18 watt Stout & Plexi amp designs

[tubenit]

As many of you know,  Doug is getting a chassis for us that will work for 18w type amps and 5E3 type amps.
http://el34world.com/Forum/index.php?topic=17502.0

The original 18w info is here: 
(layout)                                         http://el34world.com/Hoffman/files/Hoffman_Stout.pdf
(original schematic)                        http://el34world.com/projects/images/HoffmanStout18watt_No%20Switch_Schematic.GIF


What I thought I would do is offer some more designs with the goal that:
1)  will work with the chassis
2)  will use the Hoffman 18w PT & OT
3)  will use the Hoffman style 18w layout board

So, I offer the following ideas that should work with chassis, trannies and layout board!  All are DRAFTS.  I have NOT built any of these.

CHECK for errors!  Compare schematics to one another.  Compare schematics to the Hoffman layout.  Post any concerns or questions.

- Original 18w Stout
- 18w Stout & VVR
- 18w Stout 6BM8  (actually 9 watts)
- 5E3/18w hybrid with 6V6
- 5E3/18w hybrid with 6AQ5  using a VVR


NOTE:  all  editable SCH schematics are on the same SCH schematic.  There are 8 pages each with a different schematic.

With respect, Tubenit

[tubenit]

CHECK for errors!  DRAFT ideas.

the following ideas that should work with chassis, trannies and layout board!

With respect, Tubenit

[EL34]

Cool, Thanks for all this work Jeff


I'll check it out tomorrow when I get to the shop

[tubenit]

IF I am thinking thru this well, these should also work just fine with Doug's chassis and 18w PT & OT. 

I drew these to match the tube socket punch outs for his chassis.  Note on the 6V6 Plexi, you would need to use a solid state rectifier to make this work.

However, the Stout layout board would not work. IF someone is truly interested in one of these and needs a layout board designed, then PM me and I'll consider helping with that.

DRAFT ideas!  CHECK for errors!

6BM8 Plexi
6V6   Plexi
18w   Plexi  EL84
6V6   Plexi TBM

With respect, Tubenit

[kagliostro]

Cool I like the 9W version 


Franco

[tubenit]

Made a couple of corrections on two of the schematics. IF you see an error in the GIF schematic, check the SCH version posted below to see if the correction has been made on it.

There are 9 pages with 9 different schematics on the attached file. All of these use Doug's chassis and trannies. 5 of them also use his Stout layout board

With respect, Tubenit

[kagliostro]

Please Tubenit

can you say which are the schematics

that agree with the Stout layout ?

Thanks

Franco

[tubenit]

can you say which are the schematics that agree with the Stout layout ?

All the ones that have Stout in the title.  None of the Plexi ones.

With respect, Tubenit

[EL34]

looks good
I am prodding Andy over at Mojo to see when we can expect some chassis


Still don't have a firm date

[kagliostro]

All the ones that have Stout in the title.  None of the Plexi ones.

Seems that Stout label is only in the title of two schematics (I refer to the 9 sheet .sch file)

but as the Plexy label is present in the sheet # 6 - 7 - 8 - 9

I think that the Stout layout is compatible with the schematics of sheet # 1 - 2 - 3 - 4 - 5

Am I correct on that ?

Thanks

Franco

[Ed_Chambley]

Thanks, all great ideas and a nice variety as well.  Thanks for the work!

[MakerDP]

Dang... that 6BM8 version has captured my eye... 

[tubenit]

the Plexy label is present in the sheet # 6 - 7 - 8 - 9 &  I think that the Stout layout is compatible with the schematics of sheet # 1 - 2 - 3 - 4 - 5

Am I correct on that ?

Yes, sheets 1-5 will accept the Hoffman layout , the trannies and the chassis.

Sheets 6-9  will accept the trannies and chassis only & will need a layout drawn up.

With respect, Tubenit

[DummyLoad]

you're not worried the B+ may be too high with the 6BM8 if you use the 18W PT? haven't played with the 6BM8 much (lafayette escadrille), IIRC it seemed like 300V was pushing it with that tube.


