EL34PP kit questions

OneyedK

Active Member
Hello,

I'm planning to build me an EL34PP amp somewhere around the end of the year.
I've been eyeballing ST-70 kits, but the 7199 penthode/triode driver worries me.
7199 are rather expensive and not really future proof.
Also, I've never had much luck using penthodes (EF86 mostly) in pré and driver stages.
So some questions:

Is there a consensus about wich alternative driver board is "the best"?

Is there a difference between the output transformers included in the kits of Triode and Dynakitparts?

Are there other kits I should consider?

Or should I forget about kits and grab myself a pair of Lundahl LL1679's and start from scratch? (Mind you, my metalworking skills are -err- poor)
http://www.lundahl.se/wp-content/uploads/2013/05/1679.pdf

Thanks for answering my questions!
 
Hello,

I'm planning to build me an EL34PP amp somewhere around the end of the year.
I've been eyeballing ST-70 kits, but the 7199 penthode/triode driver worries me.
7199 are rather expensive and not really future proof.
Also, I've never had much luck using penthodes (EF86 mostly) in pré and driver stages.
So some questions:

Is there a consensus about wich alternative driver board is "the best"?

Is there a difference between the output transformers included in the kits of Triode and Dynakitparts?

Are there other kits I should consider?

Or should I forget about kits and grab myself a pair of Lundahl LL1679's and start from scratch? (Mind you, my metalworking skills are -err- poor)
http://www.lundahl.se/wp-content/uploads/2013/05/1679.pdf

Thanks for answering my questions!

None of the recent kits ( tubes4hifi, dynakitparts or troide ) uses 7199.
12au7 is used by tubes4hifi, they are available as NOS and new production.
 
Is there a consensus about which alternative driver board is "the best"?

Are there other kits I should consider?

There is no "best" IMHO, just different. And the tube rolling options for some are mind boggling.:D

Here's an older thread re. the Dynamutt Octal board. There's also a Dynamull driver board, but it uses a pentode up front which you may not want. There's also a 9-pin Dynamutt board, which is the only version I've heard. It gives the amp a very clean neutral sound.

http://www.audiokarma.org/forums/showthread.php?t=307160

jeff
 
Dyi options

I checked on those Dynakit ST-70's they are over $600.00. Have you considered building your own? I'm working on a build right now using a PC board (stereo) bought from eBay. It is nice thick board and has a bias circuit on the board. Each channel is very similar to the Mullard 5-20 circuit except for the bias. The Mullard uses cathode bias. All you would need to do is add a power supply. The bias circuit that is shown in the auction schematic is actually on the board but power supply is not. The board is $29.00 from China and I have $200.00 in the Edcor power and output transformers. It would save you a few hundred dollars over the Dynakit.
http://www.ebay.com/itm/EL34-PP-power-stereo-amplifier-PCB-1-piece-/221442485094?pt=US_Home_Audio_Amplifiers_Preamps&hash=item338f002b66
 
That board sure looks nice!
The only thing I would worry about is the balance of the phase splitter, a 12AU7 is not easy to work with if you want the outputs to be well matched.
A currect source in the tail would help, combined with a negative supply even better. But you'd loose the direct coupling with the first stage...

In the mean time, I've contacted Bob Latino, as (for now) I think his kit offers the best out of the box performance. But price is rather steep.
$978 + 25% (VAT and import duties), that's $1223.
Maybe I should investigate the diy route further...
 
That board sure looks nice!
The only thing I would worry about is the balance of the phase splitter, a 12AU7 is not easy to work with if you want the outputs to be well matched.
A currect source in the tail would help, combined with a negative supply even better. But you'd loose the direct coupling with the first stage...

In the mean time, I've contacted Bob Latino, as (for now) I think his kit offers the best out of the box performance. But price is rather steep.
$978 + 25% (VAT and import duties), that's $1223.
Maybe I should investigate the diy route further...

I can only say positive things about bob latino and the vta-70. Kit is well documented
and evertything fits. In addition there is an excellent support in another fora.
 
Kits are nice

Actually the phase inverter balance will not be too bad. The plate resistors 39K and 33K will get it close. From calculations the inverted gain should be 6.77 and the non inverted gain should be 7.04. That is a gain difference of .37. I can live with that. But I'm sure you would be satisfied with one of the kits. I enjoy working from scratch and using off the shelf components and boards but kits are nice because you know going in what the results will be. Have you looked at ANK Audiokits? They are expensive but nice.
http://www.ankaudiokits.com/
 
Phase splitter balance of the VTA boards using 12AU7 or the octal version with 6SN7's should be very good as it uses a CCS in the tail. It's been proven by others that even with wildly mismatched tubes, a good CCS will still enforce AC balance.

Have fun with your project.
John
 
Have you looked at ANK Audiokits? They are expensive but nice.
http://www.ankaudiokits.com/
I just had a look. Seems they know what they are doing, but at a serious cost!

Phase splitter balance of the VTA boards using 12AU7 or the octal version with 6SN7's should be very good as it uses a CCS in the tail. It's been proven by others that even with wildly mismatched tubes, a good CCS will still enforce AC balance.

Have fun with your project.
John
Ah, good to know! Thanks! I haven't seen the schematic of the VTA70 yet, but the reviews wouldn't be as good if the design wasn't solid.

/edit: the missus just told me that she wants a bigger house :s Project could be spostponed if she pushes thru...
 
I just had a look. Seems they know what they are doing, but at a serious cost!


Ah, good to know! Thanks! I haven't seen the schematic of the VTA70 yet, but the reviews wouldn't be as good if the design wasn't solid.

/edit: the missus just told me that she wants a bigger house :s Project could be spostponed if she pushes thru...
As for the vta-70 from tubes4hifi; Design is solid, sound amazing. Schematic is not published(but you will get one with the kit). And yes it has CCS's in the cathod of the phase splitter.
 
I built a Triode ST 70 kit and have a Dynaco with the VTA board installed. I like the Triode a bit better, but that would change if I put an upgraded PS transformer in my Dynaco. I can hear the larger tranny. Latino's amps are GOOD.
 
I have built a Latino ST70 kit about 2 years ago. still think it was a good decision being a complete novice. the building instructions are one of the best to follow and support is just great, even for people like me who didn't know what the hell they were doing at times.
the only downside for me were the steep shipping costs ( I think the whole package was around 21kg!) and import duties/VAT.
total shipping costs were $151 and import duties were €160 IIRC.
then again, I don't believe there are true alternatives as far as tube amp kits over here in the EU.
I haven't regretted this whole project for one second. ...and I have had some mishaps with this amp due to my poor skills in the past. it's been running steady and beautifully for quite some time now thanks to all the help that I have received on their support forum.
 
Thanks! Shipping costs stayed about the same, but import duties here in Belgium are about double what you payed.

At the moment, I'm looking at the well documented "Dynamutt" noval board.
Not that I don't like the octal version, but I've had my fair share of troubles (hum) when using octal préamp tubes. Unless I decide to go for DC heaters.
1.5A 6.3V is not easy to do in a chassis with not too much ventilation.

/edit: Just noticed that 12SL7 and 12SN7 are still available, 12.6V 750mA is a lot easier...
Still, I don't know if there's an advantage from 6SL7 to 5751 or 6SN7 to 6CG7?!
 
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