heinz is defintely a path to a smoother overdrive, especially with this control at lower settings. The tone is very consistent with the Boost circuit off. It is a bit less predictable with the Boost circuit on. Apparently there is a certain interaction between the Boost Tone control and the Pre Master control.

I have not yet wired the Boost switch with a relay. I just used a simple DPDT push-pull pot for the Boost Tone control. When I don't play everything is fine, i.e. no pop. When I switch while a note is held there is a pop. Any solution to this?

My power transformer has the following rectifier winding: 0 - 5 - 6.3V. I am using the 0 and 6.3V for the EZ81 rectifier tube. The 5V is currently not used. Am I correct that this could be used to power a relay? I will then only need a spot for the footswitch. That could be either the hole below the input or I have to drill a hole in the back of the chassis.

My feeling is that the Boost or Bump circuit could be used in a AC30/DC-30/Lightning/Club Deluxe/Bassman/JTM-45 circuit as well.

Cheers Stephan

[macula56]

why does your preamp schematic show V1 as an EL84?

[darkbluemurder]

Oops - it's a mistake, it should read 5879 of course. Updated plan is attached.

Cheers Stephan

[PRR]

> It seems that the screen grid voltage of V1 (5879) is a bit low

Don't fret about it. Power tubes high, gain tubes low.

For best gain, Vg2/Mu should be slightly greater than your peak-peak signal input. Triode-mode Mu of 5879 is 21, 43V/21= 2Vpp or 0.7Vrms, which is a hot guitar pluck. Perfect. You meant to do it that way.

56V, 37V.... bah, all the same. YOU try winding grids and holding 20% tolerance. It really is not too important what the G2 current is. 0.6V or 0.9V input overload is not a real difference. You may feel it, it won't ruin your tone.

Your GIF schematic shows "0,07V" on the 470 Rk. This is surely a mis-type? 0.7V is reasonable.

> why does your preamp schematic show V1 as an EL84?

He wants a VERY BIG preamp!!

(And EL84 could be used as a preamp; but little pentodes cost less to buy and feed.)

[darkbluemurder]

Thanks PRR!

I did an updated schematic (V_2.2) and indeed the V1 cathode voltage should have read 0.7V - it's now 0.87V. 

Good to know that I can leave the screen grid voltage of V1 alone. No ill effects noted anyway.

Cheers Stephan

[darkbluemurder]

Did some more changes. I was not really satisfied with the Fender tone stack - too nasal and thin. I changed the values to "Zinky Fender" - 150pf treble, 100k slope, 47nf bass and 22nf mid. I like this much better. This removed the nasal high mid peak, brought back the sparkle and added a lot of substance.

I also removed the 250pf snubber cap again to get more sparkle. I further changed the Pre Master to a simple 500kA pot.

I must say this amp is growing on me. I noticed how touch responsive the amp is. With a strat and the Gain set at about 2 o'clock I can roll the guitar volume back a bit and have an almost clean tone. Roll up the guitar volume and pick lightly I get a very slight crunch. Dig in with the pick and it crunches more but the volume stays about the same.

Here is the current preamp schematic.

Cheers Stephan

[Geezer]

I noticed how touch responsive the amp is. With a strat and the Gain set at about 2 o'clock I can roll the guitar volume back a bit and have an almost clean tone. Roll up the guitar volume and pick lightly I get a very slight crunch. Dig in with the pick and it crunches more but the volume stays about the same.

Right on, bro! 

I've modded another of my designs to include a 5879 (the old "Crazy Like a Vox")........I'll post a new thread on it.
Sounds fantastic, as does every single amp I add this tube to. My favorite tube, by far!

Thanks for keeping us updated on your work,
G

[darkbluemurder]

Some more changes:

1. Changed the un-bumped midrange resistor from 3.9k to 5.6k and the bumped midrange resistor from 5.6k to 8.2k. This improved the sound in both modes.

2. Replaced the 500kA bass pot with a 250kA pot to make the tone stack "exactly Zinky". This lowered the bass range somewhat (there is still plenty) but also slightly increased the low midrange. Together with Change no. 1 this made the unbumped sound slightly fuller.

3. Changed the boost cap on V2a from 10uf to 2.2uf. This is a definite keeper. It retains the high gain sound especially with the bump circuit on but the bass is much tighter now 

4. Changed C9 from a Mallory 150M to a Roederstein of the same value. In most amps I changed Mallories to Roedersteins the amp got clearer and more detailed. This was not so much evident here but the amp's response seems to be faster now. This is a keeper, too.

