EL83 / 6CK6 valves in place of EL84

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DaveW
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EL83 / 6CK6 valves in place of EL84

Postby DaveW » Sat 06/13/09 4:51 am

Since reading this thread ref. Rory Gallaghers modified AC30 using EL83s in place of EL84s I have been tempted to try these. I have finally done so and am really impressed. I think they give a slightly emphasised mid range and break up very well. They are also very cheap: picked up NOS Teslas off eBay for a couple of pounds each. I have had these running for a few weeks now with no problems.

Original link to Rory's AC30

http://vintageamps.com/plexiboard/viewt ... 30#p795629

Just a bit of a wiring change, didn't need to change any component values. I have now fitted a small toggle switch in between the bases to allow me to fit either. Having the switch set to the wrong position doesn't seem to do any harm either, they just don't work.

If anybody else wants to try I have listed what I did here.

http://s59.photobucket.com/albums/g293/ ... cture6.png

I ignored the screen connection on the EL83, would welcome any opinions on whether this is correct.
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Re: EL83 valves in place of EL84

Postby zaphod_phil » Sat 06/13/09 7:51 am

DaveW wrote:I ignored the screen connection on the EL83, would welcome any opinions on whether this is correct.
8O
If they're pentodes or tetrodes, I would have thought it would be essential to connect the screen grids.
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Postby DaveW » Sat 06/13/09 8:12 am

Hi Zaphod,

I don't believe it is a screen grid (which I think is pin 1) , I think that it is some sort of interference screen. see base diagram and let me know if you agree.

Dave
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Postby zaphod_phil » Sat 06/13/09 8:26 am

I just looked up the spec sheet - www.mif.pg.gda.pl/homepages/frank/sheets/030/e/EL83.pdf

Yes, it seems to be just an internal shield (pin 8). Probably to keep interference either in or out, as this appears to be a TV valve. Personally, I would ground it, rather than just leaving it floating....
Last edited by zaphod_phil on Wed 10/21/09 2:31 pm, edited 1 time in total.
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Postby DaveW » Sat 06/13/09 8:41 am

Thanks for the info Zaphod. I probably would have grounded it had I not gone for the switched option. Pin 1 is marked as an internal connection on an EL84 so I would have had to switch the ground connection on each valve, but I only had a 4 pole switch. If I see an inexpensive 6 pole switch or build an amp with only EL83s I would certainly do this.

That said I have had no problems to date with it left floating. I have tried Tesla and Mullards EL83s for compatibility and both worked fine.
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Postby rayandkerry » Mon 06/15/09 8:43 am

Hi, guys.

Really cool concept! I am just about to whip together my first 18W and am really glad I read this thread before I drilled my chassis!

DaveW, you say you used a 4 pole switch. That's a 4PDT, right? Also, is it one of those mini-switches, or more heavy duty one (like a Carling power switch)? What Amperage rating?

Thanks, in advance, for your help!

Ray
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Postby rayandkerry » Mon 06/15/09 10:03 am

For example, do I need something heavy-duty like product number 453-425 here (bottom left of the page):
http://www.rpelectronics.com/Data/RPCAT-115.pdf

Or would 451-420 suffice (middle of page).

Thanks, again!

Ray
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Postby DaveW » Mon 06/15/09 10:50 am

Hi Ray,

I used one of these

http://www.maplin.co.uk/Module.aspx?ModuleNo=2343

I reasoned that the currents are not high and it will only be switched when the amp is off.

If I were you I would install the switch, build the amp stock and prove it works OK and then wire the switch in to the circuit and test with EL83s.

Let us know how you get on.

regards,

Dave
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Postby rayandkerry » Mon 06/15/09 12:07 pm

Thanks, Dave!

I'm going to pick up the switch on the way home so I can plan how to drill the chassis.

You said: "If I were you I would install the switch, build the amp stock and prove it works OK and then wire the switch in to the circuit and test with EL83s."

Yes, thank you. That's a very good suggestion...one I will certainly follow (and one I would not have thought of on my own). KISS, to start...i.e. Keep It Simple, Stupid!

I think I will take that to heart with all amp modifications I try going forward. Thanks for the sound advice!

Ray
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Postby dotfret » Mon 07/13/09 9:28 am

So I went to look at those AC30 pics - somebody noticed that one of the preamp valves was "rather large" - the one with red print in the pictures. Looks like it might be a Sylvania 12BZ7 (he guessed glibly).
Whatever, something tells me that there may be quite a lot of strange things that happened to that AC30 ...
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Postby dgriff » Wed 10/21/09 1:53 am

Hi, I'm going to try some El83's in my lite 2b this weekend. Dave, how have they held up since your last post on the subject? Have you experienced any problems, or needed to tweak any component values yet? Any advice or opinions are apreciated.
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Postby PepeJara » Sat 11/28/09 3:05 pm

I have done the mod in my 18 watt, and have installed a pair of Valvo el83, I couldn´t be happier...my other el84 amps are well equiped (mainly with Mullard el84) and this Valvo el83 are in the same league :wink:
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Postby dgriff » Sun 11/29/09 2:03 am

I have have Telefunkens and Siemens which sound great. Just waiting for the Mullards to arrive :D Great mod to use cheap NOS. I will have to try some Valvo's, my supplier has some.
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Postby PepeJara » Mon 01/04/10 8:56 pm

Just two questions about the wiring:

Since the pin 6 isn´t used by El84, is there a reason for not leaving pin 3 and 6 conected permanently? I mean, without switch...

And the same question for pin 9 and 1...In el84 mode, pin 9 is used and 1 without connection, in el83 mode, the inverse, why not a wire between 9 and 1 permanently? Will I damage anything if doing so?
:wink:
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Postby DaveW » Tue 01/05/10 3:11 am

I did try leaving the other pins connected but it caused problems, after this time I can't remember what these were but I did in the end have to switch all the pins. I guess there are some internal connection issues.
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