--pete

[tubenit]

you're not worried the B+ may be too high with the 6BM8 if you use the 18W PT?

triode max on plate 300v   pentode max on plate 600v

page 2 data sheet:  http://www.tubebooks.org/tubedata/HB-3/Receiving_Tubes_Part_1/6BM8_ECL82.PDF

With respect, Tubenit

[DummyLoad]

that's peak pulse. look at ecl82 datasheet.


--pete

[tubenit]

that's peak pulse. look at ecl82 datasheet

Pete, can you help me out?  I honestly don't know what that means?  I am not sure how to read some of the data sheets?

What do you understand the max voltages to be?  I am anticipating 330v on the 6BM8 pentode plates.

With respect, Tubenit

[Willabe]

Some tubes are not used for audio that have more of a constant duty cycle, more or less.

6V6 tubes (and others) were also used for vertical amplifiers in TV's, tube working duty cycle was pulses (so it's turning off for part of the cycle) and looking in the GE tube manual it gives a 'max positive pulse voltage = 1200, max dc cathode current = 40mA.'

So like DL said your looking at the peak pulse voltage rating, not the audio voltage rating.

You can think of it sort of like when you run power tubes in class A (both SE and PP) the duty cycle is more constant (running tubes closer to being full on all the time, so their running hotter) then if you run them in class AB1. So you have to lower the plate voltage to compensate.


                           Brad   

[lego4040]

  thank you tubenit. I am building the stout using 6v6's and finished board today. I made the 8.2k's grids 5.6k and the screens I brought down to 220k already. I've been bouncing back and forth with the stout sch, Sluckey's tweed 5e something and a TrainWreck. I bought the classictone 18watt OT but wondering if I can go up to a TW style 30 watt OT?  I can't view your SCH on my phone but will on computer later. I already had the tube rectifier gone two weeks ago with SS in mind because of room issues. My PT reads 350-0-350 and I have a 50v center tap as well. This amp I'm building is being converted from a AllenAmp I built about 7 years ago. His trannies are Heyboers so I'm happy bout that. Can't wait to piss the neighbors off

[sluckey]

I am building the stout using 6v6's and finished board today... My PT reads 350-0-350...

I bet sometime down the road you'll be asking that old familiar question, "How can I lower my B+?"   

[tubenit]

Pete and Brad,

Both of you have suggested that what I posted in reply 14 was "peak" voltage and that the schematic with 330v might be too high?  (if I am understanding you?)

IF I  am reading correctly, I am seeing 550v max for the 6BM8 pentode plates, with "peak" volts being 600v?   
pg 5  here:  http://www.mif.pg.gda.pl/homepages/frank/sheets/010/e/ECL82.pdf

This site says "average" plate voltage is 300v, so I would understand average to mean some applications have voltages more then that and 330v is only 10% more?
http://www.drtube.com/datasheets/6bm8-sed1996.pdf

Electro-Harmonix 6BM8 data sheet lists the pentode plate maximum voltage at 600v and screen at 550v (peak is 900v?):
http://www.svetlana.com/pdf/electro-harmonix/6bm8eh.pdf

And I found this:

Curiously enough the 6BM8 does have some unusually high voltage ratings. According to my Amperex tube manual (Vol. 3 Semiconductors and Special Purpose Tubes) for the pentode section Vp w/o current is 900v. Max Vp is 600v. Peak pulse Vp is 2500v at 4% of one cycle or 0.8 milliseconds max. And peak inverse Vp is 500v. Max Vg2 is 550v without current & 300v with.

For the triode section Vp w/o current is 550v. Max Vp is 300v, and peak pulse Vp is 600v. These are absolute maximum ratings and typical operating levels are much lower for both sections.

IF I am not understanding this correctly (and I may not be?), can either tell me what you believe the max voltage is and list a reference or link, please?  It would be helpful to know what the correct answer is IF I am listing incorrect information, please.   

I will say that I ran my 56T  at around 297v (or more) on the plates for several years with NO issue.

