low wattage el34 amp

[blindopher]

Hi,

 I'm considering my next amp build and I wanted to know is there any way to enjoy a Marshallesque EL34 driven tone at 15W? I'm limited budget-wise to using my 1X12 cab loaded with a 30W driver. As I understand, my amp should in this case not exceed 15W RMS. I know one way to employ an EL34 topology would be a single ended amp, but I don't think SE would get me close to a Marshall tone. I think part of the Marshall mojo is the cathode follower into tone stack into phase inverter. So, is there anyway to employ two EL34s in this scheme and stay close to 15W? If not, how would I go about making two EL84s sound as close to a Marshall as possible? I don't really play clean and i'm looking for that Zeppelin classic rock plexi tones. (I play a Les Paul).

 thanx

[jazbo8]

If not, how would I go about making two EL84s sound as close to a Marshall as possible?

You mean like the 18W?

[kagliostro]

PI & Final Tubes under VVR + PPIMV

---

I've an old Geloso G 227-A PA amp that uses a pair of EL34 in PP with 320v B+, but also at this low voltage the power is around 30-35W

You can use EL84 tubes in place of EL34, the sound of the two tubes is claimed to be similar to each other

and the 18W is an example with good results

K

[jojokeo]

Just using EL34s with a CF stage, etc. does not a Marshall make. Same with VVR because when used while lower voltages the pi is affected as well as the EL34 grids becoming much more sensitive and things just don't sound and feel the same. You can get sort of "close" but all considered will not "be like". Also, you need high plate voltages to get the '34s to scream at their best - well into the 400s. Operating them in the B+ ranges of the 200s or even 300s just doesn't get the tubes singing properly.
 
Having multiple speakers all pushing air along with a feel of your guitar strings vibrating as well as the sound is all part of the total Marshall experience too. Hard to replicate in another way. But the 18watt is a good alternative. Aside from all this info, it is not stated as to what type of Marshall grind you're wanting? JTM characteristics driven hard or JCM800, 900, DSL...?
Most of those are having preamp gain differences. This could be simulated via effects pedals and is actually a very viable consideration at much lower money and risk of a build which may not hit your Marshall happy spot? All the newer Marshall high gain amps achieve their high gain through built-in effects pedal circuits anyways. Look inside and you'll see a host of op-amps and transistors in the preamp stages.

[blindopher]

Thanx to all,

So my next question concerns power scaling, attenuation etc. If I build say a 30 - 50W push pull amp using a pair of el34's, then attenuate, will this effectively reduce the power output of the amp so I could safely use my 30W 1X12 cab?

[kagliostro]

If you use an attenuator your speaker will be preserved,


but as to have a good sound is easy that you have all the time the power tubes at full roar,


so you preserve your speaker (and ears) at the expense of the life of the tubes

K

[Willabe]

Same with VVR because when used while lower voltages the pi is affected as well as the EL34 grids becoming much more sensitive and things just don't sound and feel the same.

Just VVR/Power Scale the power tubes and let the PI run as normal. Then use a PPIMV to adjust the drive to the EL34's.


               Brad   

[jojokeo]

Same with VVR because when used while lower voltages the pi is affected as well as the EL34 grids becoming much more sensitive and things just don't sound and feel the same.

Just VVR/Power Scale the power tubes and let the PI run as normal. Then use a PPIMV to adjust the drive to the EL34's.


               Brad   

That's probably what I'd do to meet that objective having to still use '34s.

[tubenit]

Just VVR/Power Scale the power tubes and let the PI run as normal. Then use a PPIMV to adjust the drive to the EL34's.

Great idea!   With respect, Tubenit

[PRR]

Another speaker is maybe quicker-cheaper than building an amplifier.

EL34 at 250V puts you in your zone; but hard to find 175V PT for 250VDC, and you pay for 3 times more bottle and heater-power than 15W needs.

And there's no replacement for big Watts, BIG speaker array, and gut-thumping air waves.

[DummyLoad]

Another speaker is maybe quicker-cheaper than building an amplifier.

EL34 at 250V puts you in your zone; but hard to find 175V PT for 250VDC, and you pay for 3 times more bottle and heater-power than 15W needs.

And there's no replacement for big Watts, BIG speaker array, and gut-thumping air waves.

PRR, would the hammond 263CX/363CX will get him in the 250VDC ballpark with enough juice? if yes, he'll need a 6.3V filament transformer though...


--pete

[Ed_Chambley]

I helped a friend build one of these.  It is a Parallel EL34 SE amp with a JCM800 preamp and switchable caps to change the coupling cap values.

FARGEN MINI PLEX MKII TECH SPECS 2010

It is really the closest thing to a 15 watt cranked EL34 tone.  Ben Fargen uses DC heaters, but we found with proper filtering AC is quiet, but if you want to record with it DC may not be a bad way to go.  It still has a tad of noise.

[Big_Mike]

I helped a friend build one of these.  It is a Parallel EL34 SE amp with a JCM800 preamp and switchable caps to change the coupling cap values.

