Newish guy here with a few questions and doubts. After checked a few schematics of some low budget around 5W SE guitar amps (like Peavey Valve king Royal8, Marshall Class5, Epiphone Valve Junior,TT-sam-markII) i decided to try to build myself an amp using 2 EL84 (or EL90 which is 6V6 in a smaller package) in parallel instead of only one EL84 hoping to get out a bit less than 10W. So i combined some sections of already working amps toghether and i would like you EXPERT FRIENDS to have a look and tell me if it's doable and what's wrong (i'm sure you'll find a lot of mistakes).
At least this is how i immagined it could be.
By adding one output tube in parallel the OT should be easyer (and cheaper) to be done as the impedance needed would be of 2.6k Ohm instead of 5.2 (if i understand correctly). Correct me if i'm wrong - in theory the signal could be devided to op to 4 EL84 in parallel, but i guess some buffers should be put to provide strong signal. As i marked on the schematics i made, the position of the buffer(s) should be just before the output tubes or am i mistaken?
I also marked possible positions of tone stack but IMO it should be put in J1 position right after the first signal amplification of ecc81 - reason for that is the loss of signal of about -20dB, which is quite a lot, but the following stages should be able to re-gain the lost signal?
All B+ voltages are subject to change if needed (everything is still only on paper). Feel free to modify if you wish. Any good suggestion would be greatly appreciated!
Thanks in advance for your help!!!
At least this is how i immagined it could be.
By adding one output tube in parallel the OT should be easyer (and cheaper) to be done as the impedance needed would be of 2.6k Ohm instead of 5.2 (if i understand correctly). Correct me if i'm wrong - in theory the signal could be devided to op to 4 EL84 in parallel, but i guess some buffers should be put to provide strong signal. As i marked on the schematics i made, the position of the buffer(s) should be just before the output tubes or am i mistaken?
I also marked possible positions of tone stack but IMO it should be put in J1 position right after the first signal amplification of ecc81 - reason for that is the loss of signal of about -20dB, which is quite a lot, but the following stages should be able to re-gain the lost signal?
All B+ voltages are subject to change if needed (everything is still only on paper). Feel free to modify if you wish. Any good suggestion would be greatly appreciated!
Thanks in advance for your help!!!
Agree^^^^
I myself prefer the pdf format.
Not sure what your transformer difficulty might be. A single tube? One option is simply to buy the transformer from Peavey or whoever. It works in their amp, why wouldn;t it work in a single output tube amp for you? Peavey, for example, sells their parts to anyone direct, and their prices are reasonable.
As to the difference between 5w and 10w output, the difference is not much, 3 decibels if all else is the same.
I myself prefer the pdf format.
Not sure what your transformer difficulty might be. A single tube? One option is simply to buy the transformer from Peavey or whoever. It works in their amp, why wouldn;t it work in a single output tube amp for you? Peavey, for example, sells their parts to anyone direct, and their prices are reasonable.
As to the difference between 5w and 10w output, the difference is not much, 3 decibels if all else is the same.
yea difference between 5w and 10w won't be much depending on what speaker you will be running and its sensitivity 5watts can still be loud as hell lol
Hi,
I can't see why the output transformer would be easier or cheaper.
The right impedance might be more difficult to find, and of
course it needs twice as much iron in it for 10W versus 5W.
rgds, sreten.
I can't see why the output transformer would be easier or cheaper.
The right impedance might be more difficult to find, and of
course it needs twice as much iron in it for 10W versus 5W.
rgds, sreten.
the way you paralel el84 does not look right
looks like you have just doubled a simple SE output
but it should not be hard to find a good schematic
and I guess 6V6 is a very good guitar tube
tried a quick search, and nice looking Angela super-single-ended came up
and on Lone Wolf site an interesting 3x6V6SE
(but more tricky with the fixed grid bias)
but also have an easier 2x6V6SE
looks like you have just doubled a simple SE output
but it should not be hard to find a good schematic
and I guess 6V6 is a very good guitar tube
tried a quick search, and nice looking Angela super-single-ended came up
and on Lone Wolf site an interesting 3x6V6SE
(but more tricky with the fixed grid bias)
but also have an easier 2x6V6SE
Hi,
FWIW you will be lucky to get near 10W out of an EL34 on a good
day, single ended with optimum bias and a really good transformer.
