W5M blowing fuses

[Thunderbud]

it won't hurt the tubes. That whole thing about cathode stripping is over-hyped. Yes it happens but a few times for testing isn't going to destroy the tubes. Its possible you have too much inrush between the caps charging and the tubes already being hot. Maybe try a resistor across the relay contacts to get the caps partly charged and reduce the current surge before the relay closes.

worth asking, but what type fuse are you using? If its not a slow-blow that may be part of the problem.

Or just put a vacuum rectifier and stock value caps in there like its supposed to have.

Ok, I'll try that. I doubt the fuse is the problem. Remember, it's lasting long enough to take out one and sometimes both of my 3a 1000v diodes. I have one of SDS Labs earlier cap boards in my other W5m, and it's working fine, so I might go back to that setup for this one.

 

[Thunderbud]

Ok, I'll try that. I doubt the fuse is the problem. Remember, it's lasting long enough to take out one and sometimes both of my 3a 1000v diodes. I have one of SDS Labs earlier cap boards in my other W5m, and it's working fine, so I might go back to that setup for this one.

it won't hurt the tubes. That whole thing about cathode stripping is over-hyped. Yes it happens but a few times for testing isn't going to destroy the tubes. Its possible you have too much inrush between the caps charging and the tubes already being hot. Maybe try a resistor across the relay contacts to get the caps partly charged and reduce the current surge before the relay closes.

worth asking, but what type fuse are you using? If its not a slow-blow that may be part of the problem.

Or just put a vacuum rectifier and stock value caps in there like its supposed to have.

I've tried so many things, I forgot to mention that

If you have huge B+ at startup you are probably exceeding the PIV rating of the rectifiers. Lots of filter cap will do that. Just one possibility.

I wondered about that. The diodes are rated for 3 amps @ 1000 volts. The board has 9 caps, 270 uf at 450 volts each.

 

[primosounds]

I've tried so many things, I forgot to mention that

I wondered about that. The diodes are rated for 3 amps @ 1000 volts. The board has 9 caps, 270 uf at 450 volts each.

If you can bring it up to full voltage with a variac starting at 60vac, wait a few minutes , go to 90vac wait a couple minutes then to full power, and you don't blow a fuse and nothing starts smoking, plates start glowing or speakers howling or other odd noises, then perhaps your fuse for the cap board or the cap board itself is not correct. Is this power supply board designed for the Heathkit W5? It seems like a lot of capacitance for the W5

 

[Thunderbud]

If you can bring it up to full voltage with a variac starting at 60vac, wait a few minutes , go to 90vac wait a couple minutes then to full power, and you don't blow a fuse and nothing starts smoking, plates start glowing or speakers howling or other odd noises, then perhaps your fuse for the cap board or the cap board itself is not correct. Is this power supply board designed for the Heathkit W5? It seems like a lot of capacitance for the W5

Yes it's for the W5M but I maaaayy have overdone it on the cap values.

 

[Thunderbud]

Yes it's for the W5M but I maaaayy have overdone it on the cap values.

There is no specific value quoted or recommended by SDS Labs for the board that I am aware of. The earlier version uses ( 9 ) 47 uf caps, which I believe was roughly equivalent to the original total capacitance for the circuit.

 

[Thunderbud]

If you can bring it up to full voltage with a variac starting at 60vac, wait a few minutes , go to 90vac wait a couple minutes then to full power, and you don't blow a fuse and nothing starts smoking, plates start glowing or speakers howling or other odd noises, then perhaps your fuse for the cap board or the cap board itself is not correct. Is this power supply board designed for the Heathkit W5? It seems like a lot of capacitance for the W5

Don't have a variac so I have to sacrifice a few fuses to troubleshoot it.

 

[Thunderbud]

Swapped caps to 120 uf 450 v, got 4, maybe 5 seconds before it blew. Going to go back to earlier SDS Labs board with plug-in SS rectifier. Thanks to all who offered suggestions / insight.

 

[s-petersen]

I'm afraid to put all that HV to the tubes before they're warmed up. That's why I have the relay in there. Forgot to mention, with power tubes removed, no drama. Things go wrong when they are in the circuit. tried a pair of 6L6s, and a pair of Gold Lion KT66s. Same result.

It sounds like a bad coupling cap,or cathode bypass cap.if it doesn't blow fuses with the output tubes removed.

