Re: Dyna 70 now dead after turning on with no input

Posted by corerosin (A) on March 14, 2007 at 09:52:10

In Reply to: Dyna 70 now dead after turning on with no input posted by benhen on March 13, 2007 at 18:27:56:

Did you do what Michael Samra asked you to do, to pull the 5AR4 rectifier tube? There's a reason why he asked you to do that. By pulling the rectifier tube and turning the amp on, the high voltage secondary will be stopped at 5AR4 tube socket and no high voltage will get further. If there is something wrong with the actual power transformer, there will still be hum and chances are the fuse will blow. Chances are that is not the case. What you have been describing sounds like a leaky, faulty, defective filter cap. Do you still have the original aluminum can cap that has the four filter caps in it? It should say 30,20,20,20uf/ 525WV on the side. It may say Dynaco on the side and have an actual date on it. If you still have that in place, you will need to replace it.

The filter capacitor is two conductive plates separated by an insulator. It is used to turn the pulsing DC output from the rectifier and turn it into smoothed DC voltage. When filter caps fail, either of two things happen; either the capacitance can go low, in which case the cap doesn't filter very well and 60 cycle hum will sneak into the output of the amp; or either the capacitor will become resistive and start to draw more and more current from the power transformer through the rectifier. It sounds like you have had a little of both of those situations. If, when you attempt to repower the amp without the 5AR4 in place, the fuse doesn't blow, I would recommend that you replace the filter cap. I really wouldn't try to power the amp with the 5AR4 in place. A shorted filter cap can tear up a tube rectifier and/or the power transformer. But having said all that....that's probably all that's wrong with the amp.

This post is made possible by the generous support of people like you and our sponsors:

Follow Ups Full Thread

Topic - Dyna 70 now dead after turning on with no input - benhen 18:27:56 03/13/07 (13)

Ok - pulled the rectifier tube - fuse held - slight hum from unit - benhen 07:24:23 03/15/07 (2)

Re: Ok - pulled the rectifier tube - fuse held - slight hum from unit - corerosin 07:42:45 03/15/07 (1)

Re: Ok - pulled the rectifier tube - fuse held - slight hum from unit - zacster 08:51:04 03/15/07 (0)

Re: Dyna 70 now dead after turning on with no input - corerosin 09:52:10 03/14/07 (2)

I was going to pull the rectifier next - but the fuse blew - benhen 10:31:13 03/14/07 (1)

Re: I was going to pull the rectifier next - but the fuse blew - corerosin 13:46:45 03/14/07 (0)

Re: Dyna 70 now dead after turning on with no input - beermanpete@socal.rr.com 22:23:41 03/13/07 (1)

Haven't put in the new fuse yet - - benhen 09:09:18 03/14/07 (0)

Unless your Dyna has been properly (fully) restored to an electrically safe state - Quest 20:39:41 03/13/07 (0)

Fuse is blown - is this normal? - benhen 18:37:46 03/13/07 (3)

Re: Fuse is blown - is this normal? - Door Nail 18:53:19 03/13/07 (2)

Re: Fuse is blown - is this normal? - BOONIERAT 06:40:03 03/14/07 (1)

It's supposed to be rebuilt already - - benhen 09:11:21 03/14/07 (0)

Follow Ups

Re: Dyna 70 now dead after turning on with no input - corerosin 09:52:10 03/14/07 (2)

I was going to pull the rectifier next - but the fuse blew - benhen 10:31:13 03/14/07 (1)

Re: I was going to pull the rectifier next - but the fuse blew - corerosin 13:46:45 03/14/07 (0)

You can not post to an archived thread.