HoSo56 amp project...design input sought

[marcoamf]

Hi tubenit,
would you have by any chance the layout for the DG 56 HoSo? (the schem you sent recently)

Thanks!

[tubenit]

You're new here, so ........................  
 

PLEASE download ExpressSCH which is a FREE download (if you have not already done so).  

http://www.expresspcb.com/expresspcbhtm/Free_schematic_software.htm

I drew up Geezer's version with a PPIMV in the layout for you.

With respect, Tubenit

IF you're interested in other versions of the original HoSo56 (such as with 6BM8 tubes) look here:
http://www.el34world.com/Forum/index.php?topic=6176.0

IF you want a version with "pseudo channel switching" and a layout look here:
http://www.el34world.com/Forum/index.php?topic=10999.0

IF you want a version with 6V6's and an extra "gain stage boost"  (schematic and layout) then look here:
http://www.el34world.com/Forum/index.php?topic=15863.0

IF you want a version that will support 6V6's and 5881's and has reverb then look here:
http://www.el34world.com/Forum/index.php?topic=9049.0

LOTS of options for you!

With the ExpressSCH program, you will have access to 100's of editable schematics and layouts here:
http://www.el34world.com/Forum/index.php?board=12.50

With respect, Tubenit

[foghornleghorn]

Yes, my handle on TAG is my real name, David Root. Thanx again for your invaluable help with this project.

[tubenit]

Yes, my handle on TAG is my real name, David Root. Thanx again for your invaluable help with this project.
 

David, welcome to EL34 World! 

I've appreciated your posts on TAG.  You've generously offered great information & I am impressed with what I have seen about your builds & insights into building.  Thanks for joining us!

With respect, Tubenit   (10thtx on TAG)

[foghornleghorn]

You're too kind! One thing I try to do which I find really helps is read the tube data sheet closely (no s**t Sherlock).

But all datasheets are not equal, for example the GE 6L6GC sheet has far more info than any other.

Closer to what I'm doing now, I had been using the Tung-Sol 5879 datasheet, but I recalled that the RCA sheet had recommended to ground pins 2 & 6, because that will reduce hum level from the AC heater supply by shielding grid #1 and plate from the heater.
Pins 2 & 6 are marked NC so I can't see how this would work if they're not connected to anything, but, hey, these guys knew what they were doing.

This morning I re-read the RCA sheet and the very helpful bullets on the maximum voltage chart that explain how the screen, cathode bypass and plate coupling caps' values were derived. Very useful in picking the right values for a driver application, which is the second 5879 in my current build. I had read these before but it didn't sink in until now.

As it happens it looks like I have used lower cap values that will be good for overdriven condition ie cut bass below 250Hz or so. How they will sound in clean mode remains to be seen, but I cut only the bypass caps, the coupling cap is as per the chart.

[marcoamf]

Nice... I'm going to start buying parts.

The schematic has SS rectifiers, which I think will be great to save a little on the tube side (and possibly PT).
What diodes are those?

What are good specs for the PT and OT? (current, taken the voltages in the schem are ok)

After I build it, is it "easy" to include a reverb if I already consider the space for tube and tank?

thanks!

[tubenit]

Which version and power tubes?   

6AQ5, 6BM8, 6V6, 6L6 or EL84?

We need more information from you.

I found it reasonably easy to add a one tube reverb, so if you have space and would be happy with a subtle reverb, then I think it's doable.

With respect, Tubenit

[marcoamf]

I'll build the 56 & PPMIV you posted recently, with EL84s.

I hope the PPIMV has the crunch that the VVR gives to the original 65s.

If this gets good, it will prob be my main amp, so I'll leave some space for reverb, that I like, as well as send / return, footswitch, etc.

[marcoamf]

The HoSo schematic (HoSo & PPIMV) shows the filter capacitors of 40uF, 20uF, 16uF and 8uF. I know that even though not common here in Brazil, 16uF is common in amps.
I know I can use 22uF caps in the place of 20uF, but not sure if using 47uF won't be a too big difference in the place of 40uF.

I could not find 40uF or 20uF caps even on eBay, except some engine / machine starter capacitors like this one
 http://www.ebay.com/itm/AC-Motor-Capacitor-Washing-Machine-Start-Capacitor-CBB60-450VAC-40uF-/110906187167?pt=LH_DefaultDomain_0&hash=item19d2861d9f.

Is that right? Should I use one of those??? Seems quite weird.
If so, how to place them on the chassis?

thanks a lot!

[tubenit]

IF your rectifier can handle 47uf use that.

22uf instead of 20uf is fine.

10uf is OK if you can't find 8uf. 

Their not that critically important, IMO.

With respect, Tubenit

[marcoamf]

Thanks, Tubenit!

I'm also trying to figure out which diodes to use as SS rectifier. I understand that with SS rectifier I might need a PT with less voltage than would with a tube rectifier, right?
Will a 500v PT provide me with de 350v B+ using SS rectifier? Will these diodes handle the 47uF cap you mentioned?

