RockerVerb 50 blowing HT fuses

DoyleFan · 01-06-2009, 05:49 PM

Blowing fuses with NO POWER TUBES in. Very strange. This happens intermitantly, and when it does the plate voltage drops to around 200 volts. I have replaced the on/off/standby switch. I'm drawing at straws. Any help?
Thanks,
doylefan

hasserl · 01-07-2009, 01:31 AM

Got a schematic?

Does the amp have a rectifier tube? That could be the culprit. If not, there is a short circuit somewhere on the PT secondary HV circuit, it could be the power transformer itself.

Enzo · 01-07-2009, 02:54 AM

I think so too. Disconnect the center tap wire from the output transformer. Now watch the B+ and see if it still sinks. if not, then the output transformer may well be bad. If the B+ still droops to 200v with the transformer disconnected, you more likely have a failing filter cap or an arc somewhere like a tube socket.

PlinytheWelder · 01-07-2009, 05:24 AM

Schematic is here:
http://www.shortscale.org/forum/view...6a24c523219363

DoyleFan · 01-08-2009, 04:41 PM

thanks guys, i'll try these suggestions now and let you know how I make out.

DoyleFan · 01-08-2009, 09:47 PM

I think I tracked it down to C5 (filter), I'll try replacing it. Tough because this is an intermittent problem.

DoyleFan · 01-09-2009, 10:08 PM

No luck. seems to be ok when i disconnect the choke. strange because I disconnected the preamp, removed the power tubes, lifted the bias circuit to isolate the problem and it's still there. You can see the fuses arcing inside.

Alex R · 06-12-2009, 08:39 PM

- just had this same problem. On this amp it was caused by C3 shorting out. I put new fuses on, fired it up on the light bulb and traced it by the smoke

.

I'll put the schematic page on here.

So what's C3 for?

Enzo · 06-13-2009, 02:05 AM

Transient suppression.

Alex R · 06-13-2009, 07:34 AM

Thanks Enzo. It looks like an accident waiting to happen sitting there, but (here comes the confession) as I haven't quite fully grasped cap-fed bias I didn't know whether this was some strange permutation of it, so instead of binning it as I was tempted I replaced it with a 1kV. Couldn't read the rating of the little burned blue disk I took out. Maybe it really did get a transient!

There to satisfy some safety reg. or other I guess?

Enzo · 06-13-2009, 08:00 AM

Or noise.

janne · 09-22-2009, 05:02 PM

sorry to reopen this..

I am having something similar.. Blowing HT fuses constantly.
Have umplugged the Choke to confirm the 1st section and the TP6 to completely eliminate the transformers etc.

I am coming up with Cap 5?

Thoughts?? Is this common?

Thanks

Janne

01-06-2009, 05:49 PM	#1
DoyleFan Junior Member Join Date: Jan 2009 Posts: 4	RockerVerb 50 blowing HT fuses Blowing fuses with NO POWER TUBES in. Very strange. This happens intermitantly, and when it does the plate voltage drops to around 200 volts. I have replaced the on/off/standby switch. I'm drawing at straws. Any help? Thanks, doylefan

01-07-2009, 02:54 AM	#3
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 9,266	I think so too. Disconnect the center tap wire from the output transformer. Now watch the B+ and see if it still sinks. if not, then the output transformer may well be bad. If the B+ still droops to 200v with the transformer disconnected, you more likely have a failing filter cap or an arc somewhere like a tube socket. __________________ Education is what you're left with after you have forgotten what you have learned.

06-13-2009, 02:05 AM	#9
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 9,266	Transient suppression. __________________ Education is what you're left with after you have forgotten what you have learned.

06-13-2009, 08:00 AM	#11
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 9,266	Or noise. __________________ Education is what you're left with after you have forgotten what you have learned.

09-22-2009, 05:02 PM	#12
janne Junior Member Join Date: Sep 2009 Posts: 1	.. sorry to reopen this.. I am having something similar.. Blowing HT fuses constantly. Have umplugged the Choke to confirm the 1st section and the TP6 to completely eliminate the transformers etc. I am coming up with Cap 5? Thoughts?? Is this common? Thanks Janne

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Similar Threads

01-07-2009, 01:31 AM	#2
hasserl Senior Member Join Date: May 2006 Posts: 623	Got a schematic? Does the amp have a rectifier tube? That could be the culprit. If not, there is a short circuit somewhere on the PT secondary HV circuit, it could be the power transformer itself.

01-07-2009, 05:24 AM	#4
PlinytheWelder Junior Member Join Date: Jun 2008 Posts: 7	Schematic is here: http://www.shortscale.org/forum/view...6a24c523219363

01-08-2009, 04:41 PM	#5
DoyleFan Junior Member Join Date: Jan 2009 Posts: 4	thanks guys, i'll try these suggestions now and let you know how I make out.

01-08-2009, 09:47 PM	#6
DoyleFan Junior Member Join Date: Jan 2009 Posts: 4	I think I tracked it down to C5 (filter), I'll try replacing it. Tough because this is an intermittent problem.

01-09-2009, 10:08 PM	#7
DoyleFan Junior Member Join Date: Jan 2009 Posts: 4	No luck. seems to be ok when i disconnect the choke. strange because I disconnected the preamp, removed the power tubes, lifted the bias circuit to isolate the problem and it's still there. You can see the fuses arcing inside.

06-13-2009, 07:34 AM	#10
Alex R Supporting Member Join Date: Mar 2007 Location: in bosky Surrey, England Posts: 630	Thanks Enzo. It looks like an accident waiting to happen sitting there, but (here comes the confession) as I haven't quite fully grasped cap-fed bias I didn't know whether this was some strange permutation of it, so instead of binning it as I was tempted I replaced it with a 1kV. Couldn't read the rating of the little burned blue disk I took out. Maybe it really did get a transient! There to satisfy some safety reg. or other I guess?

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Classic 30 blowing fuses...	HojoMojo	Maintenance, Troubleshooting & Repair	11	06-29-2008 09:12 PM
Blowing Fuses	EETStudent	Maintenance, Troubleshooting & Repair	11	05-08-2008 07:10 PM
Blowing Fuses....	Bob M.	Maintenance, Troubleshooting & Repair	10	03-28-2008 07:18 AM
Blowing fuses	lowell	Maintenance, Troubleshooting & Repair	7	03-24-2008 01:14 AM
Blowing fuses...	riscado	5 E 3	7	08-21-2006 04:06 PM