W5M blowing fuses

[Thunderbud]

As the title says, my Heath W5M is blowing fuses immediately upon start-up. Any insights/thoughts would be appreciated. All tubes have been removed, and still blowing fuses.

 

[mswanson65]

Not to step on your thread but I also have a W-5M that is immediately blowing a fuse. Would also be interested in knowing what to check first.

 

[gadget73]

Hm, no tubes and fuse blowing usually means either transformer or a short in the wiring to/from the transformer. Have an eyeball at the wiring to see if you can find anything. failing that, I don't have good feels about your power transformer's health.

 

[willyrover]

Power transformer is shorted...which seems to be more a matter of "when" than "if" with the W-5M.

 

[Thunderbud]

Hm, no tubes and fuse blowing usually means either transformer or a short in the wiring to/from the transformer. Have an eyeball at the wiring to see if you can find anything. failing that, I don't have good feels about your power transformer's health.

Thanks for the tip ! I'll check the associated wiring , but what should I get for readings on the trans ? Other than a dead short of course.

 

[gadget73]

It may not show up with an ohm meter unfortunately. A single shorted turn internally won't read anything off but it will draw loads of current.

 

[Brice]

I also think the PT is shorted. I blew one in those amp like that, no warning nothing. Not fun.

 

[Thunderbud]

It may not show up with an ohm meter unfortunately. A single shorted turn internally won't read anything off but it will draw loads of current.

Ok. Thanks. Ha
ve a spare amp for parts, guess it's time to start pulling things off it......

I also think the PT is shorted. I blew one in those amp like that, no warning nothing. Not fun.

Thanks. Plan to check it tonight after work. Miss hearing them sing through those Fortes !

 

[Fuzzbuster]

Those potted transformers Heathkit used are prone to failure. 3 of 5 I worked on had replacement transformers. I personally would source a different part. Using one from another W5M is just inviting problems..in my opinion.

 

[Thunderbud]

Those potted transformers Heathkit used are prone to failure. 3 of 5 I worked on had replacement transformers. I personally would source a different part. Using one from another W5M is just inviting problems..in my opinion.

Perhaps. For the time being I'll go with what I have on hand. Do you have a recommendation for a suitable replacement ?

By the way, I disconnected the two HV leads from the circuit, and VOILA' !! No more blown fuses.

Thanks to all who kindly offered advice. You were right, bad power xformer.

 

[Thunderbud]

Did you also lift the CT lead from ground?

No. Have already pulled the unit from the chassis. Can I ring it out on the bench and learn anything that way ?

 

[Thunderbud]

Thought I had all the information I needed when the fuses quit blowing. Is there more to the story that I'm missing here ? Or have I root-caused it already ?

 

[trainbuftony]

Let me get this straight, you removed the high voltage leads from the rectifier, left the others connected and the fuses quit blowing at that point? If that's the case I would expect to see shorted filter caps not a dead transformer.

 

[Thunderbud]

Just realised that I left out a piece of information. I'll apologize in advance. I've switched to one of SDS Labs cap boards with diode rectifier. The rect. socket is only being used as a tie point for the hv trans leads to the board.

 

[Thunderbud]

Let me get this straight, you removed the high voltage leads from the rectifier, left the others connected and the fuses quit blowing at that point? If that's the case I would expect to see shorted filter caps not a dead transformer.

Yes that's right but see my post below. No rect tube being used, just the socket pins for tie points to the board. Hv leads go to socket then board.

 

[Thunderbud]

Yes that's right but see my post below. No rect tube being used, just the socket pins for tie points to the board. Hv leads go to socket then board.

Or my post above, as it were.

 

[Thunderbud]

You may not have a bad tranny. When you pulled the rectifier and it still blew fuses, you effectively took the HV leads out of the circuit. You didn't need to disconnect them from the socket to remove them from the circuit. So if you left the CT connected to ground and the short dissappeared when you moved the HV leads, it means the short could be anywhere along the leads themseves, even on the socket itself. It could be on a lead where it comes out of the tranny, if it has a broken covering from rubbing or whatever... So again, when you pulled the rectifier and it blew fuses, it means that any tranny short would go through CT to ground. Or whatever the failure would have been internally. Just moving the leads which were supposed to be open circuit at the socket would not be expected to halt the fuse blowing.

Yes I see your point. Then I am mystified ( again ) as to why removing those leads from the socket would elim. the short. Filter caps are new, mounted on the SDS Labs board. This all started a few days after I installed a Tube Depot solid state rectifier in the rect. tube socket, along with a 60 second delay timer. Started blowing fuses (and the rectifier) a few days later.

 

[Thunderbud]

OK, is this a new mod for you that hasn't worked for any length of time, or old mod suddenly gone south?

Well both, in a way.. I've had Sheldon's cap boards ( the original version ) in both my W5Ms for some time.The trouble began after I installed the ss rectifier, but only in one amp. While it was down for the short problem I bought and installed his new board, which contains a diode pair as the rectifier. The fuse- blowing predates the new board installation. The other amp is trouble-free with his old style cap board and the Tube Depot ss rectifier.

 

[gadget73]

Could just be high voltage overwhelming the cap until things load down. That is one nice thing about indirectly heated rectifiers, they don't come up much before the output tubes so the voltage spike isn't nearly as severe.

If the transformer were bad, you could lift all of the leads except the power input leads and it would still draw too much current. If it stops when you unhook the HV secondary, that makes me think its something the HV secondary connects to.

 

[Thunderbud]

The original amp used a 5R4 rectifier which is a high voltage drop tube. Your SS is gonna create high B+. You gotta know how to handle that with magasuperfiltergigantorSSrectifiermodzillas. Your PT is OK, don't blow it.

Ok - so you got a part number for that ? Lol