This is my second amp project and I'm sorry if I'm asking basic things. I really want to build the HoSo56 and there aren't many pages on this amp.

I know I'll post many questions as I move forward, but I already know I'll get stuck when defining the Choke (which to use?), Relay (is that even a component or a circuit I need to build)? and some components that are in the schematic that are not in the layout (maybe taken for granted...)

[John]

Hi Marco, if by 500v PT you mean a 250-0-250, then yes that'll give you around 350 unloaded; actually a bit more because our wall voltages are often more than 120. The diodes won't have a problem with any size reservoir cap you want to use. Use the diodes that Doug sells, the 3A/1000 volt jobbies. Probably more than you need but at .50, pfft.

Use the choke that Doug sells, it'll be fine. I believe there is a BOM somewhere on here for the HoSo.

As far as the relay goes, *if it were me* I'd leave a little room for the components, but first get the amp built and working the way you want, and then add the relay. I put the relay in from the start, and spent mucho time trouble shooting my mistakes with it. Eventually I disconnected it and voila, the amp was quiet as a mouse and sounded great.

One thing to note is that humbuckers will sound much darker through this amp (built to schem) than single coils, so you may want to play with the cathode bypass caps. The 5879 gives it a nice smooooth sound that I'm sure you'll love!

[HotBluePlates]

... The way I heard the amp, and peter stroud explain it, this is the way I would assume the bump circuit is done, again my assumption,  Bump circuit is they put a resistor underneath the mid resistor to make slight boost, and more mids and warmth, also disabling the rest of the tonestack from there.  Then using a relay to switch that resistor in, they use another pole of the relay or a second relay to connect in the tone control. ...

Sounds about right to me. What I *think* I heard in the video is a large resistor (100k-220kΩ) between the "mid pot" location of the tone stack and ground to defeat the tone circuit, giving a midrange boost and the impression of more gain (cause it's not being tossed in the tone circuit). At that point the added tone control comes into play, and being a single-knob is probably something like a tweed Deluxe tone control. That is, it seems to make the sound more-trebly or more-bassy; naturally there could be some other 1-knob variant that does the same thing but in a slightly different way.

[marcoamf]

First of all, I'd like to thank Tubenit for the work on the layout for this.
I spent a few hours on this thread this weekend and trying to understand more of this project before moving on. I'm still using the "HoSo 56  & PPIMV.sch"

I already got a 20 x 2 turret board, EL84s, 12AX7s and a 5978, as well as tube sockets. I did not look into chassis yet because I still don't know if I'll make it a big amp with room for future expansion (reverb, foot switch, tube rectifier, etc) or as small as possible to take to band rehearsals without regret.

I hope I now have more focused questions for my build. I have added an extra sheet in the sch layout file, it would be great if someone could help validate that.

So, some questions:
- We just use 2 diodes and not a 4-diode bridge? I know diodes will drop less voltage than most tubes, so, will 270-0-270 HV secondary take me to 350v DC output? Or should I get a 250-0-250 transformer? (I'll order PT custom here in Brazil, with 127v primary that I get at home - up to 132v sometimes)
- I've tried to create an output impedance selector (see layout sheet 2). Is that possible / does that exist? What's the easiest way of doing this?
- What kind of switch is used for the boost? (I'll include in a BOM I've built and post here)
- 20x2 turret board is enough for the existing layout, but I realized it does not include any of the big capacitors. Guess I should look into buying another small board for these and the rectifier diodes, right? (I tried drwaing this on sheet 2)
- I saw that some of you built this amp in a very small chassis. Maybe too small. What chassis size would you recommend (I'll also have to order custom, probably).

I see that no one has yet posted any sound sample or video.
More pictures and gut shots would also be of great help.

Thanks a lot!
- marcoamf

[tubenit]

I'd use a chassis that is a minimum of 17 or 18" X 2" X 6.5".      OR you can use a tweed style 18watt type chassis.

IF you are using solid state rectification,  I'd use the 250-0-250 PT which will give you around 350 v on the EL84's.  Frankly, I'd prefer to use a 250-0-250 PT with tube rectification so you have more options.

You can use a relay switch for the boost.  Doug sells all the parts on his website. And there is an abundance of info in ARCHIVE under relay switching.

With respect, Tubenit

[marcoamf]

Ok, I'll try to go with tube rectification.
Any difference between EZ-81 and 5AR4 that should be considered? Cost, maybe...
So still keep 250-0-250, right?

Any comments on the other questions?

Thanks a lot, again!

[tubenit]

I'd personally go with 250-0-250, but that's just my personal preference because I think it would allow me the most options.

solid state   250 x 1.4 = 350
GZ34   1.3 =  325
5V4  1.2 = 300
5Y3GT   1.1 = 275

With respect, Tubenit

[arjepsen]

Hey.

I've been looking at the gutshots that someone posted a link to, back on the second page of this thread.
There's something that puzzles me a bit.
If I'm not mistaken, there are some components in shrinkwrap under the two resistors before one of the big caps.
I'm not entirely sure what to call those resistors, but I think they are the ones that you usually swap out for the LarMar ppimv.
What puzzles me are those two thingies under the resistors... What could they be? I haven't seen other amp schematics that had any components parallel to these two resistors.
Anyone got a good gues?

