So My Quicksilver keeps blowing the fuse..

similost

Rockin and Rollin....
How to start looking?

Just a little background on this one amp..

It's one of their 8417's that was converted by the factory to EL34's

One amp I've had a slight problem from almost day 1. Some times it doesn't like to put out sound... If I would knock on one of the two large caps, it would crackle and come back. It was only one of the caps that this would work for...

I've been through the amp and looked for cold solder joints and reflowed a few.. It was always fine other wise.. worked and sounded great. Would just drop off every now and then, and a rap or two on the cap and life was good again..

I've got hundreds of hours on the amp like this...

About a week ago, turned it on.. and about 15 seconds later, it popped the fuse. Both of my amps will do this if the speaker wire works loose. I check the wire, and sure enough, it's loose.. tighten it back up, put in a new fuse.. life is good and I listen to it for about 10 hours or so..

A week later, I turn it on, and about 15 seconds in.. POP... check the wires.. fine... move the wires to a new speaker.. power up.. POP..

Now I pop the fuse after the amp is on for about 15 seconds or so..

How would I even begin to troubleshoot what is wrong?

I know test the tubes first.. but I swapped them to the other amp and all is good... If I can't keep the amp on, what and how do I check what?
 
It may be time to replace the PS and bias caps. Check the resistors associated with the output tubes too.
Those tend to drift off spec and/or open up. Best of luck with it!
 
Thanks Celt.. Yeah, I was actually thinking the first thing I was gonna do was replace the big caps on top.. Man I bet those ain't gonna be cheap.. Mallory's almost the size of coke cans..

I haven't ever had problems with the bias or anything.. always really close, and not hard to set.... adjustment is in about the middle of the bias adjustment..
 
Yup...but the bias caps tend to age along with the PS caps. I'd go ahead and replace the one or two that helps to control the bias.
 
Thanks Celt.. Yeah, I was actually thinking the first thing I was gonna do was replace the big caps on top.

From the schematic it looked like they might be 475v caps on a power supply rail at 465v. You might want to crack open the wallet a little wider and get something a little higher rated. Please disregard if the actual caps are higher rated.

edit: do you have a 330uf cap right after the rectifiers?
 
Last edited:
I think the caps on top are rated at 500V... I can't remember what the pharos on it are.. but they's som biggins...

I guess it wouldn't hurt me to just go through the things and replace all the caps.. They've been great amps, and I'm sure a little better stuff inside sure wouldn't hurt..

I got no problem opening the wallet.. now to convince the wife.. I still haven't let on to what the Stroms are gonna cost..
 
What's the B+ voltage on the good amp? Just in case you missed my edit above, do you have a 330uf cap right after the rectifiers?
 
I have no idea what size caps are anywhere in that amp.. .I will say, around 300uf does seem to be what I remember on one of the large caps.. The two on top are different values..

I was just looking at schematic in this post, and it shows two 330's.. interesting..
http://www.audiokarma.org/forums/showpost.php?p=2752404&postcount=1

After I get home this evening, I'll post what the two on top are.. Manybe hopefully someone here will have a good source for them.. I kind of remembered looking around before trying to find some, and was having a not so good time finding replacements..
 
The 330uF caps are too high a value. The GZ34 is rated for 60uF for the first cap and that amp has two GZ34s so the max capacitance should be 120uF. If you replace the caps you might want to reduce that first cap value.
 
The 330uF caps are too high a value. The GZ34 is rated for 60uF for the first cap and that amp has two GZ34s so the max capacitance should be 120uF. If you replace the caps you might want to reduce that first cap value.

Hi Tinkerbelle.. long time no talk to..

What is GZ34? This has EL34's in it.. It was modded by Quicksilver.. so if they did put in too much cap.. why would they do that?

The rectifiers in mine are 5ar4's Same thing I guess?
 
...That's why I started at 120uf. I don't understand how they can hammer the rectifiers with that size of cap and I don't understand how they can hammer the cap with that kind of voltage.
Apparently, these do suffer from arcing and other instability issues, so it seems that the 330uF and low cap voltage rating does cause issues.
 
hhhmm... so.. not only should I swap out caps.. but I should do some modding..

Well all righty then... I'm sure I'll be f8ckin these amps up :para:
 
Apparently, these do suffer from arcing and other instability issues, so it seems that the 330uF and low cap voltage rating does cause issues.

Coupled with EL34s drawing lower current than the original tubes probably leading to an even higher B+. Did they modify the power supply when they changed the tubes?
 
oh please don't shut up...

Ya'll got me real lost now.. .

So tell me.. what's gonna be my best bet...

Replace the caps with smaller ones? Do the triod mod from that post?

I gots no tubes at the moment, and I really need to get these back up and running.. That, or maybe I need to pull the Bogens back out and do just a little bit of work on them they need.. .tighten a couple pins, and replace a resistor..
 
Lemme get home tonight, then get a couple pictures and list some values on the my amp, then we can go from there????
 
Do the triod mod from that post?

If you're gonna start modding this thing then you might as well use different tubes than 12ax7 and 12au7. Use something with a hard to remember code that costs way less. I'm sure Kegger will stop by with a suggestion or two. He's the front end guy around here, I'm more leg guy.
 
Back
Top Bottom