el84 amp

[mark_titano]

I want to build a new amp...I've bought four el84 but I'm not sure which is the best way to use them. I need 7/10W so the I think that the options could be:
1) sep, pentode connection with local negative feedback
2) push pull, maybe ultraliner connection.

For push pull design I like solution like this:

http://www.meta-gizmo.com/Tri/interstage.html

What's about phase splitting by using an interstage transformer ? I think this could be an interesting solution, perhaps better than pse pentode connection

Thankyou in advance

Mark

 

[SY]

Using an IT can work, but is (IMO) unneccessarily expensive and removes many design options. The nice thing about EL84s is that they don't require much drive- difficult tubes are a better argument for ITs.

If it were me, I'd build a simpler, more classic design. Have you seen the Bevois Valley amp in Morgan Jones's book?

 

[Bas Horneman]

If it where me...I would build http://www.meta-gizmo.com/Tri/interstage.html as well..

can't get any simpler than that.. and to me it IS a classic design.
It sure is a little more expensive...but what is 200$ for something that provides you with years and years of problem free amplification......and the phase splitting does not suffer through time like I suppose a tube based phase splitter does. Plus I happen to believe that adding feedback is like castrating your amp. (Term stolen from the Positive Feedback review of the sixpacs amps...http://www.positive-feedback.com/Issue6/sixpac.htm).

The Bevois valley apparently sounds quite good But is actually quite complex and therefore less suited as a first time build IMO.


Cheers,
Bas

 

[mcs]

This simple amp works well: http://stiftsbogtrykkeriet.dk/~mcs/EL84_Amp.html

It would be quite easy and cheap to make, if you want to try something simple first.

Best regards,

Mikkel C. Simonsen

 

[audiousername]

You could use the "Simple EL84" design from www.diyparadise.com (the site is down - bandwidth exceeded). From memory... it's a UL push-pull design with the output serving as phase-splitter since the tubes are mounted in differential.

No idea how it sounds... or how good the phase splitting balance is when done this way

Will check if I saved the schematic

It has been assumed that this is mark_titano's first amp. He hasn't said this

 

[audiousername]

schematic:

 

[planet10]

It sure is a little more expensive...

This little beauty does a good job for almost no money...

http://www.edcorusa.com/transformers/audio/wsm/wsm10k-10k.htm

dave

 

[planet10]

This simple amp works well: http://stiftsbogtrykkeriet.dk/~mcs/EL84_Amp.html

That is the same topology as the Morgan Jones amp which SY mentioned. Morgan's amp probably has the detail down better.

dave

 

[planet10]

You could use the "Simple EL84" design from www.diyparadise.com

An elegant amp, but you oonly get half the power.

dave

 

[mark_titano]

Thankyou All

It seems that pse design is not a good idea...hehehe
Ok I will try push pull, I never built one ( I'm listening an El34 SE, my second diy amp), I think this could be a good experience.
Maybe I'll try pse design later...

I think that I'll try somethink like this:

http://www.audiodesignguide.com/my/pp3.html

Maybe with better power supply...ccs source for the el84...and battery bias for the input stage.
What's about?

I found two LL1671 (second hand) for 100Euro:

http://www.lundahl.se/pdfs/datash/1671.pdf

what you say? I buy them? I'm not sure that they are ok for small triode like 5842...

Thankyou in advance

 

[mark_titano]

Now I'm looking for a good output transformer for the push pull design. What primary impedance for the el84 is a good solution? 10k? 8K? I've never try Hammond transformer, someone knows how are they? I can buy 1608 or 1609 for about 55Euro each:

http://www.tubes.it/Hamm_1608_5C0051-52.pdf

I don't want to invest more than 150 euro for the first implementation. I want to try also pse design (maybe with 4 el84 triode connection) and my budget is not unlimited.
For this money can I find something better?

Mark

 

[Norris Wilson]

Cloned Dyna ST-35 output transformers!

Hi Mark,

If you do not mind purchasing your transformers from a vendor in the USA, here are some nice EL84 transformers that should fall close to your 100 Euro budet.
http://store.yahoo.com/triodeel/z517wadyoutr.html

Ned Carlson from www.triodeelectronics.com that offers the above EL84 transformer has been a long time supplier of vacuum tubes and related parts for many years, he has a dedicated following of customers.

Here is a company that offers a Dyna ST-35 circuit board so one can make an updated clone of the original design. www.diytube.com
There is a test of several EL84 capable output transformers listed under their ST-35 clone section in the forum, I think they label the ST-35 section of the forum baby blue.

I hope this will help in narrowing down your search.

Good luck

Norris Wilson

 

[mark_titano]

Tankyou very much!
It seems one good transformer. I just don't understand if there are UL taps...and I'm a little bit afraid to buy it from USA . The price is good but I don't know how much does cost the shipment and if I have to pay VAT. I'll write an email to triodel...

Well, do you think this is better than Hammond?
I've seen the test and I think, maybe, yes.
Someone know something like this in Europe?

thanks again Norris

 

[Bas Horneman]

Hi Mark,

Relatively expensive transformers...but apparently good ones (and therefore excellent value for money) are the Lundahl..they are sold in Italy.

Cheers,
Bas

 

[planet10]

Relatively expensive transformers...but apparently good ones (and therefore excellent value for money) are the Lundahl..they are sold in Italy.

Lundahl is definitly towards the high end of the spectrum... if NA pricing is any indication, once transport across the Atlantic is factored in, they should be relatively reasonable.

I hope someday to transition up from Dynaco iron to Lundahl in my PP EL84s.

(Yes Dyanaco OPTs are UL)

dave

 

[mark_titano]

Lundahl are a very good solution...just too expensive in this moment, I want to buy two 1660 interstage transformers ( 84€ each... here http://www.studiomaudio.com/ ,Torino, Italy) so my budget go down quickly.
I'm not sure that el 84 push pull will be my last amp but for sure I'll try other solutions with the 1660...so this is my priority.
Lundahl were my first choice...but I can't print money

 

[planet10]

If on a budget you can always do what i did... buy an old, but nice, amp to use as a parts donor... i have Dyanaco, Scott, Telefunken, and i'm sure Philips must have built a suitable beast (as well as any number of Euro brands i don't even know about)

dave

 

[Bas Horneman]

Philips must have built a suitable beast

Sure did..but even some Pioneer et al..has half decent output transformers...since europeans have smaller homes...most are in landfills..

 

[EC8010]

Now I'm looking for a good output transformer for the push pull design. What primary impedance for the el84 is a good solution? 10k? 8K? I've never try Hammond transformer, someone knows how are they? I can buy 1608 or 1609 for about 55Euro each:

For PP U/L EL84 you want 8ka-a. I borrowed and tested an amplifier using the Hammond 1608 transformer (not with EL84, mind) and it was very good. After a bit of tweaking, I was able to pass a good 10kHz square wave, and low frequency distortion was surprisingly good - especially given the size of the core. If I needed an EL84 transformer, that's the one I would buy.

 

[Brett]

As you're in EU, check out the Lundahls