Regards
Anders

[sluckey]

I've been looking at the gutshots that someone posted a link to, back on the second page of this thread.
There's something that puzzles me a bit.

I don't see that picture on page two. What is the reply # you are referring to???

[John G]

Hi,
I was told................?? there are series connected diode/zener diodes connected in parallel with each of the grid resistors. This would help reduce any blocking distotion.
Havn't seen the amp in the flesh to comfirm this.
Cheers,
John

[arjepsen]

Now that you mention diodes + zener it occurs to me that I have seen something similar before on 18watt.com
People seemed to often have trouble with fizz/buzz and there is talk of a "Paul Ruby fix" to help reduce this.
I''m curious though, 'cause in that circuit those two resistors to ground (are they called grid-leak resistors?) are 470k's.
In the circuit in the pics, they could look like they are 100k's, and I assume that would mean the signal is hitting the el84 less hard, so I wonder why they could be needed.
If I understand it correctly, this fix only reduces the fizz originating in the el84's, or am I wrong?

[John G]

Hi,

Maybe this is the site you are refering to.
John

http://www.paulamps.com/18watterbuzz.html

[arjepsen]

That seems to be the original  work for the info I found on 18watt.com yes.

But I'm still curious - I haven't met other amp-designs with lower value for those mentioned resistors, that needed such a fix.

[marcoamf]

Hey Tubenit, I saw your pictures of the HoSo but none were from front panel.
What are the switches, knobs, lights and plugs and order? I'm looking for reference for the "real state" of the front panel.

thanks!

[marcoamf]

Publishing again on this forum since I finally finished my build.

Here's a simple demo of the sound:
https://youtu.be/cKPd9zB1R-0

Thick bass (I can't say it's as thumpy as my 5E3, though), chimey with great harmonics.
Nice clean sounds with the volume knob down and low gain knob.
Awesome crunch with gain up, bump on and bridge pickup.

Definitely a must build.

Only one voltage that doesn't match the schematics. 70v on V3 cathodes is at 45v on mine. The rest is on the 10% range.
Any clues why this happens?

I want to build an effect loop for this. Also would like some tips on how to do it. Anyone?

thanks to all of those involved in this project!

[tubenit]

I want to build an effect loop for this. Also would like some tips on how to do it. Anyone?

Sure, this works well and I use it on the D'Mars ODS build.

Very nice job on your build!  Thank you for sharing the video.  Sounds good.

With respect, Tubenit

AND there are LOTS of examples here:  http://el34world.com/Forum/index.php?topic=10208.0

[marcoamf]

I still haven't been able to figure out the issue with the voltage at the v3 (second 12AX7) cathodes.

These are the voltages I'm getting:
https://dl.dropboxusercontent.com/u/7505544/voltagens_Soho.png

I just feel the smell of something burning when I play too much (BTW one of the best amps I've ever heard).
I smell it around the 2 12AX7's and the relay board.

Do you think it could be a defective tube? I don't think so, so I didn't have the courage to put another one there.
I've checked the voltages on the filaments (a bit high, around 6.4v) and remade some soldering wherever suspicious.

As you can see from the images, even though in general my voltages are lower than specs, they get actually higher at C, D, and E.
Apparently no issues with the 10K/5W resistor.

 

[marcoamf]

I think I found my mistake, I'm using 250k dual gang pot for the ppimv.
For some reason I believe it was the only one available at the store when I bought it (and still now, there are no 2M dual gang pots in here).

I don't believe I could use it, right?
Might take some time until I get get my hands on 2M dual gang pots...
 

[sluckey]

I think I found my mistake, I'm using 250k dual gang pot for the ppimv.

That dual pot IS supposed to be a 250K, not 2M. That MV will not affect the voltages you have on the PI tube. I would not be concerned about the voltage on your PI cathodes if you like the sound.

[marcoamf]

Thanks, sluckey, but isnt the plate dissipation much higher than acceptable?
Could be unrelated, but the smell of smoke was a bit suspicious (near the 12ax7s)


If the pot is 250k, should the resistors on them be 2M?

[sluckey]

but isnt the plate dissipation much higher than acceptable?

No. It's actually kinda low. Your low cathode voltage and high plate voltage are indicators that the tube is drawing a small current (about 1.2ma) so plate dissipation will be low. If plate dissipation was higher than acceptable, the tube current would be higher, resulting in a higher cathode voltage and a lower plate voltage.

If the pot is 250k, should the resistors on them be 2M?

Correct. But, please confirm which type of MV you have. Your pic with the voltages and red arrows shows a simple 2M crossline MV but your schematic from November, 2014 shows a dual gang 250K MV with 2.2M resistors. Which do you actually have in the amp? In either case, the MV pot(s) will not be the source of your burn smell, nor will they be causing something else to burn. That's providing the MV is wired IAW the schematic.