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Old 30th July 2005, 04:25 PM   #1
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Default 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
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Old 30th July 2005, 04:51 PM   #2
SY is offline SY  United States
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Just to clarify, do you have an ECC88 or ECC83 for the input? At one point you mention "12AX7," so pardon my confusion.
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Old 30th July 2005, 05:10 PM   #3
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ohh i'm sorry, thanks for the remark, it's an 12ax7 so, an ecc83 if i'm right
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Old 31st July 2005, 01:31 AM   #4
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Default 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.
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Old 31st July 2005, 01:51 AM   #5
Sheldon is offline Sheldon  United States
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You could do something like this in triode mode (or pentode). I made a similar 6CK4 amp and it sounds very nice.

http://www.wdehaan.demon.nl/mono/mono/el84dc.html

Sheldon
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Old 31st July 2005, 02:07 AM   #6
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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/afbe..._amplifier.gif

http://www.dhtrob.com/projecten/afbe...owersupply.gif
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Old 31st July 2005, 02:40 AM   #7
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Default El84

I mean the EL84; with the 807 (far better alternative , the DHT 1624, same pin-out) you need Ia of about 40- 45mA, and you may expect saturation in the EL84 OPT. Starting with an irritating s-sound.

Dogie

PS
807->1624: http://tdsl.duncanamps.com/tubesearch2.php?TSD=1624
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Old 31st July 2005, 10:33 AM   #8
EC8010 is offline EC8010  United Kingdom
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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.
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Old 31st July 2005, 07:08 PM   #9
jim is offline jim  Belgium
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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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Old 1st August 2005, 12:58 PM   #10
have' is offline have'  Netherlands
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Default Simple EL84

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.
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