FARGEN MINI PLEX MKII TECH SPECS 2010

It is really the closest thing to a 15 watt cranked EL34 tone.  Ben Fargen uses DC heaters, but we found with proper filtering AC is quiet, but if you want to record with it DC may not be a bad way to go.  It still has a tad of noise.

Do you have a schematic for this build?  I really want to build a Fargen Miniplex clone, and would be interested in a schematic or a layout.  How close to the original was your build?  Was it based off of an actual Miniplex?

[Ed_Chambley]

I helped a friend build one of these.  It is a Parallel EL34 SE amp with a JCM800 preamp and switchable caps to change the coupling cap values.

FARGEN MINI PLEX MKII TECH SPECS 2010

It is really the closest thing to a 15 watt cranked EL34 tone.  Ben Fargen uses DC heaters, but we found with proper filtering AC is quiet, but if you want to record with it DC may not be a bad way to go.  It still has a tad of noise.

Do you have a schematic for this build?  I really want to build a Fargen Miniplex clone, and would be interested in a schematic or a layout.  How close to the original was your build?  Was it based off of an actual Miniplex?

Big Mike,
I have no schematic or layout, but we used a Mojotone JTM45 to build it.  I simply got some Edcor Iron.  Since he just was tired of the JTM 45 we simply changed it to a JCM 800 values with a MV.  We did use larger coupling cap values and a rotary switch for the "Decade" selection.  The tonestack values were changed from Marshall values as they were dark.


His turned out nice.  He has changed his speakers so we could tweak it some.  I am planning on building another one and this one will have some changes.  Mainly I would get the noise down so it could be used in a studio.  I plan to bring the voltages up in the PA to about 450.  I really do not care for the "Decade" switch since it is just one of those things I always set and leave when using s distorted amp.


PM me if interested in building it.  Finding Fargen Schematics are not easy, but I have a ole 800 build I copied from an original.  Compared to the schematics it is the same a JCM 800, but handwired and Sozo/Sprague, carbon film Mercury Magnetics.....etc.

[Big_Mike]

Thanks for the info.  I'd like to build a good copy of the Miniplex instead of shelling out a ton of money for one.

[Scsoul]

 I built a superlite a few years back with a 315-315 power transformer with a 5ar4 and the amp sounded awsome the el34 had pretty low plate voltage, there,s also the phat ass amp there building over at the weber forum that are basicly a liteIIb these amps are pretty marshally 

[jazbo8]

I have no schematic or layout, but we used a Mojotone JTM45 to build it.  I simply got some Edcor Iron.  Since he just was tired of the JTM 45 we simply changed it to a JCM 800 values with a MV. 

I built a superlite a few years back with a 315-315 power transformer with a 5ar4 and the amp sounded awsome the el34 had pretty low plate voltage, there,s also the phat ass amp there building over at the weber forum that are basicly a liteIIb these amps are pretty marshally 

Aren't both of the above amps push-pull instead of parallel SE used in the Fargen?

[jojokeo]

I think it's an interesting idea to utilize various output tube combinations. It could be done by utilizing a common cathode resistor on a switch for each type that's plugged into to it's socket: 6V6/6L6/5881/KT66, EL34/6CA7/KT77, 6550/KT88 for whatever two combo you'd like to run. For the Decade switch control it would be more difficult but can be done using an elaborate switching (& maybe biasing) system for the three preamps. Lots of options with this kind of amp but sure would be a waste of a lot of potential power (& headroom) for basically the same amount of money invested in it. Wasting a lot of money also for the iron & tubes to only run two EL34s to get 15 watts for EL84 performance. It's like paying for and building a "muscle car" using a 454cc big block motor to run at less power than a small block 307cc and expecting the thing to still sound the same to do burn-outs with and you can't race (ie perform) with it because you neutered it.

[Ed_Chambley]

I think it's an interesting idea to utilize various output tube combinations. It could be done by utilizing a common cathode resistor on a switch for each type that's plugged into to it's socket: 6V6/6L6/5881/KT66, EL34/6CA7/KT77, 6550/KT88 for whatever two combo you'd like to run. For the Decade switch control it would be more difficult but can be done using an elaborate switching (& maybe biasing) system for the three preamps. Lots of options with this kind of amp but sure would be a waste of a lot of potential power (& headroom) for basically the same amount of money invested in it. Wasting a lot of money also for the iron & tubes to only run two EL34s to get 15 watts for EL84 performance. It's like paying for and building a "muscle car" using a 454cc big block motor to run at less power than a small block 307cc and expecting the thing to still sound the same to do burn-outs with and you can't race (ie perform) with it because you neutered it.

True, it is an expensive build.  I started this hobby because I just had too much money laying around.

EL34's sound different than EL84 especially in a SE amp.  Will it sound like what my brain says 2 EL34's should sound like.  No way.  The Power Tubes are bypassed individually with 220uf.  Did not get a chance to see what changing the value does. 

There is not really much to the amp.  I did not get a change to tweak it as the owner loved it and took it straight away.  What I found and plan to work out is if you tried to get the bottom to have that Marshall Crunch and Chug the upper mids would get way too tight.  Leave it greasy and it has great harmonic content.  I think the trick is to get the PA tight and use preamp distortion. 

Anyway, making the previous build gave me serious experience.  You think if I would have used Sozo caps and Mercury Iron it would have sounded just like the original?

I am really digging el34's in an SE.  In playing the Fargen you do not get Power Tube breakup easily.  I do not know how it is 15 watts either.  The one I built came in at almost 20 watts. 

BTW, the amp does NOT like to be pushed much.  I tried a RC booster and the amp distorted (bad) immediately from the EL34's.  Anyway, this is my ongoing project.

Oh yea, don't you worry your pretty little head.  When I want to pull out the old big block, I got it covered.  I may not have a Major, but I have plenty of power.

When I am playing with that much power the ONLY way to get me to turn down is put sheet music in front of me.

[jojokeo]

I wasn't speaking to anybody rather just "speculating out loud" about the possibilities of how to go about creating an amp like that. I was thinking of biasing each set-type at each socket with a specific cathode resistor on a 3-way switch for each socket. Then one could simply set the socket's switch according to what tube was inserted into it's corresponding socket. That way an EL34 would be happy and if a KT88 was in the other it would be happy too. Anyway, that's how I imagine using any two tubes in parallel would work best?
I think I already have a good system in place for multiple preamp biasing stages to work along with something like this. I may give it a whirl some day since I (like you Ed) have lots of iron sitting around!?   But then again, I already have a single EL34 to play with, I'm not sure building another entire amp is needed just to put two of 'em together to do the same thing?

[DummyLoad]

ed, et-al, something like this for the fargen clone?


--pete

[jojokeo]

It doesn't have all the bells & whistles of the Fargen but I like that schema a lot Pete. I'm not sure about all the switching on the CF as I often like it w/out a bypass cap but occasionally the extra sizzle and brightness is useable. I have one where I can switch a bypass cap earlier on V1b also. Then each one gives a different sound and feel. The pseudo pi/ parallel recovery is a cool idea too. Have you built this actually??? Me thinks you have by the specifics of the tranny info, etc.

[DummyLoad]

thanks jo.

i have not built yet. the OT is the same one i used in the zilker parallel EL34 SE project recently. this has been on the drawing board for some time. originally it was a true split amp with kt88 finals using UBT-2 SE output iron making about 15W each half. in the original design, one half is a plexi the other is a princeton reverb. the concept is an old one and i scrapped the idea. see date on the schema.

attached is schema of original concept. it's a C size drawing. finding a chassis to fit without using PCB and cramped build is/was the challenge and why i scrapped the idea. 9 valves need a lot of space working in high gain. 

--pete

[jazbo8]

Wasting a lot of money also for the iron & tubes to only run two EL34s to get 15 watts for EL84 performance. It's like paying for and building a "muscle car" using a 454cc big block motor to run at less power than a small block 307cc and expecting the thing to still sound the same to do burn-outs with and you can't race (ie perform) with it because you neutered it.

+1, I do not get the attraction of the high-power SE amplifiers either - other than "just because we can"... 

[Ed_Chambley]

ed, et-al, something like this for the fargen clone?


--pete

Do you have the OT?  Where did you get it?  I need to get one.

The one I have may be underrated for a build like this.  The OT on the Fargen is a Mercury and it only has SE-20 on the label.

I have a Edcor https://www.edcorusa.com/gxse10-4-1_7k
on the shelf, but it is too small.

[Ed_Chambley]

It doesn't have all the bells & whistles of the Fargen but I like that schema a lot Pete. I'm not sure about all the switching on the CF as I often like it w/out a bypass cap but occasionally the extra sizzle and brightness is useable. I have one where I can switch a bypass cap earlier on V1b also. Then each one gives a different sound and feel. The pseudo pi/ parallel recovery is a cool idea too. Have you built this actually??? Me thinks you have by the specifics of the tranny info, etc.

Well Joe, give us some Bells and Whistles.  I need a lower powered EL34 amp.

[jojokeo]

Well Joe, give us some Bells and Whistles.  I need a lower powered EL34 amp.

C'mon Ed, you certainly don't need any of my help. What's interesting with almost all of my builds is that no matter how hard I try to plan ahead or design or even use parts of circuits from prior builds even - is that I invariably end up having to either modify or even replace or remake things for that specific design/build. Best efforts to do so beforehand just seem to be a waste of time because of this. So on ocasions when others are spending so much time on planning & designing ahead asking so many questions while the days and weeks go by - I will advise to, "just get started on it and adjust things later."
 
Now because of this, I'm glad I don't have faceplates made ahead of time as you might imagine. Entire layouts and controls can sometimes come and go rendering that useless. So I will modify & design w/ the holes in the chassis and circuit board real estate available. In the end, everything works out for the best.
 
Sorry for the long drawn out answer if you can call it that, I'm not on the home computer so no access to any schemos if that's what you're wanting? But with several gain stages cascading, they don't all need to be bypassed is what I meant above. There's a better smoothness you get to your sound. I think what is also mentioned by Merlin in his book when he refers to not having too many hot biased stages (towards saturation / grid current limiting) as your sound becomes too "brittle" too easily. So having something like this on a switch rather than using that switch for a simple "Bright" control for example, I find is MUCH more useful on certain builds. Same for the ability to switch the bypass cap for a cathode follower stage. Sometimes you like and want it playing a certain style that day and sometimes you don't. And it's nice to have that option available to you rather than not.
 
I hope this answers your question? If not, please let me know if there's something else I'm missing?

[Ed_Chambley]

Well Joe, give us some Bells and Whistles.  I need a lower powered EL34 amp.

C'mon Ed, you certainly don't need any of my help. What's interesting with almost all of my builds is that no matter how hard I try to plan ahead or design or even use parts of circuits from prior builds even - is that I invariably end up having to either modify or even replace or remake things for that specific design/build. Best efforts to do so beforehand just seem to be a waste of time because of this. So on ocasions when others are spending so much time on planning & designing ahead asking so many questions while the days and weeks go by - I will advise to, "just get started on it and adjust things later."
 
Now because of this, I'm glad I don't have faceplates made ahead of time as you might imagine. Entire layouts and controls can sometimes come and go rendering that useless. So I will modify & design w/ the holes in the chassis and circuit board real estate available. In the end, everything works out for the best.
 
Sorry for the long drawn out answer if you can call it that, I'm not on the home computer so no access to any schemos if that's what you're wanting? But with several gain stages cascading, they don't all need to be bypassed is what I meant above. There's a better smoothness you get to your sound. I think what is also mentioned by Merlin in his book when he refers to not having too many hot biased stages (towards saturation / grid current limiting) as your sound becomes too "brittle" too easily. So having something like this on a switch rather than using that switch for a simple "Bright" control for example, I find is MUCH more useful on certain builds. Same for the ability to switch the bypass cap for a cathode follower stage. Sometimes you like and want it playing a certain style that day and sometimes you don't. And it's nice to have that option available to you rather than not.
 
I hope this answers your question? If not, please let me know if there's something else I'm missing?

Joe,
I am waiting on parts to build a couple of SE amps.  I was really just prodding you to join in on the discussion and share things like how you bypass a tone stack and such.  Seems to be a lot of interest in the Fargen Mini Plex and I can borrow one to get specs from.

DL has been gracious in adding what seems to be very close except for the Bells.  The decade switch on the fargen is cool, but in mine I simply will use a rotary switch with caps on it like I did on the AC15.  Really nice to be able to have a treble cut with switching coupling caps.  Pretty much covers a tonestack and is better to me in small amps.

I am still going to do a TMB or maybe just TB, but I want to be able to bypass it, or lift it as most say.

Share anything you have found.  I am sure you can teach me a lot, don't be all "awwwwwwwwwwwwwww shucks dude, you got this".

Really, me an a friend are playing with SE.   He is new to the hobby.  Soon as his amp that he helped a LOT building made sound he had that look in his eye.  He is hooked.  I told him to join the forum, but he is bashful because he feels he needs to know more before he joins.

I am not that way.  I have gotten to the age where my brain says "what is that smell" and my eye see something smoking.  The a little while later, maybe 5 seconds or so my brain says maybe you ought to unplug that thing.

You are correct tho.  I do like to get info from those who have built something similar.  Like what is your preferred method to tighten up the bottom in an SE build?  Have you found additional filtration beneficial in keeping noise down?  Do you normally elevate heaters?

You know, what works well and what you dig.

[DummyLoad]

ed, the OT's i have were wound for me a some time ago, nearly 7 years now, invoice is dated 2/25/2008.
they are experimental model made by edcor: CEM0683 3.5K:4 25W, what edcor calls their guitar range, 40Hz-18KHz. it's about the same size as the twin 100W iron, a bit thicker in the laminations but same size EI at about the same weight.   

--pete

[Ed_Chambley]

What do you think about this piece of iron.

https://www.edcorusa.com/cxse25-8-3_75k

I also have coming a couple of those overpriced jobs, but they cost less than the link above.

[DummyLoad]

What do you think about this piece of iron.

https://www.edcorusa.com/cxse25-8-3_75k

I also have coming a couple of those overpriced jobs, but they cost less than the link above.

probably. it is much larger than the "guitar" 25W SE. the footprint of the CEM0683-4 and CEM0683-8 are 2.375" x 2.5" the "HI-FI" model you linked to is 3.0" x 3.313": both have a 25W rating. the guitar is 40Hz-18KHz and the "HI-FI" is 20Hz-20KHz. i'd go with the smaller and lighter "guitar" model - phyllis @ edcore will wind either 4 or 8 ohm for you - if she tries to spin you with the $80.00 custom fees, tell her i've already paid for both of the designs. i'll PM you my full name: you'll probably need it. 
CEM0683-4 is the 4 ohm sec. part.
CEM0683-8 is...ya...

the PT P/N is XPWR268-120 it's 120V 60Hz to 650VCT @ 150mA & 6.3VCT @ 4.5A - same footprint as OT. easier machining... ;-)   

what make and model and specs are the "overpriced jobs" that you mention?

mine were shipped this morning. just over 4 weeks (31 days) from order to ship.

