DYNA kIT st-70 -- OLD MODS -- Audio amatuer 1976

Hello Fellow DYNA/DYNACO re-builders /collectors .

I have have an OLD st70 that ihave to get going again .

It suffers from the bLown Fuse problem ~I have often read about .


The Filter cHOKE is rather discolored looking/with wax drippings on it.  -I suspect it is shorted out .

what Value is that damn choke???

I have  only used this amp 3 or four tymes in a 20 year peroid , kept it in storage  and had it Modded back in 1997 < had a vERY REPuTable TECH>  do a  Audio by  VAN ALSTYNE  -IN put Filter Mod on it . and the tech installed a 40 Mfd Axial  500 V Cap in parallel with one of the Multisection Cap lugs , plus he replaced the Bias Caps  , and replaced the Selenium diode witha 1n003/4 ?? solid stater .

So waht should I look for as faras a Shorting Cause??



BTW  (TITLE of my Letter)  anyone here do any of the AUDIO AMATEUR  MAGAZINE  Modifications  that entailed replacing the GZ r4 Tube with a pair of Silicon Diodes ?? < Iwould use 4 in series on each leg of X~former secondary>.  Plus an Increase in Capacitor Value   to  get rid of those old UInreliable CAN Capacitors.

Reagrds - dyna Blow

Forget the choke, it's not uncommon that the vax melts .
Fuze blows , remove the rectifier and power on, if fuze will stay problem is in the B+ area

Then the best way is to slowly feed the B+ with a variable DC source and keep watching for
current. If you can get to 400 Volt with only a few mA then the GZ34( rectifier tube ) needs
replacement.
Alternativly if no DC source is available, remove the EL34 tubes, insert the GZ34
and power on while watching the B+ If fuze will stay you have a problem with EL34 or bias
circuits.


And, remove the extra 40iuF axial !

Use Slo-Blo fuses, if your not already.