I still have not found the solution to the heavy compression I get when I turn up the gain all the way (with either bump on or off or boost cap on or off). Not that it really bothers me but I like to design my amps so that the full range of the controls can be utilised. I will check whether a small grid stopper before V2a will help.

So far my tweaks were aimed at improving the OD tones without impairing the clean tones, and I feel I am getting closer. Attached are the now current plans for preamp and power amp.

Cheers Stephan

[darkbluemurder]

I must say the longer I play this amp the more I like it! I compared it with my Liverpool 18W build and found that the HoSo can do all the tones that the Liverpool does and more and does so with a lot less hiss. The Liverpool has a tad more punch but I believe I can tweak the HoSo to match the punch I get out of the Liverpool.

The amp also has a bigger range of tones than any of my other builds. It does the same good clean and crunch as my Club Deluxe but the Club Deluxe does not do high gain (well maybe it would if I replaced the parallel 12AX7 with a 5879 - food for thought ). The HoSo is cleaner than my Chieftain build - even though it is less loud and less punchy - and can go higher gain with the bump circuit engaged.

I have not changed anything since I posted the V_2.4 schems but there is not much tweaking necessary. Just maybe a bit more punch and a bit more tightness and I am there. For this purpose I will increase the output coupling caps to .047uf and decrease the coupling cap off V1 to either 2200pf or 3300pf. This should not be detrimental to the clean tone. What do you think?

Cheers Stephan

[darkbluemurder]

Hi,

Attached is the v 2.5 plan. I changed the B+ rail to get higher voltages to the PI and 2nd preamp stage. Now the amp has more punch. Getting better and better ...

Also corrected some drawing errors.

Cheers Stephan

[darkbluemurder]

A happy new year to you all!

Here is Version 2.6 and this will be the final version as far as parts values go.
I reduced the coupling cap after V1 to 2200pf. This reduced flabbiness to nothing and increased attack speed. I increased the PI input cap to 0.022uf to recover the bass lost by step 1. Finally I added a 10k grid stopper before V2a.

Next step will be the relay for remote bump switching.

Cheers Stephan

[darkbluemurder]

Well it's almost two weeks without further tweaks so I guess that says a lot about my satisfaction with that amp 

However I found that with overdrive sounds I was constantly backing off the cut control to tame some annoying fizziness. Following some discussions over at www.18watt.com I read that some believe that the 1.2k cathode resistor in the PI accounts for fizziness. I replaced it with an 820R.

Plugged in and wow - that thing really screams, is creamy with full of singing sustain in the bump mode and is a lot easier to listen to in the unbumped mode. I can now turn the cut control to 12 o'clock where I had it on 9 o'clock before the change. It lost a bit of the chime to the clean tones but there is still plenty.

Attached is the new plan, version 2.7.

BTW: what tubes do you use as V2 and V3? Currently I have JJ83ECC in there. I haven't gone through my preamp tube box yet so I would like to get some opinions.

Thanks and cheers
Stephan

[tubenit]

Thanks for continuing to update us on this amp and your tweaks!  It is appreciated.  I use a 5751 in V2 for my 56T.  If I am needing a cleaner tone for some reason, I use a 12AT7.


With respect, Tubenit

[snoof]

Which 5879 are you using??  Seems all I can find are RCA's (and various others that are re-branded RCA's).

[darkbluemurder]

The 5879 is a Philipps ECG.

Good idea to use a 5751. I have one or two NOS GEs in my box.

Cheers Stephan

[snoof]

Did you happen to get that tube form a vendor?  I've tried ebay and all the regular suspects, and all i find is RCA...

[darkbluemurder]

I got the tube from Tube Amp Doctor in Germany. Actually the website specified it as RCA (EDIT: they now specify "NOS from various manufacturers (RCA, Philipps ...)").

Cheers Stephan

[TIMBO]

Hi Timbo here, I've followed your story and i'm keen for a build. I have some of the parts 2x EL84 12ax7 JJ803s 12AY7 EZ81. I was wondering if i could use an EF86 instead of the 5879 also i have a 372jx Trany (300-0-300) and hammond 1650F OT. I've just purchased a marshall valvestate combo to do the retro on and it has 2x30w gold speakers and reverb tank. Look fordward to some feedback . Thanks

[darkbluemurder]

Hi Timbo,

I am sure that an EF86 would work - that is what 65Amps used in the Soho. Please note that the pinout is different from the 5879.

