Dynaco ST70 clone, tubes substitution question

[bembel]

Hi all,

I've just purchased an ST-70 chinese clone (Dynavox VR70E-2).
And I wonder which tubes are valid substitutes ?

* power stage : fixed bias, B+ = +420V EL34. ---> 6550 ? 6L6 ? (suppressor pinout ? bias ?, filament supply should be enough with 3.5A per pair)

* driver chinese 6F2 tube should be exact match to 6U8/ECF82 (do you confirm ?) what about ECF80 ? (I got some of them) ECF 802 ?
It seems also that filament supply of the driver is too strong (2 tubes alone on a 4A supply, they are glowing too much, maybe two magic eyes can help )

Wath bias will you suggest for JJ E34L ? it's actually breaking in @35mA (haven't hooked an oscilloscope yet)

thanks

PS: for the price this amp is a real killer.

[magpietim]

Hi Bembel,

Had two of these myself for about two months and i agree with you...they are amazing for the money....can't help with your query though....i'm a tube newbie but i'm finding the experience very interesting.

The two signal tubes do seem to glow rather brightly....but with the lights off it looks lovely.

I'd be interested to hear what anybody says about them and any improvements i can make....at the moment i have EL34 Groove tubes in them.....and i'm bi-amping with them.

Tim.

[jmateus]

Hi guys

Could you please give a link for these chinese boards?
I have a ST70 I would like to modify and I'd be interested in a
good modification.
Thanks

[bembel]

Here it is Jmateus,

the model rev 2 (already including mods)---> http://www.tomwip.de/tmp/neueDynavoxPlatine.jpg

the modelo rev 1 (with mods pictures) ---> http://www.retro-optonica.de/Dynavox/Dynavox.htm

but I think, there are more sites refering to original ST70 mods.

hope this helps

[Holger Barske]

I've gone for 37mA Bias. Sounds great.

[jmateus]

Hi Bembel
Sorry I must have misanderstoood your posting, I tought Dynavox
was a chinese company that sold those boards.
I was mostly interested in buying the boards.
Thanks anyway