• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

el84 - 807 ?

hello everybody,

i have a few questions as tubes-noob.

i have an old amp (push pull el84 with ecc88 in front) but it is completely broken. so i wanna rebuild it. but i want very good sound. the output trannies have no UL-connection; So it is pentode or triode. If i go for triode, i will only have 5 watt or so.
I think the R of the trannie is 8K. (it's an old amp so i have to guess about this)


The el84 has an ecc88(12ax7) in front of it. But i wanna replace it with a better driver: like an ecc99 or 6sn7 or something else. But the power transformer isn't up to the task. it is designed for a simple push pull el84 in ab-class i think. and for a few mA in the ecc88.

So if i'm gonna buy another power trannie there are a few options that opens up.


1)let's suppose that i stick with the el84, driven by an ecc99 (let's say parafeed design) is it possible to make a parrallel pus pull triode ? so that you end up with 10 watt ? 'i know that the output trannies will not have the right R but just for knowing if it is possible to make a parralle push pull in triode : does anyone every build it, and how would it sound.


2)but since i wanna keep the output trannies (if not i could just build a new amp from the scratch) so what i was thinking about is to take an 807pp in triode, it gives 10 watt. the only problem then is : could the output trannies sustain the higher voltage (~400 in stead of the 300 of the el84). How can i know this, without burning down the house ?

3)if all this is not gonna work, i will stick to the ecc88 and the el84 push pull configuration. it's cheap, because i will have to buy only tubes and parts, but no trannies; i will build the ecc88 parafeed and then the triode push pull el84. (a lot of people say it sounds very good, even nobody really likes the ecc88 that much. i would use new jj tubes for el84 and the ecc88) any comments on this ?

4)i like the idea of a very good sounding amp without costing an that much.So i'm very fond of the el84 and the 807. But i would like to know, what sound the best. an el84se; el84pp, an 807se, 807pp. I know that there is a lot of difference in the power output.

5)at this moment i'm gonna start building my backloaded horn for my coral flat 8(so with 5 watts i have enough, but having more wouldn't hurt either) ; up until now they are running in an open baffle with a tweeter and 15 inch open baffle woofer. (i have to quit that because it is to big, but within a few years i will start building it again.


anyway guys thanx very much already
greetings filip
 
El84

As you do'nt have all the data of your Raa 8K OPT's, ik would say, keep using the EL84 , 6V6 in penthode or 12BH7 parallel (Rk 500R) with an Ia around de 22-24mA per tube.
A 807 has far more Ia and is Ia above about 24mA, you get often with these OPT an irritating sss-sound.

As input/driver tube I have very good tesults with the 5965 (far better 6072A) in steat of the ECC83/12AX7.
Or a 6CQ7 EH (6SN7) if less input sensivity is enough.

A final tube sounds as best, as it's is made for. I do'nt like penthodes/tetrodes in semi-triode. Then I prefer real triodes.
 
thanx guys,

but dogie_hogan what do you mean with: often these opt gives an irritating sss-sound. do you mean with the 807 or with the original el84 ?

to sheldon: i have looked at it, it looks nice, but i have found in the meanwhile something else

i found a design that uses my amp, well sort of, but a different power trannie. mine hasn't an recifier tube (or at least the connections nor the power for it)
so probably i'm gonna build this ecc99 with the el84 and with a rectifier tube, (so i have to add an extra trannie: 6.3 volt at some ampere's )

http://www.dhtrob.com/projecten/afbeeldingen/EL84PP_amplifier.gif

http://www.dhtrob.com/projecten/afbeeldingen/EL84PP_powersupply.gif
 

EC8010

diyAudio Moderator Emeritus
2003-01-18 7:57 am
Near London. UK
Provided that the new output valves' currents are perfectly matched and don't actually melt the transformer primary wire, then you can pass as much DC through a push-pull output transformer as you like and it will not saturate. Saturation is an effect that occurs at low frequencies (typically 50Hz and below). If it were my output transformer, I'd take a chance on using 807 with an HT of 400V, but you never know if the interwinding insulation is on the verge of breaking down. It would be a risk you'd have to take.

I see no difference between a triode-strapped pentode and a pure triode. EL84 makes a very good triode, as does (famously) KT66.
 