--pete

[jojokeo]

I was really just prodding you to join in on the discussion and share things like how you bypass a tone stack and such.  Seems to be a lot of interest in the Fargen Mini Plex and I can borrow one to get specs from.

That would be nice to "borrow one" :)  I have bypassed several ways, on smaller amps I will use a switched 25k pot. When turning the pot "off" it opens the tone stack's ground. On smaller amps that are already either too small for extended bass to be an issue with farting out or becoming muddy, etc. this works great and is the most simple. On others I will simply use say a .002uF cap to go around the tone stack when switched, but don't forget that you need grid return resistor to ground after it - say anything between 56k - 1M depending how much gain you're wanting to preserve OR depending on the power tube's spec sheet requirements for this value (don't forget to check this). Lastly, is where I get a bit more tricky but it's not always needed. Say I'll use a .01uF cap going into a .001uF cap paralleled with a 100k resistor. Or on another one I used a .003uF cap connected to .001uf paralleled with a 220k resistor. The theory is that the first cap sets the total amount of signal that can get through to the next cap & paralleled resistor. The following smaller cap allows all highs above it's value but some lows can get through the resistor still depending on it's value.

The decade switch on the fargen is cool, but in mine I simply will use a rotary switch with caps on it like I did on the AC15.

I do not see it the same way when referring to the Decade control. Maybe I need to re-watch the demo but I see it as switching between the Plexi/JCM800/DSL modes? This to me is where it gets fun - but complicated. I see it as changing the signal flow through various gain stages, different biasing, etc. to achieve the character & feel of those amp designs. The Plexi and 800 preamps are easy to model, it's the DSL that appears to be the most challenging. I can think of over 10 ways to accomplish what this amp does. The devil's in the details. The Devil is also most certainly in the DSL part (to me) as it has a whole host of switching & stages not to mention various issues & versions over a decade which were released. There are also various transistors, jFETs, LDRs, and OpAmps in there. I could emulate the entire three preamps with jFETs but then that would maybe be better to do in a pedal (even though jFETs are tube cousins)? I could do something entirely with tubes-only and get the first two emulations but likely not the DSL section w/out using at least a few jFETs, OpAmp, and/or MOSFETs? So that is the one that's the trickiest to me. Another thing is by properly biasing/bypassing & routing I could come close to all three and afterwards looking at the schematic it may not have any one stage exactly like a clone of any of the originals. It's the overall impression they give to the player is what's important and also how they correspond to each other, right? Can you take the Fargen amp in DSL mode and A/B it to a real DSL and hear & feel the same result??? I kind of doubt it but I honestly don't know? Maybe you actually could try something like this and possibly with all three settings against the real counterparts? I'd love to hear your impressions! I'm just saying that there are no hard rules. I don't have to use a 100k load resistor and 2k7 cathode resistor bypassed w/ a 0.68uF cap to say "this is the Plexi stage, therefor it is the Plexi setting." Maybe the voltages are different therefore the values would be too?! I also don't see it as simply one stage for any of the three emulations but rather several stages which adds up to form the whole emulation. (Don't forget there's VVR in that thing too) Okay enough BS right? 

[jojokeo]

...continued: my gabbiness ran short of characters (is this like eBay now?) 

Like what is your preferred method to tighten up the bottom in an SE build?  Have you found additional filtration beneficial in keeping noise down?  Do you normally elevate heaters?

Usually it can be as simple as the smallest coupling caps which gets the job done, messing with low value bypass cap(s) and/or a tweak to the tone stack. Other times gain is not an issue & I like to use a lower value load resistor for higher plate voltages and get a better response and tone this way. But filtration, yes - having good filtration w/ higher uF's than one might expect - at least for the first two or three nodes of the string (whether se or pp) really helps lower end... and ultimately noise as well in the preamp (trying to remember where I learned about this?) something like 200uF > choke or power resistor > 200uF... isn't out of the question. I ALWAYs elevate my heaters if not via the power tube's cathode(s) then it's with the usual voltage divider & cap off the B+. I think ~35v-40vDC is plenty and don't feel it's a "higher is better" deal and in fact not good to go too high here.

[Ed_Chambley]

What do you think about this piece of iron.

https://www.edcorusa.com/cxse25-8-3_75k

I also have coming a couple of those overpriced jobs, but they cost less than the link above.

probably. it is much larger than the "guitar" 25W SE. the footprint of the CEM0683-4 and CEM0683-8 are 2.375" x 2.5" the "HI-FI" model you linked to is 3.0" x 3.313": both have a 25W rating. the guitar is 40Hz-18KHz and the "HI-FI" is 20Hz-20KHz. i'd go with the smaller and lighter "guitar" model - phyllis @ edcore will wind either 4 or 8 ohm for you - if she tries to spin you with the $80.00 custom fees, tell her i've already paid for both of the designs. i'll PM you my full name: you'll probably need it. 
CEM0683-4 is the 4 ohm sec. part.
CEM0683-8 is...ya...

the PT P/N is XPWR268-120 it's 120V 60Hz to 650VCT @ 150mA & 6.3VCT @ 4.5A - same footprint as OT. easier machining... ;-)   

what make and model and specs are the "overpriced jobs" that you mention?

mine were shipped this morning. just over 4 weeks (31 days) from order to ship.

