Need someone to look at my Dynaco 70

Happy New year,

My modified Dynaco 70 has started popping the main fuse. It also blew the rectifier tube (GZ34). I installed another fuse and tube and after playing for a while, it blew the same fuse. I didn't install another rectifier tube, deciding it'd be better for someone to see why the tube is blowing before potentially wasting a new tube. I am in the Sacramento area, does anyone know a person who has the expertise to diagnose what is happening?

Thanks in advance.


you will need to check power tubes first; also check resistors for anode supply as they act like fuses as well

Could be a short in the 5 volt winding on the power transformer. The stock Dynaco power transformers are under-sized for the circuit's tube load. If so, buy a higher-rated power transformer.

 Just answer the poor guys question... Do you know a tech that can help him out or not .....?


have you looked into Paradyme? I’m not from the area, but they list Vintage Stereo Repair as one of their services (along with car audio and home automation/installs). They’re on Fulton Ave. in Sacramento.

The ST-70s seem to eat rectifiers with regularity…new market 5AR4s especially. I run vintage 5U4Gs in my VTA (Bob Latino) ST-70 as they seem to have the best reliability.

The suggestion to upgrade the power transformer is a good one if you haven’t done that yet. You mentioned mods, but I’m not sure which ones.

Best of luck with the fix!

     THE MAN to contact regarding Dynaco info/advice, upgrades or repairs: