• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Power & Fuses

KD2KGA

KD2KGA

New Member
Quick story with advice and then a question at the end.

I have a Pioneer SA-8800 that I had recapped by a tech years ago. Now I'm getting into doing things for myself and recently recapped a Technics SA-200 that I found. And look, I'm still alive.

I had some power issues a few months back with the SA 8800. Loud intermittent pops heard in the speakers. I pulled the cover and started poking around looking for the culprit. A loose or blown component, cold solder joint, wiring harness issue, etc.

Couldn't find the source of the issue in the amp. It was frustrating.

I turned my focus to a power problem and it was a cheap power strip that the system was plugged into that was causing the problem. Picked up a Furman for $35.00 on Amazon and the problem disappeared. I also installed a better A/C Outlet.

That issue is now gone and the lesson here is to make sure you have clean power feeding your amps and sensitive, vintage gizmos.

Since I started on this path, I figured I would do some more power section cleanup, including replacing the power cord with a polarized plug and considered new higher quality fuses as the old ones looked dingy. I found two of the fuses (FU 2 and FU 3) are 1 amp rated fuses when they should be 0.8 amp (800 ma) fuses.

One of them doesn't even have a brand or other ID on it. Just a 1A and even that is badly stamped. I'm glad I pulled these and not sure why the "tech" would leave these in place. Did they even look?

FU 1 is the proper rating at 6 amps but it appears to be a slow blow. Is my thinking this is ok as it cushions the in rush when the power is turned on correct? Or should I pull that and put in a fast blow?
 
Register to hide this ad
Pioneer specified that all the fuses are to be Slow Blow hence the (T) before or after the fuse rating. This means Time delay which is another name for slow blow. Amplifiers in general NEED slow blo fuses as they all have inrush due to their large capacitors. The bigger the amp, the more inrush. A fast blow fuse would just mean that every time you went to switch on the amp, the fuse would blow. Because for around 0.2 seconds or less, the inrush current will peak at many times over the usual operating rating for the amp - while the capacitors charge and the magnet field in the transformer is established.

This is especially true for the donut shaped transformers known as Toroidal transformers. Most amplifiers that have toroidal transformers in them have some form of soft start circuit to help reduce the inrush current as in these applications it can quite easily draw in excess of 20A for a very short period.

The SA-8800 has an EI core transformer. These present a more resistive load at power up and so their inrush is much smaller that a toroid. That said, the SPEC-2 has a very large toroidal transformer and four 15,000uF capacitors. According to Pioneer, the inrush current can exceed 300A at power up. So a soft start circuit is used to prevent the fuse, and the wall outlet from going boom. Though your neighbours might know when your about to start a listening session! :music::naughty:

Fuse ratings are very important though and you should definately change those 1A fuses back to their specification of (T)800mA.

With respect to the power connections. Once you've got good quality (and I mean standard recognised brands) wall sockets/extension leads etc that make good tight contact with the pins on your socket or cable, then there is no need to go any further and start spending $70 on a "hyper pure cryogenically frozen silver power cable". Power is power. and if the resistance between the wall outlet and the power switch of your amp is less than 1 Ohm which it will be if the connections are good. Job done.:thumbsup:
 
QSilver said:
Pioneer specified that all the fuses are to be Slow Blow hence the (T) before or after the fuse rating. This means Time delay which is another name for slow blow. Amplifiers in general NEED slow blo fuses as they all have inrush due to their large capacitors. The bigger the amp, the more inrush. A fast blow fuse would just mean that every time you went to switch on the amp, the fuse would blow. Because for around 0.2 seconds or less, the inrush current will peak at many times over the usual operating rating for the amp - while the capacitors charge and the magnet field in the transformer is established.

This is especially true for the donut shaped transformers known as Toroidal transformers. Most amplifiers that have toroidal transformers in them have some form of soft start circuit to help reduce the inrush current as in these applications it can quite easily draw in excess of 20A for a very short period.

The SA-8800 has an EI core transformer. These present a more resistive load at power up and so their inrush is much smaller that a toroid. That said, the SPEC-2 has a very large toroidal transformer and four 15,000uF capacitors. According to Pioneer, the inrush current can exceed 300A at power up. So a soft start circuit is used to prevent the fuse, and the wall outlet from going boom. Though your neighbours might know when your about to start a listening session! :music::naughty:

Fuse ratings are very important though and you should definately change those 1A fuses back to their specification of (T)800mA.

With respect to the power connections. Once you've got good quality (and I mean standard recognised brands) wall sockets/extension leads etc that make good tight contact with the pins on your socket or cable, then there is no need to go any further and start spending $70 on a "hyper pure cryogenically frozen silver power cable". Power is power. and if the resistance between the wall outlet and the power switch of your amp is less than 1 Ohm which it will be if the connections are good. Job done.:thumbsup:
Click to expand...

Thanks QSilver for this great response!

On the topic of properly rated fuses, I do have a concern about not being able to find 125V rated fuses. A 250V hit would be needed to blow that fuse, wouldn't it? SA 8800 Service Manual and the PCB say 125V.

I'll find T rated fuses and go with those across the board in all three slots.

What's your (or anybody else's) take on HIFi rated fuses? The price ranges are quite wide and I would never spend three figures on something like that. However, I do see fuses from a company named HiFi Tuning that makes reasonably priced fuses. They start at around $12.00 and go up from there.

And I agree on the power cord item. I already bought the extension cord I'm going to cut the end off of. :-)
 
125V vs. 250V. That's the Maximum voltage that the fuse is rated for. The 250V fuse (standard buss 3AG fuses or equivalent) in the appropriate amperage will work fine and will cause no problems. Been using them since the 60's with no problems. The fuse blows more from over amperage, not over voltage.

HI-FI fuses don't do anything special except make your wallet squeal like a stuck pig. Save your $$.
 
All I say is prove it, with referenced evidence, graphs and comparisons. Scientific basis and not things like "The bass suddenly became much more up tempo and rhythmic, the midrange became smooth and opened out and the highs mellowed" :rolleyes:

"Oh, sorry, it seems I wandered into the wine tasting tour and not the science lab... my bad." :biggrin:
 
The two glass fuses 800 mA on the power board FU 2 and FU 3 for the Pioneer SA-8800 1979 model through research should be fast blow. I cannot find any where in the service manual saying they have a rating T for time delay. Google search for this fuse size and model indicate fast blow. These fuses have a tiny filament. Not an expert at all just want to replace mine with the correct rating so I can do a dim bulb test to see if this prevents these two fuses from blowing. Thanks
 
pinky6 said:
The two glass fuses 800 mA on the power board FU 2 and FU 3 for the Pioneer SA-8800 1979 model through research should be fast blow. I cannot find any where in the service manual saying they have a rating T for time delay. Google search for this fuse size and model indicate fast blow. These fuses have a tiny filament. Not an expert at all just want to replace mine with the correct rating so I can do a dim bulb test to see if this prevents these two fuses from blowing. Thanks
Click to expand...
QSilver, I opalogize as your much more experienced than I am. I will go with what you say about the fuses and time delay.
 
You must log in or register to reply here.
Back
Top Bottom