Hi,

I build both an EL84 and 807 (in triode mode) pushpull amplifier using the same outputtransformers from an old Lafayette amplifier (very popular in Belgium & The Netherlands).

They both performed very well, I found the 807 amp slightly better
than the EL84. No sign of an irritating sss-sound here.

Quescent current for a typical PP-EL84 stage is around 35-40mA per tube so a few milliamps more for a 807 won't hurt your outputtrannies.

Good luck,

Jim.

My PP-807
 

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amperex

Member
2005-02-20 1:42 pm
MI
6L6 - 807 not good..........

However, 8K is great for a pair of 6V6GT or inexpensive 7C5 tubes (same tube in loctal base). Triode connected 6V6GT are especially good sounding with say 6-7 watts out. I used up to 330 volts on the plates & screens triode connected without any failures.

Best tubes are 1940s to 1950s Sylvania or, believe it or not, GE 6V6GTA even with the cheap 'coin-base' (wafer) socket.
 
Re: Simple EL84

have' said:
Why don't you try this:
http://diyparadise.com/simpleel84.html

Realy easy to build with exellend sound.
I've build mine using El84 drive EL84.It beat the Copland CTA501,the Rotel...driving Rogers Studio7.


i have looked at it, this is what got me thinking of rebuilding the amp, but i have red here on the diyaudio, and also on the web that distortion levels are high, and that this amp does a good job on a single driver but not on one with crossover. so that's why i was a little afraid.

not only that but i would have to buy another power trannie.
But i'm not shure if the power trannie can hold it; i can give 4amp in 6.3volt so 4*el84 and 1*ecc99 is just possible (can't do the 6*el84 version).

and also : the trannie is switchable between 120-240, so it has two parrallel 0-115 taps; on the ouput of the trannie stands 0-140 (0.190dc). So i think that it puts 140 at 0.19A no matter how connected. (am i right ?). with a voltage doubler you get 280 volt, but at the half of A : 0.095A; (that was enough for the original 4*el84 (at 20ma per tube) and 5*ecc83 at 1ma : so that makes up 85mA. but for the simple el84 i need the double.

So i have a little problem, if i rebuild it without a lot of costs, (so only caps, tubes, socket, resitor) i don't have a lot of choise, i have to use the ecc83 and no tube rectifier.

i can build ecc99 and el84, but then i have to buy an extra trannie. and the same with the simple el84. I have calculated and it will cost me 300 euro; (this is because i need to buy everything except the output trannies; I wast just wondering : at this price i can buy on ebay rahter good second hand amps, or if i pay 500 euro i could build a more powerfull or more refined amp.


(i'm gonna let go the idea of the 807, on this ouput trannie, i don't know if it gonna hold, the Raa isn't right and i don't know the current)

so a lot of options,
bye
 

amperex

Member
2005-02-20 1:42 pm
MI
I guess you are in Europe or? In the US, so much old electronics is disgarded everyday, major parts are not an issue. Find an old tube type organ & get larger power transformer, tubes, sockets, perhaps a choke & sell the remaining parts/tubes to pay for your project.

You know, to achieve an audiophile quality amp costs a fair amount in quality components. Any component of low grade can spoil the sonics. For example, I first tried Sprague orange drops as coupling caps & it ruined the sonics. Switching to AuriCap was a night & day difference.

The 6V6 or less expensive 7C5 are noted to be a great sounding tube triode connected. I find NOS 7C5 for $3-4 each. The loctal sockets are more expensive than the 7C5 tubes at times. Other quality tubes are Brimar 12AU7, Sylvania 6SN7GT 'T' plate, Mullard 12AX7, etc

Anyways, your B+ estimate is correct. Even with cathode bias. 280-290 volts & the 17-20 volts bias will work fine with 6V6s. You should achieve 5 to 6-watts PP triode connected.

A fine amp is the Poindexter 6V6 design. Perform a Google search to find it. I would replace the 5965 with a Siemens 6922 having the A0 code & grey color center divider. Super quality in my 6V6 amp. Or even the Amperex PQ 6922 will rock the 5965 into a 'backup only' tube.
 