Two EL84's are near universally used push pull with some class A
bias for about 10W clean, not sure about overdriven power output.
The transformer for this will be a lot cheaper as there is no DC
current required to be supported as in the single ended case.
Similarly the less stressed mains transformer can be smaller.
rgds, sreten.
FWIW you will be lucky to get near 10W out of an EL34 on a good
day, single ended with optimum bias and a really good transformer.
Two EL84's are near universally used push pull with some class A
bias for about 10W clean, not sure about overdriven power output.
The transformer for this will be a lot cheaper as there is no DC
current required to be supported as in the single ended case.
Similarly the less stressed mains transformer can be smaller.
rgds, sreten.
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Hi to all,
Yes i was wrong saying it would be easyer and cheaper to make an OT like that for you do need to double the iron and yes, it would be much easyer to put the two EL84 as push-pull and get rid of DC component. But my reference schematics was the attached TT-sam-mkII, and i just thought of modifying it IF possible.
What about the rest of schematic (values of resistors, position of tone stack)?
I'm having second thoughts...maybe my idea is totally wrong and is not worth even trying...
Yes i was wrong saying it would be easyer and cheaper to make an OT like that for you do need to double the iron and yes, it would be much easyer to put the two EL84 as push-pull and get rid of DC component. But my reference schematics was the attached TT-sam-mkII, and i just thought of modifying it IF possible.
What about the rest of schematic (values of resistors, position of tone stack)?
I'm having second thoughts...maybe my idea is totally wrong and is not worth even trying...
One real cool single ended amp OT that hammond makes is a 125 ESE. Multiple primary impedeance taps, And you can use it for several different projects till you find what you like.
The EL90 is a 6AQ5 for those on this side of the world. It has been used in dozens of guitar amps over the years. From my experience it does sound a lot like a 6V6 but can not be abused like one. There is a very small range between overdriven and melted! Yes, the glass will melt, crater and suck air if you red plate these for long. I have blown up a few dozen over the years.
I made an amp a long time ago that had a bunch of 6AQ5's wired in parallel. I just kept hooking in more tubes in a quest for sound. I don't remember how many...maybe 10.
I see no reason why your idea won't work. It might not make the sounds that you have in your head on the first try, but you have to start somewhere. I have made several similar amps over the years, all variations off of the Fender Champ. Build it, then tweak until you get what you want. Maybe start off with one output tube....then add more if you like.
I tried the seperate drive pot for each tube idea and I didn't think it was worth the effort in an SE amp. The SE stages all sound the same. Make them identical, fed from the same gain pot, then put a switch in the screen grid of one tube to turn it off.
A seperate gain pot for the two sides of a P-P amp can be used to alter the harmonic structure and IS worth doing. So is using two DIFFERENT types of output tubes....but that is a different story.
His PDF schematic shows a 125CSE which has the same taps. The ESE is too big and can't be driven into distortion with these tubes. I couldn't get it to scream with a KT88 on 450 volts. I used the 125CSE in my Turbo Champs and drove it with a single KT88. Wire every output tap to a switch feeding the speaker/speakers. Intentional mismatching can often be used to your advantage.
I am enclosing a schematic of my "Turbo Champ" amp. I drew this schematic from memory after the last amp left my hands so there may be some errors in the component values. I made a dozen or more of these over a 10 year period. Every one was different. The last few used a 450 volt power supply and a single KT88 and made about 15 watts. A few used two 6X9 car speakers in parallel. They were loud but couldn't get very dirty at low volumes. The early ones did use one or two 6V6's and about 335 volts of power supply.
The little EL90/6AQ5's don't like much over 300 volts for guitar amps.
Attachments
The problem with those Hammond Universal transformers is that as the power goes up, so does the required B+. They don't offer a low enough primary impedance for small tubes in parallel. I think to get 10W, the B+ is over 450V. That eliminates most small tubes.
