I'm in the throes of restoring a 30 valve 1959 Hammond organ. Part of the resto includes converting it from 110 volt to 240 volt mains operation. To accomplish that I have obtained a replacement power transformer that is the original Hammond option and is NOS out of the sealed box. This may be the only such transformer left in creation so I'm very keen to protect it from circuit failure.

It's been said of Hammond at the time this organ was designed that their attitude was "We don't need no stinking fuses!" and also "We don't need no stinking grounds!"

I will ground (earth) the unit as a matter of course, and I intend to fuse the primary of the tranny, but I'd also like to protect each of the 3 secondary windings, voltages being 350-0-350 for B+, 5 for the 5U4 rectifier, and 6.3 for the remaining 29 valves. (The latter winding being almost as thick as fencing wire!)

There is room in the power supply chassis for a panel mount style primary fuse, but not really enough room for another 3 fuses to cover each secondary.

The VA rating of the (large!) tranny is not documented and I haven't measured the operating currents for the secondary circuits as yet, but I'm thinking of perhaps employing the sacrificial resistor trick on the 5U4 anodes in the case of the B+, but am out of ideas for the low voltage high current filament and heater windings.

I may have to resort to bare household type fuse wire between lugs of a tag strip.

Any other ideas?

The big issue with the filament rectifier is that it has B+ riding on the 5V. On the 5Y3 in my bench power supply I just used one of the PCB Thermal circuit breakers.

That is chosen for the draw of the filament rather than what the winding is capable of. Due to the voltage, it is actually on a tag strip in mid air. The heater winding same deal (6L6 regulator). HT is fused.

Blade fuses are the next most compact and can be put into spade connectors, which can be soldered to tag strip, or buy a socket. Beware of blade fuses, as on most , there is a bare terminal each end: on top. This can short if the fuse is left to "float"

You will also get away with an inline 3AG fuse holder on the 6.3V Winding if there is room for it. Also consider chassis mount Automotive circuit breakers on 6.3V only Jaycar SF-4100 to SF-4108 series

Marc

A fuse is the way to go. Under a dead-short situation a fuse will blow a lot faster than a circuit breaker and they are also fail-safe providing the correct rating is chosen.

You would need to calculate (or measure, if you have a tong tester) what your normal load is on each winding and add 10 or 15% to that to work out the rating you would need. Normal glass 'fastblow' fuses will do fine. HRC fuses aren't really necessary for this application.

Jaycar or Altronics are the go for supplies like this. Tandy's gone due to Woolworths' most recent consolidation programme and Dick Smith simply don't cater for hobbyists these days - nor people who want a decent portable hard disc it seems...

And the difference between DS &Harvey Norman is what?

When I went to school "Chinese Junk" was a boat

Marc

Ad the difference between DS &Harvey Norman is what?

Not much difference at all. About two years ago when Woolworths changed the logo for Dick Smith I went into their Gore Hill store (which is now shut down - go figure) and wanted to buy some bits and pieces and the whole shop had been changed from what we would have found familiar into shelves of laptops, televisions and MP3 players. I was beside myself with complete disbelief and when I complained to the store manager I was told "Dick Smith is changing". Obviously not for the better.

There's not much left for the home brewer and I thank the man upstairs that we still have Jaycar maintaining the rage.

It is getting to the point where locally prices and availability do force us to consider and initiate, buying from outside Australia.

I recently required an Analogue Panel Ammeter. I ended up sourcing one that came in a box with genuine Elephant stamps on it, and for around half the price of the unsuitable one s here.

I also note the reluctance of the supermarkets to list the working volts of their resistors. I did see an English company advertising 800V ones. England tends to be expensive.

EVATCO seems to have started a move in the right direction, by stocking resistors above 1Watt & below 5 Watt. Having to use WW can be a serious issue in the RF section. Using modern 1/2 watt supermarket resistors can be a risk, as many cannot stand the voltages of Valve radio.

Some modern components cannot even handle being in the crappy CFL's. Seen / had several explode & vapourise bits. They are also massive generators of RFI.

Although we can expect that with ineffective regulatory authoritys that just sit in front o computers & write more silly regulations, & shuffle paper. None of which adds to the country's productivity, or safety if there is no quality assurance.

I note the comment re grounds: If you look at the radio's on the American forum, a huge proportion are transformerless and many European ones are as well. Even in transformer ones, grounding is rare.

A lot of Australian sets through the fifties had no mains grounding. Some claimed the set to be sealed and you could not touch anything alive.

