Ampeg V4.com

forum

You are not logged in.

#26 2012-06-15 17:17:12

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: Internal fuse blow before external?

Didn't mean to offend.   If you like to believe that the flybacks are helping... Even though they are just another thing in the amp to fail (and they do fail) ,  and v4 output transformers still fail at a similar rate to the rest of the non flyback diode using world...
Tell me this though... What is the benefit?  If you can't prove that they are helping,   And we all know they fail.

Offline

 

#27 2012-06-15 17:40:24

sewage666
VIP
From: Oakland, CA
Registered: 2010-11-19
Posts: 79
Website

Re: Internal fuse blow before external?

I'm all for redundancy, and since my amp now works, I'll assume the rock protected me from the tigers.

I replaced the flyback diodes and my amp is working fine again. Considering that this all happened when I had a blown speaker and therefore an Ohm mismatch, I think it's fair to say there is a chance they did their job. There's also a chance the fuse blowing saved it. Frankly, I don't care, I just appreciate all the help and getting my amp working again for under $5!!! Thanks!

Just to help the next guy out there like me with a similar problem, I prepared some pictures to help along this process...

http://i27.photobucket.com/albums/c160/sewage666/IMG_7275s.jpg

http://i27.photobucket.com/albums/c160/sewage666/IMG_7282s.jpg

http://i27.photobucket.com/albums/c160/sewage666/IMG_7283s.jpg

If I got anything wrong there in my labeling, lemme know and I'll fix it. I don't wanna lead any future info seekers astray.

Offline

 

#28 2012-06-15 17:44:22

sewage666
VIP
From: Oakland, CA
Registered: 2010-11-19
Posts: 79
Website

Re: Internal fuse blow before external?

hangman wrote:

Didn't mean to offend.   If you like to believe that the flybacks are helping... Even though they are just another thing in the amp to fail (and they do fail) ,  and v4 output transformers still fail at a similar rate to the rest of the non flyback diode using world...
Tell me this though... What is the benefit?  If you can't prove that they are helping,   And we all know they fail.

Being the novice I am, I have to submit to the manufacturer, and try and get it back to the way I found it. It did fire up fine without the diodes in place. I just want it back to as close to stock as possible.

Thanks for your help, you diagnosed the problem instantly. If only I'd had more time on the road and knew where to source the parts in whatever city I was in, I'd have had my amp going again in no time. As it is, I bought extra diodes and taped them up in a baggy inside the amp should the problem arise again. Redundancy!

Offline

 

#29 2012-06-15 20:14:26

sewage666
VIP
From: Oakland, CA
Registered: 2010-11-19
Posts: 79
Website

Re: Internal fuse blow before external?

One more question... my V4B was running fine for awhile after I bought it with a 5A quick blow fuse in the external fuse (I didn't know it). I replaced it with the prescribed 6A slow-blow that did not, as I stated in my initial post, blow before the internal 10A fuse.

Theoretically, if it had been a 6A quick blow fuse, might it have blown first and saved me all this trouble? Or, would the Ohm mismatch I accidentally suffered have blown the flyback diodes and internal fuse anyway?

I guess I'm just not sure which protects what when and in what order.

Offline

 

#30 2012-06-16 21:49:50

sewage666
VIP
From: Oakland, CA
Registered: 2010-11-19
Posts: 79
Website

Re: Internal fuse blow before external?

hmm, now I feel creepy and kinda like I'm talking to myself here... but back to my original question:

Looking more carefully at the circuit, it looks like the 10A fuse is wired to the main power before the 6A fuse. So, if there was a power spike over 10A, it kinda makes sense it would blow first. I think.

And I declare this thread is officially done.

Offline

 

#31 2012-12-19 17:01:34

Liquids
Member
From: CT
Registered: 2010-08-01
Posts: 491

Re: Internal fuse blow before external?

Liquids wrote:

Just to offer a perspective outside of my own (which is purely from what I've been told from other people I respect as well - I'm far from anything but a novice to think for my own on this subject), I just now asked Merlin, this guy, for his take:

http://www.freewebs.com/valvewizard/links.html

Me: "Merlin,

whats your perspective on using flyback diodes on the output transformer of a push pull high powered amp?"

Merlin: "They're a good idea as far as I'm concerned!"

Me: "Would you say that they sometimes protect an output transformer from blowing?"

Merlin: 'Well, theoretically they should work. Of course, it's hard to be sure if they're really doing anything useful, just like the rock that keeps tigers away, but they don't hurt, so its cheap insurance."

Just a third voice in the mix. 
Resultant conclusion: I personally don't think always or never are good policies here.

Just to be even handed about info - just stumbled across this when looking for some other info; this came from the well-respected R.G., on his website at geofex.com:
http://www.geofex.com/tubeampfaq/tubefaq.htm#morepower

Q: I've seen circuits that use reverse biased diodes connected from ground to the plates of output tubes as "transient spike preventers". How does this work?

A:The 1N4007's serve mainly as an amulets against the voltage gods in this case. An inductive flyback pulse will go to literally ANY voltage until it finds a discharge path. Ideally, transients that would cause very high positive voltages on one push-pull plate would cause high negative voltages on the other plate, and the diodes on the negative going plate would clamp the voltages on the positive going plate through the output transformer. This does indeed happen for small, extremely-tightly coupled transformers. However, any leakage inductance between the two primaries prevents the tight coupling that would let the negative going diodes protect, and worse yet, it's the leakage inductances that cause the spikes on transients anyways."

What really happens is that the first few flyback pulses that occur will break over the 1N4007's rather than than arcing the plates on the positive side, so there really is some protection, it's not just where it looks like it is. If you're lucky, the 1N4007's break over before the transformer insulation punches through, and all is well until the 1N4007's go leaky or short. Probably better than nothing, but not a whole lot of additional protection, either. Heck, amulets are not harmful, I guess."


Matthew

Offline

 

#32 2012-12-19 20:38:37

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: Internal fuse blow before external?

The idea of flyback diodes is a good one... But in practice,  I end up repairing more amps with flybacks for blown diodes than I do amps without them for blown transformers,  by a huge margin.   

Also, I still see v4s that had flybacks come I with blown output transformers. 
Of the 4 or so v4 output transformers I have replaced in the last five years half of them had the flyback diodes.   Although this is a very small sample size,  it leads me to believe that the output transformer failure rate is not affected by the use of flyback diodes.

I certainly wouldn't blame anyone for continuing to use them,  if it makes them feel better.  Especially if they are tech savvy and could replace blown diodes at the drop of a hat for the price of the diode, plus their own time...  But as someone like myself that needs to guarantee their work for a period of time,  i am not willing to use them.

Frankly,  I wonder if fender or peavey or any of the modern companies that use flyback diodes have done studies regarding this, as i have done so many of these diode replacements under warranty for fender/peavey and that costs them a fair amount every time.

Offline

 

#33 2012-12-20 00:38:55

Liquids
Member
From: CT
Registered: 2010-08-01
Posts: 491

Re: Internal fuse blow before external?

Yeah, I think RG was saying "they may do something in just the right situation...but they may not be any more helpful than a rabbit foot." Wanted to be even handed about the info I find from reputable sources.

Last edited by Liquids (2012-12-20 00:39:14)


Matthew

Offline

 

Board footer

Powered by PunBB
© Copyright 2002–2005 Rickard Andersson