 

[Thunderbud]

It sounds like a bad coupling cap,or cathode bypass cap.if it doesn't blow fuses with the output tubes removed.

Thanks ! I'll check that.

 

[fredtroy]

As others have stated OP W5M probably does not have a failed power transformer. With that said, does anyone know a source for a W5M power transformer replacement?

 

[heyraz]

As others have stated OP W5M probably does not have a failed power transformer. With that said, does anyone know a source for a W5M power transformer replacement?

Yeah,
I have five of them. Five complete amps all original iron that I bought for restoration because the Peerless OPT's were supposed to be "the finest iron known to man". All 5 were said to be in good working order but I never proceeded further.
Why? Because as I began to research the W5M it became clear it is an unreliable amp. Both versions of the OPT's and the Mains Transformers are unreliable. So I shelved them and bought an amp I can depend on.

As far as I'm concerned, the best way to rebuild a W5M is so that both transformers can be swapped out with minimal effort. I'd use high voltage connector plugs underneath.
With that in mind, if I ever were to rebuild two W5M's, I'd keep the other three for parts.
If I sell them, it will be locally because the chassis is too flimsy to support that much iron during shipment.
Fred, in my opinion you should buy whatever replacement Mains Transformer people are recommending because the original is unreliable. I realize an "all original" W5M fetches more on eBay, but I think the amp is a money pit.

 

[gadget73]

not sure I'd use plugs, but terminal strips with screw-clamp connections would be fine. Those exist for industrial control stuff and can be had with fairly high voltage ratings.

 

[heyraz]

not sure I'd use plugs, but terminal strips with screw-clamp connections would be fine. Those exist for industrial control stuff and can be had with fairly high voltage ratings.

Another option I've considered but I'm talking about simplicity, no confusion and no or reduced possibility for error.

The possibility for error exists if a wrong wire is inserted into the wrong terminal using terminal strips with screw down clamps.

Polarized male and female inline locking connectors on the installed and spare transformers eliminates at least one possibility for an error to occur . Something like Molex Connectors only heavier duty.

Tranny blows, quick swap, no confusion and back in business. As plug and play as it gets for transformer replacement.

I really think for this amp you need to have available spare transformers like you have spare tubes.

I'm not a fan of unreliable equipment. You'll never hear me recommend that amp for this reason.

And that's why I have 5 of them. I did my research too late and after they were purchased. I learned an expensive lesson.

 

[s-petersen]

I had 2, one had a blown power transformer, the other a blown output transformer, I made 1 good one, and one bad one.

 

[gadget73]

I'm not a fan of unreliable equipment.

yeah me either. I like things I can accidentally leave on for days at a time and have no real concerns about it other than for the wasted power.

 

[heyraz]

I had 2, one had a blown power transformer, the other a blown output transformer, I made 1 good one, and one bad one.

My point exactly.
When they worked, what were your impressions? "Finest Iron Known to Man"?
Does the amp sound so good that you would be willing to keep spare transformers on hand, like I keep spare tubes?

 

[s-petersen]

Someone was looking for a good one, so I helped him out, I didn't fully rebuild it, I just got it going to make sure the Iron was good.
Someone (else?) just wanted the other chassis, so I sent him the one with the bad iron in it. IIRC he wanted the bad iron for rebuild(it was quite a while ago)
Although they sound great, I usually go for a little more power than the W5M can supply

 

[heyraz]

I gotta say, I've been really conflicted about selling the five I own.

Once I realized any version of the W5M had issues, I put them into storage because I didn't want to waste anymore time and money. Not even to check them over. Now I can't in good conscience sell them individually because I don't trust a single one of them.

In case you're wondering how I came to own five of them, the first two didn't have matching OPT's. So I purchased two more so I could have two sets each with matching OPT's. The fifth had good tubes and was too cheap to pass up.

I own five unreliable amps and the best I can comfortably do is to sell them "for parts, not working" as a collection of five and hope that out of the five, at least 2 sets will work for someone else.

Ugh.

 

[s-petersen]

The beet thing to do is to slowly variac them to 80v, test and sell the good ones as tested working,needing a recap, sell the others asis for parts

 

[trobbins]

Seems like some owners are technical enough to change a power transformer, but not technical enough to add extra protection to avoid the transformer failing in the first place.