--pete

Mercury Magnetics

1. SE-3.5K- 2 and 4 ohm taps

2. SE-MT-3k, 5k, 9k-4 and 8 ohm tap

PM Me the OT info for the Edcor Order.  I am going to try to order it anyway.
 

[Ed_Chambley]

Joe,
The Decade switch just changes  From JTM45, to Plexi to Jcm800.  I cannot see exactly how.  It is not anything special.

Here are some gut shots.  It has a london power scale in it.  Look at the photos.  When I get close to what I want to build I will go over and look at the values in my friends amp.

[Ed_Chambley]

I'd love to hear your impressions! 
Don't forget there's VVR in that thing too) Okay enough BS right? 

Joe,
Now you know I own the original amps of the Decade Switch.

To me the VVR is rather useless since an amps volume is not problem.  I plan to put one in there anyway.  The amp scaled very little at all and it is like playing any other amp using preamp distortion.  It is cool if you are moving some air, but if not it sounds like playing through headphones.

None of the Decade switches positions sound like a cranked version of any amp.  Simply sounds like changing caps, however if you close your eyes while playing it and really listen closely while someone else plugs your cord into a Plexi, it sounds just like a Plexi.  Imagine that?

All joking aside, it is a nice sounding amp that could use what seems to be more NFB or somethings to strengthen the bottom.  I know it is SE, but I am sure I can get it tighter.  This is all just preference.  If I owned an original I would do the same.

I believe what I missed on the first attempt was the gain structure Dummyload has addressed.  I can almost hear the difference in my head.

Here is my biggest question now.  On the Fargen site it states the amp is 8 to 12 watts which I believe is not correct.  Maybe it is 12 watts Pout, but how are you getting 12 watts with 2 tubes parallel?

[jojokeo]

I'd love to hear your impressions! 
Don't forget there's VVR in that thing too) Okay enough BS right? 

Joe,
Now you know I own the original amps of the Decade Switch.

To me the VVR is rather useless since an amps volume is not problem.  I plan to put one in there anyway.  The amp scaled very little at all and it is like playing any other amp using preamp distortion.  It is cool if you are moving some air, but if not it sounds like playing through headphones.

None of the Decade switches positions sound like a cranked version of any amp.  Simply sounds like changing caps, however if you close your eyes while playing it and really listen closely while someone else plugs your cord into a Plexi, it sounds just like a Plexi.  Imagine that?

All joking aside, it is a nice sounding amp that could use what seems to be more NFB or somethings to strengthen the bottom.  I know it is SE, but I am sure I can get it tighter.  This is all just preference.  If I owned an original I would do the same.

I believe what I missed on the first attempt was the gain structure Dummyload has addressed.  I can almost hear the difference in my head.

Here is my biggest question now.  On the Fargen site it states the amp is 8 to 12 watts which I believe is not correct.  Maybe it is 12 watts Pout, but how are you getting 12 watts with 2 tubes parallel?

Crap Ed, my bad - somewhere or somehow I thought they were emulating a DSL for the third emulation. When I'm at work & multitasking while also driving too (triple tasking?) and being in a hurry things can sometimes go off the rails if not careful. Looks to be the case here, sorry 'bout that.

You are correct about using some or more NFB to try to tighten things up. It may be best to keep on a pot so that you can always dial it in to suit your taste. I've done this also on a 3-way switch too for better consistency over the pot.

They might be giving that power rating as clean watts? That amp doesn't stay clean for too long I don't think and should pump out closer to ~20w I would think?

Could you send me the largest sized photos you've got to my email please???

[Ed_Chambley]

I'd love to hear your impressions! 
Don't forget there's VVR in that thing too) Okay enough BS right? 

Joe,
Now you know I own the original amps of the Decade Switch.

To me the VVR is rather useless since an amps volume is not problem.  I plan to put one in there anyway.  The amp scaled very little at all and it is like playing any other amp using preamp distortion.  It is cool if you are moving some air, but if not it sounds like playing through headphones.

None of the Decade switches positions sound like a cranked version of any amp.  Simply sounds like changing caps, however if you close your eyes while playing it and really listen closely while someone else plugs your cord into a Plexi, it sounds just like a Plexi.  Imagine that?

All joking aside, it is a nice sounding amp that could use what seems to be more NFB or somethings to strengthen the bottom.  I know it is SE, but I am sure I can get it tighter.  This is all just preference.  If I owned an original I would do the same.

I believe what I missed on the first attempt was the gain structure Dummyload has addressed.  I can almost hear the difference in my head.

Here is my biggest question now.  On the Fargen site it states the amp is 8 to 12 watts which I believe is not correct.  Maybe it is 12 watts Pout, but how are you getting 12 watts with 2 tubes parallel?

Crap Ed, my bad - somewhere or somehow I thought they were emulating a DSL for the third emulation. When I'm at work & multitasking while also driving too (triple tasking?) and being in a hurry things can sometimes go off the rails if not careful. Looks to be the case here, sorry 'bout that.

