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.

sparkymaui

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 .....?

@sparkymaui 

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. www.paradyme.com

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!