A 300-0-300 PT would yield a pretty high B+ for EL84. I used a 290-0-290 and got about 345V with an EZ81. Maybe drop the screen voltage a little more. Or use different output tubes, e.g. 6V6. Actually I would have liked to build this with a pair of EL34 tubes.

Cheers Stephan

[darkbluemurder]

Post no. 100!

I have not made any further changes to my HoSo56 build - the amp sounds great as is. I put it in a smallbox 18W headshell. It has yet to make the gig test but that will happen soon.

What I noticed is that the amp is not very speaker sensitive. It sounds great through all the cabs I played it through which housed the following speakers:

1. 2x12" Bluesbreaker style (where the Chieftain build sits in) with Jensen Neodym and Jet Tornado
2. 1x12" 18W style (where the Club Deluxe build sits in) with a Celestion Alnico Gold
3. 1x12" 18W style (where currently my Liverpool build sits in) with a Weber Ceramic Blue Dog
4. 2x10" cab with Ruby Alnicos (unfortunately they are no longer available).

I guess there are many more good speaker options. Since the amp design is so versatile an allround speaker would work best unless one has a specific preference for cleaner or more driven tones.

Cheers Stephan

[Geezer]

What I noticed is that the amp is not very speaker sensitive.

Same here....it may be a little brighter or darker, or breakup a little earlier or later, but those things are easily compensated for thru minor adjustments to the controls.
IOW, I can make the amp sound pretty much the same with any (reasonably efficient) speaker I run it into.

BTW, putting the finishing touches on the "New Opus II" schematic/layout (dual channel HoSo56 +5879 OD) & will soon post it.

Geezer

[darkbluemurder]

BTW, putting the finishing touches on the "New Opus II" schematic/layout (dual channel HoSo56 +5879 OD) & will soon post it.
Geezer

Looking very much forward to this!

BTW: I decided that I will convert my Liverpool to another (albeit slightly different values, tone stack and boost) HoSo-Build. This time I will strive for maximum overdrive out of this design but still retaining some of the clean tones. That way I can keep the faceplate  . Basically it will be a HoSo in Liverpool disguise. I will save the 18 Watt with switchable 5879 pentode for another project.

Cheers Stephan

[Geezer]

This time I will strive for maximum overdrive out of this design but still retaining some of the clean tones.

That's what I'm going for in the "B" channel (w/ OD) in my new amp.
I'm going to try a trick from Merlin's site, "bootstrapping" the cathode follower for more gain (as described in the link below, bottom of the page).

http://www.freewebs.com/valvewizard1/dccf.htm

[darkbluemurder]

I'm going to try a trick from Merlin's site, "bootstrapping" the cathode follower for more gain (as described in the link below, bottom of the page).

Me, too, me, too! Great minds think alike!
The book describes this a bit more detailed. As I understood it you can control the bass response of this circuit through the cap connecting the joint of the split plate load with the CF cathode. This is important as the cathode cap by which the bass response was previously controlled will no longer be there (at least I want to kick it out).

We probably should make an archive where all the HoSo variants are collected.

Cheers Stephan

[Geezer]

the bass response of this circuit through the cap connecting the joint of the split plate load with the CF cathode. This is important as the cathode cap by which the bass response was previously controlled will no longer be there (at least I want to kick it out).

Ah, good to know, as I am also planning on leaving the Rk bypass cap out.

We probably should make an archive where all the HoSo variants are collected.

I agree. I'll think about how best to do that......maybe start a new thread in the archives section & place links to all the varients? Or maybe it should just be in the schematics section? Any suggestions (from any & all)?

[sluckey]

Help. I can't catch up! I've been wanting to build one of these for a long time. Everytime I get close to pulling the trigger, you guys come out with a new and improved model. And then I have to have it. I may have to just build Butteries' proto board so I can constantly modify the amp.   

[darkbluemurder]

Help. I can't catch up! I've been wanting to build one of these for a long time. Everytime I get close to pulling the trigger, you guys come out with a new and improved model. And then I have to have it. I may have to just build Butteries' proto board so I can constantly modify the amp.   

So far I have built only one model even though it has been improved many times (see this thread). But let's see what we have:

- the SoHeinz
- Geezer's original HoSo56
- the HoSo56T (tubenit's) with reverb, EL84, 6AQ5 or 6BM8 output tubes
- CraigB's take on the HoSo (he actually has two variants as I understand)
- and my first one here.

Add to that all the variants in which the HoSo preamp is paired with a second channel. Lot's of variants to choose from.
Still we don't have one with an EL34 power stage - I guess if nobody builds it I will have to convert my Club Deluxe which will be mostly a matter of replacing the parallel input triodes with a 5879 and a bit of rewiring.

Cheers Stephan

[sluckey]

I want all of those. And the EL34 too! It's like that song by the ever popular Charlie Horse....

This is a song that never ends.
It just goes on and on my friends.

I hope you don't sing that in your head for the rest of the day!      

[tubenit]

I also have built a 6V6 and 5881 HoSo56 version. Still have the 6V6 version. The 5881 version became the T'Lite.

Tubenit

[Geezer]

I'm sure an EL34/6CA7 version would be killer, but I would never be able to use it to full potential.....I rarely have the chance to crank up the 18w/EL84 version, much less a 40-50 watter!  

However, I *am* using 4x of the 16GK6's (16v filament EL84 types) in the new Opus, simply for the increased poweramp "headroom" when I want or need it. I will ground G1 of 2 of the power tubes when not in use (for standard "18w" output).

[jojokeo]

DBM - "Following some discussions over at www.18watt.com I read that some believe that the 1.2k cathode resistor in the PI accounts for fizziness. I replaced it with an 820R.

Plugged in and wow - that thing really screams, is creamy with full of singing sustain in the bump mode and is a lot easier to listen to in the unbumped mode. I can now turn the cut control to 12 o'clock where I had it on 9 o'clock before the change. It lost a bit of the chime to the clean tones but there is still plenty. "

Did this change increase the output drive voltage going into the power tubes? Is it similar a cathode resistor for a normal triode gain stage where it also pronounces gain of given freqencies or the overal signal as a whole? Now the lack of driving the power tubes properly caused this "fizz or fizzing" effect or sound description?
I'm trying to better inderstand the cathode resistor's function of the LTPI and PI manipulation technique.

[Fresh_Start]

jojo - you might want to read Aiken's bit on designing a LTPI:
http://www.aikenamps.com/LongTailPairDesign.htm

Let us know when you understand it all... then you can explain it to me

Chip

[jojokeo]

 
Yes, I've read it a number of times and calculated values 5 or so times for my clone of Geezer's Little Wing amp using a 5879 & 6BM8's. Depending on 82k or 100k Ra's my value worked out as either a 1.8k or 1.2k w/ a 33k or 39k tail r. But, I was having too much compression & not enough headroom for my tastes. I played around w/ the values and ended up w/ 1.8k w/ a 22k tail resistor to get it right.

Now, I built in send/return jacks (prior to the pi as usual) and took the send from my modified Firefly clone amp into the return and it was MUCH louder! Sounded really nice. So, it makes me wonder why my 5879/CF stage is lacking so much more signal than the cascoded/two stage Firefly amp?

As I'm writing this, I realize my mistake in thinking the loudness difference was not from the pi stage.  My LW clone gets a lot of compression when the volume is turned up btwn 8 & 10. It doesn't take more than 3 or 4 on the gain control to start noticing distortion/driving in the signal. This volume is only after the tone stack and is not a Master volume which normally is after the PI. Thinking out loud - I was thinking that my distortion from the volume was from too much signal feeding the pi but that's not the case or the firefly's input would have strongly done the same. So it much be that my normal compression is occuring from the the CF stage but at a lower signal strenth/volume as compared to the firefly's preamp. I suppose that I would need one more gain stage after the CF stage to get the same volume level as the firefly preamp?
All this being said, the LW  clone gets very loud anyway - louder than my single ended EL84 & 6V6 amps (which are very loud themselves) and the 6BM8's are putting out atleast 7 watts as I have them at the max dissipation and voltages of their ratings.

*Any help w/ how the cathode resistor works/applies for the LTPI is still wanted / needed for better understanding on what this does and how it affects please?

[darkbluemurder]

Did this change increase the output drive voltage going into the power tubes? Is it similar a cathode resistor for a normal triode gain stage where it also pronounces gain of given freqencies or the overal signal as a whole? Now the lack of driving the power tubes properly caused this "fizz or fizzing" effect or sound description?
I'm trying to better inderstand the cathode resistor's function of the LTPI and PI manipulation technique.