You are correct about using some or more NFB to try to tighten things up. It may be best to keep on a pot so that you can always dial it in to suit your taste. I've done this also on a 3-way switch too for better consistency over the pot.

They might be giving that power rating as clean watts? That amp doesn't stay clean for too long I don't think and should pump out closer to ~20w I would think?

Could you send me the largest sized photos you've got to my email please???

No problem Joe.

The photos are not any larger.  Someone sent them to me, I did not take them.  Had I taken them I would have gotten the values.

Quickly.  The guy that owns the amp was sort of in a hurry and also it was brand new.  He brought it over for me to play.  First thing I did was put it on my bench and started removing the chassis.

I did not get enough time with it, but I will.  I have some more photos, but none are closeups.  The ones I have are just good enough to piss me off.

No worries, I think we are almost there.  I REALLY need to get a couple of OT's.  DL hooked me up.

[Big_Mike]

Are those gut shots of the MK1 or the MK2?   My understanding is that there is a significant difference with regard to the tone stack for each version.

I'm really interested in building a clone myself, so I will be following this thread!

[HotBluePlates]

Here is my biggest question now.  On the Fargen site it states the amp is 8 to 12 watts which I believe is not correct.  Maybe it is 12 watts Pout, but how are you getting 12 watts with 2 tubes parallel?

Let's say you selected the OT to give ~10-11w with a single EL34. From the data sheet, we could guess the primary impedance will be around 4kΩ.

Now if you add a 2nd EL34 and keep the same primary impedance (and B+), you'll still only get 10-11w; the 2x tubes don't pass any bigger signal current because the primary impedance limits the current (just like a resistor) and you get the same power output. The resulting output stage will feel different, because it will take ~1/2 the drive signal to cause the output stage to generate full output power (because 2x tubes yields 2x transconductance).

Of course, 4kΩ would be perfect for 2x 6V6's to yield 2x 4w (that a single 6V6 would gt with 8kΩ) for an 8w output stage.

Similar logic applies across all the output tubes. A 6550 wouldn't yield any real power increase, because power output has already been set by B+ and primary impedance. And that's the core of why the power scaling reduces power output: same-Z, but lower B+ means lower power output regardless of the output device in the sockets.

[Ed_Chambley]

Are those gut shots of the MK1 or the MK2?   My understanding is that there is a significant difference with regard to the tone stack for each version.

I'm really interested in building a clone myself, so I will be following this thread!

Mike,
There is a difference, you are correct.  The First one had a toggle Decade Switch.  I don't know much about any tone stack differences.  The one I looked into was Traditional Marshall Values except the slope resistor was 56K.  I would tweak it anyway since I like to be able to get more bottom when playing on the cleaner side of things.  The fargen is very mid centered.

Let's hope we can get something done.

[Ed_Chambley]

Here is my biggest question now.  On the Fargen site it states the amp is 8 to 12 watts which I believe is not correct.  Maybe it is 12 watts Pout, but how are you getting 12 watts with 2 tubes parallel?

Let's say you selected the OT to give ~10-11w with a single EL34. From the data sheet, we could guess the primary impedance will be around 4kΩ.

Now if you add a 2nd EL34 and keep the same primary impedance (and B+), you'll still only get 10-11w; the 2x tubes don't pass any bigger signal current because the primary impedance limits the current (just like a resistor) and you get the same power output. The resulting output stage will feel different, because it will take ~1/2 the drive signal to cause the output stage to generate full output power (because 2x tubes yields 2x transconductance).

Of course, 4kΩ would be perfect for 2x 6V6's to yield 2x 4w (that a single 6V6 would gt with 8kΩ) for an 8w output stage.

Similar logic applies across all the output tubes. A 6550 wouldn't yield any real power increase, because power output has already been set by B+ and primary impedance. And that's the core of why the power scaling reduces power output: same-Z, but lower B+ means lower power output regardless of the output device in the sockets.

OK, you hooked me.  You always do.

Why wouldn't you change the impedance?  I mean, what would be the purpose of parallel tubes if not to gain horsepower.  I was told by Willabe that it adds muscle.

Like you are running a pair of EL34, to 3.5k/8 ohms if connected 8 ohms would not be as efficient as a pair connected to 1.7K/8 ohms. So just changing from one speaker to another this happens?

Basically asking to elaborate if you will on the possible potential problems and also let me ask, do you think this amp may be this way because I know the plate voltage.  Above 420, not much above.

[Willabe]

Why wouldn't you change the impedance?  I mean, what would be the purpose of parallel tubes if not to gain horsepower.  I was told by Willabe that it adds muscle.

Now if you add a 2nd EL34 and keep the same primary impedance (and B+), you'll still only get 10-11w; the 2x tubes don't pass any bigger signal current because the primary impedance limits the current (just like a resistor) and you get the same power output. The resulting output stage will feel different, because it will take ~1/2 the drive signal to cause the output stage to generate full output power (because 2x tubes yields 2x transconductance).

Of course, 4kΩ would be perfect for 2x 6V6's to yield 2x 4w (that a single 6V6 would gt with 8kΩ) for an 8w output stage.