I would stick with your EL84s. They are great tubes, pentode or triode connected. I have a rebuilt leak stereo 20 and it sounds pretty damn good, really. Also EL84s are easy to drive, they don't need much more than 1/2 a 12AX7 really. 10-12W is actually damn loud too! I preferred the EL84 PP to the 807 triode PP that I built...

Also don't worry about getting a new power transformer, spend your money on chokes and decent power supply capacitors. If your old power transformer isn't smoked, it will probably last another 50 years. If it gets too hot, buy a $10 6.3V 5A transformer and power all the filaments off that. No way that you need to spend 300 euro!

Another thing, if there are tubes already in the amp, they are probably ok. Mostly capacitors, resistors, and tube sockets are fubar and need replacing. Resistors might be the cause of the hiss sound.

Make sure you use a star earth and for gods sake read the safety thread! :smash: :devilr:
 
Hello,


i can build ecc99 and el84, but then i have to buy an extra trannie. and the same with the simple el84. I have calculated and it will cost me 300 euro; (this is because i need to buy everything except the output trannies; I wast just wondering : at this price i can buy on ebay rahter good second hand amps, or if i pay 500 euro i could build a more powerfull or more refined amp.

NO, it will not cost you 300 euro, for about 75 euro you can get a decent new power trannie !
Since you live in Belgium like me you can order Amplimo transformers at your local electronics shop. You can choose to buy a dedicated tube transformer or make a combination of a high voltage trannie(2 x 115V, wich gives you 320V rectified, just what you need for a PP EL84 ) and a separate 6V heater tranformer.
For example : Amplimo 48070 : 120VA / sec 115/115 at 0,52A each (30,5 euro ex. btw) + Amplimo 28010 : 50VA / sec 6V/6V at 4,17A each. (24 euro ex. btw).
With this setup you have also the benefit of being able to swith on the heaters separetely.

Hope this helps,

Greetings,
Jim
 
hello guys,

i mean 300 euro for everything : power tranny+tubes+sockets+caps+resistors+wiring+chokes.

i suppose good sound comes with a price; (we'll isn't that expensive, but i can use the older tranny with a tube gainclone or something like that, or with a headphone amp, we"ll see.
but i'm gonna go for it;

think i'm gonna start building the simple el84, just because it's simple, if it doesn't work out, i'll make the ecc99+el84 design which i have posted.

thanx guys
 
SHiFTY said:
I would stick with your EL84s. They are great tubes, pentode or triode connected. I have a rebuilt leak stereo 20 and it sounds pretty damn good, really. Also EL84s are easy to drive, they don't need much more than 1/2 a 12AX7 really. 10-12W is actually damn loud too!

10W in Class A triode PP with the EL84? I am old that this will only poduce 2W or so.

even so, then_dude, I would like to knwo how you made out?
 
planet10 said:


about 4 W. An SE EL84 triode can do ~2W.

A class A EL34 triode is about 8-10W.

dave

Dave, you are everywhere!

a) EL84 PPClass A triode = 4-5W
b) EL34 PP Class A Triode = 8-10W
c) EL 84 PPP Class A Triode = 8-10W
moving to Class AB1 would double the available power right.

I am thinking of using (a) to power a Scan Speak tweeter and (b) or (c) to power a pair of (push push) Scan Speak 18cm woofers. Sensitivity is around 90db for the tweeter and 88db for the woofer (push push should compensate for the 6db baffle step).

I'm a bit confused and would appreciate your advice

you may have seen this...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=68013&pagenumber=4

and this...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=68413&pagenumber=2

and this...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=68488&perpage=10&pagenumber=3
 
As far as I know, the EL84 is optimised for both triode and pentode operation when the 807, if it work well in triode, is not optimised for that. (The 807 is optimised for both audio and high frenquency.) Because of this, a triode mounted PP will sound better with 2xEL84 as with 2x807.

But in pentode operation, a PP with 2x807 will sound as good as one with 2XEL84 and you will get much more power with the 807 as with the EL34.

You can do a wonderfull guitar amplifier by combining the 2 tubes, an EL84 in triode montage for the driver and 2x807 (or 2xEL34) in pentode (PP) for the output. The advantage of using a such driver in a guitar amplifier is at you will get some power on the grids of the 807, and that power is needed when the 807 are in clipping.