Move P1 to between the first and second stages and nix the clipping diodes. If you must have clipping diodes, move then to one side of the tone stack.
Move P1 to between the first and second stages and nix the clipping diodes. If you must have clipping diodes, move then to one side of the tone stack.
Did you use any buffers to provide enough current for all output tubes?
Thanks for encouragement, i really need it on this one.
Anyway i was thinking of picking 6V6, but i thought since EL90/6AQ5 has the noval socket, and as for what i have read about it it should be the same (more or less) just in the "small package" as well as low price (specially the russian version) decided to go for EL90....but as i already written before, it's still on paper so anything can be changed..
Well, it's not that i must have diode clipping, but it helps to get a nice distorsion without squeezing the 5W amp (i forgot to mention that i have bought 2 Peavey's VK Royal8 - yes, i bought 2 for they came about 125$ each, and one i use for testing various components like speaker, homemade toroidal OT of which i am very proud, caps,...and the other is completely original) so that my neighbours half a mile away would send police car over to calm me down. And since it's a simple and alreadyproven device why not having it.
So replacing the P1 instead of 1M resistor on the input of the first half of 12ax7 and vice versa...ok it makes sense.
@tubelab.com :
Getting rid of the separate pots at the output tubes only in case i use the same tube, right? Because if i do the same as the TT-SAM-mkII design and use one EL84 and one EL90 it makes sense for to have two different sounds mixing and maybe ending up with something i would like...
I'm adding some parallel SE schematic just to maybe get someone some ideas. Not guitar amps though.
Attachments
Hi,
Doubling EL84's as single ended doubles the iron for the mains and output.
Its simpler to use a bigger single valve like the EL34 rather than two parallel
EL84's for a single ended amplifier with twice the iron, so you don't see many
paralleled valve single ended amplifiers, not that it can't work, as it can.
But there is no implied cost saving, there is with push pull with two valves,
about 4 times the output power with ~ the same iron as the single ended
one valve version.
If its all about the tone of single ended, then parallel valves and double
the iron at twice the cost are a poor reward for for +3dB in max level.
(Using big speakers as opposed to small make a far bigger difference.)
rgds, sreten.
its all up to what you want man I love the 6v6 and el34s to my ears depending what circuit they are in they sound more like el34s than el84s do most of the time el84s just have no bottoms and its all top end chime to me
it depends though with 6v6 sounds hell of a lot weaker with low B+ on plates but you start getting up to 400v+ they really start cooking haha just be careful with current with them voltages like with my stealth 420v on plates and damn near around 400 on screens they are really getting pushed lol and I will never buy the current production EH 6v6 ever again I bought pair while back popped em in I have bias pot set low just in case and Ill check every now and then but I don't even have to I can hear it man, 16-19ma range somewhere around there but anyways them EH red-plated instantly so didn't even get to hear how they sounded heard they sounded good but still that's crap man the EH and Tungsol are suppose to be able handle 450 plate volts and like over 400 on screens so Current production is crap shoot other option is the JJ6v6 its cool sounding but its still not 6v6 tone so if you go the 6v6 route pretty much gotta roll NoS for real tone and reliability, of course maybe I just have bad luck getting current production tubes but man these sellers really need to start screening/testing their **** better
The EL90/6AQ5 is not a noval. It uses a 7 pin socket that was common in radios made in the 1950's. Chinese ceramic sockets are available today. Avoid the cheap plastic ones, they melt!
I did this long before I discovered mosfet buffers, so it was likely a typical Champ circuit with too many output tubes. I did this just to see what would happen.
There is a point of diminishing returns probably at 2 or 3 small tubes like the EL90. There are fixed DC resistance losses in the OPT. Each extra tube will pull more current through the OPT raising the amount of loss in the transformer. A pair of EL90's will draw about the same current as one EL34. I have used the 125CSE up to 100mA with good results in a guitar amp.
I have not tried two different tubes in an SE amp. Two pots would make sense here. The dynamic output impedance of the amp will change with pot settings, but this is not as big a deal as some say it is. Still, an OPT with multiple taps can be a good idea in this case.
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