OK the transformers were virtually double insulated. But more often, thn not, there was an earth and aerial the primary coil of which was connected to the chassis......?

Marc

Thanks for the ideas folks. I will tong the circuits and allow a bit of headroom.

And don't get me started on Woolworths and DSE. Not so many years ago I could walk to a local DS or Tandy shop. Since Woolworths buggered both of those up and killed off Tandy altogether I now have a 20km round trip to the nearest Jaycar, which sends me crazy if I just need one small component urgently.

Towards the end DS staff were utterly clueless. They were just checkout kids with no training and no background in electronics.

Otherwise I tend to use Farnell (now Element 14) as they deliver free for orders over $10 and it's next day if you order before 6pm. RS Components has a similar delivery deal.

Okay, new 240v transformer wired in with a 3AG panel fuse in the primary. Hammond rates this organ as 150 watts on the input side and I have measured it at 155.5 watts, with the mains at 251 volts (last night I saw 268 volts!)

I have decided not to bother with a bunch of separate fuses on the secondary, instead relying on the 1A slow blow that I've put in the primary which allows about 33% headroom for inrush current, etc, although I haven't measured any noticeable inrush in this transformer.

(On the other hand, depending in circumstances, the big stepdown transformer I was using previously, which is fused at 7.5A, has up to 10 amps inrush and an audible 'whoom'.)

I have run an earth to all the metal parts, including the knee-operated volume bar which also switches 240v. Getting an earth to that bar was quite a trick.

A careful going over of underside of the chassis with an small artist's brush and vacuum cleaner removing decades of dust and fluff eliminated entirely the hisses, clicks and pops, and there is no hum.

Boy does this little thing have some grunt! Output is a pair of 6V6s push-pull into two 10 inch Jensen speakers.

All of the electrolytics are housed in two large cans (a 4 section and a 2 section) which going by the soldering on them look to be original (1959). Logic tells me that I need to recap these. I think I'll try to get some new old stock, or parts from a wrecked unit, and gut and re-stuff those on the bench before pulling out the originals.

Surprised that they did not use 6L6 with 10" How many volts are on the plate?

Watch the modern caps they do not give a surge voltage.

Marc

GTC, if you are keen on getting hold of another Hammond organ, a chap in Canberra has advertised one for free to a good home. See letters in the January, 2012 edition of Silicon Chip for more details.

I am not sure if it is the same model as yours or not but the writer says it is from the 1950s.

Surprised that they did not use 6L6 with 10" How many volts are on the plate?

290v on the plates of the 6V6s. Phase inverter is 12AX7. Even with 6V6s they retrofitted a 5lb metal brick between the speakers to counter baffle vibration on the bass notes under power.

It makes sufficient noise with the 6V6s as my neighbours are noticing -- at least those which my workshop faces.

B+ is officially 300v, though mine is running a bit above that because the mains are rarely 240v here.

Watch the modern caps they do not give a surge voltage.

Yes, I intend to source high voltage and high ripple current types, from the USA if necessary.

GTC, if you are keen on getting hold of another Hammond organ, a chap in Canberra has advertised one for free to a good home. See letters in the January, 2012 edition of Silicon Chip for more details.

Thanks, I'll take a look. I probably don't have room for it, but then if it has valves ...

What I could be talked into taking is a Leslie speaker (complete with amp).

At that voltage there should be a voltage divider on the screens. At the maximum of 315V the screen should be 225V. Albeit Philips say 285V with 285V on the plate 14 watts RMS

The voltage rating of the filters (be guided by what is there) depends on the rectifier being a filament type, a filament type with cathode sleeve, or a heater valve. The biggest start up surge will be from a filament type like 5Y3 / 80, or diodes.

Spragues tend to be one I use for high ripple. They do tend to filter better than many. (and would want to at the price).

Marc

Brad, my local (large) newsagent doesn't have Jan 2012 issue of Silicon Chip yet. He said he got a big delivery this morning, but SC wasn't in it. Said holidays are playing havoc with deliveries.

Could you please email me the contact details of the guy in Canberra so I can find out what it is he's offering?

At that voltage there should be a voltage divider on the screens. At the maximum of 315V the screen should be 225V. Albeit Philips say 285V with 285V on the plate 14 watts RMS.

Schematic shows 280v on the screens. I haven't measured them.

Spragues tend to be one I use for high ripple. They do tend to filter better than many. (and would want to at the price).

Yes, I'll use Spragues if I can get the values I need.