I don't think it increased the output drive voltage. In order to increase that you would have to reduce the PI tail resistor (the 39k in my schematic) and/or increase the power tube grid leak resistors (the 220ks).  It is just that with a lower cathode resistor the PI's bias is warmer. The fizz of a cold biased PI will probably be swamped once the power tubes start to distort. But since I use a master volume the power tubes will never distort anyway. Hence I need a good overdrive out of the preamp and PI.

Up to now I just built PIs according to what the schematics showed me based on "the amp companies used it so they gotta work". I am only starting to tweak the PI circuit for specific tones.

Cheers Stephan

[darkbluemurder]

Well, I left off with the attached plan. But after having completed the HoSo Super Lead Overdrive (SLO) I went back tweaking this one and made a few minor changes:

1. Increased the PI output caps to 0.047uf. I may increase them even further. The HoSo SLO has 0.1uf caps here.
2. I removed the 1000pf snubber cap at V1 so there is now just the 56k plate resistor (the HoSo SLO has 100k here without a cap). However this will not be the end of it because now there are some harsh artifacts present even with the amp played clean. If I turn back the cut control I also lose the sparkle along with the harshness. I will first increase the plate resistor so that the plate voltage drops just under 140V and then add a small snubber. I could imagine ending at 68k/500pf or 82k/330pf.
3. I put a 100k resistor right in front of the gain pot to reduce the gain at lower pot settings and to get the entire range of the pot to be usable.

Even though both amps have the same architecture they sound rather different but that's a good thing. Both can do good clean, mean and lead tones. The HoSo SLO has definitely a more Marshall-Vibe to it whereas the HoSo56 has more Vox-Vibe. Maybe I should reduce the cathode follower resistor to ground from 100k to 56k to enhance this (and rename it "HoVox")?

Cheers Stephan   

[Geezer]

DBM.........sorry to sort-of leave you here & not comment.

I read your updates w/ interest, but have little time to comment, as I've "moved on" to the new "Dumble SE" build.
I haven't done a full-out scratch build in over a year & am having a hard time "gettin' it together"....     It's going REAL S-L-OOOO-WWW  

You seem to be getting it tweaked to your taste 

[darkbluemurder]

Geezer,

No problem at all! After all it was me who was late to the party.

Yes, I am definitely tweaking. I have already tweaked this amp to a state where it only resembles the original HoSo56 design. A new schem will follow.

I plan to play the amp on our gig next Saturday. While the amp was still in one of its earlier stages I took it with me on one gig with the intention to play it but after the soundcheck I decided to use my Club Deluxe instead and only keep it as a backup. We will see how it turns out this time around.

Cheers Stephan

[darkbluemurder]

Attached is the new schem with the latest tweaks.

For the pentode plate resistor I ended up with a 82k which brought the plate voltage down to 130V. This increased the gain considerably but also made the amp slightly instable so I added a 500pf snubber cap. That was the ticket - gone is the slight trace of brittleness in the clean tone and the overdrive is smooth and singing.

I also changed the cathode resistor of V2a to 1k to get the plate voltage a bit closer to B+/2. Don't know why but I like the sound better that way.

It really sounds like a high gain Vox now  . That's how it will go to the gig on Saturday - looking very much forward to it.

Cheers Stephan 

[darkbluemurder]

Finally I did the gig test last Saturday with the country rock band that I play in. I used a strat and set the controls for a clean sound as follows:

Gain just under 9.00
Treble 14.00
Bass 15.00
Pre Master full
Bump tone 15.00
Bump level 9.00
Post Master full
Cut 14.00, later 15.00

The clean tone was excellent, warm yet bright and transparant but no trace of harshness whatsoever. This is due to the 500pf snubber cap on the pentode - that was the trick to get it smooth. For clean leads I used a transparent boost pedal or engaged the bump section. For overdrive tones I used two higher gain pedals (one for rhythm, both on for lead). All in all I was really pleased with the amp's performance. Together with the pedals it does everything I want it to.

Once again thanks to all who contributed to this preamp design. It is reasonably simple to build (fits really well into a standard 18W chassis), has a wide range of tones and is extremely flexible to tweak to personal taste.

Cheers Stephan