Similar logic applies across all the output tubes. A 6550 wouldn't yield any real power increase, because power output has already been set by B+ and primary impedance. And that's the core of why the power scaling reduces power output: same-Z, but lower B+ means lower power output regardless of the output device in the sockets.

Maybe I'm wrong but I seem to remember that when I finally got my 1st computer at age 50 (yeah, yeah I know, go ahead and laugh) and hit the internet that at 1st I found Kevin O'Connor's Power Scaling forum, then I found Doug's forum.

(I seem to recall that a good number of our members were there too, including you HBP, maybe I'm wrong?)

I think that you (HBP) have just added/helped explain what I posted about what Kevin wrote in 1 of his TUT books about a '5100' which would get you the sound of a Marshall 50 or 100 without increasing the dB level of the amp.

It was about building a Marshall amp that could/will have the same tone of a 50w and a 100w without changing the amps output volume.

It was the same deal, keeping the same power supply, same B+ filtering, AND same OT Z. Makes no difference if it's
PP or SE. You can have, PP 1x2 or, PP 2x4, or 1SE or 2xSE in parallel, it's the transconductance, all things being the same that gives you the 'muscle' or the 'feel' of 'muscle'.

When we talk about dB's with any amp's power, I think about the 'muscle' any amp has on stage.

I had a BFSR with original Jenson 10" alnico speakers that I played out at gigs for years. The 'boss men' I played for as rhythm guitarist always had a bigger Fender, BFTR or something that was at least 80 to a 100+ watts with a pair of 12" speakers. If we were both playing with both amps set at 5 or 6 or 7 he would BARY me volume wise, no if ands or buts!!!!!  To me that's 'muscle'! Forget about 'cutting through the mix' with high end. Yes it has it's place but..... try playing 'over' 3, 4, 5, 6 horns + the boss man with double the ummp under his fingers!


                        Brad                    

[HotBluePlates]

Why wouldn't you change the impedance?  I mean, what would be the purpose of parallel tubes if not to gain horsepower.

I didn't design the amp (and haven't spoken to the guy who did), so strictly, I don't know.

What I see with a designer's eye is this:
  - SE isn't about more power, it's about output tube distortion at less power (otherwise, why on earth would you need power scaling on a SE amp?).
  - If more power isn't a goal, then parallel SE only makes sense if you want to mix the sounds of dissimilar tube types, or have a small tube distorting while a big tube stays clean.
  - Amp designers/builders know they can change primary impedance to get more out of the bigger tubes by swapping a speaker load to a "wrong tap" to reflect a different impedance. But designers/builders can just make their own amps, so there's no profit marketing just to that niche group.
  - And since the amp will be marketing to the mass of non-technical guitar players, the goal of "plug and go" seems to be the best option.

Could you change the primary impedance and get something different out of the amp? Yeah. But even without doing that, and even with the actual output power locked-in by primary Z and B+, each tube type will bias to a different voltage with the same cathode bias resistor, and each carries a different transconductance, so the resulting response will change with each tube type. Add that true pentodes (like the EL34, EL84 and 6K6) will distort differently than beam power tubes (6V6, 6L6, 6550, KT66, KT88), and you still get the desired bang for the tube-change buck.

[Big_Mike]

I'm still thinking about doing this build sometime in the future.  I am debating between doing a build based on the Fargen Miniplex or the Fargen Olde 800.  From what I understand, the Olde 800 is different from the Miniplex only with regard to the size of the iron in it, as well as without power scaling.  From what I understand, though, the master volume circuit on the Olde 800 is outstanding.  The Olde 800 is also 25 watts.

[Big_Mike]

Ed -

Did you ever get around to building a Miniplex clone?  I am still looking to build one myself.  I am thinking that instead of running two EL34s in parallel, I might go with just a single EL34/Octal tube.  If you built one, do you have a schematic?

[shooter]

is there any way to enjoy a Marshallesque EL34 driven tone at 15W?

I took blues jr - plexi - voxish front end, melded it with a matchless clubman PA, and it's one of my best amps.
specs out at about 23W into 8ohms

EDIT - I didn't implement the send return, and there are *mods* not documented

[Big_Mike]

Here is another single-ended plexi schematic that I found on the web.  I have not tried it, but it looks interesting:

[Big_Mike]

The SEPlex looks like an interesting design.  The sound clips on the site seem promising.  I am interested in his idea of creating a pseudo phase inverter stage and a negative feedback loop.

[Paul1453]

Here is another single-ended plexi schematic that I found on the web.  I have not tried it, but it looks interesting:

I'm going to give this one a try soon.

I already did a simpler 1 12AX7 - EL34 on my BB to test if my little 2.65K @8 ohms SE OTs could handle the power.
The little OTs seems to be fine with my circuit using 250V B+ and pulling around 70-75mA of current.
Maybe a bigger, heavier, higher wattage, more expensive OT would sound better, but I'm cheap and have 5 of these little OTs.
This sounded really good to me, much better than when I used it with a smaller 6V6/6AQ5/EL84 tube.