Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on October 13, 2014, 04:33:25 am

Title: IN4007 diodes shorted out
Post by: TIMBO on October 13, 2014, 04:33:25 am

Hi guys, Found some time to tinker with the Fi Sonic and things were going great.

TILL, after having a bit of a canoodle turned it to standby and the main fuse blow.  :think1:
Replaced the fuse and couldn't even get it to standby without the fuse blowing.
Removed tubes and disconnected the heaters to eliminated any shorts there, no good.
Finally disconnected the HT wires and checked all voltages and the tranny is good.

The clincher, two 1N4007 in series on each leg of the HT as you would.
Checked around diodes for shorts to ground,OK.
Checked the diodes and one set has an open circuit from end to end  :sad2: :help:
I can't say that I have had this happened to me so an underlying problem I would think  :think1:

Sheet 2 is the circuit. Thanks

Title: Re: IN4007 diodes shorted out
Post by: John on October 13, 2014, 05:12:12 am

Only idea I have is to check your first 2 filter caps, make sure 1 of them isn't shorting to ground (which you probably already did)


Other than that, replace the diodes and plug into your lamp limiter and go from there.


Good luck!

Title: Re: IN4007 diodes shorted out
Post by: shooter on October 13, 2014, 08:45:10 am

I've had 2 builds blow a single diode of a 4 diode bridge for no apparent reason, swapped the 4-diode for a beefier molded bridge, added .01 bypass? caps, problem solved, except, I never got that sense  that the fix was a real cause - effect fix.

Title: Re: IN4007 diodes shorted out
Post by: Ken Moon on October 13, 2014, 03:26:33 pm

I guess this is overboard, but I've used the Fairchild ISL9K8120P3 Stealth dual diode (120V/8A) in a few builds. It works great, doesn't need any snubbers, or a heat sink in guitar amps (I usually mount it to the chassis anyways because it's convenient).

Unfortunately, the 1200V version is obsolete, but they have a 600V/4A version, p/n ISL9K460P3.

http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/ISL9K460P3/?qs=%2fha2pyFadujrsISAbBpzX3z3Bm66ZlLDXq5Xhi3U%2f%252bU%3d (http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/ISL9K460P3/?qs=%2fha2pyFadujrsISAbBpzX3z3Bm66ZlLDXq5Xhi3U%2f%252bU%3d)

Title: Re: IN4007 diodes shorted out
Post by: TIMBO on October 16, 2014, 01:56:42 am

Hi guys, Some direction from the local guys and I think I have this sorted.