Per Geezer regarding his 6BM8 mini-Bassman:

Hmmm.....I just noticed that the recto I had in there for the voltage test was a 5Y3, and the sound samples had the GZ34 installed.
I just checked the plate volts w/ the GZ34 & it's ~320v.    BTW, I like the tone better at the higher voltages. I have a SS module that I made up to plug into the recto socket & personally prefer it over even the GZ34, but I like as much clean headroom as possible. The SS takes the plate volts up to ~335v

Worse case scenario,  we use zeners to drop voltage or a VVR to use a 6BM8 tube. Either would be reasonably easy to do.

IF anyone has a concern about the B+ of around 320v being too high on their 6BM8 pentode plates, you can use the "zener diode trick", a VVR or the mosfet follies  B+ reduction idea here: 
http://el34world.com/Forum/index.php?topic=17595.0


With respect, Tubenit

[lego4040]

  yes. So what do I do Steve? My mind is fried lately, wife is on way to Atlanta and I got my CC in my lap while I load up shopping cart so Doug can keep this site going I have a big ass 330ohm 25watt aluminum resistor that might help, maybe. If not I'll order a new PT, It's only money

[lego4040]

Someone needs to come up with a plane going over a avatars head, sometimes when I read what you guys are talking about I get lost.

[MakerDP]

I found this about a couple of 6BM8 builds... one with 300V and one with 350V on the plates...

http://www.tdpri.com/forum/shock-brothers-diy-amps/266390-reinventing-wheel-6bm8-powered-5f6a-bassman.html

It actually links to the Little Wing build here on this forum...

http://el34world.com/Forum/index.php?topic=562.0

[Willabe]

Both of you have suggested that what I posted in reply 14 was "peak" voltage and that the schematic with 330v might be too high?  (if I am understanding you?)

No, I just thought that a max of 600v was too high for a 9 pin triode/pentode in 1 bottle. Octal base tubes have a little more room inside and at the base pins/socket, so they can handle a (little) more voltage and current before arc over.

Plus Pete said 'peak pulse' which I remember reading guys talk about with 6V6 tubes and that (some?) tubes with this high 'peak pulse' voltage can withstand higher voltages then what the tube manuals max audio max voltages are listed as. IIRC it's because of the spacing of the grids/cathode/plate/filament to handle not internally arcing over from 1 element/socket pin to another. (Jim Kelly 6V6 amps ran their plates at 500vdc.  )

Looking at what you just posted (note it lists a reference from 'specialty tubes' for 6BM8) I think your correct as 'peak pulse' is listed as 2500v.       (But at 4% duty cycle for a 'frame amplifier', for movies/video or still TV's?)

Above my pay grade, Pete, PRR, Sluckey, HBP will know more.


                   Brad         

[tubenit]

Two more ideas that I think will work great with Doug's trannies and chassis!  You'd use a 8pin hole to 9 pin hole adapter on one of the 8 pin holes, so you could have a 3rd 12A_7 tube.   The 6V6's would be in one of the 6V6 holes and in what original was to be the rectifier tube hole. You'd just use a solid state rectifier.

The Carolina Blues Special is still one of my favorite amps.  My best friend and my son in law both have one.  It's like a 5E3 tone but cleaner and with reverb.  I played this with HotBluePlates when HBP brought his 5E3 to my house. Similar tone, cleaner and verb. I built two CBS amps out of Bogen DB-110 chassis, so I am confidant you could put this in the chassis that Doug is getting.

The Tweed BluezMeister clean has a beautiful tone, IMO.  I think Doug's chassis might not have room for relay switching, but you could sure use mini-toggle DPDT to have the mid-boost (very useful with strat pickups) and the PAB (preamp boost).  Engaging the midboost and the PAB really does increase the sustain on the clean channel.  One of my favorite blues tones is the clean on the TBM with those engaged.

Carolina Blues Special soundclip: http://www.soundclick.com/player/single_player.cfm?songid=6775767&q=hi&newref=1

Tweed BluesMeister  (clean at start of soundclip): 
http://www.soundclick.com/player/single_player.cfm?songid=10251365&q=hi&newref=1

With respect, Tubenit

[lego4040]

I remember the little wing, I'll check it out

[tubenit]

I realized using the triode/pentode of the 6BM8, that one could build a HoSo56 (Geezer's design) using a 5879 V1.
This is a very very touch sensitive great sounding amp, IMO.

This would be a GREAT amp to build in this lunchbox chassis! 

IF anyone has a concern about the B+ of around 320v being too high on their 6BM8 pentode plates, you can use the "zener diode trick", a VVR or the mosfet follies  B+ reduction idea here: 
http://el34world.com/Forum/index.php?topic=17595.0


With respect, Tubenit

[tubenit]

I have added some editable SCH layouts for the   56T,  TBM clean and the Carolina Blues Specials here:

http://el34world.com/Forum/index.php?topic=17585.0

These would use Doug's 18w PT & OT & then you can use his tagboard ..........OR build a paralleled turret board.

[/b]With respect, Tubenit

[tubenit]

OK, there are 12 different designs that will use Doug's 18w chassis, his 18w PT & OT. 

The 3  Stout  designs will use his original Hoffman style 18w turret board.

The  other 9 designs will use his 18w chassis, his 18w PT & OT and his tagboard .......... OR you can make an even smaller paralleled turret board. 

(NOTE:  Doug's tagboards are 28 tags per 11.8".     20 tags would be 8.42"     16 tags would be 6.74") 

All 12 designs have a layout board referenced for them:   http://el34world.com/Forum/index.php?topic=17585.0

With respect, Tubenit

[kagliostro]

Hi Tubenit, great job 

Do you think that without the vibrato circuit Tubeswell's 6H3 can fit in Doug's chassis and use his 18W PT and OT ?

Of course a SS rectify must be used (or do you think that with a SS the B+ will rise too much ?), and an adaptation must be done about bias circuit as to have it from HV winding

http://el34world.com/Forum/index.php?action=dlattach;topic=13872.0;attach=30191

I like this circuit

Franco

[tubenit]

I think because of the vibrato, it would be VERY challenging to get Tubeswell 6H3 circuit into a 12" chassis.  Not saying it can not be done, but it would take some careful planning.


I added one more schematic and layout (both) to the SCH thread.  It's the Tweed BluezMeister Reverb (clean).  I think this would be a very nice amp and I have built something similar to this in the past and liked it.  I explain in the SCH thread, how I would approach this.

With respect, Tubenit 

[kagliostro]

I think because of the vibrato, it would be VERY challenging to get Tubeswell 6H3 circuit into a 12" chassis.

I agree with you, I was asking about a version without the vibrato and with SS rectifier


Franco

[tubenit]

I agree with you, I was asking about a version without the vibrato and with SS rectifier

Oh, sure!  I think that is easily do-able!  That shouldn't be a problem at all. IF you need help drawing up a schematic and layout, let me know & I'll see what I can do to help.

With respect, Tubenit

[tubenit]

As you guys think of different amp designs that you ponder for this chassis and trannies ...........................

AND the length of the layout board that you will need in the 12" chassis,  I thought this visual picture might be useful to you.

It should be noted that IF you use Doug's turret board material and turrets, that you can make even an shorter length turret board.

Respectfully, Tubenit

[EL34]

Cool designs you are doing here Jeff


I can't wait to get some of these chassis out there and see what you guys can do with it


Still waiting on the final release date

[tubenit]

It occurred to me with the success and interest of the Tweed Overdrive Special, that we could do a "junior" version of it in this chassis with Doug's 18w PT & OT and using his tag board or making a turret board.

Tweed Overdrive Special Jr.

I think this would be a really nice amp for those of you who like an overdrive tone that is smooth.  I'd probably try a 12AY7 in V1.  Doug sells the 12AY7's and that's what I use in my amps.

The layout is in the previously referenced SCH Library thread.  The layout board should be about 7.4" length and fit OK.

I added a 5879 OD version also.

With respect, Tubenit